Obturator hernia

Obturator hernias (alternative plural: herniae) are characterized by bowel herniating between the obturator and the pectineus muscles. They are a rare type of abdominal hernia and can be a challenge to diagnose clinically.

Epidemiology

Typically obturator hernias occur in older women ^2,3 or patients with chronically raised intra-abdominal pressure (e.g. ascites, COPD, chronic cough) ³. They can occur in pregnancy, due to relaxation of the pelvic peritoneum and a wider and more horizontal obturator canal ³.  It has been suggested that there is a female predominance with this type of hernia, and they occur in less than 0.04% of all hernias ⁶. 

Clinical presentation

In general, obturator hernias are asymptomatic unless they ¹:

• compress the obturator nerve: Howship-Romberg sign (only present in approximately half of cases) ³
• contain bowel which incarcerates/obstructs/strangulates

Pathology

The obturator foramen is occluded by the obturator membrane, which is pierced anterosuperiorly by the obturator artery, vein and nerve. This neurovascular bundle then travels along a 2-3 cm oblique tunnel, the obturator canal. It is through this deficiency that an obturator hernia occurs. Presumably, due to the sigmoid colon on the left, these hernias are more common on the right ³. 

The layers that the hernial neck passes through include:

• obturator internus muscle fibers
• obturator membrane
• obturator externus muscle fibers 

The hernia will then lie superficial to obturator externus and deep and inferior to pectineus muscle.

The hernia may contain any of the following:

• no more than peritoneum filled with fluid, as seen in patients with ascites
• small bowel (most common)
• colon ³
• appendix
• omentum
• Meckel diverticulum
• ovary/fallopian tube
• and even uterus ³

Radiographic features

The diagnosis is readily made on CT/MRI with either fluid or bowel able to be traced along the aforementioned course to lie in the medial upper thigh.

Signs of complication, including:

• bowel obstruction
• strangulation resulting in perforation

Treatment and prognosis

Treatment involves surgery and repair of the hernial orifice. 

History and etymology

Howship-Romberg sign is named for the German neurologist, Moritz Heinrich Romberg (1795-1873) ⁵, and British surgeon John Howship (1781-1841) ⁴.

Differential diagnosis

If a hernia contains bowel or can be clearly traced through the obturator foramen, then there are very few alternative diagnoses.

If seen with ultrasound, it may be mistaken for a bursa or acetabular labral cyst.