Development of Visceral Mastocytosis Three Years After Low-grade MCT Removal

Dr. Emily Evans

PATIENT INFORMATION:

Age: 9 year old

Gender: Female Spayed

Species: Canine

Breed: Boxer Mix

HISTORY:

Patient presented for progressive appetite reduction over 2 weeks. History of being a “picky eater” with dietary sensitivity to chicken(produces gastroenteritis). Hypoproteinemia was noted on labs the day of the ultrasound. Previously diagnosed protein losing nephropathy(>4 years duration) currently managed with benazepril. Owner was concerned with the potential progression of PLN causing patient to feel hyporexic. Patient had a low grade mast cell tumor removed with clean margins 3 years ago with no dermal masses or tumor regrowth noted in the past three years or on the day of exam.

IMAGE INTERPRETATION:

The liver is moderately increased in size, mildly rounded in shape with a moderately coarse hyperechoic echogenicity. There is a hyperechoic rounded ill-defined non-contour altering nodule in the left liver(1.4x1.5cm). The gallbladder is of normal size and shape and the wall is clean.

The stomach contains a mild amount of gas, the gastric walls are subjectively thickened (7.4mm). The muscularis layer of the stomach is subjectively thickened. The pylorus is free of obstruction. The small intestine has normal to mildly increased wall thickness with normal layering distinction and proportions. A thin hyperechoic band is seen paralleling the submucosa. There is mild-moderate ileus in the small intestine.

The spleen is mildly enlarged(2.8cm at the hilus) with a rounded shape and a moderately mottled echotexture. No focal lesions noted.

Multiple mesenteric lymph nodes are severely enlarged(~2.3cm in thickness) with irregularly rounded shape having mildly heterogenous hypoechoic echogenicity.

There is a scant amount of free fluid present in the abdomen.

Normal size, shape, and corticomedullary distinction to the kidneys.

DIAGNOSIS AND SONOGRAPHIC ANALYSIS:

Lymph nodes - the findings are severe - DDx: infiltrative neoplasia (lymphoma vs. mast cell vs. other) vs. IBD vs. infection vs. reaction vs. metastatic neoplasia

Liver - the findings are moderate - DDx: Infiltrative neoplasia (lymphosarcoma vs. mast cell) vs. Chronic vs. Acute hepatitis or cholangiohepatitis (bacterial vs. sterile vs. toxin) vs. Steroid hepatopathy / Vacuolar hepatopathy / Glycogen storage disease / Copper storage disease vs. Diabetes mellitus vs. Fungal infection vs. Hepatotoxin

Liver Nodule - the findings are mild - DDx:metastatic neoplasia vs. benign nodules of regeneration vs. emerging primary hepatic neoplasia

Spleen echotexture - the findings are moderate - DDx: extramedullary hematopoiesis (EMH) vs. infiltrative neoplasia vs. benign nodular regeneration

Splenomegaly - the findings are moderate - DDx: Infiltration(Neoplasia—lymphosarcoma; acute and chronic leukemia; malignant histiocytosis; multiple myeloma; systemic mastocytosis; plasmacytoma) vs. Inflammation (Splenitis) vs. Hyperplasia vs. Congestion vs. Extramedullary hematopoiesis

Ascites- this finding is mild(scant) - DDx: transudate vs. hemorrhagic vs. exudate

Stomach - the findings are mild - DDx: active gastritis vs. gastric ulceration with secondary granulation and thickening/edema vs. primary neoplasia vs. infiltrative neoplasia (lymphosarcoma, mast cell tumor, etc).

Intestines - the findings are mild - DDX: inflammatory bowel disease vs. food allergy/intolerance vs. infiltrative neoplasia

Ileus- the findings are mild DDx:

Physical vs Metabolic vs. Functional vs. Neuromuscular

ADDITIONAL DIAGNOSTICS:

Fine needle biopsies of the spleen and mesenteric lymph nodes were obtained.

Cytology results indicated a definitive diagnosis of a mast cell tumor (100% confidence) for both locations, consistent with a metastatic process.

CASE OUTCOME:

Once this unexpected metastatic mast cell tumor was confirmed, oral diphenhydramine and famotidine were recommended. The mast cell tumor is likely the cause for gastrointestinal changes and poor appetite. The patient’s appetite improved with the addition of maropitant. Patient was referred to a veterinary oncologist for continued care. Vinblastine chemotherapy and prednisone were initiated. Ascites continued to develop and clinical signs progressed so the patient was recently changed to CCNU protocol. Diphenhydramine, famotidine and maropitant have all been continued.

PROGNOSIS:

Visceral mast cell tumors carry a guarded long term prognosis; with chemotherapy and prednisone together life expectancy is approximately 6 months; with prednisone alone 3 months.

Image 1: Mesenteric lymph nodes severely enlarged and heterogeneous hypoechoic echogenicity. Fine needle aspiration identified mast cell tumor effacement of node.

Image 2: The spleen was found to be mildly enlarged, with a rounded mottled echotexture. Mast cell tumor was confirmed in the spleen with fine needle biopsies.

Image 3: The slides of moderate to high cellularity consist of few aggregates of splenic stroma, often interspersed with hemosiderin, and a nucleated cell population largely predominated by mast cells, with fewer hematopoietic precursors of various … — Image 3: The slides of moderate to high cellularity consist of few aggregates of splenic stroma, often interspersed with hemosiderin, and a nucleated cell population largely predominated by mast cells, with fewer hematopoietic precursors of various linage and stages of maturation, mixed lymphoid cells predominated by many small lymphocytes, and rare plasma cells. These mast cells are moderately to well granulated with a centrally located round to oval nucleus with finely stippled chromatin. Anisokaryosis is mild to moderate

A special thanks to one of our local Richmond veterinary partners and Dr. Casey LeBlanc DVM, PhD, ACVP (Clinical Pathology) at EasternVetPath for his help with this case.