Anatomy

The inferior epigastric vessels are the surgeon's landmark dividing the two inguinal hernia types. The deep (internal) ring — an opening in transversalis fascia at the midpoint of the inguinal ligament — lies lateral to the inferior epigastric vessels; an indirect hernia enters it, travels within the coverings of the spermatic cord along the canal, and can descend to the scrotum. It follows the path of the processus vaginalis and is the type that presents in the young as well as the old. A direct hernia is an acquired weakness: it bulges forward through the posterior wall of the canal medial to the inferior epigastric vessels, through Hesselbach's (the inguinal) triangle — bounded laterally by the inferior epigastric vessels, medially by the lateral edge of rectus abdominis, and inferiorly by the inguinal ligament — lying outside the cord coverings, and rarely reaching the scrotum. At operation (or laparoscopy, where the vessels are seen directly on the posterior wall), the sac's relation to these vessels makes the diagnosis; both types are repaired by mesh reinforcement of the posterior wall, so the distinction is anatomical understanding more than a change of operation.

Why the others are wrong: A and E — lateral-to-vessels through the deep ring defines indirect; direct hernias push through the triangle and essentially never traverse the deep ring to the scrotum. B — the deep ring is lateral to the vessels. C — the femoral vein bounds the femoral canal, not Hesselbach's triangle.

Key point: Indirect = lateral to the inferior epigastric vessels, through the deep ring, within cord coverings, can reach the scrotum; direct = medial to the vessels, through Hesselbach's triangle (epigastrics laterally, rectus medially, inguinal ligament below) — the vessels are the dividing landmark at open and laparoscopic repair alike.

Guidelines: HerniaSurge International groin hernia guidelines 2018: sound repair rests on this anatomy — mesh repair (open Lichtenstein or laparo-endoscopic) is recommended for most adult inguinal hernias, with the myopectineal orifice fully assessed at minimal-access repair.

The femoral sheath — a prolongation of transversalis and iliac fascia beneath the inguinal ligament — contains the femoral artery, vein and, most medially, the femoral canal: a centimetre of loose areolar tissue and Cloquet's node that acts as dead space for venous expansion. Its ring is bounded by the inguinal ligament in front, pectineus and the pectineal ligament behind, the femoral vein laterally, and — the defining feature — the crescentic, unyielding free edge of the lacunar ligament medially. A hernia forcing itself through this small, rigid, three-quarters-ligamentous ring is gripped at the neck: femoral hernias have the highest strangulation rate of any groin hernia (a third or more presenting as emergencies, typically in elderly women — the anatomy behind the elderly-woman-with-a-groin-lump-and-obstruction vignettes elsewhere in this bank). At operation, releasing a strangulated hernia may require careful division of the lacunar ligament medially — with the classical caution that in a significant minority an aberrant obturator artery (the 'corona mortis', from the inferior epigastric) arches across it, and blind division invites serious haemorrhage. Surface anatomy separates it from the inguinal hernia: femoral emerges below and lateral to the pubic tubercle; inguinal above and medial.

Why the others are wrong: B and D — the canal is the most medial sheath compartment, bounded laterally by the vein. C — the femoral nerve lies outside (lateral to) the sheath. E — above-and-medial describes the inguinal hernia.

Key point: The femoral canal — inguinal ligament anteriorly, pectineal ligament posteriorly, femoral vein laterally, lacunar ligament's rigid edge medially — strangulates hernias at its unyielding ring; it emerges below and lateral to the pubic tubercle, and the lacunar ligament is divided warily for the corona mortis.

Guidelines: HerniaSurge International groin hernia guidelines 2018: the narrow, rigid femoral canal explains the high strangulation risk — femoral hernias are repaired promptly even when asymptomatic, and a low threshold for emergency repair applies in women.