"Idiopathic" Trochlear Nerve Paresis Revisited with Gadolinium Diethylenediaminepentaacetic Acid

Magnetic resonance imaging (MRI) with gadolinium diethylenediaminepentaacetic acid (Gd-DTPA) detected a small enhancing lesion along the tentorial course of the fourth cranial nerve in each of 2 patients who had diplopia for longer than 6 months caused by paresis of the superior oblique muscle. Because of the small size and inaccessibility of the tumors, histopathological diagnosis has not been made. The appearance of similar lesions along other cranial nerves in previously reported patients, particularly the eighth nerve, and the discovery of similar lesions in patients with neurofibromatosis, argue that these lesions in the 2 patients are most likely nerve sheath tumors, the smallest yet detected by clinical diagnostic methods. To identify this and other causes of "idiopathic" cranial neuropathy, it is recommended that Gd-DTPA-enhanced MRI be part of a thorough evaluation of patients with chronic cranial neuropathy causing diplopia.