A direct inguinal hernia arises from protrusion of abdominal viscera through a weakness of the posterior wall of the inguinal canal medial to the inferior epigastric vessels, specifically through the Hesselbach's triangle.
This type of hernia is termed direct as the hernial sac directly protrudes through the inguinal wall in contrast to indirect ones which arise through the deep ring and enter the inguinal canal. Since direct hernias do not have a guiding path, they seldom extend into the scrotum unless very large and chronic.
Direct hernias are generally acquired and increase in incidence with age. They result from weakening of the transversalis fascia in the Hesselbach triangle
Therefore, they are seen in the elderly with chronic conditions which increase intra-abdominal pressure over a long period, e.g. COPD, bladder outflow obstruction, chronic constipation etc. Increased abdominal pressure is transmitted to both sides and as a result, direct hernias are usually bilateral. Compared to indirect hernia, they are less susceptible to strangulation as they have a wide neck.
A lateral crescent of fat (lateral crescent sign) is a useful diagnostic sign of direct inguinal hernia. Also, they occur anteromedial to the origin of the inferior epigastric artery 2.
High-frequency linear transducers are preferred for sonographic interrogation of inguinal structures due to the superficial nature of the structures of interest. Examination of the patient supine, standing, and during a Valsalva maneuver increases the sensitivity of the examination. With the transducer aligned parallel to the inguinal ligament, a cranial sweep should be performed to identify the inferior epigastric artery arising from the external iliac artery, which will serve as a sonographic landmark to differentiate inguinal hernias. The peritoneal stripe will be visualized just deep to the inferior epigastric artery. A direct inguinal hernia will be identified with the following sonographic features 5:
- deformation of the peritoneal stripe medial to the inferior epigastric artery
- primarily visible when intra-abdominal pressure is increased
- peristaltic bowel is often visualized within the hernia sac
- identified as a redundant, tubular structure with lamellated walls
- may contain hyperechoic fat
- herniation should be interrogated for signs of incarceration
- release of valsalva or probe pressure should restore continuity of peritoneal stripe
- bowel should demonstrate peristalsis
- blood flow, as demonstrated by power Doppler, should be present
- bowel wall should be < 4 mm, layered, and lack surrounding free fluid
Treatment and prognosis
Treatment is surgical repair which consists of reduction of the sac and reinforcement of the posterior wall of the inguinal canal usually with a synthetic mesh.
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