A 63-year-old man reports left lower quadrant abdominal pain that has steadily worsened over two days, accompanied by nausea and a fever measured at home.

One similar episode two years ago that resolved with oral antibiotics. Chronic constipation managed with intermittent laxatives and a habitually low-fiber diet. No recent travel, no sick contacts, and no blood in the stool.

HR 98, BP 142/86, RR 18, Temp 38.2 °C, SpO2 98% on room air. He appears uncomfortable but is well perfused.

Focal tenderness in the left lower quadrant with voluntary guarding and a vague palpable fullness. No rebound tenderness and no rigidity. Bowel sounds are hypoactive. He reports urinary urgency but no dysuria.

WBC 14,800/µL. C-reactive protein 62 mg/L. Lactate 1.4 mmol/L. CT of the abdomen and pelvis with contrast shows sigmoid wall thickening to 8 mm, pericolic fat stranding, and a contained 2 cm phlegmon without free air or abscess.

Diagnose It — Archive Puzzle #33