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
List options of splenic biopsy
- Tru-cut (not if cavitary)
- Direct surgical (needle biopsy, pinch or punch, partial splenectomy
- Laparoscopic
- Transgastric endoscopic sampling
What suture/pattern is recommended for splenorrhaphy
- 4-0 to 5-0 monofilament rapidly absorbable in an interrupted mattress pattern
List some options for partial splenectomy
- Suture (continuous with second line of continuous or interrupted mattress)
- CO2 laser
- Ultrasonic cutting device
- Vessel sealing device
- Bipolar electrosurgical devices
What is the maximum vessel size for a haemostatic clip?
3mm
What breeds are overrepresented for splenic torsion?
Great Danes, Saint Bernards, GSD, Irish Setters
What condition is splenic torsion hypothesised to occur concurrently with?
What additional procedure is strongly recommended during surgery if the patient is stable enough?
- GDV
- Gastropexy strongly recommended
What substances can be released if a splenic torsion if derotated?
- Sequestered blood, thrombi and microthrombi
- Free radicals
- TNF
- vasoactive compounds
What % nontraumatic heamoabdomen is from the spleen?
What % are HSA?
- Splenic haemorrhage in 73.6%
- HSA in 63.3%
List DDX for splenic neoplasia in dogs
- HSA
- undifferentiated sarcoma
- FSA
- OSA
- LSA
- myxosarcoma
- MCT
- Chondrosarcoma
- Lymphoma
What are the 2 most common forms of splenic neoplasis in cats?
- Lymphoma
- MCT
What are some negative prognostic indicators in dogs undergoing splenectomy of mass lesions?
- Marked preoperative thrombocytopaenia or anaemia
- Intraop ventricular arrhythmias
What is the main chemotherapeutic agent used for splenic HSA?
Doxorubicin - shown to increase survival after splenectomy
What are some other, less common, options for adjunctive Tx of splenic HSA?
- Liposomal encapsulated immunotherapy
- ## Intraperitoneal and oral continuous low-dose therapy (etoposide/cyclophosphamide/piroxicam)
List potential post-op complications after splenectomy
- Haemorrhage
- Vascular compromise (left pancreatic artery, portal vein thrombosis [PVT])
- Arrhythmias 35-44%
- SIRS, ARDS, DIC, PTE (marked preop thrombocytopaenia and anaemia and intraop arrhythmias identified as risk factors)
- GDV
- Infection (Splenectomized animals are at higher risk of infection)
- Oxygen transport - higher risk of hypoxia and ischaemia as have no splenic reserve (important for dogs with airway compromise e.g. BOAS, laryngeal paralysis, restrictive lung disease etc)
- IF BONE MARROW DISEASE –> catastrophic anemia and death following splenectomy
When should VPCs be treated?
- Haemodynamic instability
- Multiform ECG complexes
- Very rapid v-tach
- R-on-T complexes
What are hypothetised causes of arrhythmias?
What medication can be sent home if the arrhythmias have not resolved?
- Myocardial ischaemia and hypoxia secondary to reduced cardiac return and hypovolaemic shock as well as impaired venous return from compression (by the mass)
- Acid-base imbalances, microemboli, myocardial depressant factors associated with pancreatic ischaemia
- Lidocaine while in hopital
- Can go home on mexiletine or sotalol
What is the maximum vessel size for a haemostatic clip?
3mm
