Giant Multiloculated Cystic Trochlear Nerve Schwannoma Between the Tentorial Leaflets: Case Report and Systematic Review

Background: Trochlear nerve schwannomas (TNSs) are exceptionally rare benign tumors, accounting for a very small fraction of intracranial schwannomas. Due to their deep locations and slow growth, they often reach a considerable size before diagnosis. Giant or multiloculated cystic variants are exceptionally uncommon and present significant diagnostic and surgical challenges. Methods: A 32-year-old female presented with headache and dizziness but no diplopia. Magnetic resonance imaging revealed a giant multiloculated cystic lesion extending from the posterior fossa to the right temporal lobe, causing obstructive hydrocephalus. The mass was removed through a right paramedian supracerebellar transtentorial approach under intraoperative neurophysiological monitoring. The tumor was confined between the two tentorium leaflets with the trochlear nerve entering and exiting the lesion. Gross total resection was achieved with an uneventful postoperative course. Histopathology confirmed a World Health Organization Grade I schwannoma with Antoni A–B architecture and diffuse S-100 positivity. A systematic literature review was conducted in accordance with the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA 2020) guidelines, identifying forty-six surgically treated cases, analyzed together with the present case (n = 46). Results: Mean age was 44.7 years with an approximately equal sex distribution. Most tumors (76.1%) were located in the ambient or crural cisterns, followed by the quadrigeminal cistern (10.8%) and cisterno-cavernous region (8.7%). Diplopia and trochlear nerve palsy were the most common presenting symptoms. Gross total resection was achieved in 80.4% of patients, while postoperative trochlear palsy occurred in 60.8%. No malignant transformation or early recurrence was reported. Conclusion: This case represents one of the largest TNSs described and the second known lesion arising between the tentorial leaflets. Awareness of this unique anatomic configuration is essential for accurate preoperative diagnosis and surgical planning. A meticulous, anatomy-guided microsurgical approach enables complete resection while preserving neurological function in select cases.