Trochlear nerve schwannoma: A case description and review of the literature.

Background: Trochlear nerve schwannomas are exceedingly rare, accounting for <1% of all intracranial schwannomas. Their deep-seated location, small size, and motor function pose significant diagnostic and surgical challenges. Due to their rarity, most cases are reported as isolated case studies. Case Description: We report the case of a 57-year-old woman who presented with progressive vertical diplopia and headache. Neurological examination revealed isolated right fourth cranial nerve palsy. Magnetic resonance imaging (MRI) showed a well-defined, contrast-enhancing extra-axial mass in the right ambient cistern, suggestive of a cranial nerve schwannoma. A subtemporal transtentorial approach was used for surgical resection. Intraoperatively, the tumor was found to originate from the trochlear nerve, which was thinned and incorporated within the lesion. Gross total resection was achieved, but anatomical preservation of the nerve was not possible. Histopathological examination confirmed a World Health Organization grade I schwannoma. Postoperatively, the patient experienced transient worsening of diplopia, which improved with prism correction. At 6-month follow-up, she reported resolution of headache and no evidence of tumor recurrence. Conclusion: Sporadic trochlear nerve schwannomas are rare entities that require a high index of suspicion for diagnosis and an individualized therapeutic strategy. Microsurgical resection through a subtemporal approach remains a safe and effective treatment in symptomatic cases. Long-term follow-up with MRI is recommended given the potential - although low-risk of recurrence. Case reports remain essential for informing clinical and surgical decision-making in these uncommon lesions.