A Case Report of Feline Intestinal Mast Cell Tumor

An 8 year old female spayed domestic short hair cat was referred for abdominal ultrasound due to a 7 month history of chronic intermittent vomiting, diarrhea and inappetence.

Sonographic exam of the abdomen revealed mild to moderate thickening of the muscularis layer throughout the entire length of the small intestinal tract.  Additionally there was a pair of markedly enlarged, rounded hypoechoic lymph nodes at the ileocolic junction.  Ultrasound guided fine needle aspiration of the lymph nodes was attempted with the patient sedated however the lymph nodes were extremely firm, difficult to penetrate with the needle and yielded relatively acellular samples.  Surgical biopsies of the intestines and lymph nodes were recommended as the next diagnostic step.

Exploratory laparotomy was performed and incisional biopsies obtained from the stomach, duodenum, jejunum, and ileocolic lymph node.

Histopathology of the stomach demonstrated infiltration of the lamina propria with low numbers of lymphocytes, eosinophils and plasma cells as well as superficial mucosal fibrosis and edema.  Lamina propria of the duodenum was moderately infiltrated with plasma cells.  The lamina propria of the jejunum was moderately infiltrated with increased plasma cells, low numbers of lymphocytes and eosinophils and multifocal clusters of atypical round cells presumed to be mast cells.  Submucosa was also infiltrated with lymphocytes, plasma cells and eosinophils.

The ileocolic lymph node contained multifocal islands formed by sheets of neoplastic round cells having irregular round to oval nuclei with inconspicuous nucleoli and moderate to abundant amounts of foamy cytoplasm with distinct cell borders.  Moderate anisokaryosis was present with low mitotic activity (1 per 10 high power fields).  Numerous eosinophils and few macrophages were also present.  The final histopathologic diagnosis was mast cell tumor of the jejunum and ileocolic lymph node as well as mild lymphoplasmacytic and eosinophilic enterits.

Chronic intermittent vomiting, diarrhea, inappetence or weight loss are common clinical signs prompting abdominal sonography in cats.  Diffuse small intestinal thickening, particularly of the muscularis layer along with mesenteric lymphadenopathy can be common sonographic findings in these patients and has been associated with inflammatory diseases and infiltrative neoplasias of intestinal tract.  It can also occasionally be noted in cats with no clinical signs referable to the gastrointestinal tract.  While lymphocytic-plasmacytic enteritis is the most common histopatholgic form of inflammatory bowel disease, eosinophilic enteritis is also occasionally diagnosed (1).  Cats with eosinophilic enteritis tended to have a slightly greater intestinal wall thickness with a thicker muscularis layer.  Peripheral eosinophilia can also be documented in some but not all cats.

Lymphoma is the most common gastrointestinal neoplasia in cats.  The classic sonographic description of lymphoma has been that of hypoechoic mural masses and symmetric or asymmetric circumferential thickening with a loss of normal wall layering detail (2,3).  Enlarged, hypoechoic and rounded mesenteric lymph nodes may or may not be present.  This form of lymphoma tends to be a B-cell lymphoma and can be associated with hepatic or renal lesions as well.  More recently a sonographic appearance of muscularis layer thickening with preserved intestinal layering detail and the absence of mass lesions has been described in cats with gastrointestinal lymphoma.  These cases tended to be a small cell T-cell variety of lymphoma (4,5).  Mesenteric lymphadenopathy may or may not be present in these cases.

Mast cell tumor can be seen in both the cutaneous and visceral form in cats.  The visceral form can occur as both intestinal and splenic infiltration with mast cell tumor being the third most common intestinal neoplasia of cats, comprising approximately 4% of intestinal neoplasias (6,7).  Mast cell infiltration can occur in the small intestine or colon.  The sonographic appearance of feline intestinal mast cell tumor can be that of either single or multifocal mural mass lesions or more diffuse small intestinal thickening, particularly of the muscularis layer.  Metastasis to the mesenteric lymph nodes, liver or spleen may be noted.  In contrast to the cutaneous form of MCT in cats the prognosis with the intestinal form is very poor (8).

In conclusion muscularis layer thickening and mesenteric lymphadenopathy are common sonographic findings in cats present for chronic intermittent vomiting, diarrhea, inappetence or weight loss.  While these serve as important imaging biomarkers for intestinal disease they are not specific enough to differentiate between inflammatory or neoplastic conditions.  Also, in addition to the commonly discussed and diagnosed lymphocytic-plasmacytic enteritis and lymphoma, other inflammatory and neoplastic diseases must be considered including eosinophilic enteritis and visceral mast cell tumor.  These imaging findings should prompt intestinal biopsies as the next diagnostic step to obtain a histopathologic diagnosis and allow for formulation of an appropriate treatment plan as well as more accurate prognosis.

Submitted by Christopher T Ryan, VMD, Dipl. ABVP, Dipl. ACVR


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Figure 1:  Sonographic appearance of feline visceral (intestinal) mast cell tumor.  No the markedly enlarged, hypoechoic rounded mesenteric lymph node as well as the thickened muscularis layer of the jejunum demonstrated with yellow arrows.


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