A splenic mast cell tumor in an 11-year old Siamese cat: Radiology perspective

Dr. Janina BartelsDiagnostic imaging in cats with suspected splenic mast cell disease plays an important role in the diagnosis, presurgical staging and continued monitoring of disease progression after splenectomy. Survey radiographs of the abdomen are useful to identify splenomegaly and potential dissemination in other organs, most commonly the liver, followed by abdominal lymph nodes and, less frequently, the intestinal tract (Figures 6A and 6B).1 Loss of serosal detail compatible with peritoneal effusion may be identified on abdominal radiographs in up to one third of splenic mast cell tumor cases, and the effusion is characterized by eosinophils and mast cells.1

Figures 6A and 6B. Left lateral (6A) and ventrodorsal (6B) abdominal radiographs of the cat in this case. Severe hepatomegaly and splenomegaly are seen. The kidneys are mildly decreased in size and irregularly shaped, consistent with bilateral chronic kidney disease. (L: liver; S: spleen; LK: left kidney; RK: right kidney.)

Thoracic radiographs are recommended to rule out pulmonary metastasis and concurrent diseases that may affect clinical decision or disclose an increased risk for anesthetic procedures such as occult cardiomyopathy. It is important to note that no specific ultrasonographic changes are characteristic of mast cell disease, and cytology or histopathology are necessary for definitive diagnosis. However, ultrasonography is useful in determining the extent of the disease, if used in conjunction with cytology/histopathology via ultrasound-guided fine-needle aspiration or biopsy.2 Fine-needle aspiration of the spleen is easily performed and provides reliable results with a low risk of complications.5 Pretreatment with antihistamines is recommended because of the concerns of mast cell degranulation and anaphylaxis.6

Many authors suggest that liver and splenic aspirates should be obtained in all cases of mast cell staging, despite normal sonographic appearance of the liver or spleen, since normal appearance of these organs does not rule out mast cell infiltration (Figures 7A and 7B).2,3 Abnormalities associated with mast cell-infiltrated spleens include increased size, irregular margins, mottled echotexture and multiple hypoechoic or hyperechoic nodules throughout the parenchyma.2

Figures 7A and 7B. Sonographic longitudinal images of the spleen (7A) and the liver (7B) from the cat in this case. The spleen is markedly enlarged and mildly heterogeneous. The liver margins are mildly rounded, but there is otherwise normal echogenicity and echotexture. Definitive diagnosis requires cytologic examination or biopsy. Tissue sampling was performed via ultrasound guidance, which yielded a diagnosis of splenic mast cell neoplasia and mild hepatic lipidosis with rare atypical mast cells within the liver. (S: spleen; L: liver; D: diaphragm.)

Additionally, ultrasonography may identify regional lymphadenopathy (Figure 8), which has been described as a negative prognostic factor in the case of metastatic spread.4 Metastatic lymph nodes may have abnormal echogenicity (often hypoechoic), abnormal shape and increased size.2 Therefore, diagnostic imaging is an important feature in feline mast cell tumor staging and may be useful for predicting prognosis and long-term survival.

Figure 8. Sonographic longitudinal image of a splenic lymph node in the patient of this case. The lymph node is hypoechoic and mildly enlarged (5.3 x 10.2 mm, height x length).

References

1. Withrow SJ, Page R, Vail DM. Mast cell tumors. In: Small animal clinical oncology. 5th ed. St. Louis, Missouri: Elsevier, 2013.

2. Sato AF, Solano M. Ultrasonographic findings in abdominal mast cell disease: a retrospective study of 19 patients. Vet Radiol Ultrasound 2004;45:51-57.

3. Stefanello D, Valenti P, Faverzani S, et al. Ultrasound-guided cytology of spleen and liver: a prognostic tool in canine cutaneous mast cell tumors. J Vet Intern Med 2009;23:1051-1057.

4. Kraus KA, Clifford CA, Davis GJ, et al. Outcome and prognostic indicators in cats undergoing splenectomy for splenic mast cell tumors. J Am Anim Hosp Assoc 2015;51:231-238.

5. O'Keefe DA, Couto CG. Fine-needle aspiration of the spleen as an aid in the diagnosis of splenomegaly. J Vet Intern Med 1987;1:102-109.

6. Ettinger SJ, Feldman EC. Mast cell disease. In: Textbook of veterinary internal medicine. 6th ed. Philadelphia, Pennsylvania: Elsevier, 2005.