Abstract
CASE SUMMARY: A 4-year-old spayed female domestic shorthair cat was presented for evaluation of multiple abdominal masses and hyperglobulinemia. Thoracic radiographs and abdominal ultrasonography revealed a cranial abdominal mass with extension through the aortic hiatus of the diaphragm and into the caudodorsal mediastinum. A diagnosis of feline eosinophilic sclerosing fibroplasia (FESF) with intralesional methicillin-resistant Staphylococcus aureus (MRSA) was obtained based on necropsy results. RELEVANCE AND NOVEL INFORMATION: To the authors' knowledge, this case report is the first to describe extension of a primary FESF lesion through the diaphragm and is the first confirmed case of intralesional MRSA in an FESF lesion. In addition, this case is one of a growing number of reports of FESF lesions that do not involve the gastrointestinal tract. This case further contributes to the growing evidence that FESF should be considered as a differential diagnosis, in addition to neoplasia, feline infectious peritonitis or abscessation, in cats with masses, especially when there is concurrent hyperglobulinemia, a low albumin:globulin ratio and/or eosinophilia. This case also highlights the importance of considering this differential for masses outside the abdominal cavity, those involving both the chest and the abdomen, and those that do not involve the gastrointestinal tract.