Microsurgical anatomy of the interpeduncular cistern and related arachnoid membranes

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.

Microsurgical anatomy and pathoanatomy of the outer arachnoid membranes in the cerebellopontine angle: cadaveric and intraoperative observations

PURPOSE

The cerebellopontine angle (CPA) is a frequent region of skull base pathologies and therefore a target for neurosurgical operations. The outer arachnoid is the key structure to approach the here located lesions. The goal of our study was to describe the microsurgical anatomy of the outer arachnoid of the CPA and its pathoanatomy in case of space-occupying lesions.

METHODS

Our examinations were performed on 35 fresh human cadaveric specimens. Macroscopic dissections and microsurgical and endoscopic examinations were performed. Retrospective analysis of the video documentations of 35 CPA operations was performed to describe the pathoanatomical behavior of the outer arachnoid.

RESULTS

The outer arachnoid cover is loosely attached to the inner surface of the dura of the CPA. At the petrosal surface of the cerebellum the pia mater is strongly adhered to the outer arachnoid. At the level of the dural penetration of the cranial nerves, the outer arachnoid forms sheath-like structures around the nerves. In the midline, the outer arachnoid became detached from the pial surface and forms the base of the posterior fossa cisterns. In pathological cases, the outer arachnoid became displaced. The way of displacement depends on the origin of the lesion. The most characteristic patterns of changes of the outer arachnoid were described in case of meningiomas, vestibular schwannomas, and epidermoid cysts of the CPA.

CONCLUSION

The knowledge of the anatomy of the outer arachnoid of the cerebellopontine region is essential to safely perform microsurgical approaches as well as of dissections during resection of pathological lesions.

Delineation of Subarachnoid Cisterns Using CT Cisternography, CT Brain Positive and Negative Contrast, and a Three Dimensional MRI Sequence: A Pictorial Review

The basic anatomy and morphology of subarachnoid cisterns of the brain are interesting and challenging topics with high clinical significance. These enlarged CSF-filled expansions are important as they transmit various neurovascular structures. The cisterns can be classified based on their location as supratentorial, at the level of the tentorium, and infratentorial. They are also classified as paired and unpaired cisterns. The anatomical and radiological information about the cisterns is clinically and surgically relevant in diagnosing and managing many neurological disorders. It is also essential in medical teaching. This pictorial essay reviews the radiological images where the subarachnoid cisterns are delineated in four unique circumstances.

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.

Neurosurgical anatomy of the floor of the third ventricle and related vascular structures

PURPOSE

Anatomical knowledge of the floor of the third ventricle (FTV) is essential in avoiding surgical complications during endoscopic third ventriculostomy. The purpose of this study was to characterize the morphometry of FTV and related arteries, particularly the basilar artery (BA), as well as the factors that influence it.

METHODS

Twenty-six formalin-fixed adult brains and two hundred adult brain MRIs were studied focusing on FTV and related arteries. Dimensions of interest were measured using image analysis software. Morphometric data obtained were statistically analysed.

RESULTS

Distances between FTV, intermammillary sulcus (IMS), infundibulum, BA bifurcation, and posterior communicating arteries (PCoAs) were described on the cadavers and the MRIs. Distance between right and left PCoAs was greater at their anterior extremity (p < 0.001). Right PCoA was longer (p = 0.016). BA was lateralized in 58.4% of cases and its calibre was larger in males (p < 0.001). The distance from BA apex to FTV was inversely correlated with BA diameter (p < 0.001) and age (p = 0.004). Distance from IMS to infundibulum and the distance between both PCoAs were greater in MRI series when compared to cadaver series (p < 0.001).

CONCLUSIONS

A quantitative description of the morphometry of the region of the FTV and related vessels was obtained, helping neurosurgeons in planning their surgical approach. The distance from BA apex to FTV was shorter in individuals with larger BA calibre and in older subjects. MRI studies were qualitatively superior to cadaveric studies in evaluating the anatomy of this region.

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.

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.

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.

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.

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.

The distance between the posterior communicating arteries and their relation to the endoscopic third ventriculostomy in adults: An anatomic study

BACKGROUND

The diencephalic leaf of the Liliequist's membrane is a continuous structure that should be perforated in the endoscopic third ventriculostomy. Its lateral borders are penetrated by the third cranial nerve and the posterior communicating arteries. The most important complication of endoscopic third ventriculostomy is the vascular injury, such as the posterior communicating artery. The purpose of this study is to measure the distance between posterior communicating arteries located below the third ventricle floor and anterior of the mammillary bodies.

METHODS

In this observational prospective study 20 fresh brains from cadavers were utilized to measure the distance between the posterior communicating arteries in April 2008 at the Death Check Unit of our Institution. A digital photograph of the posterior communicating arteries was taken and the distance between the arteries was measured. The measurement was analyzed using descriptive statistics.

RESULTS

In the descriptive analysis of the 20 specimens, the posterior communicating arteries distance was 9 to 18.9 mm, a mean of 12.5 mm, median of 12.2 mm, standard deviation of 2.3 mm.

CONCLUSION

The detailed knowledge of vascular structures involved in the endoscopic third ventriculostomy as to the posterior communicating arteries distance provides a safe lateral vascular border when performing such procedure.

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.

The Oculomotor Nerve

OBJECTIVE

This study was performed to assess the anatomy of the oculomotor nerve and to describe its course from the brainstem to the orbit. A new anatomically and surgically oriented classification of the nerve has been provided to illustrate its topographic and neurovascular relationships.

METHODS

Fifty-nine human cadaveric heads (118 specimens) were used for the anatomical dissection. Forty-four of these were embalmed in a 10% formalin solution for 3 weeks, and 15 were fresh frozen injected with colored latex. The nerve was exposed along its pathway via frontotemporal, frontotemporo-orbitozygomatic, and subtemporal transtentorial approaches. These approaches were performed to expose each segment of the nerve. An endoscopic endonasal transsphenoidal approach was performed on 9 heads to visualize and compare the neurovascular relationships of the same areas from an inferomedial perspective. Measurements of each segment of the nerve were taken in all specimens during the dissecting process.

RESULTS

The nerve was divided into 5 segments: cisternal, petroclinoid, cavernous, fissural, and orbital. The simultaneous use of a microscopic transcranial and an endoscopic endonasal route allows a better understanding of the spatial relationship of the nerve.

CONCLUSION

The knowledge of the dural, bony, and neurovascular relationships of the oculomotor nerve may help to prevent common complications during both microsurgical and endoscopic approaches to the cavernous sinus, interpeduncular, middle cranial fossa, and orbital regions. We discuss the possible significance of the observed anatomical data and propose classification of the different segments of the nerve.

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.

Microsurgical and Endoscopic Anatomy of Liliequist's Membrane: A Complex and Variable Structure of the Basal Cisterns

Objective:

Descriptions of Liliequist's membrane, as reported in the literature, vary considerably. In our cadaveric study of Liliequist's membrane, we attempted to clarify and define its anatomic features and boundaries, as well as its relationship with surrounding neurovascular structures. We describe the embryology of this membrane as a remnant of the primary tentorium. The clinical significance of our findings is discussed with respect to third ventriculostomy and surgical approaches to basilar tip aneurysms, suprasellar arachnoid cysts, and perimesencephalic hemorrhage.

Methods:

Thirteen formalin-fixed adult cadaveric heads were injected with colored silicone. After endoscopic exploration of Liliequist's membrane, a bilateral frontal craniotomy was performed, and the frontal lobes were removed to fully expose Liliequist's membrane.

Results:

Liliequist's membrane is a complex and highly variable structure that is composed of either a single membrane or two leaves. The membrane was absent in two specimens without any clear demarcation between the interpeduncular, prepontine, and chiasmatic cisterns.

Conclusion:

Understanding the variable anatomy of Liliequist's membrane is important, particularly to improve current and forthcoming microsurgical and endoscopic neurosurgical procedures. It is important as a surgical landmark in various neurosurgical operations and in the physiopathology of several pathological processes (suprasellar arachnoid cysts and perimesencephalic hemorrhage).

[Endoscopic anatomy of the terminal portion of the basilar artery and its distal perforating branches]

The aim of this study was to describe and highlight the endoscopic anatomy of the tip of the basilar artery and its perforating branches. Knowledges of the anatomy are crucial for neurosurgeons to avoid pitfalls during endoscopic third ventriculostomy.

Cranial arachnoid membranes: Some aspects of microsurgical anatomy

Although the arachnoid membranes have been known for more than 300 years, the anatomy of the arachnoid membranes has not been studied in detail. This study was performed to explore the microanatomical features of the cranial arachnoid membranes. The arachnoid membranes and cisterns were observed in eight Han Chinese adult human cadaveric brains with an operating microscope, without staining of intracranial structures or injection of colored material into blood vessels. Twenty seven arachnoid membranes and 21 subarachnoid cisterns were identified. The topographical features of each arachnoid membrane were described. On the basis of the arachnoid membranes we identified, the arachnoidal limits of the cisterns were discussed. The microsurgical anatomical research on the arachnoid membranes is a supplement to the anatomical study of the subarachnoid cisterns. The understanding of the topographical features of the arachnoid membranes is valuable to the reasonable dissection of the cisterns and the minimally invasive manipulations during microsurgical procedures.