Objectives. Schwannomas originating from the trochlear nerve are extremely rare; only 30 cases have been reported in the literature. Many operative approaches have been utilized for lesion resection, but the advantages of the anterior transpetrosal approach are numerous and include excellent exposure, minimal extradural retraction of the temporal lobe, and minimal cerebrospinal fluid leaks. We report the second case of a trochlear schwannoma resected via the anterior transpetrosal approach. Setting. A 64-year-old male presented with 3-month history of diplopia and headaches. On physical examination, he was found to have a right fourth nerve palsy. Brain magnetic resonance imaging revealed a mass within the right ambient cistern compressing the adjacent midbrain. A right-sided anterior transpetrosal approach was used—which confirmed that the trochlear nerve entered the mass—to achieve gross total resection. Pathological examination confirmed diagnosis of schwannoma. The patient was discharged on postoperative day 3. He experienced a persistent fourth nerve palsy postoperatively with an otherwise normal neurological examination. Follow-up imaging confirmed complete removal of the tumor. Conclusion. The anterior transpetrosal approach is an excellent approach for removal of trochlear schwannomas involving the cisternal course of the trochlear nerve. It affords complete visualization of this anatomical region while introducing minimal morbidity. 1. Introduction Schwannomas originating from cranial nerves account for 8% of intracranial neoplasms. The vast majority of these tumors arise from the sensory cranial nerves, most commonly, the vestibular or trigeminal nerve [1–3]. Schwannomas that originate from purely motor cranial nerves in patients without neurofibromatosis are uncommon. Of these, trochlear nerve schwannomas are exceedingly rare; to date, there have been only 30 reported cases of surgically confirmed trochlear nerve schwannomas [2–28]. Tumors arising from the trochlear nerve can present a surgical challenge because they often involve the cisternal region near the brainstem [16]. The most common approach used to resect these tumors has been the subtemporal transtentorial approach [16]. But the disadvantages of intradural approaches include retraction injury and cerebrospinal fluid (CSF) leak. The extradural anterior transpetrosal approach is ideal for trochlear schwannomas involving the cisternal portion. It affords excellent visualization of the epicenter of the lesion. Progressive enfolding of the tumor capsule into the surgical opening allows
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