Functions Of The Spleen

Anatomical Basis Of Splenic Function

• Spleen precursor recognizable by 5 weeks gestation.
• Weighs approximately 11 g at birth; enlarges to 150 g by puberty.
• Comprises two major functional compartments: white pulp and red pulp.
• White pulp: Lymphoid compartment containing periarterial lymphatic sheaths (T-zone) and germinal centers (B lymphocytes).
• Red pulp: Filtering system composed of fixed reticular cells, mobile macrophages, endothelial passages (cords of Billroth), and splenic sinuses.
• Perifollicular zone: Separates red and white pulp; rich in dendritic cells and natural killer cells.
• Receives 5-6% of cardiac output.

Reservoir Function

• Normal capacity retains 25 mL of blood; expands massively during splenomegaly.
• Sequesters specific blood components: Factor VIII, iron, plasmablasts, and plasma cells.
• Stores one-third of circulating platelet mass.
• Releases stored components upon stress or epinephrine stimulation.

Filtration And Clearance

• Slow blood flow through macrophage-lined small openings filters particles >1 micron.
• Removes excess membrane from young red blood cells (RBCs).
• Functions as primary site for destruction of senescent RBCs.
• Eliminates damaged or abnormal RBCs (e.g., spherocytes, antibody-coated RBCs).
• Phagocytoses damaged and senescent platelets.
• "Pitting" function: Removes intracytoplasmic inclusions (Howell-Jolly bodies, Heinz bodies) without inducing cell lysis.

Immunologic And Host Defense

• Constitutes largest lymphoid organ in the body.
• Contains nearly 50% of total body immunoglobulin-producing B lymphocytes.
• Processes foreign material to stimulate opsonizing antibody production.
• Generates B and T cell responses upon antigenic challenge.
• Synthesizes immune-mediating proteins: complement, opsonins, properdin, tuftsin.
• Traps and destroys intracellular parasites via phagocytosis.
• Executes early antibody production following intravenous antigen exposure.
• Mediates pathogenesis of immune-mediated cytopenias via macrophage phagocytosis of antibody-coated cells.

Hematopoiesis

• Functions as major site of red pulp hematopoiesis during 3-6 months of fetal life.
• Ceases hematopoiesis postnatally.
• Resumes extramedullary hematopoiesis in severe hemolytic anemia or myelofibrosis.

Indications For Splenectomy

Hematological Disorders

Red Blood Cell Membrane Defects

• Hereditary Spherocytosis (HS):
  • Curative in most patients; eradicates hemolysis, anemia, and hyperbilirubinemia.
  • Indicated for severe HS (transfusion-dependent).
  • Strongly considered for moderate HS exhibiting frequent hypoplastic/aplastic crises, poor growth, or cardiomegaly.
  • Generally avoided in mild HS.
  • Postponed until after 6 years of age to minimize postsplenectomy sepsis risk.
• Hereditary Elliptocytosis (HE): Considered for chronic HE and hereditary pyropoikilocytosis requiring transfusions.

Red Blood Cell Enzyme Defects

• Pyruvate Kinase Deficiency: Decreases transfusion requirements but does not arrest hemolysis. Triggers paradoxical reticulocytosis post-surgery.
• Glucose-6-Phosphate Dehydrogenase (G6PD) Deficiency: Splenectomy rarely ameliorates severe anemia; reserved exclusively for severe hypersplenism or physical impediment from massive splenomegaly.

Immune-Mediated Cytopenias

• Immune Thrombocytopenic Purpura (ITP):
  • Indicated for older children (≥4 years) with chronic ITP (>1 year duration) refractory to medical therapy.
  • Indicated for acute, life-threatening hemorrhage (e.g., intracranial hemorrhage) unresponsive to rapid platelet transfusion, intravenous immunoglobulin (IVIG), and corticosteroids.
  • Induces complete remission in 64-88% of chronic pediatric cases.
• Warm Autoimmune Hemolytic Anemia (wAIHA):
  • Indicated if hemolysis remains brisk despite high-dose corticosteroids, rituximab, and transfusions.
  • Recommended for children >5 years of age with disease duration >6-12 months. Beneficial in 60-75% of patients.

Hemoglobinopathies

• Thalassemia Major/Intermedia:
  • Indicated for secondary hypersplenism causing falling steady-state hemoglobin or rising transfusion requirements.
  • Criteria include annual packed RBC requirement >200-250 mL/kg/year with uncontrolled iron overload.
  • Indicated for symptomatic massive splenomegaly posing rupture risk or causing severe leukopenia/thrombocytopenia.
• Sickle Cell Disease:
  • Prophylactic splenectomy indicated for recurrent, life-threatening acute splenic sequestration crises.
  • Prevents fatal hypovolemic shock associated with recurrent trapping of RBCs.

Non-Hematological And Structural Disorders

Splenic Trauma

• Indicated for massive abdominal bleeding and clinical instability.
• Indicated when conservative, non-operative management fails.
• Partial splenectomy or splenic repair preferred to preserve immune function.

Splenic Malignancies And Lesions

• Primary splenic tumors (e.g., Splenic Marginal Zone Lymphoma).
• Symptomatic splenic cysts, pseudocysts, or abscesses.

Conditions Contraindicating Splenectomy

• Autoimmune Lymphoproliferative Syndrome (ALPS): Extremely high risk of fatal sepsis despite prophylaxis.
• Hereditary Stomatocytosis and Hereditary Xerocytosis: High risk of severe venous thromboembolic complications post-surgery.
• Paroxysmal Cold Hemoglobinuria and Cold Agglutinin Disease.
• Hepatic cirrhosis with thrombocytopenia.

Complications Of Splenectomy

Overwhelming Post-Splenectomy Infection (OPSI)

• Represents most severe, life-threatening long-term risk.
• Highest risk in children <5 years of age at time of surgery.
• Overall risk: 2-5 per 1000 asplenic patient-years; lifelong risk of 5%.
• Over 50% of OPSI episodes occur within first 2 years post-splenectomy.
• Risk magnitude varies by underlying disease: 2-4% in trauma or ITP; 8-30% in thalassemia, sickle cell disease, or preexisting reticuloendothelial blockade.
• Pathogens: Encapsulated bacteria dominate. Streptococcus pneumoniae (>60% of cases), Haemophilus influenzae, and Neisseria meningitidis.
• Animal Bites: High risk for fulminant sepsis from Capnocytophaga canimorsus or C. cynodegmi following dog bites/licks.
• Protozoal Infections: Increased susceptibility to severe malaria and babesiosis.
• Clinical Course: Rapid progression to fulminant sepsis and meningitis; death frequently ensues within 12-24 hours of onset.

Thromboembolic Complications

• Increased risk of arterial and venous thrombosis.
• Attributed to loss of splenic filtering function, permitting abnormal RBCs to circulate and activate coagulation cascades.
• Post-operative thrombocytosis common; usually resolves spontaneously but contributes to transient hypercoagulability.
• Portal vein thrombosis specifically reported as complication following laparoscopic splenectomy.

Pulmonary Hypertension

• Late complication increasingly recognized post-splenectomy.
• Particularly prevalent when splenectomy performed for chronic hemolytic conditions (Thalassemia, Sickle Cell Disease, Hereditary Spherocytosis).
• Pathogenesis linked to ongoing chronic hemolysis and circulation of procoagulant erythrocyte microparticles previously cleared by spleen.

Surgical And Perioperative Complications

• Splenectomy failure/relapse: Due to un-resected accessory spleens or accidental autotransplantation of splenic tissue (splenosis) during surgery.
• General surgical risks: Hemorrhage, adjacent organ injury (pancreatic tail), anesthesia complications.

Post-Operative Management And Preventive Care

Principles Of Splenic Preservation

• Defer total splenectomy until patient reaches ≥5 years of age whenever possible to mitigate OPSI risk.
• Utilize laparoscopic approach to decrease surgical morbidity and hospitalization duration.
• Consider partial or subtotal splenectomy (removing 85-95% of volume): Decreases hemolytic rate while preserving residual phagocytic immune function.

Immunization Protocol

• Administer vaccines at least 14 days prior to elective splenectomy.
• Pneumococcal Vaccines: 13-valent pneumococcal conjugate vaccine (PCV13) followed by 23-valent pneumococcal polysaccharide vaccine (PPSV23) at age ≥2 years. Second dose of PPSV23 administered 5 years later.
• Meningococcal Vaccine: Administer protein-conjugated formulations.
• Haemophilus influenzae type b (Hib) Vaccine: Ensure up-to-date status.
• Influenza Vaccine: Administer yearly; prevents viral illness that predisposes to secondary pneumococcal infections.

Antimicrobial Prophylaxis

• Essential component of post-splenectomy management to prevent fatal sepsis.
• Agent: Oral Penicillin VK.
• Dosing:
  • Children <5 years: 125 mg twice daily.
  • Children ≥5 years: 250 mg twice daily.
• Duration: Continue until at least 5 years of age, and strictly for a minimum of 2 years post-splenectomy.
• Lifelong Prophylaxis: Strongly considered for high-risk patients (e.g., Sickle Cell Disease, history of invasive pneumococcal infection, underlying immune deficiency).

Acute Fever Management

• Febrile episodes in splenectomized patients constitute medical emergencies.
• Empiric Home Therapy: Initiate amoxicillin-clavulanate or cefdinir immediately if access to medical care is delayed.
• Hospital Management: Prompt blood cultures followed by immediate administration of broad-spectrum intravenous cephalosporin (cefotaxime or ceftriaxone).
• Resistant Organisms: Add Vancomycin empirically to cover penicillin-resistant pneumococci based on illness severity and local susceptibility patterns.

Additional Preventative Measures

• Animal Bites: Administer prophylactic antibiotics immediately after dog bites/licks to prevent Capnocytophaga sepsis.
• Travel Counseling: Advise against travel to malaria or babesiosis endemic areas without stringent prophylaxis and mosquito avoidance.
• Medical Alert: Patient must wear a medical alert bracelet denoting asplenic status.
• Surveillance: Monitor for thromboembolic disease and pulmonary hypertension via clinical evaluation and echocardiography.