Surgical management of a large cystic trochlear nerve schwannoma mimicking a brainstem glioma: a case report.

Introduction: Intracranial schwannomas represent a rare group of intracranial tumors, with purely motor nerve schwannomas being the rarest of them. The anatomical proximity of these tumors to the brainstem may present a radiological challenge in differentiating them from intra-axial brainstem tumors, which can influence further decision-making and treatment options. Methods: We report on a 47-year-old male patient who was diagnosed with a large cystic intracranial tumor with radiological features suggestive of an intrinsic brainstem glioma. Results: After discussing treatment options and risks based on a presumed radiological diagnosis, microsurgical treatment via lateral-suboccipital craniotomy in semi-sitting position, under continuous intraoperative neuromonitoring was performed. Intraoperative findings proved that the tumor was an extra-axial schwannoma originating from the left trochlear nerve. Gross total removal of the lesion was achieved. Conclusion: Due to their rarity, non-specific symptoms and the possibility to mimicking intra-axial brainstem tumors on imaging, these tumors may present a diagnostic challenge and should be taken into account during treatment decision-making.