MALIGNANT EPITHELIOID SCHWANNOMA AFFECTING THE TRIGEMINAL NERVE OF A DOG

A malignant epithelioid schwannoma was diagnosed affecting the trigemi nal nerve of an 11-year-old dog. Neurologic abnormalities included an altered mental status, ataxia, left head tilt, postural reaction defic its of all four limbs, a pronounced left masticatory muscle atrophy, a nd absent left facial sensation. Histologically, a densely arranged ep ithelioid population with a very high mitotic index was surrounded by a spindle-shaped cell proliferation characteristic of schwannomas. Bot h cell populations stained positively for vimentin, but only spindle c ells were occassionally positive for S-100 protein. The histologic and immunohistochemical features of this tumor were consistent with those found in human epithelioid schwannomas.