Describe Spigelian Hernia in detail.

The Concept

A Spigelian hernia is an uncommon hernia that protrudes through the Spigelian fascia — the aponeurotic layer at the lateral border of the rectus abdominis (the linea semilunaris) — most often just below the level of the umbilicus, near the arcuate line, where the posterior rectus sheath is deficient and the wall is weakest. Its importance lies less in its frequency than in how easily it is missed.

WHY It Is Difficult to Diagnose

A Spigelian hernia is characteristically interparietal — the sac lies between the muscle layers of the abdominal wall rather than emerging subcutaneously — so it often produces no obvious visible bulge, only vague localised pain or a poorly defined swelling. This concealed position, combined with a narrow neck, gives it a significant risk of strangulation, so it should not be dismissed.

Diagnosis & Management

Because it is hard to feel, imaging (ultrasound or CT) is often needed to confirm the diagnosis and localise the defect. Treatment is surgical repair (open or laparoscopic, usually with mesh), which is generally recommended because of the strangulation risk of the narrow-necked defect.

A High Index of Suspicion

The practical message is a high index of suspicion: a patient with localised abdominal-wall pain or a vague swelling at the lateral edge of the rectus, without an obvious visible hernia, may have a Spigelian hernia, and imaging should be requested rather than the symptom dismissed. Because the narrow neck risks strangulation, a confirmed Spigelian hernia is repaired rather than observed — the diagnosis, once considered, is readily confirmed on ultrasound or CT.

The Bottom Line

A Spigelian hernia is a concealed interparietal hernia at the linea semilunaris that is easily missed, needs imaging to diagnose, and is repaired because of its strangulation risk.

Contrast with Divarication

A Spigelian hernia should be distinguished from the more benign causes of a lateral abdominal bulge, and imaging is what settles it — an ultrasound or CT demonstrates a genuine fascial defect with a sac, confirming a true hernia that warrants repair, rather than simple muscular bulging or a lipoma. This confirmation is important because the concealed Spigelian hernia is one that is repaired on diagnosis to pre-empt strangulation.

Often impalpable — ultrasound or CT is needed for diagnosis.

• Spigelian hernia = protrusion through the Spigelian fascia at the lateral edge of the rectus (linea semilunaris), usually below the umbilicus near the arcuate line.
• Interparietal (lies between muscle layers) → often no visible bulge, only vague pain → easily missed.
• Narrow neck → significant strangulation risk.
• Often needs ultrasound/CT to diagnose; treat by surgical (usually mesh) repair.