Acquired hernias are of many types. One way of classifying them is external or abdominal wall hernias [defect in the abdominal wall], internal hernias [protrusion of intraperitoneal contents through a defect in the peritoneum or mesentery] and diaphragmatic hernias [protrusion of intraabdominal contents into the chest]. Both internal and external hernias may contain bowel, omentum or both. Although the diagnosis is usually clinical, hernias may pose a diagnostic dilemma in obese patients, patients with multiple scars due to abdominal surgeries and in patients presenting with acute abdomen due to an incarcerated/ strangulated hernia. In such a situation, clinicians may have to rely on imaging findings which easily show the defect and confirm the diagnosis. In a few instances, asymptomatic occult [clinically not detectable] hernias may also be revealed by imaging.
High resolution ultrasound demonstrates the cross-sectional anatomy well and the layers of the abdominal wall up to the peritoneal layer can be well discerned unless body habitus precludes adequate visualization. In cases of ventral hernia, a defect is seen in the peritoneal layer through which the intraperitoneal contents protrude. The diameter of the defect can be measured, which helps the surgeon in deciding whether a mesh repair would be required.
In cases of hernias that are in the process of being or are incarcerated, patients may present with clinical signs of bowel obstruction or an acute abdomen. Rettenbacker et al described ultrasound findings associated with incarceration, including free fluid in the hernial sac, thickened walls of the bowel in the hernia, fluid in the herniated bowel loop, and dilated bowel loops in the abdomen. Color Doppler may show reduced blood flow in the bowel trapped in the hernial sac and is a good indicator of bowel viability. Post-operative follow up of these patients following mesh placement can also be carried out. CT is an excellent alternative modality in cases where ultrasound is inconclusive, enabling identification of the hernia and evaluation of the involved and uninvolved bowel.