Complications in Middle Cranial Fossa Surgery

Highlights

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The middle cranial fossa approach is a versatile skull base approach that is utilized to address small intracanalicular vestibular schwannomas, petroclival meningiomas, midbasilar/anterior inferior cerebellar artery aneurysms, and medial temporal bone lesions.
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Common complications encountered with the middle cranial fossa approach include facial palsy, seizures, cerebrospinal fluid leak, hearing loss from injury to the cochlea or labyrinth, and internal carotid injury.
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Complications can be avoided by use of lumbar drain, intraoperative monitoring, neuronavigation, and careful examination of patient imaging.

Introduction

The main indications for the middle cranial fossa (MCF) approach include removal of a small, predominantly intracanalicular vestibular schwannoma (VS), exposure of the labyrinthine and upper tympanic segments of the facial nerve for decompression, vestibular nerve section, and repair of superior semicircular canal dehiscence. Historically, the MCF approach offers some of the highest hearing preservation rates, but it can also place the facial nerve between the surgeon and the tumor, potentially leading to a higher risk of postoperative facial weakness. In some cases, this configuration results in the need for blind dissection. This route also requires some retraction on the temporal lobe, with the ensuing potential risk of postoperative seizures and speech disturbances, while providing a limited view of the cerebellopontine (CP) angle. The MCF approach is poorly tolerated by the elderly because extradural dissection of the adherent dura in this specific population may be difficult. This approach is suggested for younger patients with smaller tumors that harbor the predominant component of their growth within the internal auditory canal (IAC). Specifically, tumors that involve the fundus of the IAC, a location to which access and visualization are restricted during the retrosigmoid trajectory, are good candidates for the MCF route. Overall, the MCF approach provides a limited working window into the posterior fossa. This limitation is complicated by the presence of the facial nerve within the surgeon’s view and restricts the surgeon’s ability to resect large tumors. The retrosigmoid option, on the other hand, provides a more panoramic view of the tumor in the CP angle cisterns and its relationship to the surrounding neurovascular structures.

Anatomic Insights

Several structures must be identified when utilizing the MCF approach. These structures include the arcuate eminence, the tegmen tympani, the greater superficial petrosal nerve (GSPN), the internal carotid artery (ICA), the middle meningeal artery (MMA) exiting the foramen spinosum, the mandibular division of the trigeminal nerve (V3) exiting the foramen ovale, the petrous apex (Kawase’s quadrilateral space), and the true petrous ridge with superior petrosal sinus (SPS).

This approach is performed after a temporal craniotomy is completed. Craniotomy is placed two-thirds in front of and one-third behind the IAC. An extradural approach is maintained, and the temporal lobe dura is elevated from the middle fossa floor in a posterior to anterior direction. It is important to avoid working from lateral to medial in the anterior aspect (i.e., medial to the root of the zygoma) to avoid inadvertently damaging or putting traction on the GSPN. The nerve lies in the major petrosal groove and is covered by a thin layer of periosteum. Working from lateral to medial across the floor in this area risks lifting the nerve out of the groove, potentially resulting in traction on the nerve and therefore the geniculate ganglion. This is a potential mechanism for facial nerve injuries in these approaches. Regardless of the dural elevation technique, it is critical to understand the GSPN location in the middle fossa floor and to leave the nerve in its groove, protecting it from inadvertent traction. Safe bone removal centers on properly identifying the orientation of the IAC, deep to the meatal plane and petrous ridge. A number of methods have been described for this elemental task. We prefer to visualize axis lines along the GSPN and the arcuate eminence. These axes form an angle, which is then bisected. The bisection line of this angle is an approximation of the IAC position in the bone.

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