Microsurgical anatomy of the posterior fossa cisterns

Liliequist membrane: A systematic review of history, anatomy, clinical importance, and surgical challenges

BACKGROUND

The Liliequist membrane (LM) represents a crucial yet challenging anatomical structure in neuroanatomy. First observed in 1875 and later elucidated by Bengt Liliequist in 1956, the LM's precise anatomical description and boundaries remain complex. Its significance extends to neurosurgery, impacting various procedures like endoscopic third ventriculocisternostomies, aneurysm and tumor surgeries, treatment of suprasellar arachnoid cysts, and managing perimesencephalic hemorrhages. However, a comprehensive understanding of the LM is hindered by inconsistent anatomical descriptions and limitations in available literature, warranting a systematic review.

METHODS

A systematic review was conducted by searching PubMed, Science Direct, and Google Scholar for articles pertaining to Liliequist's membrane. The search employed Mesh terms like "Liliequist membrane," "Liliequist's diaphragm," and related variations. Inclusion criteria encompassed studies exploring the historical evolution, anatomical structure, radiological characteristics, and clinical implications of the LM in neurosurgery.

RESULTS

The search yielded 358 articles, with 276 unique articles screened based on relevance. Following a meticulous screening process, 72 articles underwent full-text assessment, resulting in the inclusion of 5 articles meeting the eligibility criteria. The selected studies varied in methodology, including anatomical dissections, radiological evaluations, and clinical significance in neurosurgical procedures. Insights were derived on LM's anatomical variations, radiological visualization, and its critical role in guiding neurosurgical interventions.

CONCLUSIONS

Despite advancements in understanding its clinical significance and radiological visualization, challenges persist in precisely delineating its boundaries. Further research, especially on embryological development and histological characterization, is essential. Enhancing comprehension of LM-related pathologies is crucial for accurate preoperative planning and optimizing patient outcomes in neurosurgery.

Anatomy of the pontine arteries and perforators of the basilar artery in humans

Cerebral blood flow constitutes a critical area of interest for neurologists, neurosurgeons, and interventional radiologists as a social burden related to ischemic stroke, hemorrhagic stroke, and vascular dementia is expected to intensify. There is a great need to develop new and effective therapies, therefore deepening understanding of cerebrovascular anatomy, physiology, and pathology is crucial. The main aim of the study was to develop a comprehensive classification of the pontine arteries considering their typology, relations to the cranial nerves, branching schemes, and superficial pontine blood supply areas. We prepared 100 anatomical specimens of the human brainstem with the basilar artery, the pontine arteries, and the terminal perforating arteries. With the use of microsurgical microscope, we analyzed morphometry of the basilar artery, origins, courses, and branching patterns of the pontine arteries as well as distribution of the terminal perforators in relation to pontine superficial vascular areas and the cranial nerves. Additionally, we studied presence of pontine branches of the superior cerebellar artery (SCA) and anterior inferior cerebellar artery (AICA). Repetitive branching patterns, origins, and courses led us to distinguish five types of the pontine arteries: type 1-the paramedian branches, type 2-the short circumflex branches, type 3-composition of the paramedian and the short circumflex branches, type 4-long circumflex branches, and type 5-median branches penetrating the pons along the basilar sulcus. Types 1, 2, and 4 were described in the literature previously, but the classification did not include the median branches (the most prevalent branches) and frequently occurring combinations of the types 1 and 2. There were seven pontine arteries on both sides on average that presented the following general pattern: the first pontine artery below the SCA is a type 4 vessel called the posterolateral pontine artery and it is followed by a type 2 vessel-the superolateral pontine artery; the next three arteries represent the types 1, 2, and 3 and supply most of the ventral pontine surface; the sixth artery-the anterolateral pontine artery-is a short circumflex branch and the seventh artery, originating below the AICA, represents long circumflex arteries. Occlusion of each of the abovementioned vessels relates to a specific pontine vascular syndrome. As explained by the phylogenesis and ontogenesis of the central nervous system, the pontine arteries are subject to variability. The SCA and the AICA took part in the pontine blood supply in 2.5% and 12.5% of cases, respectively, therefore neurovascular interventions involving the SCA, or the AICA may lead to pontine ischemia. Contact of the pontine arteries with the cranial nerves depends on the vessel type and origin location.

Prepontine cisternal routine for intrathecal targeted drug delivery in craniofacial cancer pain treatment: technical note

Intrathecal targeted drug delivery provides effective relief for cancer-related pain. However, its validation in management of craniofacial pain remains much less widely practiced, mainly due to the localized diffusion of analgesic agent with current approach. Here, we report our experience of prepontine cisternal routine for placement and implantation of intrathecal targeted drug delivery in two cases of cancer-related craniofacial pain. Lumbar cannulation was applied and the intrathecal catheter tip was positioned at the prepontine cistern under fluoroscopic guidance during the surgical implantation. Postoperative imaging confirmed that the catheter tip was successfully placed in the prepontine cisternal space. Satisfactory control of pain was achieved after intrathecal therapy, with significant reduction of background and breakthrough cancer pain. None obvious complications were observed in this study. Thus, our novel intrathecal routine may provide an alternative option for craniofacial pain caused by tumor, who were insufficiently treated by oral analgesic agents.

External Cerebrospinal Fluid Drainage in the Management of Nonaneurysmal Subarachnoid Hemorrhage

Distinguishing the aneurysmal from nonaneurysmal subarachnoid hemorrhage (SAH) may be difficult as acute bleeding in the subarachnoid space is a common denominator. It is believed that toxic effects of breakdown products of acute bleed, including hemoglobin, contribute to the morbidity and mortality of this condition; and that early drainage will potentially reduce them. This series focuses on our local experience with the application of external cerebrospinal fluid (CSF) drainage in the management of a series of cases confirmed to be nonaneurysmal SAH and its effects on the outcome. The objective of this report is to observe the usefulness of external CSF drainage in the management of nonaneurysmal SAH. Five consecutive cases over four years were reviewed and reported as a case series. The main points we focused on were presentation, diagnostic findings on imaging, CSF drainage, and outcome up to six months. All the patients presented with headaches described as sudden, and only one had significant impairment of consciousness Glasgow Coma Scale (GCS) 10/15. Three out of the five patients had a premorbid hypertensive condition of unclear control status. We also observed that three out of the five had a low-pressure pretruncal/perimesencephalic pattern of bleed, whereas two had the typical high-pressure SAH pattern. CT angiography (CTA) was negative in all. Four had lumbar drainage, while one had external ventricular drainage. All were discharged within three weeks and functioned optimally at six months. CSF drainage in managing nonaneurysmal SAH is achievable with minimal access procedures, including lumbar drain (LD) and external ventricular drainage (EVD), which may have further reduced the low morbidity normally associated with this condition.

Transvascular in vivo microscopy of the subarachnoid space

BACKGROUND

The micro-architectonics of the subarachnoid space (SAS) remain partially understood and largely ignored, likely the result of the inability to image these structures in vivo. We explored transvascular imaging with high-frequency optical coherence tomography (HF-OCT) to interrogate the SAS.

METHODS

In vivo HF-OCT was performed in 10 dogs in both the posterior and anterior cerebral circulations. The conduit vessels used were the basilar, anterior spinal, and middle and anterior cerebral arteries through which the perivascular SAS was imaged. The HF-OCT imaging probe was introduced via a microcatheter and images were acquired using a contrast injection (3.5 mL/s) for blood clearance. Segmentation and three-dimensional rendering of HF-OCT images were performed to study the different configurations and porosity of the subarachnoid trabeculae (SAT) as a function of location.

RESULTS

Of 13 acquisitions, three were excluded due to suboptimal image quality. Analysis of 15 locations from seven animals was performed showing six distinct configurations of arachnoid structures in the posterior circulation and middle cerebral artery, ranging from minimal presence of SAT to dense networks and membranes. Different locations showed predilection for specific arachnoid morphologies. At the basilar bifurcation, a thick, fenestrated membrane had a unique morphology. SAT average thickness was 100 µm and did not vary significantly based on location. Similarly, the porosity of the SAT averaged 91% and showed low variability.

CONCLUSION

We have demonstrated the feasibility to image the structures of the SAS with transvascular HF-OCT. Future studies are planned to further map the SAT to increase our understanding of their function and possible impact on neurovascular pathologies.

Arachnoid Membranes: Crawling Back into Radiologic Consciousness

The arachnoid membranes are projections of connective tissue in the subarachnoid space that connect the arachnoid mater to the pia mater. These are underappreciated and largely unrecognized by most neuroradiologists despite being found to be increasingly important in the pathogenesis, imaging, and treatment of communicating hydrocephalus. This review aims to provide neuroradiologists with an overview of the history, embryology, histology, anatomy, and normal imaging appearance of these membranes, as well as some examples of their clinical importance.

The Glossopharyngo-Cochlear Triangle-Part I: Quantitative Anatomic Analysis of High-Riding Posterior Inferior Cerebellar Artery Aneurysms Exposed Through the Extended Retrosigmoid Approach

BACKGROUND

An extended retrosigmoid approach can offer sufficient space for clip reconstruction of some high-riding posterior inferior cerebellar artery (PICA) aneurysms.

OBJECTIVE

To quantitatively investigate the glossopharyngo-cochlear triangle (GCT) and anatomic structures within it.

METHODS

Extended retrosigmoid craniotomies were performed on 10 sides of cadaveric heads, and the GCT was identified in each specimen. The length of the base and the area of the GCT were measured. The depth of the vertebrobasilar system and the abducens nerve to the GCT were measured. The proximal and distal exposable and controllable points on the vertebrobasilar system were identified. Two imaging-based patient selection algorithms are provided using the lengths from those points to the vertebral artery dural entry point and the superoinferior distances from those points to the inferior edge of the foramen magnum. Other factors related to accessibility via the GCT were investigated.

RESULTS

The mean (standard deviation [SD]) area of the GCT was 45.7 (12.55) mm2. The mean (SD) depth of the abducens nerve was 14.3 (1.42) mm. The mean (SD) superoinferior distances from the foramen magnum to those points were 23.1 (7.39), 24.7 (8.25), 30.0 (9.56), and 32.6 (7.79) mm, respectively. The lower segment of the vertebrobasilar system was more superficial in the setting of a high-lying vertebrobasilar junction (VBJ) than a low-lying VBJ.

CONCLUSION

We describe the GCT in an extended retrosigmoid approach for high-riding PICA aneurysms and evaluate the spatial relationship of the neurovascular structures within it. Two potential algorithms are offered for preoperative patient selection.

Arachnoid and dural reflections

The dura mater is the major gateway for accessing most extra-axial lesions and all intra-axial lesions of the central nervous system. It provides a protective barrier against external trauma, infections, and the spread of malignant cells. Knowledge of the anatomical details of dural reflections around various corners of the skull bases provides the neurosurgeon with confidence during transdural approaches. Such knowledge is indispensable for protection of neurovascular structures in the vicinity of these dural reflections. The same concept is applicable to arachnoid folds and reflections during intradural excursions to expose intra- and extra-axial lesions of the brain. Without a detailed understanding of arachnoid membranes and cisterns, the neurosurgeon cannot confidently navigate the deep corridors of the skull base while safely protecting neurovascular structures. This chapter covers the surgical anatomy of dural and arachnoid reflections applicable to microneurosurgical approaches to various regions of the skull base.

The role of the Liliequist membrane in the third ventriculostomy

Endoscopic third ventriculostomy (ETV) is a hydrocephalus treatment procedure that involves opening the Liliequist membrane (LM). However, LM anatomy has not been well-studied neuroendoscopically, because approach angles differ between descriptive and microsurgical anatomical explorations. Discrepancies in ETV efficacy, especially among children age 2 and younger, may be due to incomplete LM opening. The objective of this study was to characterize the LM anatomically from a neuroendoscopic perspective to better understand the impact of anatomical features during LM ostomy and the ETV success rate. Additionally, the ETV success score was tested to predict patient outcome after the intraoperatively difficult opening of LM. Fifty-four patients who underwent ETV were prospectively analyzed with a mean follow-up of 53.1 months (1-90 months). The ETV technical parameters of difficulty were validated by seven expert neurosurgeons. The pediatric population (44) of this study represents the majority of patients (81.4%). The overall ETV success rate was 68.5%. Anomalies on the IIIVT floor resulted in an increased rate of ETV failure. The IIIVT was anomalous, and LM was thick in 33.3% of cases. Fenestration of LM was difficult in 39% of cases, and the LM and TC were opened separately in 55.6% of cases. The endoscopic third ventriculostomy success score (ETVSS) accurately predicted the level of difficulty opening the LM (p = 0.012), and the group with easy opening presented greater durability in ETV success. Neurosurgeons should be aware of the difficulty level of the overture of LM during ETV and its impact on long-term ETV effectiveness.

Histological and intraoperative evaluations of the arachnoid in patients with Chiari I malformation

BACKGROUND

Arachnoid dissection for decompression of Chiari I malformation is controversial. Whether arachnoid changes have an impact on the clinical course is not established. This paper documents the histological spectrum of arachnoid changes and evaluates correlations with preoperative, intraoperative, and postoperative data.

METHOD

Arachnoid samples of 162 consecutive foramen magnum decompressions from 2006 to 2016 were studied. Arachnoid thickness and degrees of fibrosis and cellularity were determined with the examiner blinded for clinical data. Based on 145 first time decompressions, a histological classification for arachnoid features was developed.

RESULTS

The arachnoid was thicker in secondary compared with primary decompressions (176.1 ± 158.2 μm vs. 35.9 ± 43.5 μm; p = 0.0026) and in adults compared to children (37.3 ± 45.3 μm vs. 21.8 ± 7.7 μm; p = 0.0007). In primary decompressions, arachnoid thickness, degrees of fibrosis, and cellularity followed a normal distribution with all features shifted significantly to higher grades in secondary decompressions. The histological classification correlated with the preoperative severity of gait ataxia, motor weakness, and sensory deficits, whereas it had no predictive power for postoperative short- or long-term results. By comparison, the intraoperative evaluation of arachnoid changes accounting for relationships between arachnoid and surrounding tissues showed higher correlations with preoperative symptoms and had significant predictive power for postoperative short- and long-term results.

CONCLUSIONS

Histological changes of the arachnoid correlate with preoperative symptoms. Relationships between arachnoid and surrounding tissues show even higher correlations with predictive power for short- and long-term outcomes. These findings suggest a pathophysiological role for the arachnoid in Chiari I malformation.

Endoscopic Fenestration of Arachnoid Cysts Through Lateral Pontomesencephalic Membranotomy: Technical Note and Case Series

BACKGROUND

The ideal treatment method for cranial arachnoid cysts stills controversial, each of endoscopic and microscopic techniques has its pros and cons.

METHODS

We described cystocisternostomy technique for arachnoid cysts through fenestration medial to the edge of tentorium through lateral pontomesencephalic membrane and illustrated it's outcomes. We performed endoscopic lateral pontomesencephalic membranotomy in nine children with zero angled rigid endoscope (STORZ).The age ranged from eight months up to nine years. The cysts were Galassi type III in eight cases (five of them giant hemispheric) and Galassi type II in one case. Clinical presentations were delay in milestones, seizures, loss of consciousness, unsteady gait, and persistent headache.

RESULTS

The cysts decreased in size in five cases after three months and nearly disappeared after three and 15 months in two cases, and in 18 months in the other two. Preoperative symptoms improved in all cases. Insignificant subdural hygroma was found in five cases, one case developed hydrocephalus four months later treated with a ventriculoperitoneal shunt; contralateral massive subdural hematoma occurred in one case four months after surgery evacuated with two burr holes with good clinical outcome. There was neither cerebrospinal fluid leakage, cranial nerve palsy nor mortality.

CONCLUSIONS

The fenestration through the lateral pontomesencephalic membrane created a shortcut of cerebrospinal fluid flow to the basal cisterns especially cerebellopontine cistern and represents a reliable option with an acceptable success rate. It creates a good drainage to the large cysts.

Reimplantation Bypass Using One Limb of a Double-Origin Posterior Inferior Cerebellar Artery for Treatment of a Ruptured Fusiform Aneurysm: Case Report

BACKGROUND AND IMPORTANCE

Posterior inferior cerebellar artery (PICA) aneurysms are uncommon, and aneurysms associated with anatomical PICA variants are even rarer. Although often treated endovascularly, aneurysms associated with anatomical PICA variants may not be suitable for endovascular intervention because of the risk of compromise of brainstem perforators and may be more amenable to open techniques. This case report describes the successful treatment of an aneurysm associated with a double-origin PICA (DOPICA) by distally reimplanting one of the PICA limbs.

CLINICAL PRESENTATION

A 78-yr-old man with a Hunt-Hess grade III, Fisher grade IV subarachnoid hemorrhage secondary to a ruptured distal right PICA aneurysm associated with a DOPICA was treated with PICA-PICA bypass and trapping of the aneurysm. This is the first reported case in the literature of successful bypass of a DOPICA-associated aneurysm. Radiographically, the bypass remained patent with successful obliteration of the aneurysm, and at discharge from the hospital, the patient had a Glasgow Coma Scale score of 15 and modified Rankin Scale score of 3.

CONCLUSION

This case demonstrates a novel reimplantation bypass for a ruptured aneurysm that exploits this rare variant anatomy of a DOPICA.

The membrane of Liliequist-a safe haven in the middle of the brain. A narrative review

BACKGROUND

The membrane of Liliequist is one of the best-known inner arachnoid membranes and an essential intraoperative landmark when approaching the interpeduncular cistern but also an obstacle in the growth of lesions in the sellar and parasellar regions. The limits and exact anatomical description of this membrane are still unclear, as it blends into surrounding structures and joins other arachnoid membranes.

METHODS

We performed a systematic narrative review by searching for articles describing the anatomy and the relationship of the membrane of Liliequist with surrounding structures in MEDLINE, Embase and Google Scholar. Included articles were cross-checked for missing references. Both preclinical and clinical studies were included, if they detailed the clinical relevance of the membrane of Liliequist.

RESULTS

Despite a common definition of the localisation of the membrane of Liliequist, important differences exist with respect to its anatomical borders. The membrane appears to be continuous with the pontomesencephalic and pontomedullary membranes, leading to an arachnoid membrane complex around the brainstem. Furthermore, Liliequist's membrane most likely continues along the oculomotor nerve sheath in the cavernous sinus, blending into and giving rise to the carotid-oculomotor membrane.

CONCLUSION

Further standardized anatomical studies are needed to clarify the relation of the membrane of Liliequist with surrounding structures but also the anatomy of the arachnoid membranes in general. Our study supports this endeavour by identifying the knowledge hiatuses and reviewing the current knowledge base.

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.

The Basal Subarachnoid Cisterns: Surgical and Anatomical Considerations

The basal subarachnoid cisterns are expansions of the subarachnoid space and transmit cranial nerves and intracranial vessels. Providing neurosurgeons with key concepts, anatomical landmarks, and techniques can result in safer procedures and better patient outcomes. In this review, we discuss the major basal subarachnoid cisterns including their embryology, history, anatomical descriptions, and use during surgical approaches.

Clinical Applications for Diffusion MRI and Tractography of Cranial Nerves Within the Posterior Fossa: A Systematic Review

Objective: This paper presents a systematic review of diffusion MRI (dMRI) and tractography of cranial nerves within the posterior fossa. We assess the effectiveness of the diffusion imaging methods used and examine their clinical applications.

Methods: The Pubmed, Web of Science and EMBASE databases were searched from January 1st 1997 to December 11th 2017 to identify relevant publications. Any study reporting the use of diffusion imaging and/or tractography in patients with confirmed cranial nerve pathology was eligible for selection. Study quality was assessed using the Methodological Index for Non-Randomized Studies (MINORS) tool.

Results: We included 41 studies comprising 16 studies of patients with trigeminal neuralgia (TN), 22 studies of patients with a posterior fossa tumor and three studies of patients with other pathologies. Most acquisition protocols used single-shot echo planar imaging (88%) with a single b-value of 1,000 s/mm² (78%) but there was significant variation in the number of gradient directions, in-plane resolution, and slice thickness between studies. dMRI of the trigeminal nerve generated interpretable data in all cases. Analysis of diffusivity measurements found significantly lower fractional anisotropy (FA) values within the root entry zone of nerves affected by TN and FA values were significantly lower in patients with multiple sclerosis. Diffusivity values within the trigeminal nerve correlate with the effectiveness of surgical treatment and there is some evidence that pre-operative measurements may be predictive of treatment outcome. Fiber tractography was performed in 30 studies (73%). Most studies evaluating fiber tractography involved patients with a vestibular schwannoma (82%) and focused on generating tractography of the facial nerve to assist with surgical planning. Deterministic tractography using diffusion tensor imaging was performed in 93% of cases but the reported success rate and accuracy of generating fiber tracts from the acquired diffusion data varied considerably.

Conclusions: dMRI has the potential to inform our understanding of the microstructural changes that occur within the cranial nerves in various pathologies. Cranial nerve tractography is a promising technique but new avenues of using dMRI should be explored to optimize and improve its reliability.

Retroclival Arachnoid Cysts: Case Series, Literature Review, and New Classification Proposal

BACKGROUND

The retroclival region is among the rarest locations for an arachnoid cyst (AC), with only a few reported cases. No accepted classification system is available for these rare cysts. Such a classification system would solve the nomenclature problem and could result in easier and more systematic management. We reviewed and analyzed data from databases and reported studies of retroclival ACs (RACs) and have proposed a classification system.

METHODS

A retrospective review of RACs was conducted in Marmara and Adiyaman University Hospitals, Turkey. Cysts in the prepontine and/or premedullary cisterns that spared the chiasmatic cistern were included. Additionally, the reported data were searched for relevant studies on cysts. The findings were analyzed to establish a clear nomenclature and classification system, and the clinical presentations, treatment strategies, and surgical approaches were reviewed.

RESULTS

We identified 1 adult and 1 pediatric patient, and only the adult had undergone surgery. Additional data searches yielded 14 patients with RACs. The cysts were classified as type 1 if they had extended superiorly beyond the borders of the diencephalic leaf of the Liliequist membrane. If they had not extended, they were classified as type 2. Finally, type 2 cysts that had extended to the anterior spinal cistern were classified as type 3.

CONCLUSIONS

RACs can be more easily and systematically managed using a simple clinical classification system. Together with the previously proposed suprasellar AC classification, our proposed RAC classification should be adequate to classify all ACs in the ventral midline cistern, which could solve the nomenclature problem.

Subarachnoid Trabeculae: A Comprehensive Review of Their Embryology, Histology, Morphology, and Surgical Significance

INTRODUCTION

Brain is suspended in cerebrospinal fluid (CSF)-filled subarachnoid space by subarachnoid trabeculae (SAT), which are collagen-reinforced columns stretching between the arachnoid and pia maters. Much neuroanatomic research has been focused on the subarachnoid cisterns and arachnoid matter but reported data on the SAT are limited. This study provides a comprehensive review of subarachnoid trabeculae, including their embryology, histology, morphologic variations, and surgical significance.

METHODS

A literature search was conducted with no date restrictions in PubMed, Medline, EMBASE, Wiley Online Library, Cochrane, and Research Gate. Terms for the search included but were not limited to subarachnoid trabeculae, subarachnoid trabecular membrane, arachnoid mater, subarachnoid trabeculae embryology, subarachnoid trabeculae histology, and morphology. Articles with a high likelihood of bias, any study published in nonpopular journals (not indexed in PubMed or MEDLINE), and studies with conflicting data were excluded.

RESULTS

A total of 1113 articles were retrieved. Of these, 110 articles including 19 book chapters, 58 original articles, 31 review articles, and 2 case reports met our inclusion criteria.

CONCLUSIONS

SAT provide mechanical support to neurovascular structures through cell-to-cell interconnections and specific junctions between the pia and arachnoid maters. They vary widely in appearance and configuration among different parts of the brain. The complex network of SAT is inhomogeneous and mainly located in the vicinity of blood vessels. Microsurgical procedures should be performed with great care, and sharp rather than blunt trabecular dissection is recommended because of the close relationship to neurovascular structures. The significance of SAT for cerebrospinal fluid flow and hydrocephalus is to be determined.

Bengt Liliequist: life and accomplishments of a true renaissance man

In the 1970s, the membrane of Liliequist became the accepted name for a small band of arachnoid membrane separating the interpeduncular and chiasmatic cisterns, making it one of the most recent of the universally accepted medical eponyms. The story of its discovery, however, cannot be told without a thorough understanding of the man responsible and his contribution to the growth of a specialty. Bengt Liliequist lived during what many would consider the Golden Age of neuroradiology. With his colleagues at the Serafimer Hospital in Stockholm, he helped set the standard for appropriate imaging of the CNS and contributed to more accurate localization of intracerebral as well as spinal lesions. The pneumoencephalographic discovery of the membrane that was to bear his name serves merely as a starting point for a career that spanned five decades and included the defense of two separate doctoral theses, the last of which occurred after his 80th birthday. Although the recognition of neuroradiology as a subspecialty did not occur in his home country of Sweden until after his retirement, and technological progress saw the obsolescence of the procedure that he had mastered, Dr. Liliequist's accomplishments and his contributions to the current understanding of neuroanatomy merit our continued praise.

Visualization of Liliequist's membrane prior to endoscopic third ventriculostomy

PURPOSE

Endoscopic third ventriculostomy (ETV) is an effective treatment in patients with obstructive hydrocephalus caused by aqueductal stenosis. Operative failure may occur if an unnoticed membrane below the floor of the third ventricle is present, such as Liliequist's membrane (LM). To analyze how often LM can be visualized by high-resolution heavily T2-weighted 3D-MRI prior to ETV, and to find out potential reasons for diagnostic failure.

MATERIALS AND METHODS

Preoperative 3D-MR images of 37 consecutive patients (19 female, median 42 years) were retrospectively analyzed. Visualization of three LM segments (sellar, diencephalic, mesencephalic), dimensions of the space below the third ventricle, and extent of hydrocephalus were measured. Image quality was scored (score 1[poor] to 3[excellent]). Preoperative imaging findings were compared with intraoperative findings.

RESULTS

Patients were subdivided into group 1 (no segment of LM identified, n = 18), and group 2 (at least one segment of LM was identified, n = 19). The sellar segment of LM was most often positively identified (10 out of 19 cases). The mean distance between the pons and the sella/clivus was significantly shorter in group 1 than in group 2 (3.7 vs. 6.2 mm; p < 0.01). Other variables, such as the distance between tip of the pons and the mamillary bodies as well as the image quality, were not significantly different between both groups. Intraoperatively, LM was present in 78 % of group 2 patients, and in 28 % of group 1 patients, respectively (p < 0.03).

CONCLUSIONS

LM can be detected in about half of patients prior to ETV. Reduced PSD influences visualization of LM.

Spontaneous retroclival hematoma in pituitary apoplexy: case series

OBJECT

Pituitary apoplexy is a rare and potentially life-threatening disorder that is most commonly characterized by a combination of sudden headache, visual disturbance, and hypothalamic/hormonal dysfunction. In many cases, there is hemorrhagic infarction of an underlying pituitary adenoma. The resulting clinical symptoms are due to compression of the remaining pituitary, cavernous sinuses, or cranial nerves. However, there are only 2 case reports in the literature describing spontaneous retroclival expansion of hemorrhage secondary to pituitary apoplexy. Ten cases of this entity with a review of the literature are presented here.

METHODS

This is a single-institution retrospective review of 2598 patients with sellar and parasellar masses during the 10-year period between 1999 and 2009. The pituitary and brain MRI and MRI studies were reviewed by 2 neuroradiologists for evidence of apoplexy, with particular attention given to retroclival extension.

RESULTS

Eighteen patients (13 men and 5 women; mean age 54 years) were identified with presenting symptoms of sudden onset of headache and ophthalmoplegia, and laboratory findings consistent with pituitary apoplexy. Ten of these patients (8 men and 2 women; mean age 55 years) had imaging findings consistent with retroclival hematoma.

CONCLUSIONS

Retroclival hemorrhage was seen in the majority of cases of pituitary apoplexy (56%), suggesting that it is more common than previously thought.

Japanese neurosurgeons and microsurgical anatomy: a historical review

Research in microneurosurgical anatomy has contributed to great advances in neurosurgery in the last 40 years. Many Japanese neurosurgeons have traveled abroad to study microsurgical anatomy and played major roles in advancing and spreading the knowledge of anatomy, overcoming their disadvantage that the cadaver study has been strictly limited inside Japan. In Japan, they initiated an educational system for surgical anatomy that has contributed to the development and standardization of Japanese neurosurgery. For example, the Japanese Society for Microsurgical Anatomy started an annual educational meeting in the middle of 1980s and published its proceedings in Japanese every year for approximately 20 years. These are some of the achievements that bring worldwide credit to Japanese neurosurgeons. Not only should Japanese neurosurgeons improve their educational system but they should also contribute to the international education in this field, particularly in Asia.

Anatomical variations and neurosurgical significance of Liliequist's membrane

INTRODUCTION

Liliequist's membrane is an arachnoid membrane that forms a barrier within the basilar cisternal complex. This structure is an important landmark in approaches to the sellar and parasellar regions. The importance of this membrane was largely recognized after the advance of neuroendoscopic techniques. Many studies were, thereafter, published reporting different anatomic findings.

METHOD

A detailed search for studies reporting anatomic and surgical findings of Liliequist's membrane was performed using "PubMed," and included all the available literature. Manual search for manuscripts was also conducted on references of papers reporting reviews.

RESULTS

Liliequist's membrane has received more attention recently. The studies have reported widely variable results, which were systematically organized in this paper to address the controversy.

CONCLUSION

Regardless of its clinical and surgical significance, the anatomy of Liliequist's membrane is still a matter of debate.

Arachnoid membranes in the posterior half of the incisural space: an inverted Liliequist membrane–like arachnoid complex

Object

The aim of this study was to describe the similarity of configuration between the arachnoid complex in the posterior half of the incisural space and the Liliequist membrane.

Methods

Microsurgical dissection and anatomical observation were performed in 20 formalin-fixed adult cadaver heads. The origin, distribution, and configuration of the arachnoid membranes and their relationships with the vascular structures in the posterior half of the incisural space were examined.

Results

The posterior perimesencephalic membrane and the cerebellar precentral membrane have a common origin at the tentorial edge and form an arachnoid complex strikingly resembling an inverted Liliequist membrane. Asymmetry between sides is not uncommon. If the cerebellar precentral membrane is hypoplastic on one side or both, the well-developed quadrigeminal membrane plays a prominent part in partitioning the subarachnoid space in the posterior half of the incisural space.

Conclusions

The arachnoid complex in the posterior half of the incisural space can be regarded as an inverted Liliequist membrane. This concept can help neurosurgeons to gain better understanding of the surgical anatomy at the level of the tentorial incisura.

Anatomy of the pineal region applied to its surgical approach

INTRODUCTION

The pineal region is situated in the posterior part of the incisural space. This region includes the pineal body inside the quadrigeminal arachnoidal cistern. This article reviews the anatomic features of this region, with particular emphasis on those aspects of importance for surgical access to the pineal region.

MATERIAL & METHODS

Five cadaver heads fixed in 10% formalin and injected with colored latex were used for anatomic dissection (five other specimens were also prepared and dissected to illustrate the articles on surgical techniques and approaches presented elsewhere in this issue).

RESULTS

The pineal body is surrounded by several important structures such as: posterior part of the third ventricle, tectum, the complex of the great cerebral vein of Galen, pulvinar nuclei of the thalamus and splenium of corpus callosum.

CONCLUSION

The surgical approach of the pineal body, whatever the route or the technique used (microsurgical, endoscopic or stereotactic), creates a great challenge for the neurosurgeons due to its location in the deep part of the brain and its close relationships with complex surrounded vascular structures.

Intracavernous internal carotid artery mycotic aneurysms: comprehensive review and evaluation of the role of endovascular treatment

Mycotic aneurysms may arise in the setting of many local or systemic infections. Those of the intracranial circulation are especially worrisome due to their potential to compress vital neural structures and their propensity for rupture with consequent hemorrhage. Mycotic aneurysms of the intracavernous internal carotid artery (ICA) represent an exceedingly rare clinical entity, described in less than fifty published cases. Typically presenting as a cavernous sinus syndrome with signs and symptoms of the underlying infection, they are often missed initially, with diagnosis and treatment commencing for the triggering infection or confused with cavernous sinus thrombophlebitis, which may be additionally coexistent, confounding timely diagnosis of the aneurysmal disease. Compared to non-mycotic aneurysms of the intracavernous ICA, which typically have a benign course, the infectious etiology of the mycotic variety increases their tendency to rupture, precludes surgical clipping as a viable treatment option, and requires institution of prolonged antibiotic therapy prior to definitive intervention. Their critical location, friability, and propensity to occur bilaterally result in an unpredictable risk of rapid neurological decline and death, making the timing and specific nature of treatment a unique dilemma facing the treating physician. This review seeks to discuss the natural history of and management strategies for mycotic aneurysms of the intracavernous ICA with special emphasis on the role, safety, and efficacy of endovascular therapies.

Cystic Abducens Schwannoma without Abducens Paresis : Possible Role of Cisternal Structures in Clinical Manifestation

The abducens nerve paresis generally can aid in the presumptive diagnosis of abducens schwannoma along with the typical radiological features of schwannomas. The authors present a case of a 76-year-old male patient with a abducens schwannoma without abducens nerve paresis. Peroperatively, abducens nerve located in the cerebellopontine cistern had normal in contour and diameter, despite the mass originated from this nerve. We hypothesize that anatomic location of abducens nerve may affect the vector of tumor growth to prevent destruction of its origin, the abducens nerve.

The intracranial arachnoid mater : a comprehensive review of its history, anatomy, imaging, and pathology

INTRODUCTION

The arachnoid mater is a delicate and avascular layer that lies in direct contact with the dura and is separated from the pia mater by the cerebrospinal fluid-filled subarachnoid space. The subarachnoid space is divided into cisterns named according to surrounding brain structures.

METHODS

The medical literature on this meningeal layer was reviewed in regard to historical aspects, etymology, embryology, histology, and anatomy with special emphasis on the arachnoid cisterns. Cerebrospinal fluid dynamics are discussed along with a section devoted to arachnoid cysts.

CONCLUSION

Knowledge on the arachnoid mater and cerebrospinal fluid dynamics has evolved over time and is of great significance to the neurosurgeon in clinical practice.

The subdiaphragmatic cistern: historic and radioanatomic findings

BACKGROUND

In the past, sporadic demonstrations of the existence of a subarachnoid subdiaphragmatic cistern have been published. The aim of this study was to evaluate the anatomical characteristics of the subdiaphragmatic cistern of the pituitary gland.

METHODS

After a complete review of the literature published on the topic, we report anatomical observations of the subdiaphragmatic cistern and its relationship to the pituitary gland and to the chiasmatic cistern. Ten cadaveric heads were studied using different techniques and surgical methods (plastination, plastic casts of the subarachnoid spaces, microscopic and transsphenoidal endoscopic approaches). Moreover, 3-T magnetic resonance images of ten healthy volunteers were analyzed to investigate the presence and anatomical variability of the subdiaphragmatic cistern.

RESULTS

By means of our qualitative radioanatomic study, we found that the roof of the subdiaphragmatic cistern is formed by the diaphragma sellae, the floor by the superior face of the pituitary gland, the lateral walls by the arachnoidea extending laterally through the medial walls of the cavernous sinus, and the medial walls by the infundibular stem. The subdiaphragmatic cistern communicates by means of the ostium of the diaphragm with the chiasmatic cistern.

CONCLUSION

We confirmed the existence of the subdiaphragmatic cistern. The overused term "suprasellar cistern" refers more to a complex of cisterns, formed by the subdiaphragmatic cistern, below the diaphragma sella, and by the chiasmatic cistern, above it, in direct communication with the lamina terminalis and carotid cisterns.

Anatomical and histological study of Liliequist's membrane: with emphasis on its nature and lateral attachments

PURPOSE

In previous studies, some disagreements regarding the nature (inner or outer arachnoid membrane) and lateral boundaries (temporal uncus or tentorial edge) of Liliequist's membrane remain. The aim was to clarify whether Liliequist's membrane is an inner or outer arachnoid membrane, and the distribution of Liliequist's membrane with emphasis on its lateral attachments.

METHODS

Liliequist's membrane was investigated by microsurgical dissection in 24 formalin-fixed adult cadaver heads and by histological sections of sellar-suprasellar specimens from another four formalin-fixed adult cadaver heads.

RESULTS

The results obtained in the present study indicated that 1) Liliequist's membrane arises from the basal arachnoid membrane and has two components: a basal part comprising a folding inner layer of the arachnoid mater and an attaching part consisting of accumulated arachnoid trabeculae; 2) similar histological features are also present in other inner arachnoid membranes with attachments on basal arachnoid membrane, demonstrating Liliequist's membrane is an inner arachnoid membrane; 3) laterally, Liliequist's membrane attaches to the anterior tentorial edge constantly and to the mesial temporal uncus in more than half; 4) the oculomotor nerve courses above Liliequist's membrane and is fixed on Liliequist's membrane by the oculomotor membrane, which can also attach on temporal uncus and should be differentiated from the true temporal attachments of Liliequist's membrane.

CONCLUSION

Liliequist's membrane is an inner rather than outer arachnoid membrane. Understanding of its individual variation and topographic relationships with surrounding neurovascular and arachnoid structures is important for neurosurgical practice.

Microsurgical and endoscopic anatomy of Liliequist's membrane and the prepontine membranes: cadaveric study and clinical implications

BACKGROUND

Liliequist's membrane is mostly described as having a diencephalic leaf, mesencephalic leaf, and diencephalic-mesencephalic leaves in the literature. Also different descriptions of the prepontine membranes were reported. In this study, we visualized the regular structural forms of membranes without disturbing any attachments and defined infrachiasmatic and prepontine safety zones. We discussed the clinical significance of these structures.

MATERIALS AND METHODS

The study was carried out on 24 adult human cadavers at the Morgue Specialization Department of the Forensic Medicine Institution following the initial autopsy examination. Liliequist's membrane and the prepontine membranes were explored after retraction of the frontal lobes. Dissections were performed under the operative microscope. A 0- and 30-degree, 2.7-mm angled rigid endoscope (Aesculap, Tuttlingen, Germany) was advanced through the prepontine cistern from the natural holes of membranes, or small holes were opened without damaging the surrounding structures.

RESULTS

The basal arachnoid membrane (BAM) continued as Liliequist's membrane (LM) without any distinct separation in all specimens. The LM coursed over the posterior clinoids and split into two leaves as the diencephalic leaf (DL) and mesencephalic leaf (ML) in 18 specimens; the medial pontomesencephalic membrane (MPMM) coursed anterolaterally as a continuation of the ML and attached to the medial surfaces of the fifth and sixth nerves, joining with the lateral pontomesencephalic membrane (LPMM), which was also a posterolateral continuation of the ML in all specimens. The medial pontomedullar membrane (MPMdM) and lateral pontomedullar membrane (LPMdM) were observed in 21 specimens. The MPMdM membrane was a continuation of the MPMM, and the LPMdM was a continuation of the LPMM in all 21 specimens.

CONCLUSION

We observed that the LM is a borderless continuation of the BAM. The MPMM and LPMM split from the ML without any interruptions. The MPMdM and LPMdM were a single membrane continuing from the MPMM and LPMM. We determined infrachiasmatic and prepontine areas that can be important for inferior surgical approaches.

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.

Anatomical study of the arachnoid envelope over the pineal region

BACKGROUND

The distribution of the arachnoid membrane and its relationship with the neurovascular structures in the pineal region are still not fully understood.

OBJECTIVE

Because the arachnoid membrane has an intimate relationship with the neurovascular structures in the pineal region and it will always be encountered surgically, we attempted to clarify the formation and distribution of the arachnoid envelope over the pineal region (AEPG).

METHODS

The formation and distribution of the AEPG and its relationship with the neurovascular structures in the pineal region were examined by anatomic dissection in 20 adult cadaveric formalin-fixed heads.

RESULTS

The supratentorial and infratentorial outer arachnoid membranes converged at the tentorial apex and then embraced and ran forward along the vein of Galen to form the AEPG. The AEPG could be divided into 2 parts. Typically, the posterior part of the AEPG enveloped the vein of Galen and the terminal segments of its tributaries, and the anterior part of the AEPG enveloped the suprapineal recess, the pineal gland, and the distal segment of the internal cerebral veins. The compartment demarcated by the AEPG did not communicate with the adjacent subarachnoid cisterns or space.

CONCLUSION

Previous knowledge about the AEPG, as well as the superior boundary and the contents of the quadrigeminal cistern, needs to be revised. The arrangement and individual variation of AEPG are important for a better understanding of the various growth patterns of the pineal tumors and the relationship between the tumor and the neurovascular structures in the pineal region.

Interpeduncular arachnoid cysts in infants and children: insight into the entity based on a case series with long-term follow-up

OBJECTIVE

Arachnoid cysts occupying the suprasellar region comprise 10-15% of intracranial distribution. Unlike large suprasellar cysts, pure interpeduncular cysts (IPCs) are rare, and their natural history is unknown. We describe a small series of children diagnosed with IPC and their long-term natural history.

METHODS

A retrospective review was conducted of interpeduncular arachnoid cysts diagnosed over the years 2000-2010 at our center. Patients with clearly suprasellar cysts were excluded. Serial magnetic resonance imaging and long-term follow-up examinations were analyzed. Additionally, we conducted an extensive literature review focusing on the differences between suprasellar cysts and IPCs.

RESULTS

We identified three pediatric patients with "pure" IPC; all of these had a follow-up of more than 5 years, and none was operated. Only six additional cases were identified in the literature. In both our experience and in the literature review, IPCs proved stable over the course of time, both radiologically as well as clinically.

CONCLUSIONS

The clinical and radiological features of IPCs are not well defined. Variations in the relationship of arachnoid cysts in this area to Liliequist's membrane may explain the different subgroups that have been identified as well as the confusing nomenclature. IPCs are usually diagnosed as incidental findings or present with mild endocrine disorders. Associated findings of hydrocephalus, mass effect, and compression of neighboring structures, such as the chiasm, are not as frequent as with suprasellar cysts. Given the high likelihood of continuing stability, a conservative strategy of follow-up is recommended for pure IPCs that demonstrate preservation of the third ventricle.

Microsurgical anatomy of Liliequist's membrane demonstrating three-dimensional configuration

OBJECT

Liliequist's membrane (LM) is an important arachnoid structure in the basal cisterns. The relevant anatomic descriptions of this membrane and how many leaves it has are still controversial. The existing anatomical theories do not satisfy the needs of minimally invasive neurosurgery. We aimed to establish the three-dimensional configuration of LM.

METHODS

Fifteen adult formalin-fixed cadaver heads were dissected under a surgical microscope to carefully observe the arachnoid mater in the suprasellar and post-sellar areas and to investigate the arachnoid structure and its surrounding attachments.

RESULTS

It was found that the LM actually consists of three types of membranes. The diencephalic membrane (DM) was usually attached by the mesencephalic membrane (MM) from underneath, and above DM it was usually a pair of hypothalamic membranes (HMs) extending superomedially. The pair of HMs was stretched between the DM (or MM) and the hypothalamus and were seldom attached to the carotid-chiasmatic walls between the carotid cistern and the chiasmatic cistern. These three types of membranes (DM, MM, and HM) comprised the main arachnoid structure in the anterior incisural space and often presented as four connected leaves. However, only two thirds of the specimens had all three types of membranes, and there was considerable variation in the characteristics and shapes of the membranes among the specimens.

CONCLUSION

All three types of membranes comprising LM serve as important anatomical landmarks and interfaces for surgical procedures in this area.

Anatomic Study of the Quadrigeminal Cistern in Patients With 3-Dimensional Magnetic Resonance Cisternography

OBJECT

The aim of this study was to demonstrate the anatomy of the quadrigeminal cistern, define the anatomic landmarks, and measure the extension of the cistern in the living by using magnetic resonance (MR) cisternography with 3-dimensional reconstruction.

METHODS

The quadrigeminal cistern was examined in 38 patients. We focused on measurements of the superior, posterior, and lateral limits; the anterior and posterior maximal rostrocaudal diameter; the distance between the right and left superior colliculus and the right and left inferior colliculus; and the angle between the quadrigeminal plate and pineal gland.

RESULTS

The highest variability was observed for the posterior rostrocaudal diameter with a standard deviation of 3.1 and a range from 8 to 21.1 mm followed by the anterior-posterior diameter with a standard deviation of 2.8 and a range from 6.4 to 16.5 mm. In all cases the distance between the right and left superior colliculus (13.3 ± 1.8 mm; mean ± SD) was longer than the distance between the right and left inferior colliculus (11.4 ± 1.3 mm; mean ± SD). We classified 2 types of cisterns: closed cisterns with angles between the quadrigeminal plate and the pineal gland ranging from 39° to 63° and open cisterns with angles ranging from 63° to 76°. The analysis of variability by age and sex showed no significant differences.

CONCLUSIONS

The MR cisternography with 3-dimensional reconstruction was a simple and noninvasive tool providing detailed anatomic information in the living. It allowed measurement of the high variability of morphology of the quadrigeminal cistern. We defined the lateral landmarks and identified the lateral limit of the cistern. We classified the different shapes of the quadrigeminal cistern as open or closed cisterns. This can be helpful in the choice of the surgical approach to the lesions arising in this area.

Endoscopic anatomy of the oculomotor nerve: defining the blind spot during endoscopic skull base surgery

OBJECTIVE

The objective of this study is to define the endoscopic anatomy of the oculomotor nerve (CN III) and its neurovascular relations in order to facilitate surgical procedures and avoid injury to this nerve during endoscopic endonasal approach to the skull base.

MATERIALS AND METHODS

Endoscopic anatomy of the cavernous sinus was studied in seven fresh adult cadavers bilaterally and the basal cisterns in five fresh adult cadavers. Extended endoscopic endonasal suprasellar approach was performed to expose the oculomotor nerve in the interpeduncular cistern and the endoscopic endonasal transethmoidopterygoidosphenoidal approach to expose the oculomotor nerve within the cavernous sinus.

RESULTS

The extraorbital part of the oculomotor nerve can be divided into three segments in regard to the cisterns and venous spaces that are being transected: the interpeduncular segment, the cisternal segment, and the intercavernous segment. Of these segments, only the cisternal segment could not be exposed since this segment was located at the initial part of the roof of the cavernous sinus, anterolateral to the posterior clinoid, and posteroinferior to the anterior clinoid processes. Thus, cisternal segment of the oculomotor nerve was considered a blind spot during endoscopic approaches to the skull base.

CONCLUSION

We defined the endoscopic anatomy of the CN III and the related neurovascular structures and proposed a new segmental classification of extraorbital oculomotor nerve. Awareness of the endoscopic anatomy and the new segmental classification of the CN III may prove helpful in avoiding the risk of nerve injury during endoscopic endonasal surgery for skull base pathologies.

Neurovascular anatomy: a practical guide

Students of cerebrovascular anatomy and physiology tend to model their learning based on normal patterns of blood flow. As such, the focus tends toward arterial physiology and pathology with less than adequate understanding of the significance of the venous system. This article presents a different approach to neurovascular anatomy, starting with the venous system and demonstrating both normal and pathologic states. It reviews the cerebral circulation with attention to the microsurgical relationships, angiographic patterns, and fusion of dual-volume imaging. The importance of bony, sulcal, and ventricular anatomy is presented as it relates to the angiographic representation of pathologic lesions. Examples are given of anatomic variants seen with the operating microscope, biplanar angiography, and three-dimensional rotational angiography." Note that in the synopsis and throughout the article, first person usage has been changed to third person per journal style.

Pedunculated basilar terminus aneurysm with pseudo-septation due to anterior herniation through a perforated membrane of Liliequist

Septations within cerebral arteries or aneurysms are exceedingly rare in the absence of associated fenestrations. We report an unusual unruptured pedunculated basilar apex aneurysm, with a "pseudoseptation" between the main aneurysmal sac and an anterior compartment, which was, in fact, represented by a perforation in the membrane of Liliequist, permitting anterior aneurysmal herniation into the carotid-chiasmatic cistern. The patient was successfully treated with detachable coils. This case is unusual on 2 accounts: 1) the aneurysm's appearance, and 2) the presence of a large fenestration in the membrane of Liliequist, of which anatomic features are herein reviewed.

MICROSURGICAL AND ENDOSCOPIC ANATOMY OF THE SUPRATENTORIAL ARACHNOIDAL MEMBRANES AND CISTERNS

OBJECTIVE

A limitation of previous studies of the arachnoid cisterns and membranes is that the act of opening the sylvian and interhemispheric fissures and basal arachnoid often led to destruction of the cisternal compartments and their membranous walls. The goal of this study was to overcome this limitation by combining the surgical microscope and endoscope for the examination of the cisternal compartments and their membranous walls.

METHODS

The supratentorial cisterns were examined in 22 cadaveric brains using both the operating microscope and the endoscope.

RESULTS

There are 2 types of arachnoid membranes: outer and inner. The outer arachnoidal membrane surrounds the whole brain, and the inner membranes divide the subarachnoid space into cisterns. Twelve inner arachnoid membranes were identified in the supratentorial area: diencephalic, mesencephalic, medial carotid, intracarotid, intracrural, olfactory, medial and lateral lamina terminalis, and proximal, medial, intermediate, and lateral sylvian membranes. These membranes partially or completely separate the subarachnoid space into 9 supratentorial cisterns: sylvian, carotid, chiasmatic, lamina terminalis, pericallosal, crural, ambient, oculomotor, and interpeduncular. There is a confluent area between the carotid, interpeduncular, and crural cisterns, which frequently has no membrane separating these cisterns.

CONCLUSION

Twelve inner arachnoid membranes and 9 cisterns were identified in this study.

Microsurgical study of the interpeduncular cistern and its communication with adjoining cisterns

OBJECTIVE

Investigating the structure, contents, location, and borders of interpeduncular cistern and its communications with adjoining cisterns.

MATERIALS AND METHODS

Microsurgical anatomy of the interpeduncular cistern was studied in 14 adult cadaver brains, using a surgical microscope(x3 to x40 magnification).

RESULTS

The interpeduncular cistern was divided into two portions: superficial (free) and deep (vascular). The superior wall of interpeduncular cistern was separated into the hypothalamic and mesencephalic part. It has communication with ambient, prepontine, carotid, cerebellopontine, oculomotor, and crural cisterns.

CONCLUSION

The interpeduncular cistern is a compound bulk structure. This classification is necessary for the quantitative and qualitative study of the interpeduncular anatomy. Also, it is necessary to neurosurgeons for the guiding line in this region.