Reappraisal of the types of trigeminal porus and importance in surgical applications.

OBJECTIVE: The detailed information regarding the types of trigeminal porus (TP) and related surgical approach is lacking in the literature. Therefore, we performed this study to elucidate further the types of TP and the relationships with critical surgical landmarks in the skull base. METHODS: The study was performed on 19 formalin-fixed cadavers of the cranial base (52.6% male, n = 10; 47.4% female, n = 9) on both sides. Calculations were made of the vertical dimension (VD), horizontal dimension (HD), and types of TP, the thickness of the TP, the HD and VD of the internal acoustic meatus, the distance between the TP-IAM, the thickness of the ossifying tissue that forms the TP, the trigeminal nerve (CN V) in both types and the distance between the CN V-VI. RESULTS: The elliptical (42.1% left, 36.8% right), oval (52.6% left, 36.8% right) and slit-like (5.3% right) types of TP were detected (X2 = 11.722). The HD of the TP was, on average, 8.02 mm (female) and 9.2 mm (male) on the right side, and 8.26 mm (female) and 8.81 mm (male) on the left side. The VD of the TP was, on average, 1.99 mm (female) and 2.65 mm (male) on the right side, and 2.42 mm (female) and 2.94 mm (male) on the left side. CONCLUSIONS: In our study, ellipse and slit-like types of TP are taken into account in order to plan the surgical approaches to remove or prevent the extension of tumors. A combined surgical technique is recommended to reach the TP easily without damaging the nearby surgical structures during surgery. The oval type of TP allows a wide range of movements, so it is more advantageous in skull base surgery.

Innervation of rat and human dura mater and pericranial tissues in the parieto-temporal region by meningeal afferents.

OBJECTIVE: To reinvestigate the innervation pattern of the dura mater of rat and human middle cranial fossa, the morpho-functional substrate of headache generation, and adjacent extracranial tissues with neuronal in vitro tracing. BACKGROUND: This study was initiated by recent structural and functional findings of meningeal afferent fibers which innervate the cranial dura mater and may project to extracranial tissues. METHODS: Anterograde and retrograde neuronal in vitro tracing was made in formaldehyde fixed hemisected rat and human skulls. The fluorescent tracer DiI was applied to proximally cut meningeal nerves in rat and to distal branches of the spinosus nerve in human calvaria lined by dura mater. After several weeks, the dura mater and deep extracranial tissues were examined with fluorescence microscopy. RESULTS: In addition to a network of meningeal nerve fibers, several fiber bundles were observed, leaving the skull through emissary canals and fissures to innervate the pericranial temporal, parietal, and occipital periosteum. Traced fibers were seen spreading into deep layers of the temporal and upper neck muscles. Retrograde neuronal tracing revealed labeled cell bodies exclusively in the mandibular and maxillary division of the rat trigeminal ganglion, and centrally projecting fibers were identified in the spinal trigeminal tract. Electron microscopy of the cross-sected spinosus nerve showed myelinated and unmyelinated axons with similar numbers in human and rat. CONCLUSIONS: We conclude that a proportion of meningeal afferents innervates extracranial tissues like periosteum and pericranial muscles via collaterals projecting through the skull. These afferents may be nociceptive, some may subserve proprioceptive functions. The finding of extracranial projections of meningeal afferents may be important for our understanding of extracranial impacts on headache generation and therapy.

Branching of the foramen rotundum. A rare variation of the sphenoid.

The human orbit communicates with the middle cranial fossa through several canals and openings. Some of them (optic canal, superior orbital fissure) are constant, others (meningo-orbital foramen, Warwick's foramen, metoptic canal) are less frequent. Here we report a rare variation of the foramen rotundum which, opening into the orbit with a branching canal, represented a further connecting pathway between the orbit and the middle cranial fossa. Such variation was detected in about 1.06% of individuals and it was almost always located on the right side. Only in one cases it could be found left-sided and in another skull it was spotted bilaterally. The vari- ation consisted of the branching of a 5 mm long canal from the lateral wall of the foramen rotun- dum that opened into the orbit. In general the diameter of the canal was comprised between 0.5 and 0.6 mm but it could be as large as 1 mm or as thin as 0.2 mm. The canal, straight and directed slightly superolaterally, likely transmitted the zygomatic nerve and/or part of the infraorbital nerve. To our knowledge, an independent entrance through a dedicated canal of such nerves has never been reported. The surgeons operating in this region, either neurosurgeons or ophthalmologists, should be aware of the possible variation in the course of these nerves.

Trigeminal cave and ganglion: an anatomical review / Cavo y ganglio trigeminal: una revisión anatómica

The trigeminal cave (TC) is a special channel of dura mater, which extends from the posterior cranial fossa into the posteromedial portion of the middle cranial fossa at the skull base. The TC contains the motor and sensory roots of the trigeminal nerve, the trigeminal ganglion (TG) as well as the trigeminal cistern. This study aimed to review the anatomy of the TC and TG and determine some parameters of the TC. The study comprised two subsets: A) Cadaveric dissection on 30 sagitally sectioned formalin fixed heads and B) Volume injection. We found the dura associated with TC arranged in three distinct layers. TC had relations with internal carotid artery, the cavernous sinus, the superior petrosal sinus, the apex of petrous temporal bone and the endosteal dura of middle cranial fossa. The mean volume of TC was 0.14 ml. The mean length and breadth of TG were 18.3 mm and 7.9 mm, respectively, mean width and height of trigeminal porus were 7.9 mm and 4.1 mm, respectively, and mean length of terminal branches from TG to point of exit within skull was variable. An understanding of the precise formation of the TC, TG, TN and their relations is important in order to perform successful surgical procedures and localized neural block in the region of the TC.

El cavo trigeminal (CT) de la duramadre es un conducto especial que se extiende desde la fosa craneal posterior a la parte posteromedial de la fosa craneal media en la base del cráneo. El CT contiene las raíces motoras y sensoriales del nervio trigémino (NT), ganglio trigeminal (GT), así como la cisterna trigeminal. Este estudio tuvo como objetivo examinar la anatomía del CT y GT y para determinar algunos parámetros del CT. El estudio se realizó en dos etapas: A) la disección anatómica de 30 cabezas seccionadas sagitalmente y B) la inyección para estimar volumen. Fueron encontrados tres capas distintas de duramadre asociadas al CT. El CT se relacionó con la arteria carótida interna, el seno cavernoso, el seno petroso superior, el vértice de la porción petrosa del hueso temporal y la dura endosteal de la fosa craneal media. El volumen medio del CT fue de 0,14 ml. La longitud media y la amplitud del GT fueron 18,3 mm y 7,9 mm, respectivamente. La media del ancho y alto del poro trigeminal fueron 7,9 mm y 4,1 mm, respectivamente; la longitud media de las ramas terminales del GT al salir del cráneo fue variable. El conocimiento preciso de la formación del CT, GT, NT y sus relaciones es necesario para realizar procedimientos quirúrgicos exitosos o el bloqueo nervioso localizado en la región del CT.

Assessment of cognitive function before and after surgery for posterior cranial fossa lesions using computerized and conventional tests.

Cognitive function has not been well studied after neurosurgery for posterior fossa lesions despite its potential importance in determining surgical indications and approaches. The present study evaluated changes in cognitive functions after posterior fossa surgery to detect any differences between the middle cranial fossa and lateral suboccipital approaches in 50 patients with posterior fossa lesions such as tumors and vascular diseases. Twenty-five patients underwent surgery via the middle fossa and 25 via the lateral suboccipital approaches. Computerized test battery (CogState) and conventional neuropsychological tests (serial seven-word learning test and mini-mental state examination) were examined before, 1 month after, and 3 months after surgery. All scores of the neuropsychological tests remained within normal limits after surgery. However, the scores of one computerized test battery and serial seven-word learning tests decreased significantly 1 month after surgery and recovered within 3 months, indicating temporary deterioration of short-term memory in the middle fossa group. The computerized tests detected significantly larger numbers of patients with worsened results than the conventional tests. The middle fossa approach and operation time showed correlations with the postoperative neuropsychological declines. The computerized tests could be performed easily and were beneficial for detecting subtle changes of the cognitive function after surgery. Cognitive function, especially short-term memory, may decline temporarily with the middle fossa approach and long operation time.

Microsurgical anatomy of the superior orbital fissure.

The microanatomy of the superior orbital fissure (SOF) was studied in 96 sides of cadaver specimens. The SOF is a narrow bony cleft that lies at the apex of the orbit between the greater and lesser wings of the sphenoid. Through this fissure, many important structures enter the orbit from the middle cranial fossa including the third, fourth, sixth cranial nerves, and the ophthalmic branch of the fifth nerve. In addition, the superior opthalmamic vein exits the orbit to drain into the cavernous sinus via the SOF. The fissure can be divided into three anatomical regions by the annulus of Zinn (common annular tendon): the lateral, central, and inferior regions. The lateral wall of the SOF can also be divided between the upper and lower segments, and the angle between them was measured to be 144.27 degrees +/- 20.03 degrees . Defining these regions is useful in describing the course and placement of the nerves and vasculature in the SOF. Managing lesions at the orbital apex requires an extensive knowledge of the cranial base and the intracranial and extracranial relationships of the anatomical structures coursing through the SOF. The goal of this study was to describe the microanatomy of the SOF region in detail and to provide a reference for surgical procedures involving the orbital apex.

The extradural subtemporal keyhole approach to the sphenocavernous region: anatomic considerations.

Fourteen cadaver specimens (28 sides) and twelve dry human skulls (24 sides) were used to study the anatomic relationships between bony, neurovascular and foraminal landmarks in the floor of the middle fossa in preparation for performing the extradural subtemporal keyhole approach to the sphenocavernous region. The interforaminal distance was largest between the foramina rotundum (FR) and ovale (FO) and was smallest between the FO and foramen spinosum (FS). The largest angle between exit foramen was the FR to FO. The greater superficial petrosal nerve (GSPN) was always found to overlie and run parallel to the petrous internal carotid artery, however, its location over the artery and its separation from it by bone was variable. With a subtemporal "keyhole" placed above the posterior zygomatic root (PZR), a 0 degrees endoscope allowed easy visualization of the middle meningeal artery (MMA) and the mandibular nerve (V 3 ) however, a 30 degrees endoscope was more useful for visualizing the maxillary nerve (V 2 ) and the ophthalmic nerve (V 2 ). With a sphenoidotomy performed between V 1 and V 2, the 30 degrees endoscope was found to be the most useful for visualizing the carotid siphon and the contralateral wall of the sphenoid sinus, while the 70 degrees endoscope was the most useful for visualizing of the floor of the sella and the walls of the sphenoid sinus. Two venous concerns with respect to performing endoscopic approaches to the region were identified: a fibrous layer overlies a heavy venous plexus that encircles the petrous carotid artery, and the foramen Vesalius, which transmits a large emissary vein draining the cavernous sinus, was identified medial to the FO in 30 % of our dissected sides.