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Object: There continues to be confusion over how best to preserve the branches of the facial nerve to the frontalis muscle when elevating a frontotemporal (pterional) scalp flap. The object of this study was to examine the full course of the branches of the facial nerve that must be preserved to maintain innervation of the frontalis muscle during elevation of a frontotemporal scalp flap., Methods: Dissection was performed to follow the temporal branches of facial nerves along their course in 5 adult, cadaveric heads (n = 10 extracranial facial nerves)., Results: Preserving the nerves to the frontalis muscle requires an understanding of the course of the nerves in 3 areas. The first area is on the outer surface of the temporalis muscle lateral to the superior temporal line (STL) where the interfascial or subfascial approaches are applied, the second is in the area medial to the STL where subpericranial dissection is needed, and the third is along the STL. Preserving the nerves crossing the STL requires an understanding of the complex fascial relationships at this line. It is important to preserve the nerves crossing the lateral and medial parts of the exposure, and the continuity of the nerves as they pass across the STL. Prior descriptions have focused largely on the area superficial to the temporalis muscle lateral to the STL., Conclusions: Using the interfascial-subpericranial flap and the subfascial-subpericranial flap avoids opening the layer of loose areolar tissue between the temporal fascia and galea in the area lateral to the STL and between the galea and frontal pericranium in the area medial to the STL. It also preserves the continuity of the nerve crossing the STL. This technique allows for the preservation of the nerves to the frontalis muscle along their entire trajectory, from the uppermost part of the parotid gland to the frontalis muscle.

Objective: The vidian canal, the conduit through the sphenoid bone for the vidian nerve and artery, has become an important landmark in surgical approaches to the cranial base. The objective of this study was to examine the anatomic features of the vidian canal, nerve, and artery, as well as the clinical implications of our findings., Methods: Ten adult cadaveric specimens and 10 dried skulls provided 40 vidian canals for examination with x 3 to x 20 magnification and the endoscope., Results: The paired vidian canals are located in the skull base along the line of fusion of the pterygoid process and body of the sphenoid bone. The canal opens anteriorly into the medial part of the pterygopalatine fossa and posteriorly at the upper part of the anterolateral edge of the foramen lacerum. The vidian nerve, when followed posteriorly, reaches the lateral surface of the anterior genu of the petrous carotid and the anteromedial part of the cavernous sinus where the nerve is continuous with the greater petrosal nerve. The bone surrounding the upper part of 12 of 20 vidian canals protruded into the floor of the sphenoid sinus and one canal had a bony dehiscence that exposed its contents under the sinus mucosa. Nine petrous carotid arteries (45%) gave rise to a vidian artery, all of which anastomosed with the vidian branch of the maxillary artery in the vidian canal or pterygopalatine fossa. The vidian canal can be exposed by opening the floor of the sphenoid sinus, the posterior wall of the maxillary, the posterior part of the lateral wall of the nasal cavity, and the medial part of the floor of the middle fossa., Conclusion: The vidian canal and nerve are important landmarks in accessing the anterior genu of the petrous carotid, anteromedial part of the cavernous sinus, and petrous apex.

Objective: To define the arterial supply to the facial nerve that crosses the floor of the middle cranial fossa., Methods: Twenty-five middle fossae from adult cadaveric-injected specimens were examined under 3 to 40x magnification., Results: The petrosal branch of the middle meningeal artery is the sole source of supply that crossed the floor of the middle fossa to irrigate the facial nerve. The petrosal artery usually arises from the first 10-mm segment of the middle meningeal artery after it passes through the foramen spinosum, but it can arise within or just below the foramen spinosum. The petrosal artery is commonly partially or completely hidden in the bone below the middle fossa floor. It most commonly reaches the facial nerve by passing through the bone enclosing the geniculate ganglion and tympanic segment of the nerve and less commonly by passing through the hiatus of the greater petrosal nerve. The petrosal artery frequently gives rise to a branch to the trigeminal nerve. The middle meningeal artery was absent in one of the 25 middle fossae, and a petrosal artery could not be identified in four middle fossae. The petrosal arteries were divided into three types based on their pattern of supply to the facial nerve., Conclusion: The petrosal artery is at risk of being damaged during procedures in which the dura is elevated from the floor of the middle fossa, the middle fossa floor is drilled, or the middle meningeal artery is embolized or sacrificed. Several recommendations are offered to avoid damaging the facial nerve supply while performing such interventions.

Objective: The course of the lesser petrosal nerve is not well understood and may be confused with the course of the greater petrosal nerve during middle fossa surgery. The objective was to examine the course of the lesser petrosal nerve along the floor of the middle cranial fossa from the region of the geniculate ganglion to its outlet from the skull base. There are no studies focused on the course of this nerve in relationship to the floor of the middle cranial fossa., Methods: Twenty middle fossae from adult cadaveric specimens were examined using 3 to 40x magnification., Results: The lesser petrosal nerve was partially exposed on the floor of the middle fossa without drilling in 75% of the middle fossae and totally covered by thin bone in 25%. It crossed the floor anterior to the greater petrosal nerve and exited the middle fossa through the canaliculus innominatus in 14 cases, foramen spinosum in 3 cases, and the sphenopetrosal suture in 3 cases. The course of the lesser petrosal nerve has been shown in textbooks to be parallel to the greater petrosal nerve. However, the lesser and greater petrosal nerves diverged in the area medial to the geniculate ganglion in 90% of middle fossae with the angle of divergence averaging 11.6 degrees. The course of the lesser petrosal nerve was divided into three patterns based on the site of confluence of the three bundles of fibers forming the nerve., Conclusion: The relationships of the lesser petrosal nerve in the middle cranial fossa have been described. An understanding of these relationships will reduce the likelihood of it being confused with the greater petrosal nerve during surgical approaches to the middle fossa.

The microsurgical anatomy of the cerebellopontine cistern around the porus acusticus was studied under the surgical microscope, using the heads of 20 cadavers. The relationships among the porus acusticus, facial and acoustic nerves, and neighboring arteries were noted carefully. The arteries were the meatal loop of the cerebellar artery, the internal auditory artery (I.A.A.), the subarcuate artery (S.A.), and the perforating artery (P. A.). The cerebellar arteries made the meatal loop and the arterial-nerve complex while they passed in front of the porus acusticus. Most of the cerebellar arteries were the main or rostral trunk of the AICA. The I.A.A. supplying the facial and acoustic nerves usually originated from the meatal segment of the cerebellar artery and ran into the anterior part of the porus acusticus to enter the internal auditory canal. The S. A. penetrating the subarcuate fossa made a common trunk with I. A. A. or branched from the cerebellosubarcuate artery. One recurrent P. A., a special type of the P. A., was usually present on each side. Since the artery ran between the nerve bundles of the facial and acoustic nerves, it could not be seen through the lateral suboccipital approach.

The relationship of the anterior inferior cerebellar artery (AICA) to the facial (7th) and vestibulocochlear (8th) nerves was studied using 3x to 20x magnification in 50 cerebellopontine angles (CPAs) from 25 adult cadavers. The AICA originated from the basilar artery as a single (72% of the CPAs), duplicate (26%), or triplicate (2%) artery. Each of the 50 CPAs had one or more arterial trunks that coursed in close proximity to the 7th and 8th cranial nerves and thus were said to be nerve-related. The nerve-related arterial trunks were divided into three segments based on their relationship to the nerves and meatus: the premeatal, meatal, and postmeatal segments. The meatal segment projected to the meatus or into the canal in 64% of the CPAs. In relation to the nerves, the premeatal segment was most commonly anteroinferior, the meatal segment was inferior, and the postmeatal segment was posteroinferior. The nerve-related branches of the AICA gave rise to internal auditory arteries in 100% of the 50 CPAs, recurrent perforating arteries in 82%, and the subarcuate artery in 72%. The internal auditory and recurrent perforating arteries arose most commonly from the premeatal segment, and the subarcuate artery arose most commonly from the postmeatal segment. There were one to four internal auditory arteries per CPA, zero to three recurrent perforating arteries, and zero or one subarcuate artery. The effects of occlusion of the nerve-related arteries and their involvement in conditions treated by neurosurgeons are reviewed.

There is a consistent set of relationships on the brainstem surface facing an acoustic neuroma that provides the basis for identifying the displaced facial nerve on the medial side of the tumor. This review of the microsurgical anatomy of the brainstem surface facing an acoustic neuroma is based on the examination of the side of the brainstem during 42 operations for the removal of acoustic neuroma, and on the study of 50 cadaveric brains in the microsurgery laboratory. In the operative series, which included many large tumors, the facial nerve was preserved at operation in over 90% of the 42 patients. There was no mortality, and no need for cerebellar resection to remove the tumor in any patient.

Recent technological advances have led to increased interest in intraoperative evoked potential monitoring. Although theoretically valuable, its precise role remains to be defined, and useful criteria for predicting neurological deficit are not well established. The authors used brain-stem auditory evoked potential (BAEP) monitoring during 21 posterior fossa microvascular decompression procedures to assess the value of this technique in predicting postoperative deficit. The surgeon was notified only if there was complete disappearance of wave V. Although no patients had postoperative deafness, BAEP latencies changed significantly in all cases. In four patients, wave V totally disappeared during cerebellar retraction. The BAEP appears to be a very sensitive monitor of auditory function, such that "false positive" results will be frequent if latency criteria alone are used to trigger alterations in surgical technique.