Structure and Function of the Spleen in Dogs

Below is information about the structure and function of the canine spleen. We will tell you about the general structure of the spleen, how the spleen works in dogs, common diseases that affect the spleen and common diagnostic tests performed in dogs to evaluate the spleen. Many diseases and disorders of the spleen start with “Splen-” for example splenomegaly means enlargement of the spleen.

What Is the Spleen?

The dog’s spleen is an elongated organ located in the abdomen. Though not essential for life, the spleen performs important functions related to the blood and lymph systems. The spleen filters the blood and participates in various immune functions.

Where Is the Spleen Located in Dogs?

The spleen is located near the stomach in the left forward part of the abdomen. The exact location of the spleen depends upon its size and shape and is affected by the size of the surrounding organs, such as the fullness of the stomach.

What Is the General Structure of the Canine Spleen?

The spleen is a relatively large, dark red organ that is supplied with numerous blood vessels. The normal spleen is shaped somewhat like a tongue and is considerably longer than it is wide and slightly constricted in the middle. It is covered by a tough capsule of fibrous tissue. Bblood vessels enter and exit the spleen at one end, which is called the “pedicle.” The size of the spleen varies, and it can become engorged with blood under some circumstances. The internal structure of the spleen consists of:

• Red pulp – areas for red blood cell formation and storage and for the trapping of immune proteins called antigens.
• White pulp – areas of special immune response cells called lymphocytes and reticuloendothelial cells
• Marginal zone – an area that separates the white and red pulp and helps to filter the blood.

What Are the Functions of the Spleen in Dogs?

The spleen has five main functions:

• Hematopoiesis – The spleen produces certain blood cells and is the major site outside the bone marrow where red blood cells are made.
• Blood reservoir – The spleen is a storage site for red blood cells and platelets (clotting elements). The body has the ability to contract the spleen suddenly if additional red blood cells are needed in the bloodstream.
• Blood filtration – The spleen removes old or abnormal blood cells and particles from the blood.
• Phagocytosis – The spleen traps and removes old cells, bacteria and foreign proteins from the circulation.
• Site of immune activities – The spleen is part of the body’s complicated immune system.

What Are Common Diseases of the Spleen in Dogs?

The spleen can be a site of primary disease involving only that organ or it may become involved in a disease that affects many parts of the body. As a general rule, dogs are prone to enlargement, tumors and other growths of the spleen. Some common diseases of the spleen are:

• Generalized enlargement of the spleen associated with immune system disorders, certain anemias, massive production of red blood cells, and certain infections, following administration of some drugs
• Development of a hematoma (collection of blood) or blood clots from trauma, bleeding disorders, or bleeding tumors
• Enlargement and congestion of the spleen from twisting of the splenic blood vessels. Twisting or torsion of the spleen may accompany gastric (stomach) dilatation and torsion, a serious problem in larger breed, deep chested dogs.
• Benign tumors, such as hemangioma
• Malignant tumors/cancers, such as hemangiosarcoma. Hemangiosarcoma is a common malignant cancer in middle aged to elderly dogs, especially large breed dogs. It is a cause of serious disease or death in elderly dogs.
• Other malignant tumors, such as mast cell tumors, multiple myeloma and lymphosarcoma

What Types of Diagnostic Tests Are Used to Evaluate the Spleen?

Several tests are particularly helpful in evaluating the spleen. These include

• A complete blood count (CBC), microscopic examination of the blood smear, bone marrow aspiration, abdominal radiographs (X-rays), and tests that screen for infectious diseases or certain cancers.
• An abdominal ultrasound examination may identify abnormal splenic tissue and allow a fine-needle aspiration or biopsy to be performed on the spleen.
• Tissue is retrieved for cytology (analysis of the cells) and sometimes culture. In some cases an actual piece of spleen may be needed to reach a diagnosis. This is often done during abdominal surgery.
• In some cases exploratory surgery of the abdomen may be required to identify the underlying problem, and to remove a diseased spleen. Although the spleen is an important organ, but it is not needed for survival and many animals live healthy lives following splenectomy.