The parasellar region of human infants: cavernous sinus topography and surgical approaches

Posterior clinoid process in children: morphometric analysis, pneumatization ratio, and surgical implications

PURPOSE

To describe pneumatization and topographic position of the posterior clinoid process (PCP) in healthy children when approaching the anterior and middle fossae.

METHODS

The study consisted of computed tomography images of 180 pediatric patients (90 males / 90 females), aged 1-18 years. The presence or absence of PCP pneumatization was noted, and the distances of certain landmarks to PCP were measured.

RESULTS

The distances of the foramen ovale, foramen rotundum, superior orbital fissure, anterior clinoid process (ACP), foramen magnum and crista galli to PCP were measured as 18.59 ± 3.36 mm, 15.37 ± 3.45 mm, 14.60 ± 3.05 mm, 5.27 ± 3.24 mm, 32.03 ± 3.27 mm, and 30.45 ± 3.93 mm, respectively. These parameters increased with growth (between 1-18 years), but the distance between PCP and ACP decreased with an irregular pattern. In 11 sides (3.10%), a fusion between PCP and ACP was determined. PCP pneumatization was identified in 32 sides (8.9%). Its pneumatization correlated with pediatric ages (p < 0.001), but not gender (p = 0.459) or side (p = 0.711). Most of PCP pneumatization appeared after late childhood period (i.e., between 10-18 years).

CONCLUSION

Our study provides beneficial data for neurosurgeons to use PCP as a reference point for creating a skull base map in children, because of the incomparable position of PCP in the skull base center.

Anatomical features of the sphenoid ridge in the pediatric population

PURPOSE

To describe the relation of the sphenoid ridge (SR) with the surrounding anatomical structures in healthy children when approaching the anterior and middle fossae.

METHODS

Computed tomography of 180 pediatric patients (90 males / 90 females), aged 1-18 years were included the study. The size of the lesser wing (LW) and the distances of the LW to certain landmarks were measured.

RESULTS

The LW length was 28.48 ± 8.15 mm. The LW widths at the midline and the midpoint and lateral point of the SR were 7.78 ± 1.74 mm, 2.84 ± 0.81 mm, and 1.91 ± 0.64 mm, respectively. The distance between the midpoint of the SR and the crista galli was 28.22 ± 5.56 mm, and the distance between the crista alaris and internal auditory meatus was 51.73 ± 5.79 mm. The linear function was calculated as y = 18.748 + 1.024 × age for SR length, y = 6.046 + 0.182 × age for the midline width of SR, y = 2.367 + 0.050 × age for the midpoint width of SR, y = 1.249 + 0.069 × age for the crista alaris width, y = 21.727 + 0.683 × age for the distance between the SR midpoint and the crista galli, and y = 43.614 + 0.855 × age for the distance between the crista alaris and internal auditory meatus.

CONCLUSION

All measured parameters increased irregularly with advancing age. Furthermore, our regression equations representing the growth dynamics of SR may be used to estimate these parameters.

Radiologic evaluation of the Vidian canal in the pediatric population

PURPOSE

This examination aimed to display the size and topographic position of the Vidian canal (VC) in normal children.

METHODS

180 pediatric subjects aged 1-18 years were included this computed tomography examination. The distances of VC to certain landmarks, and VC length were measured. The locations of VC according to the sphenoid sinus, and the medial plate of pterygoid process were classified as three types, separately.

RESULTS

The distances of VC to the vomerine crest, midsagittal plane, round foramen, and the superior wall of sphenoid sinus were measured as 12.68 ± 3.17 mm, 10.76 ± 2.52 mm, 8.62 ± 2.35 mm, and 14.16 ± 5.00 mm, respectively. The length and angle of VC were measured as 12.00 ± 2.52 mm, and 16.60 ± 9.76°, respectively. According to the sphenoid bone, VC location was identified as Type 1 in 113 sides (47.5%), as Type 2 in 70 sides (29.4%), and as Type 3 in 55 sides (23.1%). According to the medial plate of pterygoid process, VC location was identified as Type A in 274 sides (76.1%), as Type B in 55 sides (15.3%), and as Type C in 31 sides (8.6%). VC location types correlated with pediatric ages, but not sex or side.

CONCLUSION

With advancing pediatric age, the protrusion of VC into the sphenoid sinus increases, and VC shifts from medial to lateral side of the medial plate of pterygoid process.

The venous system of E14.5 mouse embryos-reference data and examples for diagnosing malformations in embryos with gene deletions

Approximately one-third of randomly produced knockout mouse lines produce homozygous offspring, which fail to survive the perinatal period. The majority of these die around or after embryonic day (E)14.5, presumably from cardiovascular insufficiency. For diagnosing structural abnormalities underlying death and diseases and for researching gene function, the phenotype of these individuals has to be analysed. This makes the creation of reference data, which define normal anatomy and normal variations the highest priority. While such data do exist for the heart and arteries, they are still missing for the venous system. Here we provide high-quality descriptive and metric information on the normal anatomy of the venous system of E14.5 embryos. Using high-resolution digital volume data and 3D models from 206 genetically normal embryos, bred on the C57BL/6N background, we present precise descriptive and metric information of the venous system as it presents itself in each of the six developmental stages of E14.5. The resulting data shed new light on the maturation and remodelling of the venous system at transition of embryo to foetal life and provide a reference that can be used for detecting venous abnormalities in mutants. To explore this capacity, we analysed the venous phenotype of embryos from 7 knockout lines (Atp11a, Morc2a, 1700067K01Rik, B9d2, Oaz1, Celf4 and Coro1c). Careful comparisons enabled the diagnosis of not only simple malformations, such as dual inferior vena cava, but also complex and subtle abnormalities, which would have escaped diagnosis in the absence of detailed, stage-specific referenced data.

Association between the developing sphenoid and adult morphology: A study using sagittal sections of the skull base from human embryos and fetuses

The developing sphenoid is regarded as a median cartilage mass (basisphenoid [BS]) with three cartilaginous processes (orbitosphenoid [OS], ala temporalis [AT], and alar process [AP]). The relationships of this initial configuration with the adult morphology are difficult to determine because of extensive membranous ossification along the cartilaginous elements. The purpose of this study was therefore to evaluate the anatomical connections between each element of the fetal sphenoid and adult morphology. Sagittal sections from 25 embryos and fetuses of gestational age 6-34 weeks and crown-rump length 12-295 mm were therefore examined and compared with horizontal and frontal sections from the other 25 late-term fetuses (217-340 mm). The OS was identified as a set of three mutually attached cartilage bars in early fetuses. At all stages, the OS-post was continuous with the anterolateral part of the BS. The BS included the notochord and Rathke's pouch remnant in embryos and early fetuses. The dorsum sellae was absent from embryos, but it protruded from the BS in early fetuses before a fossa for the hypophysis became evident. Although not higher than the hypophysis at midterm, the dorsum sellae elongated superiorly after gestational age 25 weeks. In early fetuses, the AP was located on the side immediately anterior to the otic capsule. The AT developed on the side immediately posterior to the extraocular rectus muscles. At late term, the greater wing was formed by membranous bones from the AT and AP. The AT and AP formed a complex bridge between the BS and the greater wing. A small cartilage, future medial pterygoid process (PTmed) was located inferior to the AT in early fetuses. At midterm, one endochondral bone and multiple membranous bones formed the PTmed. The lateral pterygoid process (PTlat) was formed by a single membranous bone plate. Therefore, we connected fetal elements and the adult morphology as follows. (1) Derivative of the OS makes not only the lesser wing but also the anterior margin of the body of the sphenoid. (2) Derivatives of the BS are the body of the sphenoid including the sella turcica and the dorsum sellae. (3) Most of the greater wing including the foramen rotundum and the foramen oval originate from the AT and AP and multiple membranous bones. (4) The PTmed originate from endochondral bones and multiple membranous bones, while the PTlat derive from a single membranous bone.

An infantile case of posterior fossa arachnoid cyst presenting with marked engorgement of contralateral supraorbital vein

A 6-month-old, previously healthy boy presented with poor feeding and vomiting for 2 weeks. At presentation, his left supraorbital vein was found to engorge considerably. A cranial computed tomography (CT) scan revealed a large cyst in the posterior fossa with a prominent left superior ophthalmic vein (SOV). Magnetic resonance imaging delineated the well-demarcated cyst markedly compressing the right cerebellar hemisphere. The patient underwent microscopic fenestration of the cyst wall through lateral suboccipital craniotomy. The cyst wall, comprising multi-layered, opacified membranes, was extensively resected and communicated with the prepontine cistern. The histological appearance of the cyst wall was consistent with an arachnoid cyst. Engorgement of the left supraorbital vein resolved immediately after surgery. A postoperative CT scan did not identify the SOV in the left orbit. In the present case, engorgement of the supraorbital vein might reflect the increased venous pressure of the SOV caused by compression of the contralateral cerebellar hemisphere.

Fetal development of the carotid canal with special reference to a contribution of the sphenoid bone and pharyngotympanic tube

The bony carotid canal is a tube-like bone with a rough surface in contrast to smooth surfaces of the other parts of the temporal bone petrosal portion (petrosa): it takes an impression of the additional, out-sourcing product. No study had been conducted to evaluate a contribution of the adjacent sphenoid and pharyngotympanic tube (PTT) to the carotid canal. We examined sagittal and horizontal histological sections of hemi-heads from 37 human fetuses at 10 to 37 weeks. At 10 to 18 weeks, the future carotid canal was identified as a wide loose space between the cartilaginous cochlea and the ossified or cartilaginous sphenoid elements (ala temporalis and pterygoid). A linear mesenchymal condensation extending between the cochlear wall and ala temporalis suggested the future antero-inferior margin of the carotid canal. This delineation was more clearly identified in later stages. After 25 weeks, 1) the growing pterygoid pushed the PTT upward and, in turn, the PTT pushed the internal carotid artery (ICA) upward toward the petrosa: 2) a membranous ossification occurs in the dense mesenchymal tissue, the latter of which took an appearance of an anterior process of the petrosa; 3) the bony process of the petrosa involved the ICA inside or posteriorly. The bony carotid canal was made with membranous ossification in the dense mesenchymal tissue between the petrosa and sphenoid. The mother tissue was detached from the sphenoid by the PTT. The ossification of the septum between the ICA and tympanic cavity seemed to continue after birth.

Assessment of the Optic Foramen Shape and Size in Human Fetuses

OBJECTIVE

This study was aimed to obtain data on the dimensions of the optic foramen in human fetuses for early childhood surgeries.

METHODS

Twenty-five formalin-fixed fetuses (16 boys and 9 girls) with average age 21.68 ± 3.12 gestational weeks (range, 16-28 weeks) in the inventory of Anatomy Department, Faculty of Medicine were included in the study. The surface area, width, and height of the optic foramen were bilaterally measured using a digital image analysis software.

RESULTS

The forms of the optic foramen were described as oval shaped (72%, 36 foramina) and round shaped (28%, 14 foramina). The surface area, width, and height of the optic foramen were found as 2.40 ± 1.02 mm, 1.83 ± 0.59 mm, and 1.58 ± 0.36 mm, respectively. The measurements of the parameters related to the optic foramen were not statistically different in terms of sides and sexes (P > 0.05). Linear functions for the height, width and surface area of the optic foramen were calculated as: y = 0.711 + 0.040 × weeks, y = -0.019 + 0.086 × weeks, and y = -0.400 + 0.129 × weeks, respectively.

CONCLUSION

The linear functions in this study can be used to estimate the dimensions of the optic foramen. The calculated regression equations, representing the growth dynamic of the optic foramen showed that the surface area, width, and height were increasing according to gestational ages between 16 and 28 weeks. Microanatomical knowledge related to the optic foramen may be beneficial for surgeons to avoid iatrogenic injury in infants and for anatomists to understand the development of the fetal skull base.

Anatomic features of the cranial aperture of the optic canal in children: a radiologic study

OBJECTIVE

This study aimed to peruse anatomic features of the cranial aperture of the optic canal (CAOC) for obtaining an extended morphometric dataset in children.

METHODS

Computed tomography images of 200 children were included in this retrospective work to analyze the shape, location and diameters of the CAOC.

RESULTS

The CAOC area, width and height were observed as 17.53 ± 2.80 mm², 6.12 ± 0.84 mm, and 4.35 ± 0.64 mm, respectively. The angle of the optic canal in axial plane was found as 39.28 ± 5.13°, while in sagittal plane as 16.01 ± 6.76°. The distance between the CAOC and the midsagittal line was 7.17 ± 1.48 mm. The CAOC was measured as 54.04 ± 5.23 mm and 42.55 ± 3.28 mm away from the anterior and lateral boundary of the anterior skull base, respectively. The CAOC shape was described as the tear-drop (186 foramina, 46.5%), triangular (156 foramina, 39%), oval (47 foramina, 11.8%), and round (11 foramina, 2.8%).

CONCLUSION

The depth, angle and diameter measurements belonging to the CAOC were changing according to its shape or demographic data (e.g., sex and age). Therefore, preoperative radiologic evaluation containing the shape, location and size of the CAOC should be considered by multidisciplinary operating teams in terms of surgical interventions such as implant positioning.

An advanced protocol for intraoperative visualization of sinunasal structures: experiences from pituitary surgery

OBJECTIVE

The transsphenoidal route to pituitary adenomas challenges surgeons because of the highly variable sinunasal anatomy. Orientation may be improved if the appropriate information is provided intraoperatively by image guidance. The authors developed an advanced image guidance protocol dedicated to sinunasal surgery that extracts information from multiple modalities and forms it into a single image that includes fine sinunasal structures and arteries.The aim of this study was to compare the advantages of this novel image guidance protocol with the authors' previous series, with emphasis on anatomical structures visualized and complication rate.

METHODS

This retrospective analysis comprised 200 patients who underwent surgery for pituitary adenoma via a transnasal transsphenoidal endoscopic approach. The authors' standard image guidance protocol consisting of CT for solid bone, T1CEMRI for soft tissues, and MRA for the carotid artery was applied in 100 consecutive cases. The advanced image guidance protocol added a first-hit ray casting of the CT scan for visualization of fine sinunasal structures, and adjustments to the MRA to visualize the sphenopalatine artery (SPA) were applied in a subsequent 100 consecutive cases.

RESULTS

A patent sphenoid ostium-i.e., an ostium not covered by a mucosal layer-was visualized significantly more often by the advanced protocol than the standard protocol (89% vs 40%, p < 0.001) in primary surgeries. The SPA and its branches were only visualized by the advanced protocol (87% and 91% of cases in primary surgeries and reoperations, respectively) and not once by the standard protocol. The number of visualized complete and incomplete sphenoid septations matched significantly more commonly with the surgical view when using the advanced protocol than the standard protocol at primary operation (mean 1.9 vs 1.6, p < 0.001). However, in 25% of all cases a complex and not a simple sinus anatomy was present. In comparison with the intraoperative results, a complex sphenoid sinus anatomy was always detected by the advanced but not by the standard protocol (25% vs 8.5%, p = 0.001).Furthermore, application of the advanced protocol reduced the cumulative rate of complications (25% vs 18% [standard vs advanced group]). Although an overall significant difference could not be determined (p = 0.228), a subgroup analysis of reoperations (35/200) revealed a significantly lower rate of complications in the advanced group (5% vs 30%, p = 0.028).

CONCLUSIONS

The data show that the advanced image guidance protocol could intraoperatively visualize the fine sinunasal sinus structures and small arteries with a high degree of detail. By improving intraoperative orientation, this may help to reduce the rate of complications in endoscopic transsphenoidal surgery, especially in reoperations.

Radiologic analysis of the location, shape and size of the external aperture of the carotid canal in children

OBJECTIVES

This retrospective computed tomography (CT) study was aimed to assess the growth dynamic of the external aperture of the carotid canal (EACC) in children aged between 1 and 20 years.

METHODS

Two hundred patients (sex 100 females/100 males, average age 10.50 ± 5.77 years) with good head CT image quality were included in this study. CT images of the patients were used to obtain data related to the location, shape and dimension of EACC.

RESULTS

EACC shapes were identified as oval shaped, round shaped, and tear-drop shaped in 58.3% (233 sides), 24% (96 sides) and 17.8% (71 sides), respectively. EACC length, disEACC-MSP (distance between EACC and midsagittal plane), and EACC width did not change from the prepubescence period; while, the disEACC-SC (distance between EACC and supramastoid crest) seemed to reach adult size in the postpubescence period. Linear functions for EACC length and width were calculated as: y = 5.453 + 0.091 × years, and y = 5.398 + 0.059 × years, respectively.

CONCLUSION

The regression equations of the measured parameters representing the growth dynamic of EACC in children can be helpful to estimate its size, location and angulation, which suggest that the dimension and distances to certain anatomical landmarks seemed to reach adult size in different developmental periods. In this context, the findings of this study may seem to emphasize the importance of preoperative radiological evaluation on skull base, related to EACC, for multidisciplinary surgeon teams during childhood surgeries in terms of patients' positioning, and the selection of appropriate surgical approach.

Cavernous sinus and abducens nerve in human fetuses near term

A long tortuous course of the abducens nerve (ABN) crossing a highly curved siphon of the internal carotid artery is of interest to neurosurgeons for cavernous sinus surgery. Although a "straight" intracavernous carotid artery in fetuses can change into an adult-like siphon in infants, there is no information on when or how the unique course of ABN is established. Histological observations of 18 near-term fetuses (12 specimens of frontal sections and 6 specimens of sagittal sections) demonstrated the following: (I) the ABN consistently took a straight course crossing the lateral side of an almost straight intracavernous carotid artery; (II) the straight course was maintained when sympathetic nerves joined; (III) few parasellar veins of the developing cavernous sinus separated the ABN from the ophthalmic nerve; and (IV) immediately before the developing tendinous annulus for a common origin of extraocular recti, the ABN bent laterally to avoid a passage of the thick oculomotor nerve. Since the present observations strongly suggested morphologies at birth and in infants, major angulations of the ABN as well as the well-known course independent of the other nerves in the cavernous sinus seemed to be established during childhood. In the human body, the ABN might be a limited example showing a drastic postnatal change in course. Consequently, it might be important to know the unique course of ABN before performing endovascular interventions and skull base surgery for petroclival and cavernous sinus lesions without causing inadvertent neurovascular injuries to neonates or infants.

Intracranial Anatomical Triangles: A Comprehensive Illustrated Review

There are multiple anatomical triangles of the skull base. However, to our knowledge, there has been no comprehensive review of these geometric landmarks. To allow for a safe and consistent approach to lesions of the skull base such as those near the internal carotid artery, internal acoustic meatus, and cavernous sinus, a comprehensive review of the variations with illustrations is required. This article provides an overview of the anatomical borders, dimensions, and surgical implications as well as illustrations of the major skull base triangles.

Analysis of the tortuosity of the internal carotid artery in the cavernous sinus

BACKGROUND

The morphology of the internal carotid artery at the skull base is important in radiologic interpretation, surgery, and more recently, endovascular interventional and diagnostic procedures. Therefore, a thorough knowledge of the shape of the carotid siphon can be important in the clinical realm.

METHODS

In this study, we evaluated the shape of the carotid siphon from a lateral perspective on cerebral angiography. These shapes were then correlated to the Lang and Reiter classification.

RESULTS

Types A, B, and C were distributed as follows: type A 12 (30%), B 16 (40%), 12 (30%). There was no significant difference (p > 0.05) in patient ages between the three types (type A 54.6 ± 14.2 years, type B 55.1 ± 14.9 years, and type C 52.7 ± 16.9 years). Normalized for gender disproportion, there was no significant gender predominance for any type (type A female:male = 1.4:1; type B female:male = 1.1:1; type C female:male = 0.7:1).

CONCLUSIONS

Such a classification scheme with additional application in another group might be of use to future studies aimed at the morphology of the cavernous part of the internal carotid artery.

Episcopic three-dimensional imaging of embryos

Episcopic fluorescence image capturing (EFIC) and high-resolution episcopic microscopy (HREM) are related techniques that are used to generate digital volume data and create three-dimensional (3D) images. Both techniques require specimens that are embedded in an appropriate medium, and images are captured from successive sections before removal from the embedded tissue block. EFIC detects autofluorescence emitted from the embedded tissue, whereas HREM requires the tissue to be stained with a fluorescent dye such as eosin. Different procedures are therefore necessary for embedding tissue for EFIC or HREM imaging. This article describes episcopic imaging and gives the advantages and disadvantages of the EFIC and HREM techniques. It also describes the imaging setup required to collect volume data and generate 3D images.

Dural and arachnoid membraneous protection of the abducens nerve at the petroclival region

The goal of this study was to determine the membranous protection of the abducens nerve in the petroclival region. The petroclival portion of the abducens nerve was studied in ten dissections from five cadaveric head specimens. One of the heads was used for histological sections. Four heads were injected with colored latex for microsurgical dissections. The histological sections were prepared from petroclival dura mater, embedded in paraffin blocks, stained, sectioned in the axial, coronal, and sagittal planes, and evaluated by light microscopy. The abducens nerve was covered by a dural sleeve and arachnoidal membrane during its course within the petroclival area. Following the petrous apex, the abducens nerve was fixed by a sympathetic plexus and connective tissue extensions to the lateral wall of the cavernous segment of the internal carotid artery and to the medial wall of Meckel's cave. Fibrous trabeculations inside the venous space were attached to the dural sleeve. The lateral clival artery accompanied the dural sleeve of the abducens nerve and supplied the petroclival dura mater. The arterioles accompanying the abducens nerve through the subarachnoid space supplied the nerve within the dural sleeve. The arachnoid membrane covered the abducens nerve within the dural sleeve to the petrous apex, and arachnoid granulations found on the dural sleeve protruded into the venous space. The extension of the arachnoid membrane to the petrous apex and the presence of arachnoid granulations on the dural sleeve suggest that the subarachnoid space continues in the dural sleeve.

A case of aberrant abducens nerve in a cadaver and review of its clinical significance

The abducens nerve usually travels from the brainstem to the lateral rectus muscle as a single trunk. However, it has been reported that this nerve could split into branches occasionally. We attempted to show the aberrant course of abducens nerve in a specimen with unilateral duplicated abducens nerve and review relevant literatures. The micro-dissections were performed in a head specimen injected with colored latex under the microscope. The abducens nerve was duplicated unilaterally. This nerve emerged from the pontomedullary sulcus as a single trunk and splitted into two branches in the prepontine cistern. These two separate branches were piercing the cerebral dura of the petroclival region respectively. The slender lower branch passed between the petroclinoid and petrosphenoid ligaments and the thick lower one passed under the petrosphenoid ligament. These two branches united just lateral to the ascending segment of internal carotid artery in the cavernous sinus. The fact that there are several types of aberrant abducens nerve is helpful to perform numerous neurosurgical procedures in the petroclival region and cavernous sinus without inadvertent neurovascular injuries.

Three-dimensional description and mathematical characterization of the parasellar internal carotid artery in human infants

Inside the 'cavernous sinus' or 'parasellar region' the human internal carotid artery takes the shape of a siphon that is twisted and torqued in three dimensions and surrounded by a network of veins. The parasellar section of the internal carotid artery is of broad biological and medical interest, as its peculiar shape is associated with temperature regulation in the brain and correlated with the occurrence of vascular pathologies. The present study aims to provide anatomical descriptions and objective mathematical characterizations of the shape of the parasellar section of the internal carotid artery in human infants and its modifications during ontogeny. Three-dimensional (3D) computer models of the parasellar section of the internal carotid artery of infants were generated with a state-of-the-art 3D reconstruction method and analysed using both traditional morphometric methods and novel mathematical algorithms. We show that four constant, demarcated bends can be described along the infant parasellar section of the internal carotid artery, and we provide measurements of their angles. We further provide calculations of the curvature and torsion energy, and the total complexity of the 3D skeleton of the parasellar section of the internal carotid artery, and compare the complexity of this in infants and adults. Finally, we examine the relationship between shape parameters of the parasellar section of the internal carotid artery in infants, and the occurrence of intima cushions, and evaluate the reliability of subjective angle measurements for characterizing the complexity of the parasellar section of the internal carotid artery in infants. The results can serve as objective reference data for comparative studies and for medical imaging diagnostics. They also form the basis for a new hypothesis that explains the mechanisms responsible for the ontogenetic transformation in the shape of the parasellar section of the internal carotid artery.

Comparison of lateral and superior walls of the pituitary fossa with clinical emphasis on pituitary adenoma extension: cadaveric-anatomic study

Pituitary adenomas extend to the suprasellar region via diaphragmal passage and extend to the cavernous sinus via the medial wall (MW). Better understanding of the dynamics of suprasellar and parasellar extension of sellar region pathologies requires microanatomical comparison of diaphragma sellae (DS) and the MW of the cavernous sinus. This study provides the first detailed quantitative assessment between DS and MW of the cavernous sinus. Microanatomical details and histopathological examinations of the DS and MWs of the cavernous sinus were studied in sphenoid block samples obtained from adult cadavers, and the thicknesses of the DS and the MW of the cavernous sinus were measured. Mean thickness of the DS was 216.73 +/- 51.26 microm in the center and 367.33+/-133.66 microm in the periphery. Mean thickness of the lower third of the MW was 161.53+/-53.86 microm and that of the upper third was 278.46+/-162.79 microm. Difference between the thicknesses of the upper and lower thirds was significant (P<0.001). When the central thickness of the DS and lower third of the MW were compared, a significant difference was found (P<0.01). Our measurements suggest that when the DS is thick and the stalk opening is complete, the thickness of the lower third of the medial wall could be the major determinant of parasellar extension.

Microanatomical architecture of Dorello's canal and its clinical implications

OBJECTIVE

We investigated the membranous architecture of the abducens nerve at the petroclival region and describe the characteristics of this area in cadaveric specimen and two children with hydrocephalus and sixth nerve palsy using magnetic resonance imaging (MRI).

MATERIALS AND METHODS

Five adult cadaver heads were used to investigate the petroclival part of the abducens nerve. The heads were injected with colored latex for microsurgical dissection, and the length of the dural sleeve of the abducens nerve and its width at the apex were measured. In one cadaver head, the area between the petroclival entrance porus of the abducens nerve and the cavernous sinus was histologically studied under light microscopy. In two patients with hydrocephalus and abducens nerve palsy, the petroclival area was screened by using the MRI fat suppression technique.

RESULTS

In the cadavers, the arachnoid membrane on the clivus extended within the dural sleeve as far as the petrous apex, as an extension of the subarachnoid space. The average length of the dural sleeve was 9.5 mm and the average width was 1.5 mm at the apex, where the nerve entered the cavernous sinus. MRI scans showed that the cerebrospinal fluid distance of the petroclival region was 5 mm in the first patient and 7 mm in the second.

CONCLUSION

The subarachnoid space inside the dural sleeve of the abducens nerve can be defined by using thin-slice MRI scans. Enlargement of the dural sleeve at the petroclival region may coexist with the abducens nerve palsy. It has been documented in this study that the arachnoid membrane forms a membraneous barrier between the subarachnoid and subdural spaces within Dorello's canal.

The mechanism of injury of the abducens nerve in severe head trauma: a postmortem study

The aim of this study is to investigate the mechanism of injury of abducens nerve at petroclival region in severe head trauma. Twenty specimens provided from 10 autopsied cases due to severe head trauma were investigated macroscopically and histopathogically. The slices of the abducens nerve taken consecutively along its course at petroclival region were stained with Hematoxylline-Eosin and evaluated under light microscope. In addition, coexisting cervical injuries in these cases were assessed macroscopically. Edema and perineural hemorrhagia of abducens nerve were identified in all cases. Nerve injury was found more exaggerated at the sites of dural entry point and petrous apex than any other parts of the abducens nerve. Furthermore, microscopically, also remarkable perineural hemorrhage of the abducens nerve was observed at the site of its anastomoses with the sympathetic plexus on the lateral wall of the internal carotid artery (ICA). Abducens nerve is injured at the sites of dural entry point, petrous apex and lateral wall of the ICA, directly proportional with the severity of the trauma. This finding is also significant in verification of the severe head trauma.

In vivo 3D analysis of the adipose tissue in the orbital apex and the compartments of the parasellar region

As tissue dissections carried out on formaldehyde-fixed anatomical specimens demonstrate, the parasellar region (PSR), traditionally referred to as the cavernous sinus, is composed of three distinct compartments: orbital, pterygopalatine, and lateral sellar. The aim of our study was to identify and measure these compartments in the living and to describe the topography of their adipose body tissues. For this purpose data sets of 35 patients, who had undergone thin-section multislice computed tomography (CT), were examined using 3D-reconstruction software. The pterygopalatine and orbital compartments of the PSR could be identified in the images by their adipose bodies. We provide more exacting measurements of their size than have been presented in earlier studies. Furthermore, we include data about the uni- and bilateral presence of the single compartments and analyze the topography of the adipose tissue bodies in the orbital apex region. Our quantitative data and topographical descriptions confirm the compartmentalization concept of the PSR, allow for correct interpretation of CT scans of the orbital apex and anterior PSR, and provide baseline information for individual planning of surgical and radiological interventions.

Duplication of the abducens nerve at the petroclival region: an anatomic study

OBJECTIVE

During its course between the brainstem and the lateral rectus muscle, the abducens nerve usually travels forward as a single trunk, but it is not uncommon for the nerve to split into two branches. The objective of this study was to establish the incidence and the clinical importance of the duplication of the nerve.

METHODS

The study was performed on 100 sides of 50 autopsy materials. In 10 of 11 cases of duplicated abducens nerve, colored latex was injected into the common carotid arteries and the internal jugular veins. The remaining case was used for histological examination.

RESULTS

Four of 50 cases had duplicated abducens nerve bilaterally. In seven cases, the duplicated abducens nerve was unilateral. In 9 of these 15 specimens, the abducens nerve emerged from the brainstem as a single trunk, entered the subarachnoid space, split into two branches, merged again in the cavernous sinus, and innervated the lateral rectus muscle as a single trunk. In six specimens, conversely, the abducens nerve exited the pontomedullary sulcus as two separate radices but joined in the cavernous sinus to innervate the lateral rectus muscle. In 13 specimens, both branches of the nerve passed beneath the petrosphenoidal ligament. In two specimens, one of the branches passed under the ligament and the other passed over it. In one of these last two specimens, one branch passed over the petrosphenoidal ligament and the other through a bony canal formed by the petrous apex and the superolateral border of the clivus. In all of the specimens, both branches were wrapped by two layers: an inner layer made up of the arachnoid membrane and an outer layer composed of the dura during its course between their dural openings and the lateral wall of the cavernous segment of the internal carotid artery. This finding was also confirmed by histological examination in one specimen.

CONCLUSION

Double abducens nerve is not a rare variation. Keeping such variations in mind could spare us from injuring the VIth cranial nerve during cranial base operations and transvenous endovascular interventions.

Meningovenous structures of the petroclival region: clinical importance for surgery and intravascular surgery

OBJECTIVE

The goals of this investigation were to perform a detailed analysis of petroclival microanatomic features, to investigate the course of the abducens nerve in the petroclival region, and to identify potential causes of injury to neurovascular structures when anterior transpetrosal or transvenous endovascular approaches are used to treat pathological lesions in the petroclival region.

METHODS

Petroclival microanatomic features were studied bilaterally in seven cadaveric head specimens, which were injected with colored silicone before microdissection. Another cadaveric head was used for histological section analyses.

RESULTS

A lateral or medial location of the abducens nerve dural entrance porus, relative to the midline, was correlated with the course and angulation of the abducens nerve in the petroclival region. The angulation of the abducens nerve was greater and the nerve was closer to the petrous ridge in the lateral type, compared with the medial type. The abducens nerve exhibited three changes in direction, which represented the angulations in the petroclival region, at the dural entrance porus, the petrous apex, and the lateral wall of the internal carotid artery. The abducens nerve was covered by the dural sleeve and the arachnoid membrane, which became attenuated between the second and third angulation points. The abducens nerve was anastomosed with the sympathetic plexus and fixed by connective tissue extensions to the lateral wall of the internal carotid artery and the medial wall of Meckel's cave at the third angulation point. There were two types of trabeculations inside the sinuses around the petroclival region (tough and delicate).

CONCLUSION

The petroclival part of the abducens nerve was protected in a dural sleeve accompanied by the arachnoid membrane. Therefore, the risk of abducens nerve injury during petrous apex resection via the anterior transpetrosal approach, with the use of the transvenous route through the inferior petrosal sinus to the cavernous sinus, should be lower than expected. The presence of two anatomic variations in the course of the abducens nerve, in addition to findings regarding nerve angulation and tethering points, may explain the relationships between adjacent structures and the susceptibility to nerve injury with either surgical or endovascular approaches. Venous anatomic variations may account for previously reported cases of subarachnoid hemorrhage with the endovascular approach.

Compartments of the adult parasellar region

In the infant the region lateral to the sella turcica which is traditionally termed the 'cavernous sinus' is composed of 3 individual compartments. The aim of this study was to demonstrate a similar compartmentation of the adult cavernous sinus and to identify and quantify the adipose bodies which are located within the compartments. The region of the cavernous sinus in 136 adults was analysed by microdissection and histology. We demonstrate that in 66% of the cavernous sinus in adults is composed of at least 2 compartments and in 22% it is made up of 3. Assimilating the renaming in infants we termed the compartments 'pterygopalatine', 'orbital' and 'lateral sellar'. The pterygopalatine and orbital compartments are connected with extracranial tissue spaces via the superior orbital fissure and contain characteristic adipose bodies. Exact topographic descriptions and measurements of the compartments and their adipose bodies are provided. Our study clearly defines compartmentation of the adult parasellar space in most individuals and thus changes the anatomical view of this space. The direct connection of 2 of these compartments with extracranial tissue spaces and the measurements of their adipose bodies are of interest for surgeons and neuroradiologists.

Extradural neural axis compartment

The lengthy, continuous, slender extradural neural axis compartment (EDNAC), which extends from the coccyx to the orbit, has been not so much discovered as recognized. Through this compartment run arteries, myelinated and unmyelinated nerves, and valveless veins. Adipose tissue is abundant in the orbital and spinal segments, possibly due to movement requirements, although it is very sparse in the skull base segment, the last segment to be recognized as a continuation of the EDNAC, which connects Breschet's veins to the orbit. The lateral sellar compartment (in older terminology, the cavernous sinus) is an enlarged segment of this EDNAC along the skull base connecting the orbit with the extradural space through the superior orbital fissure and down the dorsum to Breschet's veins of the basilar process of the occipital bone. Understanding the continuity of the EDNAC should help the student understand any segment, particularly the skull base. As Batson noted, "Living anatomy is slowly editing and replacing the anatomy of the dead room."

Development of the cavernous sinus in the fetal period: a morphological study

The development and morphological structure of the lateral sellar compartment (LSC), an interdural space containing the cavernous sinus (CS), cranial nerves, and internal carotid artery (ICA), was investigated by histological examination of sections of the LSC and cerebral venograms from human fetal specimens. Twenty-eight LSC coronal sections were obtained from 14 fetuses of 13-32 weeks' gestation. Venograms of 11 other fetuses of 13-32 weeks' gestation were studied to observe changes in venous drainage. The CS appeared as a collection of small venous canals with an endothelial layer. These venous canals gradually became much larger through expansion and unification. The CS and basilar venous plexus were demonstrated as a faint cluster of small vessels on venograms obtained after 13 weeks' gestation. The dura mater increased in thickness and collagen fiber networks developed around all the components in the LSC after 23 weeks' gestation. The LSC lateral wall could not be histologically differentiated as separate multiple layers. Branching and joining of the cranial nerve fascicles were completed with the envelopment of collagen fibers after 23 weeks' gestation. The ICA at 13-15 weeks' gestation ran straight within the LSC, becoming tortuous before birth. CS formation occurs through the development of venous canals without smooth muscle layers, followed by web-formation by collagen fibers in the mesenchymal interstices. LSC formation, including the dense dura mater and an internal structure like that seen in the adult, is largely completed before birth.

Intimal hyperplasia of the infant parasellar carotid artery: a potential developmental factor in atherosclerosis and SIDS

Intimal cushions that project into the lumen of arteries are precursors of atherosclerotic plaque formation. The "carotid siphon, " although frequently affected by atherosclerosis, was never analyzed for the occurrence of neonatal intimal hyperplasia. This study provides a topographic and morphometric analysis of intimal cushions in the parasellar internal carotid artery (pICA) of the human infant. A total of 35 specimens were studied in detail, using both standard histological techniques and a new method of computer-aided 3D reconstruction. Intimal hyperplasia occurred at 3 characteristic locations of the pICA: (1) the convex side of the posterior knee (C5 cushion), (2) the bottom of the horizontal segment (C4 cushion), and (3) the concave side of the anterior knee (C3 cushion). The extension of the cushions and the degrees to which they occluded the vessel lumens were measured. The complex shape of the pICA required 3D computer models for exact topographical descriptions and precise measurements. Our results suggest that the occurrence and degree of intimal hyperplasia are related to shape changes of the pICA during postnatal development. We predict that individuals who retain the relatively straight course of the fetal pICA throughout their lives are less prone to develop atherosclerotic lesions at this portion of the carotid artery. A possible contribution of neonatal intimal cushions to the origin of sudden infant death syndrome is discussed.