Chapter 25 Diseases of the Spleen
The spleen can be the site of primary disease, or it can be affected by disease elsewhere as an active or passive participant. The spleen has hematopoietic, reservoir, filtering, and immunologic functions. The spleen may be affected by a variety of neoplastic and non-neoplastic disorders. It has an important role in responding to a number of infectious diseases through phagocytosis, antibody production, and modulation of hemoparasitic infections.
Splenic disorders usually are identified by a change in shape, size, and function of the spleen. Splenomegaly is defined as a localized or diffuse splenic enlargement. Splenomegaly generally can be detected on physical, radiographic, or ultrasonographic examination.
ANATOMY AND HISTOLOGY
Capsule and Trabeculae
White Pulp
Marginal Zone
Red Pulp
PHYSIOLOGY AND FUNCTION
Filtration Function
Immunologic Function
Reservoir Function
The canine spleen is able to store one-third of the dog’s red blood cell mass. This reservoir can be rapidly released, increasing the packed cell volume 10% to 20% in dogs and cats. The spleen also concentrates platelets. Up to one-third of the total body platelets are sequestered in the spleen.
Vigorous exercise results in a transient increase in the circulating platelet count. Margination of granulocytes occurs in the spleen as well.
Hematopoietic Function
ETIOLOGY
Splenic disorders can be separated into two categories, localized or asymmetrical splenomegaly and generalized or symmetrical splenomegaly.
Causes of localized splenomegaly (Table 25-1) include the following:
Table 25-1 LOCALIZED SPLENOMEGALY
Non-neoplastic | Neoplastic |
---|---|
Nodular hyperplasia | Primary |
Hematoma | Hemangiosarcoma |
Abscess | Hemangioma |
Sarcoma | |
Metastatic |
Generalized splenomegaly (Table 25-2) may result from the following:
Localized Splenomegaly
The term localized splenomegaly refers to a localized palpable enlargement of the spleen. Most splenic masses are round and irregular and can be found in the left cranial or mid-abdomen. Localized splenomegaly may have a neoplastic or non-neoplastic cause.
Neoplasia
Hemangiosarcoma is the most common neoplastic splenic mass occurring in the dog but is rare in the cat.
Nodular Hyperplasia
Hematoma
Generalized Splenomegaly
Generalized splenomegaly refers to diffuse enlargement of the spleen. Four major categories of generalized splenomegaly exist: inflammatory and infectious, hyperplastic, congestive, and infiltrative.
Inflammatory and Infectious Disease
Hyperplastic Splenomegaly
Congestive Splenomegaly

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