Lateral approaches to the petroclival region

Role of Digital Subtraction Angiography in the Preoperative Assessment of a Patient with a Petrosquamous Sinus: a Case Report

We report a case of a 15-year-old Indian girl who presented with tinnitus, pain and ear discharge for one month and was preliminarily diagnosed with Chronic Suppurative Otitis Media (CSOM) with mastoiditis. She underwent a routine presurgical CT scan which revealed an aberrant vein, making it essential to exercise caution during surgery for CSOM. The aberrant vessel was identified as a Petrosquamous Sinus. A Petrosquamous Sinus is a persistent fetal vein that connects the transverse sinus with the retromandibular vein and may regress in an individual by birth. Its importance lies in the risk of haemorrhage it carries during otological surgeries. A Digital Subtraction Angiography proved to be a vital step in isolating the path of the vein for better visualisation of the course, thus giving a better idea about the anatomical relations of the vessel during the surgery. The tympanoplasty was performed with care to prevent damaging the vein. The patient had no complications in the postoperative period and made a quick recovery.

Mandibular Fossa Approach to Petroclival and Anterior Pontine Lesions

Objective  To describe the anatomy related to a novel approach to the petroclival region through the mandibular fossa for the treatment of petroclival and anterior pontine lesions. Design  Five dry skulls were examined for surgical approach. Three adult cadaveric heads underwent bilateral dissection. One cadaveric head was evaluated with computed tomography after dissection. Setting  This study was performed in an academic medical center. Participants  Neurosurgical anatomy researchers performed this study using dry skulls and cadaveric heads. Main Outcome Measurements  This was a proof-of-concept anatomical study. Results  The mandibular fossa approach uses a vertical preauricular incision above the facial nerve branches. Removal of the temporomandibular joint exposes the mandibular fossa. The anterior boundary is the mandibular nerve at the foramen ovale, and the posterior boundary is the jugular foramen. The chorda tympani, eustachian tube, and tensor tympani muscle are sectioned. The carotid artery is transposed out of the petrous canal, and a petrosectomy is performed from Meckel's cave to the foramen magnum and anterior occipital condyle. Dural opening exposes the anterior pons, vertebrobasilar junction, bilateral vertebral arteries, and the ipsilateral anterior and posterior inferior cerebellar arteries. At completion, the temporomandibular joint is reconstructed with a prosthetic joint utilizing a second incision along the mandible. Conclusions  The mandibular fossa approach is a new trajectory to the petroclival region and the anterior pons. It combines the more anterior angle of endoscopic approaches along with the enhanced control of open approaches. Further study is necessary before this approach is used clinically.

Comparison of the Retrosigmoid Suprameatal and Anterior Subtemporal Transpetrosal Approaches After Full Exposure of the Internal Acoustic Meatus

BACKGROUND AND OBJECTIVES

Surgical approaches to the ventral brainstem and petroclival regions are complex, and standard retrosigmoid and subtemporal approaches are often inadequate. Retrosigmoid suprameatal tubercle (RSMTA) and anterior subtemporal transpetrosal (ASTA) approaches may provide extended surgical exposure with less brain retraction. The objective of this study was to evaluate advantages and disadvantages of RSMTA vs ASTA, and illustrate the surgical corridors and 3-dimensional microsurgical anatomy of the related structures.

METHODS

Four silicone-injected adult cadaver heads (8 sides) were dissected to evaluate the accessibility of lesions located at the petrous apex, ventral brainstem, and pontomedullary region using ASTA and RSTMA.

RESULTS

Both ASTA and RSMTA provide access from the petrous apex to the ventral lower pons and pontomedullary junction. A greater extent of safely resected bone was found in ASTA vs RSMTA. ASTA provides a larger surgical view to the ventrolateral midpons, peritrigeminal region, superior neurovascular complex, pontomesencephalic junction, and posterior cavernous sinus. Meanwhile, through cranial nerve V mobilization, RSMTA provides a larger surgical view to the lower half part of the pons, ventrolateral part of the pontomedullary junction, and middle and lower neurovascular structures.

CONCLUSION

The choice of surgical approach is determined by considering the area where the lesion originates, lesion size, the anatomic structures to which it extends, and evaluation of the area that can be surgically exposed. Our study highlights the differences between these approaches and important surgical anatomic considerations.

Transpetrosal Routes to the Skull Base-Anterior and Posterior Transpetrosal Approaches

The extended middle fossa approach with anterior petrosectomy, or anterior transpetrosal approach, is a highly effective and direct approach to difficult-to-access petroclival tumors and basilar artery aneurysms. This surgical approach exposes a significant window of the posterior fossa dura between the mandibular nerve, internal auditory canal, and petrous internal carotid artery, below the level of the petrous ridge, and provides an unobstructed view of the middle fossa floor to the upper half of the clivus and petrous apex, without requiring removal of the zygoma. The posterior transpetrosal approaches, including the perilabyrinthine, translabyrinthine, and transcochlear approaches, provide direct and wide exposure of the cerebellopontine angle and posterior petroclival region. The translabyrinthine approach is commonly used for the removal of acoustic neuromas and other lesions of the cerebellopontine angle. We provide a stepwise description of how we perform these approaches and how to combine and extend them in order to achieve transtentorial exposure.

Basilar decompression via a far lateral transcondylar approach: technical note

BACKGROUND

Treatments for symptomatic or unstable basilar invagination (BI) include posterior decompression, distraction/fusion, trans-nasal or trans-oral anterior decompression, and combined techniques, with the need for occipitocervical fusion based on the degree of craniocervical instability. Variations of the far lateral transcondylar approach are described in limited case series for BI, but have not been widely applied.

METHODS

A single-institution, retrospective review of consecutive patients undergoing a far lateral transcondylar approach for odontoidectomy (± resection of the inferior clivus) followed by occipitocervical fusion over a 6-year period (1/1/2016 to 12/31/2021) is performed. Detailed technical notes are combined with images from cadaveric dissections and patient surgeries to illustrate our technique using a lateral retroauricular incision.

RESULTS

Nine patients were identified (3 males, 6 females; mean age 40.2 ± 19.6 years). All patients had congenital or acquired BI causing neurologic deficits. There were no major neurologic or wound-healing complications. 9/9 patients (100%) experienced improvement in preoperative symptoms.

CONCLUSIONS

The far lateral transcondylar approach provides a direct corridor for ventral brainstem decompression in patients with symptomatic BI. A comprehensive knowledge of craniovertebral junction anatomy is critical to the safe performance of this surgery, especially when using a lateral retroauricular incision.

Introducing the Posterior Condylar Emissary Vein as an Effective Surgical Landmark for Optimizing the Standard Retrosigmoid Approach: An Anatomo-Imaging Study

OBJECTIVE

There is a lack of definite anatomical landmarks for the inferior extension of the standard retrosigmoid approach. In this study, we evaluated whether the posterior condylar emissary vein (PCEV) can be used as an intraoperative landmark for optimizing the surgical corridor.

METHODS

We performed the standard retrosigmoid approach on 5 formalin-fixed and latex-injected cadaveric specimens and measured the distance between the PCEV near its bony canal and the vertebral artery (VA). In addition, vascular reconstructions of thin-sliced preoperative computed tomography (CT) scans were studied in 40 patients and the relationship between these 2 vessels was evaluated. An illustrative case is also included.

RESULTS

The PCEV was consistently identified on both sides of cadaveric specimens and in 87.5% and 82.5% of the left and right sides of the included CT scans, respectively. The average distance between the part of the PCEV near its osseous canal and the VA was measured to be between 8.4 mm and 8.6 mm in the specimens and between 9.2 mm and 9.3 mm in the CT scans. This distance offers a safe and effective plane of dissection during the standard retrosigmoid approach and allows easy access to the foramen magnum.

CONCLUSIONS

The PCEV near its bony canal proved to be an easy, straightforward, safe, and effective operative landmark with which the surgeon can extend the soft tissue dissection and bony exposure towards the foramen magnum. This maneuver provides ample access to the cisterna magna for cerebrospinal fluid drainage and increases visibility and surgical maneuverability to the entire cerebellopontine angle.

Importance of Sufficient Petrosectomy in an Anterior Petrosal Approach: Relightening of the Kawase Pyramid

BACKGROUND

In 1985, Kawase published an anterior petrosal approach to expose the posterior cranial fossa and to minimize retraction of the temporal lobe. However, some neurosurgeons still have difficulty with removing tumors through an anterior petrosal approach because a complete understanding of the Kawase pyramid has not been achieved. We hypothesized that if anterior petrosectomy were performed with three-dimensional understanding of the Kawase pyramid, it would have a positive effect on extent of tumor resection.

METHODS

We performed a retrospective study of patients who underwent surgical treatment for meningioma through an anterior petrosal approach. Patients were divided into total resection and subtotal resection groups, and statistical differences between the groups were analyzed. To identify factors predictive of complete tumor removal, univariable and multivariable logistic regression analyses were performed.

RESULTS

Width and height of the drilled internal auditory canal of the total resection group were significantly larger than those of the subtotal resection group (P = 0.001, P = 0.033). The operative angle of the total resection group was significantly larger than that of the subtotal resection group (P < 0.001). Regression analyses showed only drilled internal auditory canal width to be predictive of complete tumor removal, increasing the likelihood of complete tumor removal by 2.778-fold with an increase in drilled internal auditory canal width by 1 mm (P = 0.023).

CONCLUSIONS

Insufficient petrosectomy during an anterior petrosal approach adversely affects the extent of tumor resection. Furthering three-dimensional understanding of the Kawase pyramid could aid in complete tumor resection and better outcomes without causing damage to the surrounding organs.

Use of Neuroanatomic Knowledge and Neuronavigation System for a Safe Anterior Petrosectomy

Introduction: The petroclival region is among the most challenging anatomical areas to deal with in skull base surgery. Drilling of the anterior part of the petrous bone during the anterior transpetrosal approach involves the risk of injury of the cochlea, superior semicircular canal, internal carotid artery, and internal auditory canal. A thorough understanding of the microneurosurgical anatomy of this region is mandatory to execute the transpetrosal approaches, decreasing the risk of complications. The aim of this study is to describe the anatomical structures of the petroclival region, highlighting the importance of neuronavigation for safe performance of the anterior transpetrosal approach. Methods: Three adult cadaveric human heads were formalin-fixed and injected with colored silicone. They underwent an axial 1 mm slab CT scan, which was used for neuronavigation during the surgical approaches. The anterior petrosectomy was performed with the aid of neuronavigation during the drilling of the petrous bone. The surgical management of a patient harboring a petroclival meningioma, operated on using an anterior transpetrosal approach, was reported as an illustrative case. Results: The anterior petrosectomy was completed accurately with wide exposure of the surgical target without injuring the cochlea and other structures in all three cadaveric specimens. In the surgical case, no approach-related complications occurred, and a gross total resection of the tumor was achieved. Conclusions: Deep knowledge of the location and relationships of the vital elements located within the temporal bone, along with the use of neuronavigation, are the key aspects to perform the anterior transpetrosal approach safely, reducing the risk of complications.

The Neuroanatomic Studies of Albert L. Rhoton Jr. in Historical Context: An Analysis of Origin, Evolution, and Application

The incorporation of perspective into art and science revolutionized the study of the brain. Beginning in about 1504, Leonardo da Vinci began to model the ventricles of the brain in three dimensions. A few years later, Andreus Vesalius illustrated radically novel brain dissections. Thomas Willis' work, Cerebri Anatome (1664), illustrated by Christopher Wren, remarkably showed the brain undersurface. Later, in the early 1800s, Charles Bell's accurate images of neural structures changed surgery. In the 1960s, Albert L. Rhoton Jr. (1932-2016) began to earn his place among the preeminent neuroanatomists by focusing his lens on microanatomy to harness a knowledge of microneurosurgery, master microneurologic anatomy, and use it to improve the care of his patients. Although his biography and works are well known, no analysis has been conducted to identify the progression, impact, and trends in the totality of his publications, and no study has assessed his work in a historical context compared with the contributions of other celebrated anatomists. We analyzed 414 of 508 works authored by Rhoton; these studies were analyzed according to subjects discussed, including anatomic region, surgical approaches, subjects covered, anatomic methods used, forms of multimedia, and subspecialty. Rhoton taught detailed neuroanatomy from a surgical perspective using meticulous techniques that evolved as the technical demands of neurosurgery advanced, inspiring students and contemporaries. His work aligns him with renowned figures in neuroanatomy, arguably establishing him historically as the most influential anatomist of the neurosurgical era.

Important landmarks and distances for posterior fossa surgery measured by temporal MDCT

In this retrospective study, we aimed to present important anatomical structures and distances for posterior fossa surgery by temporal multidetector computed tomography (MDCT). The temporal MDCT images of 317 adult patients (158 males and 159 females) were retrieved from the hospital's picture archiving and communication system (PACS). In the coronal temporal MDCT views, the cochlea-carotid canal and jugular bulb-mastoid bone outer surface were measured. In the axial MDCT views, the carotid canal-jugular bulb and carotid canal-posterior fossa distances were measured; the carotid canal and jugular bulb anterior-posterior (AP) and transverse dimensions were also measured. The bilateral cochlea-carotid canal, jugular bulb-mastoid bone outer surface, and right carotid canal-jugular bulb distances were significantly greater in the males than those in the females (p < 0.05). The carotid canal-posterior fossa distance was not different in both genders (p > 0.05). The carotid canal-jugular bulb and the carotid canal-posterior fossa distances were greater on the left side than those on the right side in both genders (p < 0.05). In males, the outer surface distance was greater on the left jugular bulb-mastoid bone than that on the right side of that bone (p < 0.05). The difference between the carotid canal AP dimensions was not significant between males and females (p > 0.05). However, the carotid canal transverse dimension, jugular bulb AP, and transverse dimensions were significantly greater in the males than those in the females, bilaterally (p < 0.05). In each gender separately, the carotid canal AP and transverse dimensions were greater on the left side and the jugular bulb AP and transverse dimensions were greater on the right side than those on the left side (p < 0.05). Positive correlations were found between the cochlea-carotid canal, the jugular bulb-mastoid bone outer surface, and the carotid canal-jugular bulb distances as well as between the jugular bulb-mastoid bone outer surface and the carotid canal-posterior fossa distances (p < 0.05). In older patients, the carotid canal-posterior fossa distances were shorter on the left side (p < 0.05). Vascular and neural localizations should be well understood in the operative area before applying the surgical approach in the posterior fossa. Computed tomography (CT) has a greater role in the evaluation of bone structures and vascular canals in this area.

Comprehensive review of the mastoid foramen

Anatomical variations of the mastoid foramen have been observed to vary in a number of qualities including size, number, and location. These variants have the potential to become problematic during surgical approaches to the posterior cranial fossa and mastoid part of the temporal bone, and should thus be appreciated by the surgeon. Herein, we discuss the mastoid foramen in detail including issues with such foramina that should be known to the neurosurgeon.

Anatomic Analysis of the Internal and External Aspects of the Pterion

OBJECTIVE

The pterion is an H-shaped suture complex. This study's goal was to determine the location of its external and internal surfaces and extension and emphasize and discuss its surgical importance.

METHODS

Fifty dried adult human skulls were obtained from the Department of Anatomy. A 2-mm drill bit was placed externally over the pterion, and the pterion was drilled through the bone perpendicular to the skull's surface.

RESULTS

The midpoint of the H shape in the pterion area was not at the same level on the skull's external and internal pterion surfaces. According to these measurements, the external pterion lay above the internal pterion when the skull was viewed externally. Furthermore, the internal pterion was on average longer than the external pterion. The internal and external pterions were schematized such that the skull was viewed from the outside. These areas were divided into 4 quadrants (anterior-superior, anterior-inferior, posterior-superior, and posterior-inferior) by a vertical and horizontal line. In 30 cases (60%), sulci of the middle meningeal artery's parietal branches entered the posterior-superior quadrant on the bone, whereas the artery's frontal branches were located in the anterior-superior and anterior-inferior quadrants, and the Sylvian fissure's origin was in the posterior-inferior quadrant.

CONCLUSIONS

By using a subdivision into 4 quadrants, and considering our anatomic findings, we determined the way surgical procedures can be performed more easily and reliably. Even with modern localization technologies, anatomic landmarks can be useful to the neurosurgeon.

Endovascular treatment for dural arteriovenous fistulas in the petroclival region

Petroclival region dural arteriovenous fistulas (DAVFs) are rare and difficult lesions to manage. They often have very complex anatomical structures and can be further divided into the superior petrosal sinus, petrous apex, inferior petrosal sinus, upper clival, and upper clival epidural-osseous DAVFs. Most petroclival region DAVFs should be treated due to their high Cognard grades. Currently, endovascular treatment (EVT) has become the first-line therapeutic option for petroclival region DAVFs. But not all the petroclival region DAVFs could be cured with EVT. When the arterial feeders are large or the DAVF is adjacent to the venous sinus, the success rate may be higher. In petroclival region DAVFs, if EVT can be performed successfully, satisfactory outcome can be anticipated. However, there are some inadvertent complications, which include cranial nerve palsy, subsequent sinus thrombosis, and migration embolization of the internal carotid artery and vertebral artery. Currently, a review of the EVT of petroclival region DAVFs is lacking. In this article, we performed a review of the relevant literature on this issue. In addition, some illustrative cases would be provided to elaborate these specific entities.

Histology of the vertebral artery-dural junction: relevance to posterolateral approaches to the skull base

OBJECTIVE

The far-lateral and extreme-lateral infrajugular transcondylar-transtubercular exposure (ELITE) and extreme-lateral transcondylar transodontoid (ELTO) approaches provide access to lesions of the foramen magnum, inferolateral to mid-clivus, and ventral pons and medulla. A subset of pathologies in this region require manipulation of the vertebral artery (VA)-dural interface. Although a cuff of dura is commonly left on the VA to avoid vessel injury during these approaches, there are varying descriptions of the degree of VA-dural separation that is safely achievable. In this paper the authors provide a detailed histological analysis of the VA-dural junction to guide microsurgical technique for posterolateral skull base approaches.

METHODS

An ELITE approach was performed on 6 preserved adult cadaveric specimens. The VA-dural entry site was resected, processed for histological analysis, and qualitatively assessed by a neuropathologist.

RESULTS

Histological analysis demonstrated a clear delineation between the intima and media of the VA in all specimens. No clear plane was identified between the connective tissue of the dura and the connective tissue of the VA adventitia.

CONCLUSIONS

The VA forms a contiguous plane with the connective tissue of the dura at its dural entry site. When performing posterolateral skull base approaches requiring manipulation of the VA-dural interface, maintenance of a dural cuff on the VA is critical to minimize the risk of vascular injury.

The microneurosurgical anatomy legacy of Albert L. Rhoton Jr., MD: an analysis of transition and evolution over 50 years

The authors chronologically categorized the 160 original articles written by Dr. Rhoton and his fellows to show why they selected their themes and how they carried out their projects. The authors note that as neurosurgery progresses and new techniques and approaches are developed, accurate and safe treatment will depend upon continued clarification of microsurgical anatomy.

Surgical relevance of pediatric skull base maturation for the far-lateral and extreme-lateral infrajugular transcondylar-transtubercular exposure approaches

OBJECTIVE

Lesions of the foramen magnum, inferolateral-to-midclival areas, and ventral pons and medulla are often treated using a far-lateral or extreme-lateral infrajugular transcondylar-transtubercular exposure (ELITE) approach. The development and surgical relevance of critical posterior skull base bony structures encountered during these approaches, including the occipital condyle (OC), hypoglossal canal (HGC), and jugular tubercle (JT), are nonetheless poorly defined in the pediatric population.

METHODS

Measurements from high-resolution CT scans were made of the relevant posterior skull base anatomy (HGC depth from posterior edge of the OC, OC and JT dimensions) from 60 patients (evenly distributed among ages 0-3, 4-7, 8-11, 12-15, 16-18, and > 18 years), and compared between laterality, sex, and age groups by using t-tests and linear regression.

RESULTS

There were no significant differences in posterior skull base parameters by laterality, and HGC depth and JT size did not differ by sex. The OC area was significantly larger in males versus females (174.3 vs 152.2 mm2; p = 0.01). From ages 0-3 years to adult, the mean HGC depth increased 27% (from 9.0 to 11.4 mm) and the OC area increased 52% (from 121.4 to 184.0 mm2). The majority of growth for these parameters occurred between the 0-3 year and 4-7 year age groups. Conversely, JT volume increased nearly 3-fold (281%) from 97.4 to 370.9 mm3 from ages 0-3 years to adult, with two periods of substantial growth seen between the 0-3 to 4-7 year and the 12-15 to 16-18 year age groups. Overall, JT growth during pediatric development was significantly greater than increases in HGC depth and OC area (p < 0.05). JT volume remained < 65% of adult size up to age 16.

CONCLUSIONS

When considering a far-lateral or ELITE approach in pediatric patients, standard OC drilling is likely to be needed due to the relative stability of OC and HGC anatomy during development. The JT significantly increases in size with development, yet is only likely to need to be drilled in older children (> 16 years) and adults.

Intradural Combined Transpetrosal Approach for Primary Pontine Hemorrhage

OBJECTIVE

The standard combined transpetrosal approach (CTPA) is fundamentally an epidural approach that has been quite successfully practiced for many decades. However, it has some disadvantages, such as cosmetic problems, difficulties with custom-tailored petrosectomy, and cerebrospinal fluid leakage, as it is a complicated epidural procedure. We describe here a case of primary pontine hemorrhage via intradural CTPA (iCTPA), which is a modified technique of CTPA and includes intradural anterior petrosectomy and partial posterior petrosectomy without mastoidectomy and skeletonization of the sigmoid sinus.

METHODS

A 63-year-old woman with primary pontine hemorrhage underwent surgery via iCTPA to improve postoperative functional outcomes. After the temporal craniotomy without mastoidectomy and skeletonization of the sigmoid sinus, Kawase's triangle and Trautmann's triangle were identified from the intradural space. Resection of Kawase's triangle and partial resection of Trautmann's triangle were performed to approach the frontotemporal surface of the pons. The hematoma was irrigated and totally removed after corticotomy on the pons.

RESULTS

The postoperative symptoms of the patient improved within 2 weeks without surgical complication.

CONCLUSIONS

The intradural approach allows for custom-tailored petrosectomy and is more straightforward than the epidural route, although it can injure the vein of Labbé. Moreover, it can also reduce cosmetic problems and cerebrospinal fluid leakage. iCTPA could provide enough working space for the frontolateral surface of pontine and petroclival lesions without the need for mastoidectomy and skeletonization of the sigmoid sinus.

Microsurgical Anatomy of the Jugular Process as an Anatomical Landmark to Access the Jugular Foramen: A Cadaveric and Radiological Study

BACKGROUND

The jugular process forms the posteroinferior surface of the jugular foramen and is an important structure for surgical approaches to the foramen. However, its morphological features have not been well described in modern texts.

OBJECTIVE

To elucidate the microsurgical anatomy of the jugular process and examine its morphological features.

METHODS

Five adult cadaveric specimens were dissected in a cadaveric study, and computed tomography data from 31 heads (62 sides) were examined using OsiriX (Pixmeo SARL, Bernex, Switzerland) to elucidate the morphological features of the jugular process.

RESULTS

The cadaveric study showed that it has a close relationship with the sigmoid sinus, jugular bulb, rectus capitis lateralis, lateral atlanto-occipital ligament, and lateral and posterior condylar veins. The radiographic study showed that 9/62 sigmoid sinuses protruded inferiorly into the jugular process and that in 5/62 sides, this process was pneumatized. At the entry of the jugular foramen, if the temporal bone has a bulb-type jugular bulb, and if surgery concerns the right side of the head, the superior surface of the jugular process is more likely to be steep.

CONCLUSION

The jugular process forms the posteroinferior border of the jugular foramen. Resection of the jugular process is a critical step for opening the jugular foramen from the posterior and lateral aspects. Understanding the morphological features of the jugular process, and preoperative and radiographical examination of this process thus help skull base surgeons to access the jugular foramen.

Developmental Considerations in Pediatric Skull Base Surgery

Objectives  To review developmental surgical anatomy and technical nuances related to pediatric skull base surgery. Design  Retrospective, single-center case series with literature review. Setting  MD Anderson Cancer Center. Participants  Patients undergoing pediatric skull base surgery. Main Outcome Measures  Review developmental anatomy of the pediatric skull base as it relates to technical nuance of various surgical approaches and insight gained from a 25-year institutional experience with this unique patient population. Results  Thirty-nine patients meeting these criteria were identified over a 13-year period from 2003 to 2016 and compared to a previously reported earlier cohort from 1992 to 2002. The most common benign pathologies included nerve sheath tumors (11%), juvenile nasopharyngeal angiofibromas (9.5%), and craniopharyngiomas (4.8%). The most common malignancies were chondrosarcoma (11%), chordoma (11%), and rabdomyosarcoma (11%). Varied surgical approaches were utilized and were similar between the two cohorts save for the increased use of endoscopic surgical techniques in the most recent cohort. The most common sites of tumor origin were the infratemporal fossa, sinonasal cavities, clivus, temporal bone, and parasellar region. Gross total resection and postoperative complication rates were similar between the two patient cohorts. Conclusions  Pediatric skull base tumors, while rare, often are treated surgically, necessitating an in depth understanding of the anatomy of the developing skull base.

Radiographic Assessment of the presigmoid retrolabyrinthine approach

Background:

Lesions of the petroclival fissure are difficult to access surgically. Both retrosigmoid and presigmoid retrolabyrinthine approaches have been described to successfully treat these complex tumors. The retrosigmoid approach offers quick and familiar access, whereas the presigmoid retrolabyrinthine approach reduces the operative distance and the need for cerebellar retraction. The presigmoid retrolabyrinthine approach, however, is constrained by anatomical limits that can be subject to patient variation. We sought to characterize the surgically relevant variation to guide preoperative assessment.

Methods:

One hundred and seventy-seven high-resolution computed tomography scans of the head (without preexisting pathology) were reviewed. Three hundred and fifty-four temporal bone scans were analyzed for level of aeration, size of Trautmann's triangle dura, and petrous slope. Petrous slope is the angle between the anterior sigmoid sinus and the petroclival fissure at the level of the internal acoustic canal.

Results:

Trautmann's triangle area had a mean of 185.15 mm² (range 71.4–426.7 mm²). Petrous slope had a mean value of 149° (range 106–178°). Increasing aeration was found to be correlated with decreasing petrous slope and decreasing Trautmann's triangle area.

Conclusion:

The presigmoid retrolabyrinthine approach is uniquely confined. Variations in temporal bone anatomy can have dramatic impacts on the operative time, risk profile, and final exposure. Preoperative assessment is critical in guiding the surgeon on the appropriateness of approach. Preoperative measurement of Trautmann's triangle, petrous slope, and aeration can help to reduce surgical morbidity.

Combined Endoscopic Transoral and Endonasal Approach to the Jugular Foramen: A Multiportal Expanded Access to the Clivus

BACKGROUND

The expanded endoscopic endonasal ("far medial") approach to the inferior clivus provides a unique surgical corridor to the ventral surface of the pontomedullary and cervicomedullary junctions. However, exposing neoplasms involving the jugular foramen (JF) through this approach requires extensive nasopharyngeal resection and lateral dissection beyond the boundaries of the endonasal corridor, limiting the extent of resection and restricting to use of this approach to expert surgeons. Here we describe a multiportal endoscopic transoral and endonasal approach to maximize surgical access to the JF and clivus.

METHODS

A multiportal endoscopic transoral and endoscopic approach to the JF and lower clivus was simulated in 8 specimens. A transoral corridor was created through a soft palate incision. The JF and parapharyngeal space were dissected through the transoral trajectory under endoscopic endonasal view. The length of the corridor of the transnasal and transoral trajectories was measured.

RESULTS

The JF was exposed intracranially and extracranially. The exposure extended superiorly to the sphenoid floor, inferiorly to the anterior atlanto-occipital space, and laterally to the internal acoustic meatus and parapharyngeal space. The cisternal parts of the cranial nerves VII-XII and C1 nerve bundles were accessible. Exposure of the JF contents and parapharyngeal space was possible using straight scopes, without Eustachian tube resection. The working corridor to the JF was significantly shorter through the mouth than through the nose (P < 0.0001).

CONCLUSIONS

This approach provides access to the JF from a ventromedial trajectory, enabling panoramic views, and outlines an expanded surgical exposure (superolateral intradural and inferolateral extracranial). It may provide optimal access for resection of dumbbell-shaped lesions of the JF.

Microsurgical anatomy of the lateral condylar vein and its clinical significance

BACKGROUND

Although the lateral condylar vein has been encountered in some skull base approaches and used as a route to access the anterior condylar venous confluence, few descriptions can be found in the literature regarding its morphology.

OBJECTIVE

To examine the anatomy of the lateral condylar vein and its clinical significance.

METHODS

The craniocervical junctions of 3 cadaveric heads, 15 dry bones, and 25 computed tomography venography images were examined.

RESULTS

The lateral condylar vein was identified in 88.0% of paracondylar areas, with an average diameter of 3.6 mm. This vein originated near the jugular bulb, descended along the lateral surface of the occipital condyle and medial to the internal jugular vein, cranial nerves IX to XI, and rectus capitis lateralis muscle to drain into the vertebral venous plexus surrounding the vertebral artery. The veins were classified according to their origin from either (1) the anterior condylar confluence or (2) the internal jugular vein. In some specimens, the lateral condylar vein courses within a small osseous canal lateral to the occipital condyle, the paracondylar canal, which was identified in 16.7% of paracondylar areas in the dry bones.

CONCLUSION

The lateral condylar vein may be encountered in exposing the jugular bulb, hypoglossal canal, or foramen magnum. This vein has been reported to be a main draining route of dural arteriovenous fistulas, in which case it can be utilized as a transvenous route for endovascular treatment, or obliterated. An understanding of the anatomy of this vein may prove useful in planning skull base and endovascular procedures.

Anatomic comparison of anterior petrosectomy versus the expanded endoscopic endonasal approach: interest in petroclival tumors surgery

PURPOSE

Since the petroclival region is deep-seated with close neurovascular relationships, the removal of petroclival tumors still represents a fascinating surgical challenge. Although the classical anterior petrosectomy (AP) offers a meaningful access to this petroclival region, the expanded endoscopic endonasal approach (EEEA) recently leads to overcome difficulties from trans-cranial approaches. Herein, we present an anatomic comparison of AP versus EEEA. We aim to describe the limits of these both approaches helping the choice of the optimal surgical route for petroclival tumors.

METHODS

Six fresh cadaveric heads were harvested and injected with colored latex. Each approach was step-by-step detailed until its final surgical exposure.

RESULTS

The AP provided a narrow direct supero-lateral access to the petroclival area that can also reach the cavernous sinus, the retrochiasmatic region and perimesencephalic cisterns. However, this corridor anterior to the internal acoustic meatus passed on each side of the trigeminal nerve. Moreover, tumor extensions toward the foramen jugularis, inside the clivus or behind the internal acoustic meatus were difficult to control. The EEEA brought a straightforward access to the clivus but the petrous apex was hidden behind the internal carotid artery. Several variants were described: a medial transclival, a lateral through the Meckel's cave and an inferior trans-pterygoid route. Elsewhere, tumor extension behind the internal acoustic meatus or above the tentorium could not be satisfactorily assessed.

DISCUSSION AND CONCLUSION

PA and EEEA have their own limits in reaching the petroclival region in accordance with the tumor characteristics. The AP should be preferred for radical removal of middle-sized petrous apex intradural tumors like meningiomas. The EEEA would be of interest for extradural midline tumors like chordomas or for petrous apex cysts drainage.

Biomechanical effects of the transcondylar approach on the craniovertebral junction

The transcondylar variation of the far-lateral, retrosigmoid approach is intended for pathologies in the anterolateral portion of the foramen magnum. That area is more clearly visualized when a fraction of the ipsilateral occipital condyle is removed. In this study, the biomechanical effect of this approach on occiput-C2 rotation was investigated. Our hypothesis was that the biomechanical characteristics are significantly altered following the transcondylar approach. Five human cadaveric upper cervical spine specimens (occiput-C7) were used in the study. Torsional moments were applied from zero to a maximum of 1.5 N m to the left and to the right using a mechanical testing machine. The resulting rotational motions of the O-C1, C1-2, and O-C2 segments were measured in the intact specimen and after a simulated right-sided transcondylar approach with resection of 2/3 of the condyle, confirmed by CT scanning and visual inspection. After the posterior two-thirds of the occipital condyle were removed, the neutral zone (NZ) increased 1.3° to the left and 2° to the right at C0-C1, and 7.4° to the left and 6.2° to the right at C1-2. The cumulative increase in NZ between O and C2 was 8.7° to the left and 8.2° to the right. The transcondylar approach also resulted in significant increases in range of motion (ROM) in axial rotation to both sides in all segments. ROM increased 2.8° to the left and 2.4° to the right between C0 and C1, 7.3° to the left and 5.4° to the right between C1 and C2, and 10.1° to the left and 7.8° to the right between CO and C2. Upon inspection, the area of the occipital condyle where the alar ligament attaches had been completely removed in three of the five specimens. Removing the posteromedial two-thirds of one occipital condyle alters the normal axial rotational movements of the craniovertebral junction on both sides. The insertion of the alar ligament can be inadvertently removed during condylar resection, and this could contribute to atlanto-axial instability. There is a biomechanical substrate to cranio-cervical instability following a transcondylar approach; these patients may need to be followed over several years to ensure it does not progress and necessitate occipito-cervical fusion.

Microsurgical anatomy of subtotal temporal bone resection en bloc with the parotid gland and temporomandibular joint

BACKGROUND

Subtotal temporal bone resection (STBR) has been used for half a century to remove temporal bone malignancies. However, there are few reports on the detailed anatomy involved in the resection.

OBJECTIVE

To describe the microsurgical anatomy of STBR combined en bloc with the resection of the parotid gland and temporomandibular joint (TMJ).

METHODS

Cadaveric specimens were dissected in a stepwise manner using 3× to 40× magnification.

RESULTS

STBR can be combined with the total parotidectomy and the resection of the TMJ if the tumor extends into the parotid gland, TMJ, or facial nerve. In this study, we describe the step-by-step microsurgical anatomy of STBR en bloc with the parotid gland and TMJ. The surgical technique described combines 3 approaches: the high cervical, subtemporal-infratemporal fossa, and retromastoid-paracondylar approaches. Combining these 3 approaches aided in efficiently completing this modified approach.

CONCLUSION

STBR is a complicated and technically challenging procedure. This study highlights the importance of understanding the surgical anatomy of STBR and will serve as a catalyst for improvement of the surgical technique for temporal bone resection.

Anatomic study of the occipital condyle and its surgical implications in transcondylar approach

Background:

Craniovertebral surgeries require the anatomical knowledge of craniovertebral junction. The human occipital condyle (OC) is unique bony structure connecting the cranium and the vertebral column. A lateral approach like transcondylar approach (TA) requires understanding of the relationships between the OC, jugular tubercle, and hypoglossal canal. Hence, the aim of the present study was to analyze the morphological variations in OCs of dry adult human skull.

Materials and Methods:

The study was carried out on 142 OC of 71 adult human dry skulls (55 males and 16 females). Morphometric parameters such as length, width, thickness, intercondylar distances, and the distances from the OC to the foramen magnum, hypoglossal canal and jugular foramen were measured. In addition, the different locations of the hypoglossal canal orifices in relation to the OC and different shapes of the OC were also noted.

Results:

The average length, width and height of the OC were found to be 2.2, 1.1 and 0.9 cm. The anterior and posterior intercondylar distances were 2.1 and 3.9 cm, respectively. Maximum and minimum bicondylar distances were 4.5 and 2.6 cm, respectively. The intra-cranial orifice of the hypoglossal canal was found to be present in middle 1/3^rd in all skulls (100%), and extra-cranial orifice of the hypoglossal canal was found to be in anterior 1/3^rd (98%) in relation to OC. The oval shaped OC (22.5%) was the most predominant type of OC observed in these skulls.

Conclusion:

Occipital condyle is likely to have variations with respect to shape, length, width and its orientation. Therefore, knowledge of the variations in OC along with careful radiological analysis may help in safe TAs during skull base surgery.

Focal transnasal approach to the upper, middle, and lower clivus

BACKGROUND

Carefully tailoring the transclival approach to the involved parts of the upper, middle, or lower clivus requires a precise understanding of the focal relationships of the clivus.

OBJECTIVE

To develop an optimal classification of the upper, middle, and lower clivus and to define the extra and intracranial relationships of each clival level.

METHODS

Ten cadaveric heads and 10 dry skulls were dissected using the surgical microscope and endoscope.

RESULTS

The clivus is divided into upper, middle, and lower thirds by 2 endocranial landmarks: the dural pori of the abducens nerves and the dural meati of the glossopharyngeal nerves. Useful surgical landmarks exposed in the transnasal approach that aid in locating the junction of the clival divisions are the lower limit of the paraclival segment of the internal carotid artery, which is located 4.9 mm above the posterior opening of the vidian canal, and the pharyngeal tubercle. The upper, middle, and lower clival approaches provide access to the anterior midline parts of the previously described upper, middle, and lower neurovascular complexes in the posterior fossa. The nasal and nasopharyngeal relationships important in expanding the transnasal approach to the borders of the clivus are reviewed.

CONCLUSION

The transclival approach can be carefully tailored to expose focal lesions in the anterior part of the posterior fossa.

The intracranial facial nerve as seen through different surgical windows: an extensive anatomosurgical study

BACKGROUND

The facial nerve has a short intracranial course but crosses critical and frequently accessed surgical structures during cranial base surgery. When performing approaches to complex intracranial regions, it is essential to understand the nerve's conventional and topographic anatomy from different surgical perspectives as well as its relationship with surrounding structures.

OBJECTIVE

To describe the entire intracranial course of the facial nerve as observed via different neurosurgical approaches and to provide an analytical evaluation of the degree of nerve exposure achieved with each approach.

METHODS

Anterior petrosectomies (middle fossa, extended middle fossa), posterior petrosectomies (translabyrinthine, retrolabyrinthine, transcochlear), a retrosigmoid, a far lateral, and anterior transfacial (extended maxillectomy, mandibular swing) approaches were performed on 10 adult cadaveric heads (20 sides). The degree of facial nerve exposure achieved per segment for each approach was assessed and graded independently by 3 surgeons.

RESULTS

The anterior petrosal approaches offered good visualization of the nerve in the cerebellopontine angle and intracanalicular portion superiorly, whereas the posterior petrosectomies provided more direct visualization without the need for cerebellar retraction. The far lateral approach exposed part of the posterior and the entire inferior quadrants, whereas the retrosigmoid approach exposed parts of the superior and inferior quadrants and the entire posterior quadrant. Anterior and anteroinferior exposure of the facial nerve was achieved via the transfacial approaches.

CONCLUSION

The surgical route used must rely on the size, nature, and general location of the lesion, as well as on the capability of the particular approach to better expose the appropriate segment of the facial nerve.

An endoscopic-assisted technique for retrosellar access during the extended retrosigmoid approach: a cadaveric feasibility study and quantitative analysis of retrosellar working area

The retrosigmoid approach has been advocated for certain petroclival tumors but provides limited access to any retrosellar extension of tumor, necessitating a two-stage operation. Our purpose was to demonstrate preliminary feasibility of an endoscopic-assisted technique to provide retrosellar access during the extended retrosigmoid approach and compare microscopic and endoscopic retrosellar working area. Standard retrosigmoid craniectomy and partial petrosectomy respecting inner ear structures were performed on six embalmed cadaveric heads. Two balloons were inflated to simulate a 15 mm petroclival tumor. Retrosellar clival and brainstem working area and ipsilateral oculomotor nerve and posterior cerebral artery (PCA) working distance were measured using the endoscope and microscope. Artificial tumors were implanted and resected using the endoscopic-assisted technique to assess feasibility. The endoscope provided significantly greater mean working area/distance on the clivus (201.6 vs 114.8 mm(2), p < 0.01), brainstem (223.5 vs 121.2 mm(2), p < 0.01), ipsilateral oculomotor nerve (10.8 vs 6.4 mm, p < 0.01), and ipsilateral PCA (13.7 vs 8.9 mm, p = 0.01). Petrous dissection to create a 10 × 10 mm working channel and artificial tumor resection was feasible in all dissections. The superior petrosal vein required ligation in 9 (75%) cases. Air cells were exposed in 1 (8%) case. The described endoscopic-assisted technique can provide retrosellar access during the extended retrosigmoid approach to access petroclival tumors with retrosellar extension. Risks include superior petrosal vein sacrifice, bleeding that can impair visualization, injury to the trigeminal nerve during endoscopic insertion/manipulation or injury to the brainstem while working in the medial limits of exposure. Further work is necessary to determine clinical feasibility, safety, and efficacy.

[Posterior petrosal approach - analysis of the surgical technique in cadavers simulation]

The aim of the study was to present consecutive stages of the posterior petrosal approach (PPA). Eighteen simulations of PPA were performed on non-fixed human cadavers without any known pathologies in the head and neck. The consecutive stages of the procedure were documented with photographs and schemes. The starting point for PPA is a temporal craniotomy, suboccipital craniectomy and mastoidectomy with keeping the bony labyrinth intact. Approach to the middle part of the clivus is achieved by raise of the temporal lobe and section of the superior petrosal sinus and tentorium and by mobilization the sigmoid sinus. Posterior petrosal approach is a reproducible technique, which provides surgical penetration of the middle clivus and related regions. It reduces the operating distance and allows to limit the cerebellum and temporal lobe traction and to preserve the anatomic integrity of the brain stem and cranial nerves of the cerebellopontine angle.

Comparative analysis of the transcranial "far lateral" and endoscopic endonasal "far medial" approaches: surgical anatomy and clinical illustration

OBJECTIVE

The main aim of our study was to analyze and compare the surgical anatomy pertinent to the dorsal transcranial transcondylar (far lateral approach) with that of the ventral endoscopic endonasal transcondylar (far medial approach) route.

METHODS

Eight cadaveric specimens were dissected and analyzed bilaterally. Brainstem exposure and surgical corridor areas were measured. In addition, we present three clinical scenarios to illustrate the clinical feasibility of the proposed surgical strategies.

RESULTS

The hypoglossal nerve, vertebral artery, and hypoglossal canal divide the lower third of the clivus into ventromedial and dorsolateral compartments. The far medial approach provides significantly larger exposure of the brainstem in the ventromedial compartment (464.6 ± 68.34 mm(2)) compared with the far lateral approach (126.35 ± 32.25 mm(2)), P < 0.01. The far lateral approach provides a wide exposure of the brainstem in the dorsolateral compartment (295.24 ± 58.03 mm(2), 74% of the dorsolateral compartment). The exposure of the brainstem in the dorsolateral compartment is not possible using the endonasal route. The surgical corridor from one compartment to the other, through the lower cranial nerves, was significantly larger on the far lateral approach (78.19 ± 14.54 mm(2)) than on the far medial (23.77 ± 15.17 mm(2)), P = 0.03.

CONCLUSIONS

The far medial approach offers a safe, wide exposure of the lower third of the clivus for lesions that expand ventromedial to the hypoglossal nerve. The far lateral approach is most suitable for lesions located dorsolateral to the lower cranial nerves. The vertebral artery and hypoglossal canal are the most important landmarks to guide surgical planning. A combined endonasal-transcranial approach should be considered for resection of extensive lesions involving both ventromedial and dorsolateral compartments. We strive to encourage skull base surgeons to integrate endoscopic and microscopic approaches to the posterior fossa.

Anatomy and pathology of the cranial emissary veins: a review with surgical implications

Emissary veins connect the extracranial venous system with the intracranial venous sinuses. These include, but are not limited to, the posterior condyloid, mastoid, occipital, and parietal emissary veins. A review of the literature for the anatomy, embryology, pathology, and surgery of the intracranial emissary veins was performed. Detailed descriptions of these venous structures are lacking in the literature, and, to the authors', knowledge, this is the first detailed review to discuss the anatomy, pathology, anomalies, and clinical effects of the cranial emissary veins. Our hope is that such data will be useful to the neurosurgeon during surgery in the vicinity of the emissary veins.

Microanatomy and surgical approaches to the infratemporal fossa: an anaglyphic three-dimensional stereoscopic printing study

OBJECTIVE

The infratemporal fossa (ITF) is a continuation of the temporal fossa between the internal surface of the zygoma and the external surface of the temporal bone and greater wing of the sphenoid bone that is sitting deep to the ramus of the mandible. The principal structure to understanding its relationships is the lateral pterygoid muscle. Other important structures are the medial pterygoid muscle, the maxillary artery, the pterygoid venous plexus, the otic ganglion, the chorda tympani nerve and the mandibular nerve. In this study, we describe the microsurgical anatomy of the ITF, as viewed by step-by-step anatomical dissection and also through the perspective of three lateral approaches and one anterior surgical approach.

METHODS

Eight cadaver specimens were dissected. In one side of all specimens, an anatomical dissection was done in which a wide preauricular incision from the neck on the anterior border of the sternoclidomastoid muscle at the level of the cricoid cartilage to the superior temporal line was made. The flap was displaced anteriorly and the structures of the neck were dissected followed by a zygomatic osteotomy and dissection of the ITF structures. On the other side were the surgical approaches to the ITF. The combined infratemporal and posterior fossa approach was done in two specimens, the subtemporal preauricular infratemporal fossa approach in two, the zygomatic approach in two, and the lateral transantral maxillotomy in two. The anatomical dissections were documented on the three-dimensional (3D) anaglyphic method to produce stereoscopic prints.

RESULTS

The lateral pterygoid muscle is one of the principal structures to enable understanding of the relationships into the ITF. The tendon of the temporal muscle inserts in the coronoid process at the ITF. The maxillary artery is the terminal branch of the external carotid artery that originates at the neck of the mandible and runs into the parotid gland. In our dissections the maxillary artery was lateral to the buccal, lingual, and inferior alveolar nerves. We found the second part of the maxillary artery superficial to the lateral pterygoid muscle in all specimens The anterior and posterior branches of the deep temporal artery supply the temporal muscle. In two cases we found a middle deep temporal artery. The different approaches that we used provided different views of the same anatomical landmarks and this provides not only safer surgery but also the best choice to approach the ITF according with the pathology extension.

CONCLUSIONS

The ITF is a complex region on the skull base that is affected by benign and malignant tumors. The study through different routes is helpful to disclose the relationship among the anatomical structures. Although the authors have shown four approaches, there are a variety of approaches and even a combination of these can be used. This type of anatomical knowledge is essential to choosing the best approach to treat lesions in this area.

Anatomo-radiological evaluation of lateral approaches to the skull base

Our objective is to correlate the anatomical exposure provided by complex skull base approaches to the lateral skull base with their CT and MRI scans counterparts and to introduce a modular concept emphasizing the derivation of complex skull base approaches from simpler ones.We executed 10 lateral approaches to the skull base in 20 embalmed cadaveric heads (40 sides). Each approach was executed a minimum of three times on each specimen. These approaches were the pterional and its modifications, the subtemporal and its modifications, and the suboccipital and its modifications. We correlated the approaches and the areas of the skull base exposed by scanning the surgical cavity filled with material imageable by CT and MRI and throughly surveying the operative field.Visualization of the area of the skull base exposed was excellent using our CT-MRI imageable cadaveric preparation. The topographic areas of the skull base exposed correlated well with their radiological counterparts.The areas of the skull base exposed by each of the complex surgical approaches to the skull base were clearly delineated by using our anatomo-radiological correlation. Complex approaches to the skull base are formed by simple neurosurgical approaches (building blocks) to which different modules are added.

Dural and arachnoid membraneous protection of the abducens nerve at the petroclival region

The goal of this study was to determine the membranous protection of the abducens nerve in the petroclival region. The petroclival portion of the abducens nerve was studied in ten dissections from five cadaveric head specimens. One of the heads was used for histological sections. Four heads were injected with colored latex for microsurgical dissections. The histological sections were prepared from petroclival dura mater, embedded in paraffin blocks, stained, sectioned in the axial, coronal, and sagittal planes, and evaluated by light microscopy. The abducens nerve was covered by a dural sleeve and arachnoidal membrane during its course within the petroclival area. Following the petrous apex, the abducens nerve was fixed by a sympathetic plexus and connective tissue extensions to the lateral wall of the cavernous segment of the internal carotid artery and to the medial wall of Meckel's cave. Fibrous trabeculations inside the venous space were attached to the dural sleeve. The lateral clival artery accompanied the dural sleeve of the abducens nerve and supplied the petroclival dura mater. The arterioles accompanying the abducens nerve through the subarachnoid space supplied the nerve within the dural sleeve. The arachnoid membrane covered the abducens nerve within the dural sleeve to the petrous apex, and arachnoid granulations found on the dural sleeve protruded into the venous space. The extension of the arachnoid membrane to the petrous apex and the presence of arachnoid granulations on the dural sleeve suggest that the subarachnoid space continues in the dural sleeve.

Transcrusal approach to the retrochiasmatic region with special reference to temporal lobe retraction: an anatomical study

BACKGROUND

The retrochiasmatic region is one of the most challenging areas to surgically expose. The authors evaluated the transcrusal approach, which involves removal of the superior and posterior semicircular canal from the ampulla to the common crus, to expose the retrochiasmatic region and compared it with the retrolabyrinthine approach, both of which are a variation of the posterior petrosal approach with hearing preservation, with a special emphasis on the influence of temporal lobe retraction.

METHODS

Six sides of silicone-injected cadaveric heads were dissected using two approaches: the transcrusal approach and the retrolabyrinthine approach. For each craniotomy, 3 exposure parameters in the retrochiasmatic region were measured: (1) horizontal distance, (2) vertical distance, and (3) triangular area of exposure, at three different levels of temporal lobe retractions: 0, 5, and 10 mm of retraction from the level of the tentorial incisura.

RESULTS

Without temporal lobe retraction, only the transcrusal and not the retrolabyrinthine approach provided a direct exposure of the retrochiasmatic region, especially in the horizontal distance (p < 0.001). At all levels of temporal lobe retraction, the transcrusal approach provided greater exposure in the horizontal and vertical distances and in the area of exposure. Nonetheless, in the horizontal distance, the difference between the transcrusal and retrolabyrinthine approaches decreased along with increased temporal lobe retraction, and almost no difference was obtained at 10 mm of retraction.

CONCLUSIONS

Posterior petrosal approaches can provide an excellent exposure of the retrochiasmatic region. Of these two approaches, namely, transcrusal and retrolabyrinthine with hearing preservation, the transcrusal approach offers greater exposure than the retrolabyrinthine approach. The beneficial effect of partial labyrinthectomy of the transcrusal approach to the retrochiasmatic region is accentuated in the exposure of the horizontal distance with less temporal lobe retraction.

A new landmark for finding the sigmoid sinus in suboccipital craniotomies

BACKGROUND

The suboccipital craniotomy is one of the most commonly performed neurosurgical approaches.

OBJECTIVE

To define a new cranial landmark, the digastric point, located at the top of the mastoid notch in the mastoid portion of the temporal bone that may assist surgeons performing this craniotomy and to study the relationships between this point and other surface landmarks.

METHODS

Craniometric measures were taken from 127 dry human adult skulls (90 male and 37 female). The measures were taken in millimeters by a digital caliper. Transillumination of the skull with laser or light-emitting diode was used to assess the correspondence of the digastric point in the inner surface of the skull.

RESULTS

The mean distance between the digastric point and the sigmoid sulcus in 254 measures was 3.10 mm (SD, 3.11 mm). The digastric point was over the sulcus of the sigmoid sinus in 49.6% of the cases on the right side and in 29.9% of the cases on the left side. The distance between the jugular point and the stylomastoid foramen was smaller on the right side (mean, 8.89 mm; SD, 2.61 mm; P = .041). Comparing genders regardless of side, the distances between the digastric and jugular points and from the jugular point to the stylomastoid foramen were smaller in female skulls (P = .000 and .006, respectively).

CONCLUSION

The digastric point may be a useful landmark to expose the sigmoid sinus during suboccipital approaches.

Normal anatomical variations of the V₃ segment of the vertebral artery: surgical implications

OBJECT

The authors undertook this cadaveric and angiographic study to examine the microsurgical anatomy of the V₃ segment of the vertebral artery (VA) and its relationship to osseous landmarks. A detailed knowledge of these variations is important when performing common neurosurgical procedures such as the suboccipital craniotomy and the far-lateral approach and when placing atlantoaxial instrumentation.

METHODS

A total of 30 adult cadaveric specimens (59 sides) were studied using magnification × 3 to × 40 after perfusion of the arteries and veins with colored silicone. Seventy-three vertebral angiograms were also analyzed. The morphological detail of the V₃ segment was described and measured in both the cadavers and angiograms. Transarticular screws were placed into 2 cadavers and the relationship of the trajectory to the V₃ segment was analyzed.

RESULTS

The authors identified 4 sites along the V₃ segment that are anatomically the most likely to be injured during surgical approaches to the craniovertebral junction. In 35% of the cadaveric specimens the vertical portion of V₃ formed a posteriorly oriented loop that could be injured during surgical exposures of the dorsal surface of C-2. The mean distance from the midline to the most posteromedial edge of the loop was 25.6 ± 3.5 mm (range 20-35 mm) on the left side and 30.4 ± 3.8 mm (range 23-36 mm) on the right side. On lateral angiograms, this loop projected posteriorly, with a mean distance of 9.8 ± 3.5 mm (range 0-15.7 mm) on the right side and 11.7 ± 1.2 mm (range 10-13.6 mm) on the left side. The horizontal segment of V₃ can be injured when exposing the lower lateral occipital bone and when the C-1 arch is exposed. The mean distance from the inferior border of the occipital bone to the superior surface of the horizontal segment of V₃ was 6 ± 2.8 mm on the right side and 5.6 ± 2.3 mm on the left. In 12% of cases the authors found no space between the horizontal portion of V₃ and the occipital bone. The medial edge of the horizontal segment of V₃ was located 23 ± 5.5 mm (range 10-30 mm) from the midline on the right side and 24 ± 5.7 mm (range 15-32 mm) on the left side. The transition between the V₂-V₃ segments after exiting the C-2 vertebral foramen is the most likely site of injury when placing C1-2 transarticular screws or C-2 pars screws.

CONCLUSIONS

The normal variation of the V₃ segment of the VA has been described with quantitative measurements. An awareness of the anatomical variations and the relationships to the surrounding bony anatomy will aid in reducing VA injury during suboccipital approaches, exposure of the dorsal surfaces of C-1 and C-2, and when placing atlantoaxial spinal instrumentation.