Ch 83 - Spleen Flashcards
How much of the BW is the spleen in dogs and cats?
0.2%
What are the braod functions of the red pulp and white pulp of the spleen?
- Red pulp: stores erythrocytes and traps antigens. Site of foetal erythropoietis
- White pulp: SIte of immune response
What is the main anatomincal difference between the spleen in the dog and cat?
- Dogs have a sinusoidal spleen - combo of direct arteriovenous endothelial connections and some areas where RBCs must traverse a region of red pulp between vessels prior to entering the venous side
- Cats have a nonsinusoidal spleen - direct connection between arterial and venous circulation
List three braod functions of the spleen
- Haematopoiesis
- Reservoir function
- Immunologic function
How does the spleen take part in maturation of RBCs?
After production in the bone marrow, RBCs spend several days in the spleen maturing
- Intracellular material is removed
- Cell membrane is shaped into a disc
- Cell size is reduced
What are some causes for the spleen to filter out/cull RBCs?
Damaged or senile RBCs are filtered out by the spleen due to
- Inelastic cells (spherocytes, acanthocytes)
- RBCs covered with immunoglobulin or intracellular bacteria
Iron is stored in the spleen as ferritin and haemosiderin until transported to the bone marrow for haematopoiesis
How much of a dogs RBC mass and platelet mass can the spleen store?
- 10-20% RBC mass
- 30% platelet mass
What are the three pools of blood travelling through the spleen?
- Rapid pool: Approx 90% of the blood entering the spleen, takes less than 30 seconds to rejoin systemic circulation
- Intermediate pool: 9% circulating blood, 8 minutes to rejoin systemic circulation
- Slow pool: 1% of circulating blood, takes 1 hour
What immune cells is the spleen the largest producer of?
- B-cells
- T-cells
- IgM
What is the main method by which the spleen filters microorganisms from the blood?
Phagocytosis
List some broad causes of generalised splenomegaly
- Splenitis/inflammation (sepsis, chronic Ix, bacteraemia)
- Immune reaction or cellular hyperplasia (proliferation of normal cellular components)
- Congestion (CHF, vascular outflow obstruction, portal hypertension, capsule relaxation)
- Infiltration (neoplasia, amyloidosis)
List some causes of localised splenomegaly
- Nodular hyperplasia
- Pseudotumour (benign proliferation of plasma cells, lymphocytes and histiocytes
- Haemangioma
- Hamartoma (rare, benign proliferation of mature cells and tissue which are normally present)
- Abscess
- Cysts
- Segmental infarction
- Siderotic and siderocalcific plaques
- Neoplasia
List some differentials for hypoechoic and hyperechoic lesions of the spleen on ultrasound
Hypoechoic
- Lymphoid infiltration
- Infarction
- Necrosis
- Congestion
Hyperechoic
- Nodular hyperplasia
- Neoplasia
- Fibrosis from healed infarction or haematoma
What ultrasound finding is commonly seen with splenic torsion?
Hilar perivenous hyperechoic triangle
How can HSA be differentiated from nodular hyperplasia or haematomas on CT scan?
- HSA will have lower density (lower Hounsfield units) on pre- and post-contrast images