Diagnosis of inguinal region hernias with axial CT: the lateral crescent sign and other key findings.

Differentiation of direct inguinal hernias, indirect inguinal hernias, and femoral hernias is often difficult at clinical examination and presents challenges even at diagnostic imaging. With the advent of higher-resolution multidetector computed tomography (CT), the minute anatomic detail of the inguinal region can be better delineated. The authors examine the appearance of these hernias at axial CT, as the axial plane remains the diagnostic mainstay of evaluation of acute abdomen. They review and label key anatomic structures, present cases of direct and indirect inguinal hernias and femoral hernias, and demonstrate their anatomic differences on axial images. Direct inguinal hernias protrude anteromedial and inferior to the course of the inferior epigastric vessels, whereas indirect inguinal hernias protrude posterolateral and superior to the course of those vessels. The proposed lateral crescent sign may be useful in diagnosis of early direct inguinal hernias, as it represents lateral compression and stretching of the inguinal canal fat and contents by the hernia sac. Femoral hernias protrude inferior to the course of the inferior epigastric vessels and medial to the common femoral vein, often have a narrow funnel-shaped neck, and may compress the femoral vein, causing engorgement of distal collateral veins. Familiarity with these anatomic differences at axial CT, along with the lateral crescent sign of direct inguinal hernias, may help the radiologist better assist the clinician in accurate diagnosis of the major types of hernias of the inguinal region. Supplemental material available at http://radiographics.rsna.org/lookup/suppl/doi:10.1148/rg.312105129/-/DC1.