Trochlear nerve schwannoma: A 22 year follow‐up

A healthy 57-year-old man presented with binocular vertical diplopia in 1997. There was no history of headaches, orbital pain or trauma. He adopted a left head tilt and ocular motility examination revealed a right superior oblique palsy with a right hypertropia of five prism dioptres in primary position. The rest of his cranial nerve examination was normal. Contrast-enhanced MRI of the brain and orbits was initially reported as normal. On secondary review, a focal lesion involving the cisternal right fourth nerve (CNIV) was detected. Without contrast, the lesion was isointense with brain parenchyma (Figure 1A); with contrast, the lesion enhanced intensely (Figure 1B). These radiological findings were most in keeping with a CNIV schwannoma. His ocular motility examination remained stable over the next 22 years as did the radiological appearance of the presumed CNIV schwannoma (Figure 2). As his diplopia was successfully managed with prism spectacles, strabismus surgery was not required. Trochlear nerve schwannomas are an unusual cause of isolated superior oblique palsies and are quite rare even in patients with neurofibromatosis type 2. As depicted in this case, CNIV schwannomas may be overlooked if contrast is