Evaluating Injection-Site Sarcomas

Feline injection-site sarcomas are among the most locally aggressive tumors in small animals. Radical en bloc surgical excision with wide margins is recommended for complete excision. CT and MRI are used to detect peritumoral lesions that could be neoplastic extensions of a primary tumor. 

This prospective study compared CT angiography and MRI with microscopic findings for peritumoral lesions in 10 cats with injection-site sarcomas. Locations identified on imaging were marked on freshly excised specimens to determine agreement with microscopy. CT and MRI identified 87 peritumoral lesions of varying morphologies, with a median of 4 lesions per cat (range, 3-12). Of the lesions, 19.5% were neoplastic, 58.6% were nonneoplastic, and 21.8% were microscopically equivocal. Imaging characteristics were not specific to a microscopic category in 69% of peritumoral lesions. A peritumoral lesion was identified in the same location on both imaging modalities in 50 lesions. There was no significant difference in the number of peritumoral lesions identified on CT or MRI.

Determination of accurate preoperative surgical margins can be challenging, particularly with locally aggressive tumors such as feline-injection site sarcomas. These can infiltrate beyond local gross margins and can be unpredictable. Although 87 imaging lesions were specifically evaluated microscopically from 10 cats, tumors were located in various anatomic locations with varying complexity; this may limit the study’s statistical power. CT angiography and MRI detected many peritumoral lesions, although these were not predictive of neoplastic extension. However, no tumor cells were identified beyond peritumoral lesions noted on either imaging technique.—Jason Bleedorn DVM, MS, DACVS, University of Wisconsin–Madison