AN54.1-4 | Radiodiagnosis — Summary & Reflection

REFLECT

You are the duty intern at midnight. A patient presents with sudden severe abdominal pain. The casualty officer asks you to choose ONE investigation first. What would you choose between an erect X-ray abdomen and an immediate CT abdomen, and why? Consider cost, radiation, speed, and diagnostic yield. Is there a scenario where you would choose differently?

KEY TAKEAWAYS

AN54 Radiodiagnosis — Key Points:

Principles (AN54.1):
• X-ray: 5 densities (metal/bone, soft tissue, fat, air, contrast) — differential absorption
• CT: cross-sectional, Hounsfield units, IV contrast for vascular/organ enhancement
• MRI: magnetic field + radiofrequency, T1 (fat bright) vs T2 (water bright), no radiation
• PET scan: 18F-FDG metabolic imaging, PET-CT for cancer staging
• DSA: intra-arterial contrast, digital subtraction, gold standard for vascular anatomy

Plain X-ray Abdomen (AN54.2):
• Gas under diaphragm (erect) = perforation — surgical emergency
• Rigler's sign = free gas on supine film
• Psoas shadow obliteration = retroperitoneal pathology
• Systematic review: bowel gas → organ outlines → calcifications → bones

Special Radiographs (AN54.3):
• Barium swallow → oesophagus (bird-beak = achalasia, rat-tail = carcinoma)
• Barium meal → stomach + duodenum (niche = ulcer, filling defect = tumour)
• Barium enema → colon (apple-core = carcinoma, thumbprinting = ischaemia)
• IVP → pelvicalyceal system + ureter + bladder; now supplemented by CT KUB
• HSG → uterine cavity + tubal patency (infertility workup)

CT/MRI/ERCP/Arteriography (AN54.4):
• ERCP = diagnostic + therapeutic for biliary/pancreatic disease
• MRCP = non-invasive biliary imaging; replaced diagnostic ERCP
• CT abdomen = acute abdomen, trauma, tumour staging, AAA
• MRI rectum = local rectal cancer staging
• Arteriography = vascular anatomy, embolisation, pre-operative mapping