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Background
Hernias are ubiquitous on imaging and a common source of abdominal pain. Accurate identification and classification are necessary to prevent morbidity. Multidetector row computed tomography with intravenous contrast provides sufficient anatomic detail for radiologists to diagnose common abdominal hernias and direct further treatments.

Educational Goals / Teaching Points
Abdominal hernias are protrusions of abdominal contents beyond the cavity that houses them. Complications of abdominal hernias include bowel obstruction, incarceration, and strangulation/ischemia. Identifying and reporting common abdominal hernias is needed to prevent complications. CT provides sufficient anatomic detail to diagnose abdominal hernias and identify associated complications. Accurate description of abdominal hernias can aid with preoperative planning if surgery is required.

Key Anatomic/Physiologic Issues and Imaging Findings/Techniques
External hernias include inguinal, femoral, lumbar, ventral, and incisional hernias (e.g. parastomal). Inguinal hernias are the most common, and may occur medial (direct) or lateral (indirect) to the inferior epigastric vessels. Femoral hernias typically occur inferior to the inguinal ligament and medial to the femoral vein. Ventral hernias are midline (due to weakening of linea alba aponeuroses) or lateral (due to weakening of the Spigelian fascia). Lumbar hernias occur at the Grynfeltt-Lesshaft or Petit triangles. Incisional hernias often arise soon after abdominal surgery. Internal hernias include paraduodenal, foramen of Winslow, pericecal, supravesical, small bowel mesentery, transverse and intersigmoid, greater omental, and pelvic hernias. Paraduodenal hernias are the most common, involving herniation into the fossa of Landzert (left) or fossa of Waldeyer (right). Foramen of Winslow hernias lead to herniation into the lesser sac. Pericecal hernias involve displacement into the ileocecal, retrocecal, or paracolic recesses. Supravesical hernias occur in the fossa superior to the urinary bladder. Small bowel mesentery and mesocolon hernias may be transmesenteric (affecting both peritoneal layers) or intramesenteric (affecting one layer). Greater omental hernias are usually transomental. Pelvic internal hernias most commonly involve the broad ligament of the uterus. Diaphragmatic hernias include hiatal, paraesophageal, Bochdalek, Morgagni, and acquired hernias. Hiatal hernias, the most common, occur when the gastro-esophageal junction migrates proximal to the esophageal hiatus. Paraesophageal hernias involve migration of the gastric fundus. Bochdalek hernias occur through a posterolateral defect while Morgagni hernias occur through an anteromedial defect of the attachments of the diaphragm. Acquired hernias may result from traumatic or non-traumatic diaphragmatic rupture. Unidentified or mischaracterized hernias may lead to complications including; obstruction, incarceration, and strangulation with or without necrosis, which may be life-threatening.

Conclusion
Identification and proper categorization of common abdominal hernias is of paramount importance to prevent complications and guide further treatment.