Transzygomatic Approach with Intraoperative Neuromonitoring for Resection of Middle Cranial Fossa Tumors

Abstract

Access to the floor of the middle cranial fossa (MCF) is often required when performing cranial base approaches to expose various lesions of the petrous apex, petroclival junction, internal auditory canal, and posterior cavernous sinus. In many patients with these lesions, a temporal craniotomy is sufficient to reach the floor of the MCF. However, the caudal limit of a simple temporal craniotomy is the zygomatic arch, which can present an obstacle in accessing the MCF in some individuals. Several authors have advocated mobilizing the zygomatic arch by performing a simple zygomatic osteotomy or using extended frontotemporo-orbitozygomatic approaches to reach low-lying lesions. [1][2][3] Intraoperative neuromonitoring (IOM) is one of the methods in which modern neurosurgery can improve surgical results while reducing morbidity. Motor-evoked potentials (MEPs) obtained by transcranial electrocortical stimulation is routinely used to monitor major motor pathways intraoperatively during several neurosurgical procedures. 4-6 Monitoring of oculomotor, trochlear, trigeminal, and facial nerve function is usually performed using free-running electromyography (EMG) or by direct stimulation of each cranial nerve. 7-9 Keywords ► middle fossa approach ► skull base surgery ► motor-evoked potentials ► intraoperative monitoring ► neurophysiology AbstractThe authors reviewed the surgical experience and operative technique in a series of 11 patients with middle fossa tumors who underwent surgery using the transzygomatic approach and intraoperative neuromonitoring (IOM) at a single institution. This approach was applied to trigeminal schwannomas (n ¼ 3), cavernous angiomas (n ¼ 3), sphenoid wing meningiomas (n ¼ 3), a petroclival meningioma (n ¼ 1), and a hemangiopericytoma (n ¼ 1). An osteotomy of the zygoma, a low-positioned frontotemporal craniotomy, removal of the remaining squamous temporal bone, and extradural drilling of the sphenoid wing made a flat trajectory to the skull base. Total resection was achieved in 9 of 11 patients. Significant motor pathway damage can be avoided using a change in motor-evoked potentials as an early warning sign. Four patients experienced cranial nerve palsies postoperatively, even though free-running electromyography of cranial nerves showed normal responses during the surgical procedure. A simple transzygomatic approach provides a wide surgical corridor for accessing the cavernous sinus, petrous apex, and subtemporal regions. Knowledge of the middle fossa structures is essential for anatomic orientation and avoiding injuries to neurovascular structures, although a neuronavigation system and IOM helps orient neurosurgeons.

Outcomes of Transzygomatic Middle Cranial Fossa Approach for Skull Base Tumors—A Single Institutional Experience

“…In addition, it aids in achieving anterior exposure across the MCF floor when meningiomas or other lesions involve infratemporal fossa or encroach on orbital apex and lateral orbital wall. 7,8 Our results on tumor selection, operative complications, neurological morbidity, and cranial neuropathy are in line with some of the largest series in the literature. 2,3,9 Similar to Roche et al and Danner and Cueva, the majority of patients in our series had meningiomas and presented with symptoms related to cranial neuropathies involving CNs IV to VI.…”

“…The new-onset cranial neuropathy rate was 31.2% which is similar or better than what is reported in the literature. 2,3,8,9 The facial nerve function was normal in all but one patient who had a transient palsy (HB grade 3) which improved to HB grade 2 at last follow-up.…”