Clinical Practice: Abdominal Imaging
Core concepts
Abdominal imaging questions test pattern recognition across modalities. For the acute abdomen, know when ultrasound is first-line (right upper quadrant pain suggesting cholelithiasis, pelvic pain suggesting adnexal torsion) versus CT (nonspecific abdominal pain, suspected diverticulitis, small bowel obstruction). Understand the CT signs of bowel ischemia (pneumatosis, portal venous gas, decreased wall enhancement) and the distinction between simple and complicated appendicitis.
Traps in questions
- Mislabeling a dilated fluid-filled bowel loop as obstruction when it is ileus; look for a transition point.
- Overcalling a cystic pancreatic lesion as malignant without ductal dilation or solid component.
- Forgetting that renal colic CT should be noncontrast to detect stones.
- Confusing a hepatic hemangioma (peripheral nodular enhancement with centripetal fill-in) with metastasis.
Rule of thumb
Small bowel obstruction: loops greater than 3 cm with a transition point; large bowel obstruction: colon greater than 6 cm (cecum greater than 9 cm raises perforation risk).
Worked example
A patient with known diverticulosis presents with left lower quadrant pain and fever. CT shows a pericolic fluid collection with extraluminal gas. This is a complicated diverticulitis with abscess, not uncomplicated disease, and management differs (drainage versus antibiotics alone).