A Case of Bilateral Trochlear Nerve Palsy Induced by a Dorsal Midbrain Intracranial Lipoma

Intracranial lipomas are rare among all intracranial tumors. They are typically asymptomatic and discovered incidentally through neuroimaging. However, in rare cases, these lesions can produce neurological symptoms by compressing adjacent structures. We report a rare case of bilateral trochlear nerve palsy caused by an intracranial lipoma located in the dorsal midbrain. A 67-year-old man presented with long-standing binocular diplopia and visual distortion, particularly a perception of tilted vertical lines. Neuro-ophthalmological examination revealed bilateral trochlear nerve dysfunction, with significant excyclotropia and vertical deviation, more pronounced on the left side. Magnetic resonance imaging demonstrated a high-intensity lesion on both T1- and T2-weighted sequences, consistent with a lipoma in the dorsal midbrain. Given the lesion's benign nature and deep location, surgical resection was not indicated due to the high risk of neurological complications. The patient underwent bilateral nasal transposition of the inferior rectus muscles, with additional recession on the right side, to correct the torsional and vertical misalignment. Postoperative assessment demonstrated marked improvement in ocular alignment, restoration of stereopsis, and complete resolution of diplopia. This case underscores the importance of considering intracranial lipoma in the differential diagnosis of bilateral trochlear nerve palsy, especially in patients without a history of trauma. Although surgical removal of the lesion was not feasible, targeted strabismus surgery successfully alleviated the patient's symptoms. However, since the tumor has not been removed, long-term follow-up is essential to monitor for any progression of neurological symptoms due to the underlying lesion.