Emergency and Trauma · Abdomen and Pelvis
Acute Abdomen and Pelvic Emergency One-Liners
High-yield one-liners on emergency abdominal and pelvic imaging including bowel obstruction, perforation, appendicitis, mesenteric ischaemia and gynaecological emergencies.
Rapid-revision one-liners covering emergency imaging of the acute abdomen and pelvis, including bowel obstruction, perforation, inflammatory emergencies, mesenteric ischaemia and gynaecological emergencies.
- Free air on erect chest radiograph
- Erect chest radiograph detects pneumoperitoneum with sensitivity of approximately 70-80%; as little as 1-2 mL of free air may be visible under the diaphragm. Left lateral decubitus is an alternative in patients unable to stand.
- CT sensitivity for pneumoperitoneum
- CT detects pneumoperitoneum with sensitivity exceeding 95%, identifying even tiny volumes of free air; however, not all free air indicates perforation (post-procedure, post-surgical, peritoneal dialysis).
- Small bowel obstruction CT signs
- CT shows dilated small bowel loops (>2.5 cm), a discrete transition point, collapsed distal bowel and differential enhancement; closed-loop obstruction shows a U- or C-shaped dilated loop with a radial mesenteric vessel pattern.
- Large bowel obstruction
- CT identifies the transition point and cause (tumour, volvulus, stricture); caecal diameter >9 cm or transverse colon >6 cm raises concern for impending perforation.
- Sigmoid volvulus
- Sigmoid volvulus shows a massively dilated, inverted-U shaped loop (coffee bean sign) arising from the pelvis with a whirl sign of twisted mesenteric vessels at the point of torsion.
- Mesenteric ischaemia CT findings
- Key findings include SMA or SMV thrombus, bowel wall non-enhancement, pneumatosis intestinalis, portal venous gas and mesenteric oedema; arterial phase CT angiography is the investigation of choice.
- Pneumatosis intestinalis significance
- Pneumatosis intestinalis (intramural gas) in the setting of acute abdomen indicates bowel wall compromise (ischaemia, infarction or necrosis) and is a surgical emergency until proven otherwise.
- Portal venous gas
- Portal venous gas appears as branching lucencies extending to the periphery of the liver on CT; in the context of acute abdomen, it suggests bowel necrosis and carries high mortality.
- Acute appendicitis CT criteria
- CT criteria include appendix diameter >6 mm, wall enhancement, periappendiceal fat stranding, appendicolith and fluid; sensitivity and specificity exceed 95% with IV contrast.
- Appendicitis in pregnancy
- MRI without gadolinium is the preferred cross-sectional modality for suspected appendicitis in pregnancy when ultrasound is non-diagnostic; CT is reserved for cases where MRI is unavailable or non-diagnostic.
- Acute diverticulitis CT findings
- CT shows colonic wall thickening, pericolonic fat stranding, diverticula and possible complications (abscess, perforation, fistula); Hinchey classification guides management.
- Hinchey classification
- Hinchey I: pericolic abscess; Hinchey II: pelvic/distant abscess; Hinchey III: purulent peritonitis; Hinchey IV: faecal peritonitis. Stages III-IV require emergency surgery.
- Ectopic pregnancy ultrasound
- Transvaginal ultrasound showing an empty uterus with beta-hCG above the discriminatory threshold (approximately 1500-2000 IU/L) is highly suspicious for ectopic pregnancy; adnexal mass with yolk sac or cardiac activity is diagnostic.
- Ovarian torsion ultrasound
- Ultrasound findings include enlarged ovary (>4 cm), peripherally displaced follicles, absent or reduced venous flow on Doppler, twisted vascular pedicle (whirlpool sign) and free fluid.
- Ruptured AAA
- CT angiography shows aortic diameter >3 cm with retroperitoneal or intraperitoneal haemorrhage, active extravasation and discontinuity of aortic wall calcification; haemodynamically unstable patients proceed directly to theatre.
- Renal colic non-contrast CT
- Non-contrast CT (CT KUB) is the gold standard for renal colic, detecting calculi with sensitivity >95%; stone size, location and degree of hydronephrosis guide management.
- Strangulated hernia
- CT identifies herniated bowel with wall thickening, reduced enhancement, mesenteric congestion and proximal obstruction; strangulation requires emergency surgical intervention.
- Acute pancreatitis CT timing
- Contrast-enhanced CT is optimally performed 72 hours or more after symptom onset for necrosis assessment; early CT may underestimate necrosis. CT severity index (Balthazar) grades severity.
- Gallstone ileus
- Rigler triad: pneumobilia, ectopic gallstone (usually at ileocaecal valve) and small bowel obstruction; CT is the most sensitive modality for identifying the fistula and obstructing stone.
- Ogilvie syndrome
- Ogilvie syndrome (acute colonic pseudo-obstruction) shows massive colonic dilatation without mechanical obstruction; caecal diameter >12 cm significantly increases perforation risk and warrants decompression.
Caution
Management thresholds for obstruction, diverticulitis and pancreatitis vary by surgical capability, patient comorbidity and institutional protocol. Always correlate imaging with clinical and laboratory findings.
Exam pearl
In viva, always identify the transition point in bowel obstruction and state whether there are signs of strangulation or closed-loop mechanism. For mesenteric ischaemia, time to diagnosis is the most critical prognostic factor.
Viva questions
- What CT findings indicate closed-loop small bowel obstruction?
- A U-shaped or C-shaped dilated bowel loop, radial distribution of mesenteric vessels converging toward a torsion point, beak sign at the transition, and whirl sign of twisted mesentery. Closed-loop obstruction carries high risk of strangulation and requires emergency surgery.
- What is the significance of pneumatosis intestinalis in the acute abdomen?
- Pneumatosis intestinalis indicates gas within the bowel wall and in the setting of acute abdomen suggests bowel wall compromise from ischaemia, infarction or necrosis. It is a surgical emergency until proven otherwise, particularly when accompanied by portal venous gas.
- What is the Hinchey classification used for?
- The Hinchey classification grades the severity of complicated acute diverticulitis: Stage I is pericolic abscess, Stage II is pelvic or distant abscess, Stage III is purulent peritonitis, and Stage IV is faecal peritonitis. Stages III and IV require emergency surgical intervention.
- When is contrast-enhanced CT optimally performed in acute pancreatitis?
- At least 72 hours after symptom onset, as earlier CT may underestimate the extent of pancreatic necrosis. CT is primarily indicated when the patient fails to improve clinically or when complications such as necrosis, abscess or vascular involvement are suspected.
- What is Rigler triad and what does it indicate?
- Rigler triad consists of pneumobilia, ectopic gallstone (typically at the ileocaecal valve) and small bowel obstruction. It is pathognomonic of gallstone ileus, where a large gallstone erodes through a cholecystoenteric fistula and impacts in the terminal ileum.