Diseases of the spleen Flashcards
What are the roles of the spleen
The spleen has the following roles:
- immunological
- storage of erythrocytes and platelets
- extramedullary hematopoiesis
- blood filtration
Explain why we see a higher number of Heinz bodies in the normal cat than in the normal dog
Due to its high metabolic activity, the spleen contains some areas that are slightly anaerobic
- in this environment of relatively low oxygen, the membrane of old or damaged RBCs tends to become stiff and non-compliant
These RBCs are not flexible enough to pass through the microcirculation of the spleen and are thus removed by splenic macrophages
This process is highly efficient in “sinusoidal” spleens, but less so in the cat due to the “non-sinusoidal” nature in this species
- hence the higher number of Heinz bodies seen in RBCs of the normal cat
What are the general features of spleen diseases in cats
Diseases of the spleen in the cat are rather uncommon
Splenic disease is usually manifested as splenomegaly and tends to often be part of a systemic disease process in the cat
Describe the anatomy of the spleen
The spleen is composed of:
- an external capsule comprised of collagen, fibroblasts and elastic fibers which extends down into the splenic parenchyma as trabeculae
- "white pulp" which consists of germinal lymphoid nodules (primarily B-cells) and "free" lymphocytes around small arterioles (mostly T-cells) -"red pulp" that constitutes venous spaces, containing mostly erythrocytes and the structural reticular framework of the spleen where sits a significant number of macrophages
Describe the function of the spleen
Blood enters the spleen at the hilus and makes its way through small arterioles to capillaries terminating in the lymphoid nodules of the white pulp or to capillaries leading into the red pulp
- some of the arterioles entering the white pulp continue to the venous side of the circulation
Venous blood exists the spleen at the hilus and enters portal circulation
In many species (e.g., dogs, humans) the splenic sinuses are lined by special fenestrated endothelium, that mechanically filters the blood (a so-called sinusoidal spleen)
-cats have non-sinusoidal microcirculation (as ruminants and horses)
- most feline erythrocytes pass into the red pulp and flow directly into the venous circulation unimpeded by endothelial cells and unscrutinized by immune cells
Describe the patterns blood flow in the spleen
There are three patterns of blood flow through the spleen:
- 90% of the blood enters the rapid pool and flows through the spleen in 30 seconds
- the remainder flows through in approximately 8 minutes (intermediate pool) or 60 minutes (slow pool)
The proportion of blood flow through each compartment varies with physiological demand
Because of the nonsinusoidal nature of the feline spleen, splenic contraction does not result in the movement of as many erythrocytes into the circulation as it does in dogs
What are historical and physical findings for cats suffering splenic disease
Historical details for cats that are diagnosed with splenic disease can be frustratingly vague and non-specific
- inappetence or anorexia
- weight loss
- vomiting/diarrhea
The most reliable clinical signs is palpable splenomegaly, which may be due to focal or generalized enlargement
- however, in some cases non-specific abdominal enlargement and discomfort may be all that can be appreciated
Depending on the underlying cause, abnormalities of other organ systems may be detected such as hepatomegaly and/or lymph node enlargement
What would be your differentials for focal spleen enlargement
Infectious
- bacterial abscess
Neoplasia
- lymphoma
- hemangiosarcoma
- metastatic lesions
Non-neoplastic
- extramedullary hematopoiesis
- hematoma
- myelolipoma
- hyperplastic lymphoid nodules
What would be your differentials for diffuse splenic enlargement
Neoplastic
- systemic mastocytosis
- lymphoma
- multiple myeloma
- other myeloproliferative disorders
- malignant histiocytosis
Inflammatory
- hypereosinophilic syndrome
- IMHA
- lymphocytic-plasmacytic enteritis
Infectious
- hemoplasmosis
- systemic mycobacteriosis (e.g. M. avium)
- salmonellosis
- histoplasmosis
- sporotrichosis
- toxoplasmosis
- FeLV or FIV
Non-neoplastic
- amyloidosis
- extramedullary hematopoiesis
- pyruvate kinase deficiency
- excessive osmotic fragility
Congestive
- portal hypertension
- right-sided heart failure
What risk is greater in splenectomized cats
Splenectomized cats may be at higher risk of clinically significant hemotropic mycoplasma infections due to the fact that this organ plays a major role in removing parasitized RBCs from the circulation
Likewise, if the cat has questionable bone marrow function, it is inadvisable to remove the spleen, as extra-medullary hematopoiesis at this site may be all that is sustaining circulating blood cell levels
