Imaging Findings: The MR images show an 8mm diameter, T1 hypointense (image 1A & 1B), extra-axial mass arising from the origination of the trigeminal nerve (image 2A & 2B) at the level of the pons (Image 3A & 3B). The mass is strongly and uniformly contrast enhancing and extends rostrally following the course of the trigeminal nerve (enlarge image 3A). Click here to learn more about the trigeminal nerve.
Note: Click to enlarge each image:
|Image 1A||Image 1B|
|Image 2A||Image 2B|
|Image 3A||Image 3B|
Discussion: The sensation in the cornea is diminished because of the trigeminal nerve deficit. The loss of the trophic inlfluence of the trigeminal nerve on the cornea also increases susceptibility to ulceration. The fluid accumulation in the middle ear is a common finding in animals with temporalis and masseter muscle atrophy and is presumably due to eustachian tube dysfunction.
Differentials included granuloma (e.g. coccidiodomycosis, toxoplasmosis), lymphosarcoma or trigeminal nerve sheath tumor. Cocci and toxo serology tests were negative and based on the course of the lesion and its effects, lymphosarcoma is unlikely.
Diagnosis: Probable nerve sheath tumor of the right trigeminal nerve.
Treatment: These tumors tend to be slow growing but, given their location deep within the skull, are not amenable to surgical removal. Unfortunately, these types of tumors are relatively unresponsive to either chemotherapy or radiation. However, if treatment were attempted, radiation probably would have the best chance of slowing the growth of the tumor. Continued opthalmologic care is recommended for treatment of the eye ulcer.