Acute splenic sequestration crisis (ASSC) is a life-threatening emergency in sickle cell disease (SCD) defined by rapid splenic enlargement with a hemoglobin drop ≥2 g/dL below baseline, often accompanied by thrombocytopenia and reticulocytosis. [1-2] It is the second most common cause of death in the first decade of life in SCD (accounting for 15–44% of deaths in this period), and the most common cause of acute anemia in children with SCD. [2-3]
1. History
- Onset and tempo: Abrupt onset of abdominal fullness, left upper quadrant (LUQ) pain, or generalized abdominal distension — can progress over hours [2-3]
- Pallor: Parents may notice sudden pallor, listlessness, or irritability [4]
- Associated symptoms: Nausea, vomiting, lethargy, weakness, breathlessness, rapid heart rate [3-4]
- Preceding illness: Often follows a febrile illness or viral infection [4]
- Baseline hemoglobin: Always establish the patient's steady-state hemoglobin — a drop ≥2 g/dL defines the crisis [1][5]
- Prior episodes: Recurrence rate is ~50%, with diminishing intervals between crises [3][6]
- Caregiver awareness: Ask if parents have been trained in splenic palpation and whether they noticed progressive enlargement [1][6]
- Important negatives: Absence of jaundice progression (helps distinguish from aplastic crisis), no recent transfusion (rules out delayed hemolytic transfusion reaction) [2][5]
2. Alarm Features
- Cardiovascular collapse/hypovolemic shock — tachycardia, hypotension, poor perfusion, altered mental status [2][4]
- Rapidly enlarging spleen with hemoglobin dropping precipitously [1]
- Hemoglobin <5 g/dL or >2 g/dL below baseline with hemodynamic instability [5]
- Concurrent fever — raises concern for sepsis in a functionally asplenic patient [1]
- Altered consciousness or neurologic changes — may indicate concurrent stroke or hyperviscosity [2]
- Severe cases may progress to death within hours without intervention [3-4]
3. Medications
- Emergency RBC transfusion is the cornerstone of treatment — transfuse in small aliquots of 3–5 mL/kg, checking post-transfusion hemoglobin before each subsequent aliquot [1][7]
- Avoid overtransfusion: Target hemoglobin should not exceed 8–10 g/dL (NHLBI recommends avoiding >8 g/dL; AAP recommends avoiding >10 g/dL), as sequestered RBCs will re-enter circulation as the crisis resolves, risking hyperviscosity syndrome [1-2][5]
- IV fluid resuscitation for hypovolemia — isotonic crystalloid boluses as needed [5]
- Hydroxyurea: Disease-modifying therapy that may alter the natural history of splenic complications; not a treatment for the acute crisis itself [4][8]
- Prophylactic penicillin: All young children with SCD should be on penicillin prophylaxis given functional asplenia [4]
- Vaccinations: Ensure pneumococcal, meningococcal, and Haemophilus influenzae type b vaccines are up to date [4]
- Caution with ceftriaxone: If given for concurrent fever, observe for drug-induced hemolysis [4]
4. Diet
- Hydration is critical — encourage adequate oral fluids when able; IV hydration in the acute setting
- Avoid dehydration, which can precipitate sickling and worsen sequestration
- No specific dietary triggers for ASSC, but general SCD dietary guidance includes adequate folate intake and avoidance of dehydration
- Long-term: Ensure adequate caloric intake, as chronic hypersplenism can impair growth and development [8]
5. Review of Systems
- Constitutional: Fever, fatigue, lethargy, irritability
- Cardiovascular: Palpitations, dizziness, syncope, exercise intolerance
- Respiratory: Dyspnea, chest pain (evaluate for concurrent acute chest syndrome) [4]
- GI: Abdominal pain/distension, nausea, vomiting, early satiety
- Neurologic: Headache, vision changes, focal deficits (stroke screening)
- Musculoskeletal: Bone pain (concurrent vaso-occlusive crisis)
- GU: Dark urine (hemoglobinuria), decreased urine output (hypovolemia)
6. Collateral History and Family History
- SCD genotype — HbSS, HbSC, HbSβ⁰-thalassemia, HbSβ⁺-thalassemia — determines risk profile [9]
- Siblings with SCD — may need concurrent evaluation, especially if exposed to parvovirus B19 [5]
- Prior splenic sequestration episodes in the patient or family members
- Baseline spleen size — parents trained in palpation can provide critical comparison [1][6]
- Transfusion history — alloimmunization status, prior reactions
- Social context: Access to emergency care, caregiver education level, distance from hospital
7. Risk Factors
- Age: Most common in HbSS children <5 years (median onset ~1.4 years); can occur in HbSC adolescents and adults [1][9]
- Genotype: HbSβ⁰ > HbSS > HbSC in cumulative prevalence of ASSC [9]
- Preceding febrile illness or viral infection [4]
- Low baseline HbF levels — high HbF is protective [6]
- Retained splenic tissue — patients who have not yet undergone autoinfarction remain at risk [9]
- Prior ASSC — recurrence rate ~50–78% [2-3]
- Lifetime prevalence: 7–30% in children with SCD [2][9]
The following figure illustrates the cumulative prevalence of splenic complications by genotype in pediatric SCD:
8. Differential Diagnosis
- Aplastic crisis (parvovirus B19) — acute anemia with low reticulocyte count (distinguishing feature: reticulocytes are elevated in ASSC, suppressed in aplastic crisis) [2]
- Delayed hemolytic transfusion reaction — occurs within 28 days of transfusion; may mimic sequestration with falling hemoglobin [2][5]
- Hepatic sequestration — right-sided enlargement, elevated LFTs
- Acute chest syndrome — may coexist; fever + respiratory symptoms + new pulmonary infiltrate [4]
- Sepsis/bacteremia — functional asplenia increases risk; fever with hemodynamic instability [1]
- Splenic abscess or infarction — LUQ pain with fever; imaging distinguishes
- Malaria (in endemic regions) — splenomegaly with hemolysis
- Hypersplenism (chronic) — gradual onset, chronic cytopenias, distinguished from acute crisis by tempo [3][8]
9. Past Medical History
- SCD genotype and baseline hemoglobin/reticulocyte count — essential for comparison [5]
- Prior ASSC episodes — number, severity, management
- Prior splenectomy (total or partial) — if splenectomized, ASSC is essentially excluded
- Transfusion history — alloantibodies, iron overload status
- Hydroxyurea use — may alter splenic natural history [4][8]
- Chronic transfusion program — may delay but not prevent recurrence [7]
- Vaccination and penicillin prophylaxis status [4]
- History of stroke, ACS, or other SCD complications
10. Physical Exam
- Vitals: Tachycardia (often the earliest sign), hypotension, tachypnea, fever
- General: Pallor, diaphoresis, lethargy, irritability (especially in infants)
- Abdomen:
- Rapidly enlarging, palpable spleen — compare to known baseline; may cross midline in severe cases [1][3]
- LUQ tenderness, abdominal distension
- Assess for hepatomegaly (concurrent hepatic sequestration)
- Cardiovascular: Gallop rhythm, flow murmur, capillary refill >3 seconds, weak pulses
- Skin: Pallor of conjunctivae, palms, nail beds; jaundice
- Neurologic: Mental status assessment — altered sensorium suggests severe hypovolemia or concurrent CNS event
11. Lab Studies
- CBC with differential and reticulocyte count — compare to baseline; hemoglobin drop ≥2 g/dL with elevated reticulocyte count (up to 25% above baseline) is diagnostic [2][5]
- Platelet count — mild-to-moderate thrombocytopenia (<150,000/μL) is typical [1-2]
- Type and crossmatch — urgent; extended antigen matching (ABO, Rh C/c/D/E/e, Kell) to reduce alloimmunization [10]
- Peripheral smear — sickled cells, Howell-Jolly bodies (functional asplenia), nucleated RBCs
- Comprehensive metabolic panel — assess renal function, LFTs (hepatic sequestration), electrolytes
- LDH, haptoglobin, indirect bilirubin — hemolysis markers
- Blood culture — if febrile (low threshold) [1][4]
- Parvovirus B19 IgM — if reticulocyte count is low (to distinguish aplastic crisis) [2]
- Serial hemoglobin monitoring — repeat after each transfusion aliquot and q2–4h during acute phase [1]
12. Imaging
- Abdominal ultrasound — confirms splenomegaly, assesses splenic echotexture, rules out splenic abscess/infarction, evaluates for hepatic sequestration
- Chest X-ray — if any respiratory symptoms or fever, to evaluate for concurrent ACS [4]
- CT abdomen — generally not first-line; may be useful if abscess, infarction, or surgical complication suspected
- Imaging is often unnecessary for straightforward ASSC when clinical and lab findings are classic — diagnosis is primarily clinical [1-2]
13. Special Tests
- Hemoglobin electrophoresis/HPLC — confirms SCD genotype if not previously documented; quantifies HbS and HbF levels
- Extended RBC antigen phenotyping — critical before first transfusion to guide future matching [10]
- Transcranial Doppler (TCD) — not acutely indicated for ASSC but part of routine SCD screening for stroke risk
- Splenic scintigraphy — can assess residual splenic function; not used in the acute setting
- Point-of-care ultrasound (POCUS) — rapid bedside assessment of spleen size and free fluid
14. ECG
- Indications: Obtain if tachycardia is disproportionate, chest pain is present, or hemodynamic instability
- Expected findings: Sinus tachycardia from anemia/hypovolemia
- Concerning patterns: ST changes suggesting myocardial ischemia from severe anemia, arrhythmias from electrolyte derangements
- Chronic SCD changes: May show LVH or biventricular hypertrophy from chronic anemia
15. Assessment
Acute splenic sequestration crisis is a clinical diagnosis based on the triad of rapidly enlarging spleen + hemoglobin drop ≥2 g/dL below baseline + reticulocytosis, often with thrombocytopenia. [1-3] Severity ranges from mild (hemodynamically stable, moderate hemoglobin drop) to life-threatening (cardiovascular collapse). It is most common in HbSS children under 5 years but can occur at any age in any SCD genotype. [1][9] The key pathophysiology is acute trapping of sickled RBCs within the splenic sinusoids, causing effective hypovolemia despite total body RBC mass being preserved. [3]
Complications to anticipate:
- Hypovolemic shock and death (can occur within hours) [3-4]
- Hyperviscosity syndrome post-transfusion when sequestered cells are released [2][5]
- Recurrence (~50–78%) [2-3]
- Concurrent infection/sepsis [1]
16. Treatment Plan
Initial stabilization:
- ABCs — supplemental O₂, cardiac monitoring, two large-bore IVs
- IV isotonic crystalloid bolus (20 mL/kg) for hypovolemia — repeat as needed [5]
Transfusion:
- Simple RBC transfusion in small aliquots (3–5 mL/kg) — check hemoglobin after each aliquot before ordering the next [1][7]
- Target hemoglobin: restore to a stable level but avoid exceeding 8–10 g/dL to prevent hyperviscosity when sequestered cells auto-transfuse back into circulation [1][5]
- Use extended antigen-matched, sickle-negative blood [10]
- Exchange transfusion is generally not indicated for isolated ASSC
Concurrent management:
- Empiric parenteral antibiotics (e.g., ceftriaxone) if febrile [1][4]
- Pain management as needed (avoid NSAIDs if thrombocytopenic)
- Consult hematology/sickle cell specialist early [5]
Prevention of recurrence:
- Splenectomy — recommended after recurrent ASSC or a single life-threatening episode; typically deferred until age >2–3 years when possible to reduce post-splenectomy sepsis risk [5-6]
- Chronic transfusion therapy — may be used as a bridge to delay splenectomy in very young children, though evidence of benefit is limited [5][7]
- Partial splenectomy has been proposed to preserve some splenic function, though residual function may be transient [8]
17. Disposition
- All patients with ASSC require admission — this is a medical emergency [4-5]
- ICU admission for hemodynamic instability, hemoglobin <5 g/dL, need for aggressive resuscitation, or altered mental status
- Monitored bed for hemodynamically stable patients — serial hemoglobin checks q2–4h, serial abdominal exams
- Hematology consultation — mandatory for transfusion guidance and discussion of splenectomy timing [5]
- Surgical consultation if splenectomy is being considered
- Never discharge during the acute phase — risk of rapid re-sequestration and rebound hyperviscosity
18. Follow Up / Return Precautions
- Post-discharge follow-up with hematology within 1–2 weeks to reassess hemoglobin, spleen size, and discuss splenectomy planning [5]
- Parent/caregiver education:
- Daily splenic palpation — report any increase in size immediately [1][6]
- Recognize pallor, lethargy, irritability, abdominal distension as warning signs
- Seek emergency care immediately for any of the above
- Return precautions: Fever ≥38°C (100.4°F), increasing pallor, abdominal distension, lethargy, poor feeding, vomiting, or any signs of cardiovascular compromise
- Expected course: Spleen typically decreases in size over days as sequestered cells are released; hemoglobin may rise above pre-transfusion levels during this phase
- Vaccination update: Ensure pneumococcal (PCV and PPSV23), meningococcal, and Hib vaccines are current; if splenectomy is planned, administer vaccines ≥2 weeks prior [4]
- Long-term: Discuss hydroxyurea initiation if not already on therapy; address recurrence prevention strategy (splenectomy vs. chronic transfusion) with the sickle cell team [5][8]
References
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