Spleen

Trauma and salvage, ITP vs TTP, hereditary spherocytosis, OPSI/vaccination, and splenic artery aneurysm for the Surgery Shelf.

Sources: extracted/STEP2CK-Surgery.md (Spleen) + Trauma/Abdominal trauma; First Aid 2026 (first-aid-usmle-bible).

High-Yield Points

• Function: red pulp (85%) filters aged RBCs (pitting removes Howell–Jolly/Heinz bodies); white pulp (15%) clears poorly opsonized encapsulated bacteria and is the largest producer of IgM. Accessory spleen in ~20%, most commonly at the splenic hilum.
• Blunt splenic trauma: grade by the AAST scale on CT. Hemodynamically STABLE → nonoperative management (monitored bed, serial hematocrits; preserves immune function); UNSTABLE despite resuscitation → emergent laparotomy/splenectomy. After splenectomy, vaccinate against encapsulated organisms.
• ITP: autoimmune antiplatelet antibodies (made in spleen), normal-sized spleen, large platelets on smear; diagnosis of exclusion. 1st-line corticosteroids → IVIG if steroids fail → splenectomy for failure/relapse/steroid dependence (durable response 75–85%). ITP is the #1 nontraumatic indication for splenectomy.
• TTP: pentad (fever, MAHA, thrombocytopenia, renal, neuro); treat with plasmapheresis — splenectomy rarely indicated (key contrast with ITP). Death usually from intracerebral hemorrhage/ARF.
• Hereditary spherocytosis: spectrin/ankyrin membrane defect → nondeformable RBCs; ↑MCHC, spherocytes; splenectomy is curative; add cholecystectomy if pigment gallstones; defer to age >5 and vaccinate first. (Most common congenital hemolytic anemia requiring splenectomy.)
• OPSI: fulminant sepsis from encapsulated organisms (loss of IgM/clearance); #1 Streptococcus pneumoniae > H. influenzae > N. meningitidis; most episodes within 2 years; treat suspected OPSI with an immediate 3rd-generation cephalosporin. Higher risk in children and in splenectomy for hematologic disease.
• Vaccination: pneumococcus, meningococcus, Hib — ≥14 days BEFORE elective splenectomy (optimal antibody response) or ~14 days after emergency/trauma (or before discharge if follow-up is uncertain). Repeat pneumococcal q5–7 y; annual influenza.
• Splenic abscess: usually Streptococcus (e.g., septic emboli from endocarditis); splenectomy is standard (percutaneous drainage risks bleeding).
• Splenic artery aneurysm: most common visceral artery aneurysm, more common in women (multiparity, portal HTN); repair if symptomatic, >2 cm, or in women of childbearing age/pregnancy — rupture risk is high in pregnancy with severe maternal/fetal mortality.

Key Tables / Differentials

ITP vs TTP

Post-splenectomy / hyposplenism blood smear

Board Pearls

• General indications for splenectomy: symptomatic splenomegaly, hypersplenism, hemolytic anemia/cytopenia (another disease alone is not an indication without one of these).
• Recurrent ITP after splenectomy + absent Howell–Jolly bodies = missed accessory spleen → locate (nuclear scan) and excise.
• Most common complication during splenectomy = bleeding during hilar dissection; look for an accessory spleen before closing in hematologic disease.
• Post-splenectomy platelets >1 × 10⁶ → give aspirin.
• Felty syndrome = RA + splenomegaly + neutropenia; Wandering spleen = absent peritoneal attachments → torsion → detorsion + splenopexy.

Classic Vignette Triggers

• "MVA, stable, left rib fractures, low-grade splenic laceration on CT" → nonoperative management.
• "MVA, hypotensive despite blood, positive FAST in LUQ" → emergent splenectomy.
• "Petechiae, platelets 18k, normal spleen, large platelets" → ITP → corticosteroids.
• "Anemia, jaundice, splenomegaly, ↑MCHC, spherocytes, gallstones" → hereditary spherocytosis → splenectomy + cholecystectomy.
• "Asplenic patient, fulminant sepsis hours after onset" → OPSI (S. pneumoniae) → 3rd-gen cephalosporin.
• "Pregnant woman, incidental 2.5 cm splenic artery aneurysm" → repair (high rupture risk in pregnancy).