Case Study 2 (Page 1)

Patient History: An 8 year old, f/s, Bichon Frise was presented with unilateral head muscle atrophy, decreased facial sensation, and severe corneal ulceration on the right side. There were no detectable gait abnormalities or limb reflex deficits.

Question: Which abnormalities can be visualized on the MR images? Click on your answer(s) to see if it is correct:

Examination & Imaging Findings: There is atrophy of the right temporalis (1) and masseter (2) muscles which could be appreciated on the physical examination. There is fluid in the right tympanic bulla (3). The tympanic membrane appeared normal on otoscopic examination. The intracranial mass is not labeled...were you able to identify it? Continue on for more discussion.

Additional History: Cranial nerve examination results:

• menace response: absent OD (+0), likely due to descemetocele / normal OS (+2)
• palpebral reflex: OU (+2)
• corneal sensation: present bilaterally but subjectively slightly decreased OD in comparison to OS

Question: Which one of the following nerves best accounts for the patient's clinical signs?

Discussion: The decreased facial and corneal sensation as well as head muscle atrophy are indicative of dysfunction of all branches of the trigeminal nerve. The mandibular branch serves motor to the muscles of mastication, the ophthalmic branch sensation to the cornea, and the maxillary branch sensation to the face. Neoplasia and granulomatous disease would be primary rule outs with nerve sheath tumor most likely. A retrobulbar mass or olfactory lobe tumor would be located too far rostrally to affect all major branches of the trigeminal nerve.

More images from the MRI (Click to enlarge):

Question: What part of the brain is being affected by this contrast enhancing lesion?