M. Gazi Yaşargil
Médard Kakou, Christophe Destrieux and Stéphane Velut
Object. The pericallosal arterial complex supplies the callosal and pericallosal regions, as well as the anterior two thirds of the medial and superomedial aspects of both hemispheres. It is composed of the pericallosal artery (that is, the segment of the anterior cerebral artery located distal to the anterior communicating artery [ACoA]) and the median callosal artery (or third pericallosal artery), which originates from the ACoA. This system was studied in 46 specimens (23 human cadaver heads) injected with colored latex.
Methods. After being injected with colored latex, embalmed, and bleached, the specimens were studied with the aid of optic magnification.
The pericallosal artery was found to be divided into four segments (A2–A5 in the proximodistal direction). After giving rise to central, callosal, and cortical branches, it terminated near the splenium of the corpus callosum as the posterior pericallosal artery, or on the precuneus as the inferomedial parietal artery.
Conclusions. The authors propose a logical classification of the different variations in the pericallosal arterial complex based on embryological development. This complex can be considered a hemodynamic solution to an abnormal regression of one of its parts, which is balanced by the development of supplemental channels from other parts.
Vinko V. Dolenc
Johann Peltier, Nadine Travers, Christophe Destrieux and Stéphane Velut
In this study, the authors used a fiber-dissection technique to describe the optic radiation. They focused on the morphological characteristics (length and breadth) of this structure, its course, and its relationships with neighboring fasciculi and the lateral ventricle.
The authors dissected 10 previously frozen, formalin-fixed human brains with the aid of an operating microscope by following the fiber dissection technique described by Klingler in 1960. Lateral, inferior, and medial approaches were made. The optic radiation, also known as the Gratiolet radiation, extended from the lateral geniculate body to the calcarine fissure. The average distance from the tip of the anterior Meyer loop to the calcarine sulcus was 105 mm (range 95–114 mm). The breadth of the optic radiations, one on each side of the brain, averaged 17 mm at the level of the inferior horn (range 15–18 mm). This tract could be divided into three main segments: the anterior or Meyer loop, the body, and the end of the optic radiation. Adjacent anatomical structures included: laterally, the inferior longitudinal fasciculi; medially, the tapetum of the corpus callosum; and the ependyma of the inferior horn of the lateral ventricle.
Various practical surgical approaches are discussed. The knowledge gained by studying this particular anatomy will help prevent injury to the optic radiations during neurosurgery.
Emmanuel Lescanne, Stéphane Velut, Thierry Lefrancq and Christophe Destrieux
Object. The authors studied the cadaveric heads of 22 adults to describe the internal acoustic meatus (IAM) and its contents. Special attention was paid to the length of the arachnoidal and dural sheaths surrounding the neural structures, including the vestibular ganglion. An additional goal of this study was to verify anatomically the concept of arachnoidal duplication, which is reputedly induced by medial growth of vestibular neuromas and helpful in atraumatic dissection.
Methods. Twelve cadaveric heads (24 IAMs) were injected with colored latex and fixed in formalin. Cautious removal of the skull vault and the brain or the skull base allowed superior and anteroinferior views of the IAM, respectively. Photographs were obtained after removal of the bone canal and dissection of the meninges with the aid of optic magnification. Ten IAMs were prepared for histological study and the osteological anatomy of the fundus was endoscopically described for the remaining 10.
The dura mater covered the bone structures of the IAM, and the arachnoidal membrane of the cerebellopontine cistern invaginated into this dural cul-de-sac as a “muff.” The entire neurovascular content of the IAM, including the vestibular ganglion, was surrounded by this arachnoidal sheath in which cerebrospinal fluid circulated. The length of this arachnoidal sheath was the same ventrally and dorsally and, in all specimens, the entrance of the cochleovestibulofacial complex into the subarachnoid space was located at the fundus level.
Conclusions. In this study the authors demonstrated the existence of an acousticofacial cistern containing every nerve of the vestibulocochleofacial complex, including the vestibular ganglion from which acoustic neuromas develop. These findings clearly contradict the theory of the duplication of arachnoidal layers during medial growth of vestibular neuromas and may explain some of the intraoperative difficulties encountered in the atraumatic dissection of these tumors.
Christophe Destrieux, Stéphane Velut, Médard K. Kakou, Thierry Lefrancq, Brigitte Arbeille and Jean-Jacques Santini
✓ The so-called Dorello's canal was studied in 32 specimens (16 human cadaver heads) injected with colored latex and fixed in formalin (28 specimens) or studied with microscopic and ultrastructural methods (four specimens). To avoid the differences usually encountered in the description of this area, the authors preferred to consider a larger space that they have named the petroclival venous confluence (PVC). It was located between two dural layers: inner (or cerebral) and outer (or osteoperiosteal). The PVC was quadrangular on transverse section. The posterior petroclinoid fold and the axial plane below the dural foramen of the abducent nerve (sixth cranial nerve) limited the PVC at the top and bottom, respectively. Its anteroinferior limit was the posterosuperior aspect of the upper clivus and outer layer of the dura mater. Its anterior limit was the vertical plane containing the posterior petroclinoid fold, and its posterior limit was the inner layer of the dura. The PVC was limited laterally by the medial aspect of the petrous bone apex and medially by the virtual sagittal plane extending the medial limit of the inferior petrosal sinus upward. The PVC was a venous space bordered by endothelium and continuous with the cavernous sinus, the basal sinus of the clivus, and the inferior petrosal sinus. There were trabeculations between the two dural layers. The petrosphenoidal ligament of Grüber may be regarded as a larger trabeculation, and it divided the PVC into a superior and an inferior compartment. The abducent nerve generally ran through the inferior compartment, where it was fixed to the surrounding dura mater. This nerve was only separated from venous blood by a meningeal sheath of varying thinness lined with endothelium. The clinical implications of these findings are discussed.
Christophe Destrieux, Médard K. Kakou, Stéphane Velut, Thierry Lefrancq and Michel Jan
Object. The authors studied the heads of 17 adult cadavers and one fetus to clarify the anatomy of the sellar region, particularly the lateral boundaries of the hypophyseal fossa.
Methods. Vascular injections and microdissection or histological techniques were used in this study. The roof of the cavernous sinuses and diaphragma sellae were part of a single horizontal dural layer that joined the two anterior petroclinoid folds. Laterally, the direction of this layer changed; it became the lateral wall of the cavernous sinus and joined the dura mater of the middle cerebral fossa. On the midline, this layer ballooned toward the sella through the diaphragmatic foramina, created a dural bag containing the hypophysis, and attached to the inferior aspect of the diaphragma sellae. As a consequence, no straight sagittal dural wall existed between the pituitary gland and cavernous sinus; the lateral border of the hypophyseal fossa was part of this anteroposterior and superoinferior convex bag. The authors stress the importance of the venous elements of the region and discuss the structure of the cavernous and coronary sinuses.
Conclusions. Invasion of the cavernous sinus makes surgery more risky and difficult and may necessitate modification of the surgical treatment plan. The preoperative diagnosis of cavernous sinus invasion is thus of great interest, but the possibility of normal lateral expansions of the pituitary gland must be kept in mind. A lateral expansion of this gland into the cavernous sinus was encountered in 29% of the specimens, and an adenoma that developed in such an expansion could easily mimic cavernous sinus invasion.
Patrick François, Nadine Travers, Emmanuel Lescanne, Brigitte Arbeille, Michel Jan and Stéphane Velut
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.
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.
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.
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.
Patrick François, Ilyess Zemmoura, Anne Marie Bergemer Fouquet, Michel Jan and Stéphane Velut
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.
Florian Bernard, Ilyess Zemmoura, Jean Philippe Cottier, Henri-Dominique Fournier, Louis-Marie Terrier and Stéphane Velut
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.
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.
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.
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.