The orbitozygomatic infratemporal fossa approach: a quantitative anatomical study

Quantitative Anatomical Studies in Neurosurgery: A Systematic and Critical Review of Research Methods

BACKGROUND

The anatomy laboratory can provide the ideal setting for the preclinical phase of neurosurgical research. Our purpose is to comprehensively and critically review the preclinical anatomical quantification methods used in cranial neurosurgery.

METHODS

A systematic review was conducted following the PRISMA guidelines. The PubMed, Ovid MEDLINE, and Ovid EMBASE databases were searched, yielding 1667 papers. A statistical analysis was performed using R.

RESULTS

The included studies were published from 1996 to 2023. The risk of bias assessment indicated high-quality studies. Target exposure was the most studied feature (81.7%), mainly with area quantification (64.9%). The surgical corridor was quantified in 60.9% of studies, more commonly with the quantification of the angle of view (60%). Neuronavigation-based methods benefit from quantifying the surgical pyramid features that define a cranial neurosurgical approach and allowing post-dissection data analyses. Direct measurements might diminish the error that is inherent to navigation methods and are useful to collect a small amount of data.

CONCLUSION

Quantifying neurosurgical approaches in the anatomy laboratory provides an objective assessment of the surgical corridor and target exposure. There is currently limited comparability among quantitative neurosurgical anatomy studies; sharing common research methods will provide comparable data that might also be investigated with artificial intelligence methods.

Combined Exoscopic- and Endoscopic-Assisted Resection of an Interpeduncular and Middle Fossa Epidermoid Cyst via a Transcavernous Approach: Technical Note

OBJECTIVE

The endoscope and exoscope are gaining momentum as alternative visualization tools in the neurosurgical field, trying to overcome the limitations of an operative microscope and support minimally invasive approaches. However, few case series are available in the literature regarding their use in skull base surgery, especially in combined assisted resection, and their usefulness still needs to be proved.

METHODS

An illustrative case to present the feasibility and minimally invasive advantages of a combined exoscopic- and endoscopic-assisted resection is reported.

RESULTS

A 22-year-old man presented with a history of seizures and dizziness. Brain imaging showed a lesion involving the anteromedial middle fossa invading the interpeduncular cistern and impinging the brainstem, suggestive of an epidermoid cyst. A combined exoscopic- and endoscopic-assisted resection through a pterional transcavernous approach was planned and performed. No neurologic deficit occurred after the surgery, providing further evidence about the usefulness and safety of this hybrid technique.

CONCLUSIONS

Combined exoscopic and endoscopic resection is also feasible and safe in complex skull base surgery. Moreover, this technique seems to be effective for minimizing the surgical invasiveness in skull base lesions.

The Orbitozygomatic Craniotomy and Its Judicious Use

The concept of maximizing bone removal along the skull base has been advocated to expand the operative space for large, firm, and encasing ventral and ventrolateral skull base tumors. However, indications for the use of such osteotomies have not been well defined. The improved maneuverability and enhanced extent of expansion of the operative corridor via the skull base approaches compared to those of standard craniotomies have been based on cadaveric studies that might not simulate the operative environment realistically. Bony removal alone is not adequate to protect neurovascular structures, and strategic use of dynamic retraction and innovative operative routes are some of the other factors that contribute to successful microsurgery. In this analysis, the more discriminate indications and modified techniques for orbitozygomatic osteotomy are discussed.

The Ultimate Skull Base Maneuver Does Not Involve Removing Bone: Quantifying the Benefits of the Interfascial Dissection

Introduction  Several adjunctive osteal skull base maneuvers have been proposed to increase surgical exposure of the anterolateral approach. However, one of the easiest methods does not involve bone: the interfascial temporalis muscle dissection. Methods  Sequential dissections were performed bilaterally on five fixed silicone-injected cadaver heads. The amount of sphenoid drilling, scalp retraction, and brain retraction was standardized in all specimens. For each approach, surgical angles were measured for four deep targets: the tip of the anterior clinoid process, the internal carotid artery terminus, the origin of the posterior communicating artery, and the anterior communicating artery. Five surgical angles were measured for each target. Results  There were increases on the order of 20% in the anteroposterior (AP)-mid, AP-lateral, and mediolateral-anterior angles for all deep targets with interfascial approach versus a myocutaneous flap. An orbitozygomatic osteotomy additionally increased almost all the angles, but incrementally less so. Conclusion  An interfascial dissection increases the surgical exposure to a larger degree than additional osteotomies for several surgically relevant working angles. The addition of an orbitozygomatic osteotomy affords a particular benefit for the suprachiasmatic region. Increased adoption of interfascial mobilization or the temporalis muscle-an easily performed and low-risk maneuver-during anterolateral craniotomies may obviate the need for more involved skull base drilling.

Analysis of Surgical Freedom Variation Across the Basilar Artery Bifurcation: Towards a Deeper Insight Into Approach Selection for Basilar Apex Aneurysms

BACKGROUND

The orbitozygomatic approach is generally advocated over the pterional approach for basilar apex aneurysms. However, the impact of the extensions of the pterional approach on the obtained maneuverability over multiple vascular targets (relevant to basilar apex surgery) has not been studied before.

OBJECTIVE

To analyze the patterns of surgical freedom change across the basilar bifurcation between the pterional, orbitopterional, and orbitozygomatic approaches.

METHODS

Surgical freedom was assessed for 3 vascular targets important in basilar apex aneurysm surgery (ipsilateral and contralateral P1-P2 junctions, and basilar apex), and compared between the pterional, orbitopterional, and orbitozygomatic approaches in 10 cadaveric specimens.

RESULTS

Transitioning from the pterional to orbitopterional approach, the surgical freedom increased significantly at all 3 targets (P < .05). However, the gain in surgical freedom declined progressively from the most superficial target (60% for ipsilateral P1-P2 junction) to the deepest target (35% for contralateral P1-P2 junction). Conversely, transitioning from the orbitopterional to the orbitozygomatic approach, the gain in surgical freedom was minimal for the ipsilateral P1-P2 and basilar apex (<4%), but increased dramatically to 19% at the contralateral P1-P2 junction.

CONCLUSION

The orbitopterional approach provides a remarkable increase in surgical maneuverability compared to the pterional approach for the basilar apex target and the relevant adjacent arterial targets. However, compared to the orbitopterional, the orbitozygomatic approach adds little maneuverability except for the deepest target (ie, contralateral P1-P2 junction). Therefore, the orbitozygomatic approach may be most efficacious with larger basilar apex aneurysms limiting the control over of the contralateral P1 PCA.

Comprehensive Anatomic Assessment of the Pterional, Orbitopterional, and Orbitozygomatic Approaches for Basilar Apex Aneurysm Clipping

BACKGROUND

The pterional approach, along with its orbitopterional and orbitozygomatic extensions, is among the most common surgical approaches for tackling challenging aneurysms of the basilar artery apex (BAX). There is general consensus that the orbitozygomatic approach provides the best exposure for these lesions. However, there is little objective evidence to support approach selection for surgical treatment of BAX aneurysms.

OBJECTIVE

To compare different features regarding surgical treatment of BAX aneurysms between the pterional, orbitopterional, and orbitozygomatic approaches.

METHODS

The pterional, orbitopterional, and orbitozygomatic approaches were sequentially completed on 10 cadaveric specimens. The visibility of perforators, lengths of exposure, and safe clipping for major BAX branches, surgical area of exposure, and the surgical freedom for the BAX target were assessed.

RESULTS

The orbitopterional approach provided significantly greater values than the pterional approach in all variables, except for exposure of the bilateral P1 posterior cerebral artery (PCA) perforators. When compared to the orbitopterional approach, the orbitozygomatic approach did not provide a statistically significant increase in (1) surgical freedom through the carotid-oculomotor triangle, (2) area of exposure, (3) ipsilateral, and (4) contralateral P1 PCA perforator visibility, and (5) ipsilateral PCA exposure and (6) clipping lengths.

CONCLUSION

The orbitopterional approach provides significantly greater surgical exposure to BAX than the pterional approach. The orbitopterional approach is less invasive while providing similar surgical access to the BAX compared to the orbitozygomatic. The results of this study show that the orbitopterional approach may be optimal for the treatment of most BAX aneurysms, particularly to reduce morbidity resulting from the full orbitozygomatic approach.

Single piece fronto-temporo-orbito-zygomatic craniotomy: a personal experience and review of surgical technique

BACKGROUND

Fronto-Temporo-Orbito-Zygomatic (FTOZ) craniotomy has progressed from its humble beginnings. Numerous variations including one piece, two piece and even three piece FTOZ craniotomies have been described. The ideal technique still remains elusive and its use remains restricted to a few specialised centres even when benefits far outweigh the surgical difficulties.

OBJECTIVE

To analyse 11 cases in which single piece FTOZ craniotomy was used and to review the steps of surgery along with its advantages.

METHODS

A total of 11 cases of skull base lesions were operated over a period of 30 months and followed up for a minimum period of 6 months. They were analysed for intraoperative benefits, requirement of cerebral retraction, surgical difficulties, post op recovery, complications faced and post-op cosmetic appearance.

RESULT

A total of nine cases had tumours of skull base including Spheno-Petro-Clival meningiomas, Trigeminal schwannomas, Solitary fibrous histiocytoma and two had giant aneurysms of P1 segment. Intraoperative cerebral retraction was significantly less. There were two post-op deaths. Three patients had temporary and 1 patient had permanent third nerve deficit. There was no injury to periorbital fat and post op cosmetic appearance was good.

CONCLUSION

Single piece FTOZ craniotomy is no more difficult than two or three piece craniotomy, rather it facilitates a rapid craniotomy closure with excellent handling of single piece of bone. It provides a wide, multidirectional access to skull base. Lesions become shallow and their access easier. Benefits far outweigh the difficulties if any, and its use should be encouraged even at centres outside of the specialised units.

A morphometric and analytical cadaver dissection study of a tumor-simulation balloon model

We quantified the effects on anatomical cadaver dissection of a balloon-inflation tumor model positioned in the parasellar region and approached through an orbitozygomatic (OZ) craniotomy. A modified supraorbital OZ was performed bilaterally on 5 silicon-injected cadaver heads. Ten predetermined anatomical points assigned using a frameless stereotactic device were used to measure the working area of exposure, degree of surgical freedom, and horizontal and vertical angles of attack to specific target points before and after inflation of a balloon catheter mimicking a parasellar tumor. Balloon inflation displaced the central anatomical structures (pituitary stalk, lamina terminalis, anterior chiasm, and internal carotid artery [ICA]-posterior communicating artery and ICA-A1 junctions) by 14-51% (p ≤ .05). With tumor simulation, the vertical angle of attack increased by 67% (p < .01), while the area of exposure increased by 83% (p < .01) and surgical freedom increased by 58% (p < .01). This tumor model also significantly displaced central anatomical sella-associated structures. Compared to a normal anatomical configuration, the tumor simulation (balloon) opened surgical corridors (especially vertical) and acted as a natural retractor, widening the angle of access to the infundibular apex-hypothalamic junction. Although this model cannot exactly mimic a tumor mass in a patient, the effects of tumor compression and sequential displacement of important structures can be combined into and then assessed in a cadaveric neurosurgical anatomical scenario for training and research.

Resection of tumors of the third ventricle involving the hypothalamus: effects on body mass index using a dedicated surgical approach

Resection of large lesions growing into the third ventricle is considered nowadays still a demanding surgery, due to the high risk of severe endocrine and neurological complications. Some neurosurgical approaches were considered in the past the procedures of choice to access the third ventricle, however they were burden by endocrine and neurological consequences, like memory loss and epilepsy. We report here the endocrine and functional results in a series of patients operated with a recently developed approach specifically tailored for the resection of large lesions growing into the third ventricle. Authors conducted a retrospective analysis on 10 patients, operated between 2011 and 2012, for the resection of large tumors growing into the third ventricle. Total resection was achieved in all patients. No perioperative deaths were recorded and all patients were alive after the follow-up. One year after surgery 8/10 patients had an excellent outcome with a Karnofsky Performance Status of 100 and a Glasgow Outcome score of 5, with 8 patients experiencing an improvement of the Body Mass Index. Modern neurosurgery allows a safe and effective treatment of large lesions growing into the third ventricle with a postoperative good functional status.

Quantification and comparison of neurosurgical approaches in the preclinical setting: literature review

There is a growing awareness of the need for evidence-based surgery and of the issues that are specific to research in surgery. Well-conducted anatomical studies can represent the first, preclinical step for evidence-based surgical innovation and evaluation. In the last two decades, various reports have quantified and compared neurosurgical approaches in the anatomy laboratory using different methods and technology. The aim of this study was to critically review these papers. A PubMed and Scopus search was performed to select articles that quantified and compared different neurosurgical approaches in the preclinical setting. The basic characteristics that anatomically define a surgical approach were defined. Each study was analyzed for measured features and quantification method and technique. Ninety-nine papers, published from 1990 to 2013, were included in this review. A heterogeneous use of terms to define the features of a surgical approach was evident. Different methods to study these features have been reported; they are generally based on quantification of distances, angles, and areas. Measuring tools have evolved from the simple ruler to frameless stereotactic devices. The reported methods have each specific advantages and limits; a common limitation is the lack of 3D visualization and surgical volume quantification. There is a need for a uniform nomenclature in anatomical studies. Frameless stereotactic devices provide a powerful tool for anatomical studies. Volume quantification and 3D visualization of the surgical approach is not provided with most available methods.

Microsurgical anatomy of the transsylvian translimen insula approach to the mediobasal temporal lobe: Technical considerations and case illustration

Background:

Various vascular, neoplastic, and epileptogenic pathologies occur in the mediobasal temporal region. A transsylvian translimen insula (TTI) approach can be used as an alternative to temporal transcortical approach to the mediobasal temporal region. The aim of this study was to demonstrate the surgical anatomy of the TTI approach, including the gyral, sulcal, and vascular anatomy in and around the limen insula. The use of this approach is illustrated in the resection of a complex arteriovenous malformation.

Methods:

The TTI approach to the mediobasal temporal region was performed on three silicone-injected cadaveric heads. The gyral, sulcal, and arterial anatomy of the limen insula was studied in six formalin-fixed injected hemispheres.

Results:

The TTI approach provided access to the anterior and middle segments of the mediobasal temporal lobe region as well as allowing access to temporal horn of the lateral ventricle. Using this approach we were able to successfully resect an arteriovenous malformation of the dominant medial temporal lobe.

Conclusion:

The TTI approach provides a viable surgical route to the region of mediobasal temporal lobe region. This approach offers an advantage over the temporal transcortical route in that there is less risk of damage to optic radiations and speech area in the dominant hemisphere.

When is posterolateral orbitotomy useful in a pterional craniotomy? A morphometric study

Adding posterolateral orbitotomy to pterional craniotomy allows greater exposure of the anterolateral skull base. However, there is a paucity of literature quantifying the relative benefit of adding posterolateral orbitotomy for various surgical targets. Our study is a step to address this issue. We performed dissections of five cadaveric heads (10 sides). The anterior communicating artery (A-Com) complex, posterior chiasm (anterior third ventricular region), ipsilateral optic canal, and ipsilateral supraclinoid internal carotid artery (ICA) bifurcation were chosen as targets. A pterional craniotomy was performed and the targets were morphometrically analyzed. Subsequently, posterolateral orbitotomy was done and analysis repeated. The field of view and measurements quantifying the angle of attack were compared. Addition of orbitotomy to pterional craniotomy increased the angle of exposure to ICA bifurcation, anterior third ventricular region, and A-Com complex by average of 15%, 29%, and 50%, respectively. Our study shows the addition of a posterolateral orbitotomy to the pterional craniotomy improves the angle of attack to the anterior third ventricular region and the A-Com complex, thus supporting the use of orbitopterional craniotomy for suprasellar lesions extending into anteroinferior third ventricle and A-Com aneurysms that point superiorly/posteriorly.

Zygomatic anterior subtemporal approach for lesions in the interpeduncular cistern

The interpeduncular cistern is a difficult region to approach through conventional methods due to its deep location and important adjacent neurovascular structures. Therefore, it is usually difficult to expose the region sufficiently. Technical problems associated with various surgical approaches have led to emergence of combined approaches and their modifications (i.e., the removal of the zygomatic arch). In addition, a frontotemporal craniotomy is reported to provide a wide exposure of the anterior temporal base, thus allowing oblique access to the interpeduncular cistern with minimal brain retraction. This study describes clinicians' experience and the surgical results of 24 patients who underwent a zygomatic anterior subtemporal approach.

Quantitative evaluation of transtemporal and facial translocation approaches to infratemporal fossa

OBJECTIVE

To compare the extent of exposure and surgical maneuverability provided by facial translocation and transtemporal approaches for access to the infratemporal fossa and anterolateral skull base.

MATERIALS AND METHODS

Surgical procedures were performed on five fresh frozen adult cadavers (ten sides) with no known pathology. Facial transfacial approaches with and without a mandibulotomy and transtemporal approaches were evaluated. OBJECTIVE measures were (1) the distance from the surgical plane to designated anatomic landmarks and (2) the surgical angle of exposure.

RESULTS

Distances from the surgical plane to the anatomic reference points were comparable for most of the access procedures (3 to 6 cm). The extended midfacial translocation and bilateral facial translocation approaches did, however, provide a shorter operative distance (1 to 3 cm) for access to the infratemporal fossa and contralateral structures, respectively. The transtemporal approaches facilitate a better angle of exposure (74 to 84 degrees) to the petrotemporal region, while the transfacial approaches were superior for access to the infratemporal structures.

CONCLUSIONS

Based on the results, we propose a clinical algorithm for selecting a surgical approach based on the position and extent of an infratemporal or petrotemporal lesion.

Lateral orbital rim osteotomy in the treatment of certain skull base lesions

Quantitative data from a recent human cadaveric study suggested that removal of the lateral orbital rim alone may be sufficient to reach many targets for which the orbitozygomatic craniotomy has been used. Consequently, a lateral orbital rim osteotomy was substituted for an orbitozygomatic craniotomy in seven patients with a variety of pathologies located in the anterior, middle, and interpeduncular fossae. In each case, lateral orbitotomy provided a satisfactory surgical corridor for diagnosis and treatment. Compared with the orbitozygomatic craniotomy, the lateral orbital rim osteotomy offers several advantages: technical simplicity, shorter operating time, and a low risk of postoperative malocclusion. If, however, prolonged access to a wide expanse of the anterior portion of the middle fossa and inferotemporal area is needed, an orbitozygomatic approach is a better choice.

[Fronto-temporo-orbito-zygomatic approach - analysis of the surgical technique on cadaver simulations]

This paper presents consecutive stages of the fronto-temporo-orbito-zygomatic approach (FTOZA). Two simulations of FTOZA 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 schematic diagrams. The starting point for FTOZA is a pterional craniotomy and osteotomy including the orbital rim, body of the zygomatic bone and zygomatic arch. In justified cases it is also possible to temporarily remove the upper and lateral walls of the orbit. Wide drawing apart of the Sylvian fissure is an important supplement of the approach. The fronto-temporo-orbito-zygomatic approach is a reproducible technique, which provides surgical penetration of the middle cranial fossa and related regions. This approach is particularly useful in the treatment of tumours of the above-mentioned anatomical areas as well as vascular malformation of the posterior part of the arterial circle of the brain.

Temporal craniotomy for surgical access to the infratemporal fossa

We propose a surgical approach for select patients that minimizes morbidity while allowing gross total resection of lesions in the anterior portion of the infratemporal fossa. The approach we describe is an extradural approach through a subtemporal craniectomy or craniotomy with the possible addition of a zygomatic osteotomy. Lesions that have a well-defined capsule and a texture that permits manipulation are ideal for this less invasive approach. We retrospectively reviewed six cases from the primary author (C.B.H.) using a temporal craniectomy or craniotomy alone to resect lesions in the infratemporal fossa. All six cases had good clinical outcomes with no unexpected neurological deficits while achieving gross total resections. The only complication included one cerebrospinal fluid leak that was sealed endoscopically. For select lesions, a less morbid surgical approach via an extradural window through a subtemporal craniectomy or small craniotomy may be preferable to transfacial approaches. Adjuvant use of endoscopic techniques may facilitate surgical exposure and resection of large lesions.

The relationship between the zygomatic arch and the floor of the middle cranial fossa: a radiographic study

OBJECTIVE

Access to the floor of the middle cranial fossa (MCF) is often required for approaches to cranial base lesions. This study measures the craniocaudal distance between the zygomatic arch (ZA) and the floor of the MCF from a random sample of high-resolution computed tomography scans of the cranial base.

METHODS

Forty computed tomography scans were imported into an OsiriX station and reconstructed in multiple planes. The most caudal point of the MCF was determined in each computed tomography scan. The distances between that point and the root of the zygoma and the middle point of the ZA were calculated. The thickness of the temporalis muscle and the vertical height of the zygoma were also calculated. A 2-tailed, paired Student t test was used to compare right and left measurements with a 95% confidence interval and P value <.05 as statistically significant.

RESULTS

The foramen ovale was consistently the lowest point of the MCF. The average root-to-floor measurement was 5.05 +/- 0.42 mm above the floor of the MCF and distance of the mid-zygoma to the floor was 1.94 +/- 0.61 mm above the floor of MCF. The average temporalis muscle thickness and vertical height of the ZA were 22.22 +/- 0.36 mm and 8.10 +/- 0.13 mm, respectively. The muscle-to-floor measurement (muscle thickness + mid-zygoma-to-floor measurement) was 24.16 +/- 0.74 mm.

CONCLUSION

The routine use of a zygomatic osteotomy in approaches to the MCF does not provide very much increased exposure. However, in patients with exceptionally thick temporalis muscles or a high ZA, a zygomatic osteotomy may be helpful in providing exposure of the floor of the MCF.

[Extended subtemporal approach to the subtemporal fossa and related structures - analysis of the surgical technique based on cadaver simulation]

The aim of the study was to present consecutive stages of the extended subtemporal approach (ESA). Seven simulations of ESA 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 ESA is osteotomy of the zygomatic arch and craniectomy including the greater wing of the sphenoid bone. Dislocation or removal of subtemporal fossa contents allows one to penetrate its inside and related structures. Additional widening of inspection allows osteotomy of the condyloid process of the mandible. ESA is a reproducible technique which provides surgical penetration of the subtemporal fossa and related structures. This approach is particularly useful in the surgical treatment of tumours expanding in the orbit, maxillary sinus, pterygopalatine fossa, nasopharynx, sphenoid sinus, cavernous sinus, parapharyngeal space, retromandibular fossa and surroundings of the petrosal part of the internal carotid artery.

Malignant Tumors of the Anterolateral Skull Base

OBJECTIVE

Malignancies of the anterolateral skull base are clinically and pathologically distinct from those of the central anterior skull base and the temporal bone. The purpose of this report is to describe the outcomes and complications after skull base surgery and multimodality therapy in a group of patients with anterolateral skull base malignancies.

PATIENT DATA AND METHODS

The mean duration of follow-up for living patients was 57.2 months (median, 56.8 months). The median age of the 52 patients who met the inclusion criteria for this study was 47 years (range, 1–81 years). The most common presenting feature was cranial nerve palsy (60%). Of these cranial nerve palsies, trigeminal neuropathies causing facial numbness were the most common, with V2 being affected in 35%, V3 affected in 33%, and V1 affected in 17%. Abducens neuropathy was present in 14% of patients. The most frequently occurring pathologies after the various sarcomas were squamous cell carcinoma (SCC) and adenoid cystic carcinoma (ACC) in 23% and 14% of patients, respectively. Of the 30 sarcomas, 16 were classified as low grade and 14 were classified as high grade.

RESULTS

Complications of treatments were identified in 16 patients (31%). Ten patients had a single complication, whereas 6 patients experienced multiple complications. The most common complications were a new or worsened cranial nerve deficit (n = 4), pneumonia (n = 4), and flap necrosis (n = 3). Recurrence after the treatment associated with the index surgery occurred in 37 patients (71%). The recurrence was local in 30 patients (58%), both local and distant (metastatic) in 4 patients (8%), and only distant in 3 patients (12%). The median progression-free survival (PFS) was 2.1 years (range, 1.2–3.0 years). Median PFS times of 0.6 and 1.6 years were noted for patients with high-grade sarcoma (HGS) and low-grade sarcoma (LGS), respectively. The mean PFS (median not reached) for the patients with SCC was 4.6 years, whereas the median PFS for patients with ACC was 3.3 years. The overall 2- and 5-year survivals for all patients were 81% and 53% (median, 5.0 years; 95% confidence interval, 3.9–6.1 years), respectively. The median survival for patients with nonsarcomas was 6.9 years, the 2-year survival was 82%, and the 5-year survival was 55%. Patients with HGS survived the shortest time (median, 3.3 years; 2-year, 64%; 5-year, 27%), whereas those patients with LGS had an intermediate survival (median, 5.3 years; 2-year, 94%, 5-year, 72%).

CONCLUSION

It is our belief that anterolateral skull base malignancies comprise a distinct group of tumors. These lesions should be analyzed separately from central anterior skull base lesions and temporal bone malignancies. With a multimodality treatment protocol, acceptable survivals may be obtained that are comparable to results that have been reported for tumors involving less difficult areas of the skull base.

Modified orbitozygomatic craniotomy for craniopharyngioma resection in children

OBJECT

In this study, the authors evaluated the efficacy and safety of modified orbitozygomatic craniotomy for resection of craniopharyngioma in children.

METHODS

A prospective, institutional review board-approved database was retrospectively reviewed for pediatric patients undergoing craniopharyngioma resection performed by a single surgeon.

RESULTS

Ten patients underwent craniopharyngioma resection surgery between July 2000 and January 2006 (4 girls and 6 boys, ages 1.5-17 years). Nine patients presented to the authors' institution, and 1 patient was referred after surgery and radiation therapy were administered elsewhere. Nine patients presented with visual field deficits (2 with unilateral or bilateral light perception only) and 5 with endocrine dysfunction. Eight patients had large tumors that significantly displaced the optic chiasm and hypothalamus. All patients underwent a modified frontotemporal orbitozygomatic osteotomy in a single piece. The lamina terminalis was opened in 4 patients with third ventricular extension. One patient required a staged transsphenoidal operation to remove residual tumor in the sella turcica, and 1 patient underwent a contralateral subtemporal approach to resect a daughter lesion in the prepontine cistern. Complete radiographic resection was achieved in all patients. Follow-up averaged 55 months (range 12-95 months). Vision was improved in 8 patients and remained stable in 2. All patients had postoperative endocrine dysfunction. One patient experienced transient cranial nerve IV palsy and 1 suffered a small caudate stroke 5 months after surgery without sequelae. Two patients experienced polyphagia and weight gain without other symptoms of hypothalamic dysfunction. There were no other new neurological deficits.

CONCLUSIONS

Modified orbitozygomatic craniotomy provides excellent exposure of the suprasellar region with minimal brain retraction, allowing complete resection of craniopharyngiomas with good visual and neurological results.

Orbital restoration surgery in the zygomaticotemporal and zygomaticofacial nerves and important anatomic landmarks

A variety of etiologies may result in functional and aesthetic deficiencies requiring orbital reconstruction. Fractures of the zygomaticomaxillary complex in the acute stage are frequently accompanied by sensory disturbances of the zygomatic nerve (ZN). The purpose of the current study was to describe the anatomic and topographic landmarks of the ZN in 18 adult human cadavers regarding the localization and dimensions in the orbit. The zygomaticotemporal (ZTN) and zygomaticofacial nerves (ZFN) along the lateral wall of the orbit passed through the zygomaticotemporal and zygomaticofacial foramens, respectively. The angle between the ZTN and the ZFN within the orbit was approximately 42.21 degrees. The mean (SD) distance between the orbital opening of the ZTN and the meeting point of the ZTN was measured as 9.21 (5.18) mm. The mean (SD) distance between the orbital opening of the ZFN and the meeting point of the ZTN was calculated as 11.22 (4.25) mm. The mean (SD) distance between the orbital opening of the ZFN and the infraorbital margin of the orbit was 13.04. (3.21) mm. A detailed knowledge of the ZN's passage in the orbit is necessary for a surgeon while performing maxillofacial surgery. If these measurements are taken into account, there will be little surgical risk, and this will be helpful in identifying the extent of the operative field.

The supracarotid-infrafrontal approach: surgical technique and clinical application to cavernous malformations in the anteroinferior Basal Ganglia

OBJECTIVE

Many symptomatic cavernous malformations deep in the anteroinferior basal ganglia are deemed to be inoperable and managed conservatively because transcortical, transsylvian-transinsular, and transcallosal approaches are unsuitable. We present an approach to these lesions through the supracarotid triangle, between ascending perforators, and through the basomedial frontal lobe.

METHODS

The supracarotid-infrafrontal approach incorporates an orbitozygomatic craniotomy, wide microsurgical exposure of the supracarotid triangle, dissection of perforating arteries, and image-guided resection through the posterior part of the medial orbital gyrus and anterior perforated substance.

RESULTS

During 10 years of surgical experience with 269 patients with cavernous malformations, 5 patients were identified with lesions in the basal ganglia that were resected completely using the supracarotid-infrafrontal approach. Transient neurological deficits were observed postoperatively in 2 patients, and all patients had excellent outcomes (modified Rankin Scale score of 0 or 1; mean duration of follow-up, 1.4 years).

CONCLUSION

Cavernous malformations in the anteroinferior basal ganglia come to the brain surface directly behind the internal carotid artery bifurcation, and the supracarotid-infrafrontal trajectory best matches the lesions' axes. The surgical corridor runs between perforating arteries, but entrance into these lesions opens additional working space that is not normally present when the approach is used with aneurysms. Careful handling of crossing and ascending perforating arteries is critical, as is delicate dissection of the lesion's superior pole where it abuts the internal capsule.

The work horse of skull base surgery: orbitozygomatic approach. Technique, modifications, and applications

Object

The aim of this study was to describe the microsurgical anatomy of the orbitozygomatic craniotomy and its modifications, and detail the stepwise dissection of the temporalis fascia and muscle and explain the craniotomy techniques involved in these approaches.

Methods

Nine cadaveric embalmed heads injected with colored silicone were used to demonstrate a stepwise dissection of the 3 variations of orbitozygomatic craniotomy. The craniotomies and dissections were performed with standard surgical instruments, and the microsurgical anatomy was studied under microscopic magnification and illumination.

Results

The authors performed 2-piece, 1-piece, and supraorbital orbitozygomatic craniotomies in 3 cadaveric heads each. Stepwise dissection of the temporalis fascia and muscle, and osteotomy cuts were shown and the relevant microsurgical anatomy of the anterior and middle fossae was demonstrated in cadaveric heads. Surgical case examples were also presented to demonstrate the application of and indications for the orbitozygomatic approach.

Conclusions

The orbitozygomatic approach provides access to the anterior and middle cranial fossae as well as the deep sellar and basilar apex regions. Increased bone removal from the skull base obviates the need for vigorous brain retraction and offers an improved multiangled trajectory and shallower operative field. Modifications to the orbitozygomatic approach provide alternatives that can be tailored to particular lesions, enabling the surgeon to use the best technique in each individual case rather than a “one size fits all” approach.

Quantification of the frontotemporal orbitozygomatic approach using a three-dimensional visualization and modeling application

OBJECTIVE

We sought to simulate the frontotemporal orbitozygomatic (FTOZ) craniotomy in a three-dimensional virtual environment on patient-specific data and to quantify the exposure afforded by the FTOZ while simulating controlled amounts of brain retraction.

METHODS

Four computed tomographic angiograms were reconstructed with commercially available software (Amira 4.1.1; Mercury Computer Systems, Inc., Chelmsford, MA), and virtual FTOZ craniotomies were performed bilaterally (n = 8). Brain retraction was simulated at 1 and 2 cm. Surgical freedom and projection angle were measured and compared at each stage of the FTOZ.

RESULTS

At 1 cm of retraction, surgical freedom increased by 27 +/- 14% for the removal of the orbital rim and by 31 +/- 18% for FTOZ (P < 0.01) when compared with frontotemporal (FT) craniotomy. At 2 cm of retraction, surgical freedom increased by 15 +/- 5% and 26 +/- 8% for the removal of the orbital rim and FTOZ, respectively (P < 0.01). With increased retraction, surgical freedom increased by 100 +/- 26%, 81 +/- 15%, and 82 +/- 27% for the FT, removal of the orbital rim, and FTOZ craniotomies, respectively (P < 0.001). Projection angle increased by 24.2% when orbital rim removal was added to the FT craniotomy (P < 0.01).

CONCLUSION

Surgical freedom increases significantly at every step of the FTOZ craniotomy. This effect is less robust when brain retraction is increased. Brain retraction alone has a greater impact on surgical freedom than bone removal alone. Projection angle is significantly increased when orbital rim removal is added to the FT craniotomy. This model overcomes two major limitations of cadaver-based models: quantification of brain retraction and incorporation of patient-specific anatomy.

Long-term outcome following radical temporal bone resection for lateral skull base malignancies: a neurosurgical perspective

OBJECT

Primary temporal bone malignancy is a rare form of tumor for which the therapeutic strategy remains controversial. In this study, the authors reviewed their experience with radical temporal bone resection (TBR) of such lesions and analyzed the long-term results to provide treatment recommendations.

METHODS

Between 1994 and 2006, 17 patients (10 men and 7 women) underwent total or subtotal TBR for primary temporal bone malignancies. Tumors were graded according to the University of Pittsburgh system. The effects of surgical margins and tumor extensions on patient survival were analyzed using the Kaplan-Meier method.

RESULTS

All tumors, except 1, were graded T4 (most advanced). Subtotal TBR was performed in 14 patients, and total TBR was performed in 3. The surgical margin was tumor negative in 10 patients and tumor positive in 7. For large tumors extending into the infratemporal fossa or encroaching on the jugular foramen, orbitozygomatic (3 patients) and posterior transjugular (4 patients) approaches were combined with the standard approach, and en bloc resection with a negative margin was achieved in all cases but 1. The follow-up time ranged from 0.3-11.6 years (mean 3.3 years). The 5-year recurrence-free and disease-specific survival rates were 67.5 and 60.1%, respectively. When a negative surgical margin was achieved, the survival rates improved to 100 and 89%, respectively.

CONCLUSIONS

The neurosurgical skull base technique could improve the probability of en bloc resection with a tumor-free margin for extensive temporal bone malignancies, which would cure a subset of patients. The active participation of neurosurgeons would improve patient care in this field.

Management of cranial base chondrosarcomas

OBJECTIVE

Chondrosarcomas are rare, infiltrative, progressive lesions that occur at the cranial base. Their intimate association with cranial nerves and major vessels of the head and neck often precludes complete surgical resection.

METHODS

Between 1983 and 2003, 23 patients (14 females, 9 males) were treated at our institution with the diagnosis of chondrosarcoma of the cranial base (mean age at presentation, 43 yr). A retrospective chart review was performed to evaluate presentation, management, and adjunctive treatment. All living patients were contacted for a current examination and disease status.

RESULTS

The 23 patients underwent 43 surgical resections. Follow-up ranged from 8 months to 25 years (mean, 97 mo). Ten patients underwent various adjuvant radiation therapies. Five patients have died. Four patients have no evidence of disease, and 13 have residual tumor. One was lost to follow-up. Of 14 patients with 5 years of follow-up, 13 are living. Therefore, the absolute 5 year survival rate is 93%. The 10 year survival rate is 71%.

CONCLUSION

Because of the intricate nature of the cranial base, a team approach is preferable for managing these challenging lesions. Maximum cytoreductive surgery should be pursued as an initial strategy to minimize neurological injury. Adjuvant stereotactic radiosurgery can be used to treat residual disease or small recurrences. This cohort also illustrates that patients with chondrosarcomas have better long-term survival rates than patients with chordomas of the cranial base.

Patient outcome at long-term follow-up after aggressive microsurgical resection of cranial base chondrosarcomas

OBJECTIVE

To evaluate patient clinical outcome and survival at long-term follow-up after aggressive microsurgical resection of chondrosarcomas of the cranial base.

METHODS

Over a 20-year period, 47 patients underwent 72 operative procedures for resection of cranial base chondrosarcomas. Thirty-three patients were previously untreated, whereas 14 patients previously had undergone surgery or radiation. Twenty-three patients had a single operation and 24 underwent staged (more than one) operations because of extensive disease. Patients who underwent subtotal resection also underwent radiotherapy or radiosurgery. Patients were evaluated at follow-up clinically and by imaging studies.

RESULTS

Gross total resection was accomplished in 29 (61.7%) patients, and subtotal resection was accomplished in 18 patients (38.3%). The resection was better in patients who underwent a primary operation (gross total resection, 68.8 versus 46.7%) rather than a reoperation. Patients who underwent incomplete resection underwent postoperative radiotherapy, which included proton beam radiotherapy (15.6%), radiosurgery (68%), and fractionated radiation (15.6%). There were no operative deaths. Postoperative complications (cerebrospinal fluid leakage, quadriparesis, infections, cranial nerve palsies, etc.) were observed in 10 patients (18%). The follow-up ranged from 2 to 255 months, with an average of 86 months. At the conclusion of study, 36 (76.6%) patients were alive, and 21 (44.7%) patients were alive without disease. Recurrence-free survival was 32% at 10 years in all patients, 42.3% in primary patients and 13.8% in those who underwent reoperation. The Karnofsky performance score was 82.4 +/- 9.8 before surgery, 85 +/- 12.5 at 1 year after surgery, and 85.3 +/- 5.8 at the latest follow-up. Two patients died as a result of radiotherapy complications (malignancy, radiation necrosis).

CONCLUSION

Cranial base chondrosarcomas can be managed well by complete surgical resection or by a combination of surgery and radiotherapy. The study cannot comment about the efficacy of radiotherapy. Approximately half of the patients survived without recurrence at long-term follow-up (>132 mo). The functional status of the surviving patients was excellent at follow-up.

Comparative analysis of anterior petrosectomy and transcavernous approaches to retrosellar and upper clival basilar artery aneurysms

OBJECTIVE

To compare two techniques, transcavernous approach (TcA) and anterior petrosectomy (AP), used to manage retrosellar and upper clival basilar artery (BA) aneurysms.

METHODS

AP and TcA were carried out on nine sides of cadaver heads. With use of a computerized tracking system, the area of surgical exposure in the ventral surface of the brain stem, the superficial area of exposure, and the linear exposure of the BA were evaluated. The angles of approach in the horizontal and vertical axes were measured using a robotic microscope. The caudal extent of exposure was determined by an aneurysm clip applied to proximal BA, and the distance between the clip and the floor of the sella was quantified after performing TcA.

RESULTS

TcA (1127.3 +/- 438.4 mm2) provided a greater superficial exposure than AP (697.7 +/- 219.1 mm2) (P = 0.01). There were no statistical differences in the deep working exposure (P = 0.303) between TcA (206.9 +/- 40.7 mm2) and AP (260.2 +/- 137.1 mm2). The linear exposure of the BA was greater for AP (22.7 +/- 6.2 mm2) than for the TcA (12.8 +/- 2.9 mm2) (P = 0.004). The caudal extent of exposure averaged 6.1 mm from the floor of the sella. No differences were found in horizontal angles (P = 0.596); however, vertical angles were significantly greater for the TcA than AP (15.2 +/- 3.4) (P = 0.004).

CONCLUSION

From an anatomic standpoint, the TcA offers more advantages than the AP, when approaching retrosellar BA aneurysms, except for those cases in which proximal control is the principal issue and the neck of the aneurysm is located more than 6.0 mm below the floor of the sella.

Quantitative anatomic study of three surgical approaches to the anterior communicating artery complex

OBJECTIVE

To compare the angles of approach and area of exposure to the anterior communicating artery (AComA) complex associated with pterional (PT), orbitopterional (OPT), and orbitozygomatic (OZ) craniotomies before and after gyrus rectus resection.

METHODS

PT, OPT, and OZ craniotomies were performed on both sides of four heads, and the angles of approach and area of exposure to the AComA complex were measured before and after resection of the gyrus rectus.

RESULTS

The vertical angle of approach increased significantly among the PT and OPT (P = 0.001), PT and OZ (P = 0.001), and OPT and OZ approaches (P = 0.005). The horizontal angle of approach was significantly larger between the PT to OPT (P = 0.001) and PT to OZ (P = 0.001) approaches but not between the OPT and OZ approaches (P = 0.757). After gyrus rectus resection, the vertical and horizontal angles of approach increased significantly for the PT approach but not for the OPT and OZ approaches. The area of exposure to the AComA complex increased progressively from the PT to OPT to OZ approach but did not reach statistical significance (P = 0.124). Resection of the gyrus rectus resulted in significant relative gains in the area of exposure for the PT (P = 0.01) and OPT (P = 0.04) approaches but not for the OZ approach (P = 0.88).

CONCLUSION

The vertical and horizontal angles of approach to the AComA complex are significantly larger for the OPT and OZ approaches compared with the PT approach. Use of the OZ approach may decrease the need for frontal lobe retraction and resection of the gyrus rectus.

Preauricular infratemporal fossa surgical approach: modifications of the technique and surgical indications

A retrospective clinical analysis was performed to evaluate the effectiveness of the preauricular infratemporal fossa (ITF) surgical approach using modifications based on tumor pathology and extension, without compromising outcomes. Patients were surgically treated for tumors involving the ITF via a preauricular surgical approach during 1990 to 2000. Their clinical charts were reviewed to determine the association among pathological variables, details of the surgical procedure, and outcomes. Tumors in 65 patients were categorized as "malignant" and "benign." The malignant group included 44 patients (mean age, 49.5 years). Squamous cell carcinoma was the most common pathology followed by sarcomas. To achieve complete tumor resection, the ITF approach and dissection were combined with other procedures in 74% of these patients. No surgical complications were encountered in 74.4%, and a clinical cure was obtained in 55% of patients (follow-up, 2 years). The benign group included 21 patients (mean age, 36.7 years). Juvenile angiofibromas and meningiomas constituted most of the tumors in this group. An ITF approach alone was sufficient to achieve complete tumor excision in 66.7% of these patients. A clinical cure was achieved in 85% of patients (follow-up, 2 years), and 76.2% had no surgical complications. Chi-square tests revealed significant correlations between tumor extensions and surgical treatment variables. These were more evident in the malignant group, indicating the use of wider surgical exposures and more aggressive, extirpative surgery. The preauricular surgical approach to the ITF can be used to achieve a complete resection of a variety of tumors arising from or extending into the ITF. This approach can be tailored to the nature of the tumor and its extensions.

The open-mouth fronto-orbitotemporozygomatic approach for extensive benign tumors with coexisting splanchnocranial and neurocranial involvement

OBJECTIVE

To describe the advantages of a modification of the standard fronto-orbitotemporozygomatic (FOTZ) approach, consisting of the forced opening of the patient's mouth (open-mouth FOTZ), for the treatment of benign tumors massively involving the splanchnocranium and neurocranium.

METHODS

The modified FOTZ approach obtained by forced mouth opening is described. Such a procedure was introduced with the aim of obtaining a minimally invasive access to lesions involving both the infratemporal-parapharyngeal spaces and the anteromedial cranial fossae. The forced opening of the mouth allows the surgeon to keep the coronoid process of the mandible away from the operating field, producing a wide exposure of the infratemporal space like that of the posterior wall of the maxillary sinus, which can be penetrated from behind without adding destructive procedures on the mandibular bone.

RESULTS

From a series of 45 patients affected by cranial base lesions operated on during an 8-year time period, three patients affected by juvenile nasopharyngeal angiofibromas were selected for an open-mouth FOTZ approach. In all cases, a complete eradication of both the intracranial and extracranial components of the tumor was possible by this approach. The same procedure was then used in four patients affected by extensive meningiomas and two patients harboring Vth cranial nerve schwannomas, with complete tumor removal.

CONCLUSION

In our experience, the open-mouth FOTZ approach seems particularly suited for extensive benign tumors (including juvenile nasopharyngeal angiofibromas) with splanchnocranial and neurocranial involvement. No indication exists for the use of this approach in malignant tumors, in which total eradication with large tumor-free margins is required.

Temporomandibular Joint-preserving Preauricular Subtemporal-Infratemporal Fossa Approach: Surgical Technique and Clinical Application

OBJECTIVE:

The preauricular subtemporal-infratemporal (PSI) approach is commonly used to resect clival tumors and other lesions anterior to the brainstem. One of the surgical steps in this approach is a condylar osteotomy or a condylectomy, which often leads to temporomandibular joint dysfunction. We describe a modification of the PSI approach that preserves the temporomandibular joint without sacrificing the ability to mobilize the petrous internal carotid artery or gain surgical access to the clivus and anterior brainstem.

METHODS:

Anatomic studies in cadaveric specimens were performed, and the extent of exposure of critical skull base and intradural structures was documented with postdissection fine-cut computed tomographic scans. This modification of the PSI approach was subsequently used in three consecutive patients with a clival chondrosarcoma, and the completeness of tumor resection was documented with postoperative magnetic resonance imaging and computed tomographic scans.

RESULTS:

This approach allowed complete mobilization of the petrous internal carotid artery and surgical access to the mid-lower clivus, jugular tubercle, hypoglossal canal, occipital condyle, anterior brainstem, and the origin of the trigeminal through hypoglossal nerves. It also proved to be safe and feasible in the three patients who underwent surgical resection of a clival chondrosarcoma, allowing a complete tumor removal.

CONCLUSION:

This variation of the PSI approach is practical, has no additional morbidity, and provides complete access to critical cranial base regions and tumor margins. It can certainly be used as an alternative to the standard PSI approach when dealing with clival tumors and other lesions anterior to the brainstem.

“Tangential” Resection of Medial Temporal Lobe Arteriovenous Malformations with the Orbitozygomatic Approach

OBJECTIVE

Arteriovenous malformations (AVMs) of the medial temporal lobe are usually resected through subtemporal-transcortical approaches that provide a trajectory that is perpendicular to the plane of the AVM. The pterional approach is sometimes used for AVMs in the uncus and amygdala, but it is not recommended for AVMs in the hippocampal region because it provides a “tangential” approach with limited access to posterior feeding arteries and draining veins. The orbitozygomatic approach enhances exposure along this tangential trajectory and was used in a consecutive series of 10 patients to determine its advantages.

METHODS

During a 5.7-year period, 43 patients underwent resection of temporal lobe AVMs, 10 of which were located in the medial temporal lobe (amygdala and uncus [Region A] or hippocampus, parahippocampus, and fusiform gyrus [Region B]). AVMs were evenly distributed by region and by hemispheric dominance and included two Spetzler-Martin Grade IV lesions. An orbitozygomatic approach was used in all cases.

RESULTS

Complete resection was accomplished in nine patients, and one patient underwent multimodality management with postoperative stereotactic radiosurgery. Good outcomes (Rankin outcome score ≤2) were observed in all patients, and six patients were improved neurologically at late follow-up (mean, 1.3 yr). No permanent language deficits were produced by this approach.

CONCLUSION

The orbitozygomatic approach maximizes the exposure of the tangential approach to medial temporal lobe AVMs and has advantages over traditional lateral approaches. It provides early access to critical feeding arteries from the anterior choroidal artery, posterior cerebral artery, and posterior communicating artery; it minimizes temporal lobe retraction and risk to the vein of Labbé; and it avoids transcortical incisions or lobectomy that might impact language and memory function. For these reasons, it may be the optimal approach for small- and medium-sized compact AVMs in the dominant medial temporal lobe.

Modifications to the orbitozygomatic approach. Technical note

The orbitozygomatic craniotomy is one of the workhorse approaches of skull base surgery, providing wide, multidirectional access to the anterior and middle cranial fossae as well as the basilar apex. Complete removal of the orbitozygomatic bar increases the angles of exposure, decreases the working depth of the surgical field, and minimizes brain retraction. In many cases, however, only a portion of the exposure provided by the full orbitozygomatic approach is needed. Tailoring the extent of the bone resection to the specific lesion being treated can help lower approach-related morbidity while maintaining its advantages. The authors describe the technical details of the supraorbital and subtemporal modified orbitozygomatic approaches and discuss the surgical indications for their use. Modifications to the orbitozygomatic approach are an example of the ongoing adaptation of skull base procedures to general neurosurgical practice.

Quantitative analysis of the transcondylar approach to the foramen magnum

OBJECTIVE

Condylar resection with suboccipital craniotomy increases foramen magnum exposure, but guidelines for when this is necessary are not defined. Cadaveric and computed tomography evaluations were completed to guide decision-making regarding the use and extent of condylar resection.

METHODS

Quantitative analysis of foramen magnum surgical exposures was performed on 32 skulls (64 sides) and 6 cadaveric dissections (12 sides). Computed tomographic (CT) scans were performed on cadaveric heads before and after condylar resections. Digitized images of dry skulls and CT images of cadaver heads were quantitatively analyzed. Predissection CT measurements of cadaveric heads guided extent of condylar resections, and resection accuracy was assessed with postdissection CT scans.

RESULTS

Skull measurements (means in parentheses) included the foramen magnum area (7.8 cm(2)), length (3.6 cm), width (3.1 cm), anteroposterior condylar length (2.3 cm), and axial condylar length (2.5 cm). Mean widths of potential surgical exposures for skulls were obtained for A) suboccipital craniotomy (2.3 cm), B) with 25% (2.6 cm), and C) 50% condylar resection (3.0 cm). Mean angles of exposure were as follows: A, 38.4 degrees; B, 49.1 degrees; and C, 54.3 degrees. CT scans of cadaveric heads before and after dissections yielded measurements of exposure equivalent to measurements found on the dry skulls.

CONCLUSION

On average, lateral exposure increases by 3 mm (13%) and 7 mm (30%) for 25 and 50% condylar resection, respectively, compared with suboccipital craniotomy alone. Angles of exposure increase by 10.7 degrees (28%) and 15.9 degrees (41%). Measurements of CT images can be used preoperatively to help analyze the need for condylar resection and intraoperatively to guide the extent of condylar resection.