How to differentiate indirect inguinal hernia from direct inguinal hernia

Under normal circumstances, inguinal oblique hernia and direct hernia are both common types of hernias in the inguinal region. They can be differentiated based on factors such as age of onset, route of protrusion, hernia mass morphology, reducibility characteristics, and risk of incarceration. The specific analysis is as follows:

1. Age of onset: Inguinal oblique hernias commonly occur in children and young adults. During adolescence, incomplete development of abdominal wall muscles or prolonged increased intra-abdominal pressure in young adults may predispose individuals to hernia sac formation. In contrast, direct hernias primarily affect elderly patients, in whom atrophy and weakening of abdominal wall muscles make weak areas more susceptible to herniation.

2. Route of protrusion: The sac of an oblique hernia emerges through the internal inguinal ring, located lateral to the inferior epigastric artery, passes through the entire inguinal canal, and may extend through the external ring into the scrotum. A direct hernia, however, protrudes directly through the Hesselbach's triangle, medial to the inferior epigastric artery, without passing through the internal inguinal ring or entering the scrotum.

3. Hernia mass morphology: Oblique hernias typically present as a pear-shaped mass—narrow at the top and gradually widening below due to descent into the scrotum. Direct hernias usually appear as a hemispherical mass with a broad base, protruding beneath the skin of the inguinal region. The shape is relatively regular, without significant differences in width between upper and lower portions.

4. Reducibility characteristics: After reduction of an oblique hernia, if the internal inguinal ring is compressed with a finger and the patient increases intra-abdominal pressure (e.g., by coughing), the hernia does not reappear. In contrast, after reduction of a direct hernia, even with compression of the internal ring, the hernia may still protrude through Hesselbach's triangle when abdominal pressure is increased.

5. Risk of incarceration: Oblique hernias have a higher risk of incarceration because the neck of the hernia sac is narrow and the path through the inguinal canal is tortuous. Incarceration may manifest as sudden enlargement of the hernia, severe pain, and symptoms such as nausea and vomiting. Direct hernias, with their wider hernia sac necks and more direct path of protrusion, carry a lower risk of incarceration.

Distinguishing between these two types of hernias is crucial for selecting appropriate treatment strategies. For both oblique and direct hernias, surgical repair of the weakened abdominal wall is recommended as soon as diagnosis is confirmed. Postoperatively, patients should avoid conditions that increase intra-abdominal pressure—such as severe coughing or constipation—to promote healing of abdominal tissues and reduce the risk of recurrence.