Which imaging modality is recommended for a suspected strangulated hernia?

Imaging Modality for Suspected Strangulated Hernia

CT scan with contrast enhancement is the gold standard for diagnosing strangulated hernias due to its high accuracy in detecting bowel ischemia and determining the presence, location, and size of the hernia defect. 1

Initial Assessment

• A chest X-ray (both anteroposterior and lateral views) may be used as the first diagnostic study in patients with respiratory symptoms, but it has limited sensitivity (2-60% for left-sided hernias and 17-33% for right-sided hernias) 1
• Plain radiographs can be misinterpreted in approximately 25% of cases and may be normal in up to 62% of diaphragmatic injuries or uncomplicated diaphragmatic hernias 1
• Initial laboratory tests should include complete blood count, CRP, lactate, electrolytes, and coagulation profile to help identify signs of ischemia, though normal values cannot exclude ischemia 1

CT Scan: The Preferred Modality

• CT scan is the gold standard for diagnosing hernias with a sensitivity and specificity of 14-82% and 87%, respectively 1
• CT with intravenous contrast is superior to conventional abdominal radiography and ultrasound, providing critical information about the underlying cause of obstruction 1
• CT can accurately evaluate intrathoracic complications of herniated abdominal organs and detect signs of ischemia 1

Key CT Findings for Strangulation

• Forward displacement of the gastric bubble 1
• Missing gastric folds 1
• Absence of gastric wall contrast enhancement 1
• Intestinal wall thickening with target enhancement 1
• Spontaneous hyper-density of the intestinal wall 1
• Lack of enhancement after contrast injection 1
• Parietal pneumatosis with portal and mesenteric venous gas 1
• Reduced wall enhancement (56% sensitivity, 94% specificity) 1
• "Collar sign" (constriction of herniating abdominal organ at rupture level) 1
• "Dependent viscera" sign (no space between organs and chest wall) 1

Alternative Imaging Modalities

• Ultrasound may be used as the first diagnostic study in pregnant patients with suspected non-traumatic diaphragmatic hernia (weak recommendation based on very low-quality evidence) 1
• MRI is suggested after ultrasonography in stable pregnant patients (weak recommendation based on very low-quality evidence) 1
• Diagnostic laparoscopy may be useful for assessing bowel viability after spontaneous reduction of strangulated groin hernias 1

Clinical Correlation

• CT findings should be correlated with clinical parameters such as elevated WBC count and physical examination findings 1
• Arterial blood lactate level of 2.0 mmol/L or greater is a useful predictor of non-viable bowel strangulation 1
• When combined with clinical findings, CT's sensitivity for detecting strangulation and associated complications can be improved 1

Common Pitfalls and Caveats

• CT may miss small tears of penetrating injuries like stab wounds when no hernia has yet occurred 1
• Positive oral contrast is not needed and may delay diagnosis, increase patient discomfort, and risk complications such as vomiting and aspiration 1
• Positive oral contrast can potentially limit the ability to detect abnormal bowel wall enhancement in cases of ischemia 1
• Despite advances in imaging methods, up to 25% of traumatic diaphragmatic injuries can be missed initially 2

In summary, while initial assessment may include chest X-ray, CT scan with IV contrast is the definitive imaging modality for suspected strangulated hernias due to its superior ability to detect signs of ischemia and provide detailed anatomical information about the hernia.