A 48-year-old man with heavy alcohol use presents with severe epigastric pain radiating to the back, persistent vomiting, and abdominal distension for 36 hours. He is tachycardic (HR 118), hypotensive (BP 92/58), and febrile (38.9°C). Cullen and Grey-Turner signs are present. Serum lipase is 4,200 U/L and RANSON score is 4 at admission. Contrast-enhanced CT abdomen at 72 hours shows a diffusely enlarged pancreas. The structure marked **A** in the diagram demonstrates extensive non-enhancing parenchyma involving more than 30% of the gland. What is the CT Severity Index (CTSI) score and its associated mortality risk in this patient?

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D. CTSI 10/10 with 17% mortality risk. ## Why CTSI 10/10 with 17% mortality risk is right The structure marked **A** — non-enhancing necrotic pancreatic parenchyma involving >30% of the gland — is the hallmark of necrotising acute pancreatitis. According to the 2012 Atlanta Classification (Banks PA et al., Gut 2013), the CT Severity Index (CTSI) is calculated as: Balthazar grade (0–4) + extent of necrosis score (0–6). In this case, the diffusely enlarged pancreas with extensive peripancreatic fluid collections represents Balthazar Grade E (4 points), and >30% necrosis contributes 6 points, yielding CTSI = 10/10. The 2012 Atlanta Classification explicitly correlates CTSI 10 with 17% mortality and 92% morbidity in necrotising pancreatitis. This patient's clinical presentation (Cullen/Grey-Turner signs, RANSON 4, BISAP 4, APACHE II 18, metabolic acidosis, hypoxemia) all confirm severe necrotising disease with organ failure, validating the high CTSI and mortality prediction. ## Why each distractor is wrong - **CTSI 8/10 with 8% mortality risk**: This would correspond to Balthazar D (3 points) + 30% necrosis (5 points), or Balthazar E with <30% necrosis. The imaging clearly shows >30% necrosis and Grade E morphology, not Grade D or lesser necrosis extent. CTSI 8 carries only 8% mortality, which underestimates this patient's severe disease. - **CTSI 6/10 with 3% mortality risk**: This represents Balthazar C (2 points) + 30% necrosis (4 points), or Balthazar D with minimal necrosis. The patient has Grade E (diffuse enlargement with extensive peripancreatic collections), not Grade C or D. CTSI 6 is associated with mild-to-moderate disease and 3% mortality, which is inconsistent with the clinical severity and imaging findings. - **CTSI 4/10 with <1% mortality risk**: This would indicate Balthazar B (1 point) + minimal necrosis (3 points), representing mild acute pancreatitis without significant necrosis. The patient has extensive non-enhancing parenchyma (>30%) and Grade E disease, making CTSI 4 inappropriate. This score is seen in uncomplicated pancreatitis with negligible mortality. **High-Yield:** CTSI = Balthazar grade (0–4) + necrosis extent (0–6); CTSI 10 (Balthazar E + >30% necrosis) = 17% mortality; necrotising pancreatitis requires delayed step-up approach after 4 weeks of walling-off. [cite: Banks PA et al. Classification of acute pancreatitis—2012: revision of the Atlanta classification. Gut 2013;62(1):102-111.]

Answer

A. CTSI 6/10 with 3% mortality risk

Answer

B. CTSI 4/10 with <1% mortality risk

Answer

C. CTSI 8/10 with 8% mortality risk

Explanation

Why CTSI 10/10 with 17% mortality risk is right

Why each distractor is wrong

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