History and clinical signs

Cats presenting with splenic disease are typically older, with a median age of 12 years, and with no sex predilection.⁶ Presenting signs of splenic disease in cats are typically non-specific, and the history usually includes weight loss, anorexia, lethargy and vomiting.³ A palpable abdominal mass or splenomegaly is found in approximately 50% of cases,^3,6,7 although the spleen is usually enlarged in over 80% of cats with lymphoma. It is typical to find splenomegaly when the spleen is infiltrated with mast cells, and the spleen is often irregular in contour.³ These patients also often present with anorexia and vomiting due to gastric and duodenal ulcers from paraneoplastic histamine release.⁸

Hemoperitoneum

Most cases of hemoperitoneum in cats are traumatic in nature and evidence of abdominal effusion or a palpable abdominal mass is often absent.⁷ Following blunt trauma, the spleen and liver are the most likely sources of severe ongoing hemorrhage.⁹ The clinical signs tend to be non-specific and include lethargy, anorexia, vomiting, abdominal distension, generalized weakness, pale mucous membranes, hemoglobinuria, and sometimes syncope and overt signs of shock.

Cats rarely present with spontaneous hemoperitoneum, with only four cats out of 19 undergoing splenectomy having free abdominal blood in one study.⁶ In spontaneous hemoperitoneum cases bleeding occurs most commonly from the liver, with the spleen only accounting for 17% of cases.

A ruptured spleen from hemangiosarcoma is the most common neoplastic cause although neoplasia only accounted for 46% of cases. Splenic lymphoma is a rare cause of spontaneous hemoperitoneum.7,10

Blood analysis

Cats with spontaneous hemoabdomen are often anemic, with many having a packed cell volume of 20% or lower. An increased reticulocyte count and thrombocytopenia are also frequently found.6,7 Decreases in total protein, often through hypoalbuminemia, are common. Cats with hemoabdomen also often have high serum lactate levels, indicative of their low circulating blood volume and poor blood pressure. Elevations in serum urea and creatinine may also be present, typically with a pre-renal cause. With primary visceral mast cell disease involving the spleen, it is common to see a circulating eosinophilia and up to 40% of cats have a buffy coat layer that is positive for mast cells.¹¹ Erythrocytosis due to catecholamine release as seen in dogs is not expected in cats, as they lack the muscular component to the spleen and sinusoid splenic blood.¹²

Common abnormalities in the coagulation profile of cats with hemoabdomen include prolongation in prothrombin time (PT) and partial thromboplastin time (PTT).

Imaging

Ultrasound is the most useful imaging modality for examination of the spleen though inflated thoracic radiographs or computer tomography¹³ are used to screen for metastatic disease. The normal feline spleen is diffusely homogenous, has a finer echotexture than the liver (like the dog), and is more echogenic than the liver or renal cortex.

Splenic masses can appear both hypoechoic and hyperechoic on ultrasound.⁷ The spleen in cats with lymphoma is reportedly diffusely hypoechoic, mottled in texture and may contain small hypoechoic foci, although the foci can be up to 1–2 cm in diameter.^3,14 Abdominal effusion and at least one enlarged abdominal lymph node are also found. Myeloproliferative disease involving the spleen is also diffusely hypoechoic. Mast cell disease often results in a subjectively larger spleen, with a diffusely hypoechoic or nodular/mottled texture although it might present as single or multiple nodules.¹⁵ Liver involvement is also present in approximately 30% of cases. No characteristics allowing differentiation of cats with lymphosarcoma from cats with mast cell tumor have been described, although the former are more likely to have abdominal effusion or lymphadenopathy.³ Common incidental findings in feline spleens include myelolipomas which are well-defined, hyperechoic foci.¹⁶

Rarely, the splenic vein will thrombose, normally in association with feline liver disease or portal vein thrombosis; in this situation color flow Doppler will reveal no flow within the spleen.¹⁷

Computed tomography is increasingly being explored for staging of neoplasia involving intra-abdominal organs such as the spleen, or for identifying the origin of an abdominal mass.¹⁸ It is likely this practice will increase with growing availability of these scanners.

Magnetic resonance imaging (MRI) is not widely used at this time for imaging the feline cranial abdomen although the appearance of normal liver, spleen, kidneys, and pancreas has been published as a reference guide.¹⁹

Cytology

Ultrasound-guided fine needle aspirates can be used to distinguish causes of splenomegaly, and they provided a diagnostic sample in 81 of 101 cats,³ although in another study fine needle aspirates could not identify an underlying cause of splenomegaly in two of five cats²⁰ and in another study cytology only corresponded to the histologic diagnosis in 61% of splenic aspirates, although this included cats and dogs.²¹ The cat is sedated and positioned in right lateral or dorsal recumbency and a 23G or 25G 1–1.5 inch needle is used. Samples should be collected with a non-aspiration technique (needle pushed into spleen and retracted and redirected several times), as this has been shown in the feline spleen to provide higher cellularity and less blood yet the same cell morphology compared to samples obtained by aspiration techniques (applying suction through a syringe).²²

There is no evidence to suggest that bleeding is common or important after splenic aspiration in cats, even in the face of thrombocytopenia.²³ There is also no evidence in the cat or dog to suggest splenic aspiration has resulted in tumor-seeding to the needle tract in the body wall.