The spleen is not essential for life as its functions can be assumed by other organs. Functions of the spleen include:

• Cellular and humoral immunity
• Phagocytosis of bacteria and foreign particles
• Filtration of old or damaged/altered cells
• Hematopoiesis when bone marrow is unable to meet demands for cells
• Blood reservoir  

The spleen can sequester normal or abnormal cells. 10% of total RBC mass is contained in the normal spleen. Maturation of reticulocytes take place in the spleen. The normal spleen removes abnormal cells including:

• Spherocytes
• RBC with Heinz bodies on the surface
• Antibody coated cells
• NRBC

An abnormal spleen can sequester or remove normal cells including normal platelets resulting in mild thrombocytopenia.

Splenomegaly can be due to diffuse or nodular enlargement. Causes of diffuse splenomegaly include:

• increased phagocytic function of the spleen

IHA -immune hemolytic anemia
IMT - immune mediated thrombocytopenia
SLE - systemic lupus erythematosus
Systemic infection such as Haemobartonella

• Vascular causes of splenomegaly include:

Right heart failure resulting in backup of blood into the spleen along with other organs
Hepatic cirrhosis causes portal hypertension and engorgement of the spleen with blood

Splenic torsion impairs venous drainage from the spleen. Splenic torsion is most often associated with gastric torsion, although primary torsion of the spleen without concurrent gastric torsion can occur in large, deep chested breeds. Primary splenic torsion is uncommon. It can either present with an acute onset of signs of collapse and shock or vague chronic signs of vomiting, anorexia and depression. DIC may be present. The treatment is splenectomy.

• Drug induced splenomegaly occurs with the administration of barbiturates such as those used for anesthesia or long term barbiturates administered as anticonvulsants.
• Extramedullary hematopoiesis can result in diffuse splenic enlargement.  If the bone marrow is unable to meet the demand for hematopoietic cells that are either being destroyed at a rapid rate or the marrow itself is not producing hematopoietic cells, then the spleen can be a site of formation of hematopoietic cells leading to an increase in size.

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Neoplasia can cause splenic enlargement that is diffuse or may cause nodular enlargement.  Neoplastic conditions of the spleen include:

Nodular hyperplasia is a benign nodular mass that can be singular or multiple

Hematomas of the spleen can develop with trauma but are not real common

Lymphosarcoma of the spleen can be diffuse or nodular and is usually part of a more diffuse neoplastic process. Lymphosarcoma of the spleen occurs in both dogs and cats.

Mast cell tumors occur in the spleen of cats but rarely occur in the spleen of dogs. In cats, splenomegaly due to mast cell neoplasia is usually diffuse.

Hemangioma is a benign nodular tumor and occurs less commonly than its malignant counterpart, hemangiosarcoma.

Hemangiosarcoma is the most common primary splenic neoplasm in the dog.

The German shepherd is the most commonly affected breed. Signs often include weakness or collapse due to spontaneous rupture and intra-abdominal bleeding resulting in hypovolemia. On physical evaluation the mucous membranes are usually pale due to hypovolemia and/or blood loss. The dogs will reabsorb the blood cells and fluid from the abdominal cavity and may show temporary improvement in signs as the anemia and hypovolemia improve. The diagnosis may be suspected on plain radiographs which may show a large spleen or splenic enlargement may be masked by free abdominal fluid (blood) A regenerative anemia is usually present although the number of NRBC may be disproportionate to the magnitude of anemia and other indicators of regeneration. Abdominocentesis often yields non clotting blood if the mass has ruptured. Neoplastic cells may be observed in the bloody fluid but often are not. The splenic mass (es) are usually not uniform in appearance when viewed with ultrasound. Ultrasound can confirm if the mass(es) have ruptured. The mass(es) usually contain numerous cavities. Splenic hemangiosarcomas have high metastatic potential with metastases common to liver, omentum, kidney and lung. Hemangiosarcomas can also originate in the right atrium or subcutaneous tissues and metastasize to the spleen. Treatment by surgical excision of the spleen will prevent additional rupture of the primary splenic mass(es) but will not extend survival. Chemotherapy (VAC- vincristine, adriamycin, cytoxan) following splenectomy has been demonstrated to extend survival.    

Diagnostic tests to evaluate the spleen include:

 

• palpation
• plain radiographs
• ultrasound
• aspiration

• laparotomy for exploration

This page was last edited on December 15, 2003 by CRD
visits to this page since Dec. 15, 2003