On CT abdomen for a patient with acute pancreatitis, the CT Severity Index (CTSI) includes both the Balthazar grade and the degree of pancreatic necrosis. A patient with grade D (single poorly-defined peripancreatic fluid collection) and 30% gland necrosis has a CTSI score of:

• A 4
• B 5
• C 7
• D 6 ✓

Explanation

The CT Severity Index (CTSI) = Balthazar grade points + pancreatic necrosis points. Balthazar grades: A=0, B=1, C=2, D=3, E=4 — Grade D (a single ill-defined peripancreatic fluid collection) scores 3. Necrosis points: none=0, <30%=2, 30–50%=4, >50%=6 — so 30% necrosis falls in the 30–50% band and scores 4. CTSI = 3 + 4 = 7, corresponding to severe acute pancreatitis (CTSI 7–10).

Reference: Grainger & Allison's Diagnostic Radiology, 7th ed.

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