Case Study

CT – Brain Stem Mass, Moderate Rhinitis in a 13 year old FS DSH cat

History of hyperthyroidism and chronic renal disease. Owner found laterally recumbant on the stairs on 8/1115. Physical Exam: General muscle atrophy, loss of proprioception on right front limb, paresis on left rear limb with no CP deficits

DX

The findings are suggestive of a plaque like extraaxial mass within the middle cranial fossa in the region of the brain stem. A basal meningioma or round cell neoplasia would be compatible with the changes. A peripheral nerve sheath tumor is low for potential because of the symmetric midline location. A hypertensive hemorrhagic cerebrovascular event is even less likely because of the distribution and significantly increased Housfield units after contrast administration. Note that the findings are subtle and the region is prone to confounding artifacts. Verification of the findings would require MRI. There was mild right-sided and moderate left sided non destructive rhinitis. A viral and/or bacterial rhinitis is most likely. The findings of the thyroid gland are compatible with active adenomatous hyperplasia.

Image Interpretation

CT of the head, cervical spine and brachial plexus – There was a plaque like extraaxial mass lesion within the middle cranial fossa dorsal to the skull base with a mild mass effect on the brain stem. The mass was uniformly hyperattenuating compared with the brain parenchyma on the plain and post contrast series. The Hounsfield units increased by +30 after contrast administration indicating mild uniform contrast uptake within the mass.
There was mild right-sided and moderate left sided non destructive rhinitis.
Both thyroid lobes were enlarged with multifocal hypoattenuating nodules and heterogenous contrast enhancement. The right lobe was measuring 2 x 0.5 x 0.7 cm. The left lobe was measuring 2 x 0.4 x 0.4 cm.
There was an ovoid well delineated soft tissue attenuating mass with peripheral rim and lacking central enhancement within the subcutis level with the right temporomandibular joint. The size of the mass lesion was approximately 1.2 cm in diameter. There were no signs of perilesional inflammation.
There was a likely age related interstitial and bronchial lung pattern and generalized demineralization of the skeleton.

Outcome

The subcutaneous mass likely contains fluid or necrotic tissue. Differential diagnoses include soft tissue neoplasia with tumoral necrosis such as fibrosarcoma, melanoma and other or a cyst. Sampling may be considered for further workup.