History of the extradural neural axis compartment

Cognard Type Ⅴ Torcular Dural Arteriovenous Fistula: A Rare Entity

Tentorial dural arteriovenous fistulas (DAVFs) are a dangerous subtype of fistula. Lawton et al classified this type of fistula into 6 categories based on specific operative strategies. Clinical manifestations of 6 types of tentorial DAVFs vary to some extent. Cognard type V DAVFs in the tentorial region are usually petrosal/superior petrosal sinus DAVFs. DAVFs with perimedullary venous drainage around the torcular herophili are rare. The veins of the posterior fossa are intricate and variable. There are anatomic communications between the perimedullary vein and cerebellar vein or veins of the brainstem. Almost all of the Cognard type V DAVFs are found in the posterior fossa. Here, we present a Cognard type V DAVF with a fistula located around the torcular herophili.

Fine configuration of the dural fibrous network and the extradural neural axis compartment in the jugular foramen: an epoxy sheet plastination and confocal microscopy study

OBJECTIVE

The extradural neural axis compartment (EDNAC) is an adipovenous zone that is located between the meningeal (ML) and endosteal (EL) layers of the dura mater and has been minimally investigated in the jugular foramen (JF) region. In this study, the authors aimed to explore the fine architecture of the EDNAC within the JF and evaluate whether the EDNAC can be used as a component for JF compartmentalization.

METHODS

A total of 46 cadaveric heads (31 male, 15 female; age range 54-96 years) and 30 dry skulls were examined in this study. Twelve of 46 cadaveric heads were plastinated as a series of transverse (7 sets), coronal (3 sets), and sagittal (2 sets) slices and examined using stereomicroscopy and confocal microscopy. The dural entry points of the JF cranial nerves were recorded in 34 cadaveric skulls. The volumes of the JF, intraforaminal EDNAC, and internal jugular vein (IJV) were quantified.

RESULTS

Based on constant osseous landmarks, the JF was subdivided into preforaminal, intraforaminal, and subforaminal segments. The ML-derived fascial sheath along the anteromedial wall of the IJV demarcated the "venous portion" and the "EDNAC portion" of the bipartite JF. The EDNAC did not surround the intraforaminal IJV and comprised an ML-derived dural fibrous network and an adipose matrix. A fibrovenous curtain subdivided the intraforaminal EDNAC into a small anterior column containing cranial nerve (CN) IX and the anterior condylar venous plexus and a large posterior adipose column containing CNs X and XI. In the intraforaminal segment, the IJV occupied a slightly larger space in the foramen (57%; p < 0.01), whereas in the subforaminal segment it occupied a space of similar size to that of the EDNAC.

CONCLUSIONS

Excluding the IJV, the neurovascular structures in the JF traverse the dural fibrous network that is dominant in the foraminal EDNAC. The results of this study will contribute to anatomical knowledge of the obscure yet crucially important JF region, increase understanding of foraminal tumor growth and spread patterns, and facilitate the planning and execution of surgical interventions.

Clinical Anatomy of the Extradural Neural Axis Compartment: A Literature Review

OBJECTIVE

The extradural neural axis compartment (EDNAC) is an adipovenous zone located between the meningeal and endosteal layers of the dura and has been minimally investigated. It runs along the neuraxis from the orbits down to the coccyx and contains fat, valveless veins, arteries, and nerves. In the present review, we have outlined the current knowledge regarding the structural and functional significance of the EDNAC.

METHODS

We performed a narrative review of the reported EDNAC data.

RESULTS

The EDNAC can be organized into 4 regional enlargements along its length: the orbital, lateral sellar, clival, and spinal segments, with a lateral sellar orbital junction linking the orbital and lateral sellar segments. The orbital EDNAC facilitates the movement of the eyeball and elsewhere allows limited motility for the meningeal dura. The major nerves and vessels are cushioned and supported by the EDNAC. Increased intra-abdominal pressure will also be conveyed along the spinal EDNAC, causing increased venous pressure in the spine and cranium. From a pathological perspective, the EDNAC functions as a low-resistance, extradural passageway that might facilitate tumor encroachment and expansion.

CONCLUSIONS

Clinicians should be aware of the extent and significance of the EDNAC, which could affect skull base and spine surgery, and have an understanding of the tumor spread pathways and growth patterns. Comparatively little research has focused on the EDNAC since its initial description. Therefore, future investigations are required to provide more information on this underappreciated component of neuraxial anatomy.

The interperiosteodural concept applied to the jugular foramen and its compartmentalization

OBJECTIVE

The dura mater is made of 2 layers: the endosteal layer (outer layer), which is firmly attached to the bone, and the meningeal layer (inner layer), which directly covers the brain and spinal cord. These 2 dural layers join together in most parts of the skull base and cranial convexity, and separate into the orbital and perisellar compartments or into the spinal epidural space to form the extradural neural axis compartment (EDNAC). The EDNAC contains fat and/or venous blood. The aim of this dissection study was to anatomically verify the concept of the EDNAC by focusing on the dural layers surrounding the jugular foramen area.

METHODS

The authors injected 10 cadaveric heads (20 jugular foramina) with colored latex and fixed them in formalin. The brainstem and cerebellum of 7 specimens were cautiously removed to allow a superior approach to the jugular foramen. Special attention was paid to the meningeal architecture of the jugular foramen, the petrosal inferior sinus and its venous confluence with the sigmoid sinus, and the glossopharyngeal, vagus, and accessory nerves. The 3 remaining heads were bleached with a 20% hydrogen peroxide solution. This procedure produced softening of the bone without modifying the fixed soft tissues, thus permitting coronal and axial dissections.

RESULTS

The EDNAC of the jugular foramen was limited by the endosteal and meningeal layers and contained venous blood. These 2 dural layers joined together at the level of the petrous and occipital bones and separated at the inferior petrosal sinus and the sigmoid sinus, and around the lower cranial nerves, to form the EDNAC. Study of the dural sheaths allowed the authors to describe an original compartmentalization of the jugular foramen in 3 parts: 2 neural compartments—glossopharyngeal and vagal—and the interperiosteodural compartment.

CONCLUSIONS

In this dissection study, the existence of the EDNAC concept in the jugular foramen was demonstrated, leading to the proposal of a novel 3-part compartmentalization, challenging the classical 2-part compartmentalization, of the jugular foramen.

The analysis of the cerebral venous blood volume in cavernous sinus using 320 row multi-detector CT

OBJECTIVES

Functional venous anatomy in the brain has been mostly understood from the morphological and embryological points of view and no published study has directly evaluated the blood flow volume of cerebral small veins. We developed a method to directly evaluate the relative blood volume in small venous channels using multi-detector computed tomography (CT) and applied it to evaluate the blood volume in each tributary of the cavernous sinus, which plays an important role in cerebral venous drainage.

PATIENTS AND METHODS

Ten patients with small brain tumors who had normal venous anatomy were included in the present study. All of them underwent preoperative 320-row multi-detector CT. After injecting the contrast bolus, we measured the Hounsfield units (HUs) at 10 time point over 60 s in each tributary of the cavernous sinus. The gamma distribution fitting to each HU enabled us to obtain a time-density curve and determine the relative venous volume in each venous channel.

RESULTS

In terms of blood volume, the superficial middle cerebral vein and inferior petrosal sinus were the largest inflow and outflow channels of the cavernous sinus and accounted for 36.1% and 24.7% of its inflow and outflow on average, respectively. The superior orbital vein did not contribute to the blood volume passing through the cavernous sinus in the current study.

CONCLUSIONS

The present study allowed us to determine the relative blood volume in each tributary of the cavernous sinus, which was very useful to understand the physiological actual venous drainage pattern concerning the cavernous sinus in normal anatomy.

Perispinal Delivery of CNS Drugs

Perispinal injection is a novel emerging method of drug delivery to the central nervous system (CNS). Physiological barriers prevent macromolecules from efficiently penetrating into the CNS after systemic administration. Perispinal injection is designed to use the cerebrospinal venous system (CSVS) to enhance delivery of drugs to the CNS. It delivers a substance into the anatomic area posterior to the ligamentum flavum, an anatomic region drained by the external vertebral venous plexus (EVVP), a division of the CSVS. Blood within the EVVP communicates with the deeper venous plexuses of the CSVS. The anatomical basis for this method originates in the detailed studies of the CSVS published in 1819 by the French anatomist Gilbert Breschet. By the turn of the century, Breschet's findings were nearly forgotten, until rediscovered by American anatomist Oscar Batson in 1940. Batson confirmed the unique, linear, bidirectional and retrograde flow of blood between the spinal and cerebral divisions of the CSVS, made possible by the absence of venous valves. Recently, additional supporting evidence was discovered in the publications of American neurologist Corning. Analysis suggests that Corning's famous first use of cocaine for spinal anesthesia in 1885 was in fact based on Breschet's anatomical findings, and accomplished by perispinal injection. The therapeutic potential of perispinal injection for CNS disorders is highlighted by the rapid neurological improvement in patients with otherwise intractable neuroinflammatory disorders that may ensue following perispinal etanercept administration. Perispinal delivery merits intense investigation as a new method of enhanced delivery of macromolecules to the CNS and related structures.

Dissemination of prostate adenocarcinoma to the skull base mimicking giant trigeminal schwannoma: anatomic relevance of the extradural neural axis component

We report an unusual case of a large metastatic lesion from prostate adenocarcinoma with its epicenter located in Meckel's cave. The patient presented with acute neurological deterioration due to pontomesencephalic, cranial nerve, and temporal lobe compression. This lesion radiologically mimicked a giant trigeminal schwannoma. Complete surgical resection was achieved with improvement in the performance status of the patient. The anatomic relevance the extradural neural axis component in the process of dissemination of prostate adenocarcinoma to the skull base is highlighted.

The dural sheath of the optic nerve: descriptive anatomy and surgical applications

The aim of this work was to clarify the descriptive anatomy of the optic dural sheath using microanatomical dissections on cadavers. The orbit is the rostral part of the extradural neural axis compartment; the optic dural sheath forms the central portion of the orbit.In order to describe this specific anatomy, we carefully dissected 5 cadaveric heads (10 orbits) up to the meningeal structure of the orbit and its contents. 1 cadaveric head was reserved for electron microscopy to add to our knowledge of the collagen structure of the optic dural sheath.In this chapter, we describe the anatomy of the interperiostal-dural concept and the anatomy of the orbit. The optic dural sheath contains three portions: the intracranial, the intracanalicular and the intraorbital segment. Each one has specific anatomic relations which result in particular surgical considerations.

Lateral sellar angiolipoma: a tumor illustrative of the extradural compartment of the neural axis

Angiolipomas are rare tumors of the CNS that most frequently develop in the orbit, the cavernous space, and the epidural space of the spine. The authors report the case of a patient who presented with an angiolipoma of the cavernous space. Using data from the published literature and an experimental anatomical approach, they demonstrate that the cavernous space contains adipose tissue. Consequently, they suggest that angiolipomas constitute a characteristic tumor illustrating the interperiosteo-dural concept.

The authors report the clinical, radiological, and histological data of a patient who presented with a tumor of the cavernous space. In addition, they prepared 2 encephalic extremities (4 cavernous spaces) using a special anatomical preparation consisting of an injection of colored neoprene latex followed by a 6-month immersion in a formaldehyde solution enriched with hydrogen peroxide to soften the bone structures (coronal sections) while leaving the fat in the cavernous space intact.

This case report corroborates previously published clinical data and shows that the tumor was a hamartoma comprising mature fat cells associated with vascular proliferation. The tumor developed in the cavernous space, which is an interperiosteo-dural space extending from the sphenoid periosteum (osteoperiosteal layer) to the superior and lateral walls of the cavernous space (encephalic layer). This space represents an anatomical continuum extending from the coccyx to the orbit: the interperiosteo-dural concept. It contains fat tissue that is abundant at the level of the orbit and the epidural spinal space and sparser at the level of the cavernous spaces, as was shown in our anatomical study.

The authors suggest that angiolipomas represent a characteristic tumor that illustrates the interperiosteo-dural concept because they essentially develop in the fat tissue contained in these spaces.

The interperiosteo-dural concept applied to the perisellar compartment: a microanatomical and electron microscopic study

Object

The dura mater has 2 dural layers: the endosteal layer (outer layer), which is firmly attached to the bone, and the meningeal layer (inner layer), which directly covers the brain. These 2 dural layers join together in the middle temporal fossa or the convexity and separate into the orbital, lateral sellar compartment (LSC), or spinal epidural space to form the extradural neural axis compartment (EDNAC). The aim of this work was to anatomically verify the concept of the EDNAC by using electron microscopy.

Methods

The authors studied the cadaveric heads obtained from 13 adults. Ten of the specimens (or 20 perisellar areas) were injected with colored latex and fixed in formalin. They carefully removed each brain to allow a superior approach to the perisellar area. The 3 other specimens were studied by microscopic and ultrastructural methods to describe the EDNAC in the perisellar area. Special attention was paid to the dural layers surrounding the perisellar area. The authors studied the anatomy of the meningeal architecture of the LSC, the petroclival venous confluence, the orbit, and the trigeminal cave. After dissection, the authors took photographs of the dural layers with the aid of optical magnification. The 3 remaining heads, obtained from fresh cadavers, were prepared for electron microscopic study.

Results

The EDNAC is limited by the endosteal layer and the meningeal layer and contains fat and/or venous blood. The endosteal layer and meningeal layer were not identical on electron microscopy; this finding can be readily related to the histology of the meninges.

Conclusions

In this study, the authors demonstrated the existence of the EDNAC concept in the perisellar area by using dissected cadaveric heads and verified the reality of the concept of the meningeal layer with electron microscopy. These findings clearly demonstrated the existence of the EDNAC, a notion that has generally been accepted but never demonstrated microscopically.