From the Department of Radiology, Baylor University Medical Center, Dallas, Texas.

Corresponding author: Robert M. Branstetter, MD, Department of Radiology, Baylor University Medical Center, 3500 Gaston Avenue, Dallas, Texas 75246.

For diagnosis and discussion, see the following page.

DIAGNOSIS: Incarcerated obturator hernia producing small-bowel obstruction.

DISCUSSION

Obturator hernias are a rare cause of small-bowel obstruction, accounting for approximately 0.4% of all cases (1). Despite advances in modern medicine, the mortality rate of small-bowel obstructions secondary to obturator hernias remains high because of vague presenting symptoms, which make the diagnosis difficult at initial presentation and may delay treatment.

Obturator hernia is one of several types of abdominal wall hernias. Other types include incisional, umbilical, spigelian, lumbar, and epigastric hernias.

The most common abdominal wall hernia is the incisional hernia, which occurs at sites of previous abdominal incisions. These occur in up to 14% of patients with a history of abdominal surgery (2).

Unlike incisional hernias, umbilical hernias are predominantly congenital. These hernias occur more commonly in blacks, and most will spontaneously resolve by the age of 2 years. Patients with large amounts of ascites may also develop umbilical hernias.

Spigelian hernias project through the spigelian fascia, which is located at the lateral edge of the rectus abdominis muscles.

Lumbar, or dorsal, hernias protrude through the posterior abdominal wall. The most common location for these hernias is the superior lumbar triangle (Grynfeltt's), which is located immediately inferior to the 12th rib. The second most common location for lumbar or dorsal hernias is in the inferior lumbar triangle (Petit's) (3).

Epigastric hernias are produced by a defect in the linea alba at a level between the xiphoid process and the umbilicus. These hernias are more common in men (2).

Obturator hernias occur predominantly in the seventh and eighth decades of life and are 9 times more frequent in women than men (4). Large, wide pelvic bones and more horizontally oriented obturator canals, which are prevalent in women, are believed to predispose to the development of obturator hernias (5). The typical patient with an obturator hernia is a thin, elderly female. Contributing factors are prior pregnancy, chronic illness, malnutrition, and any condition that produces peritoneal weakening.

Obturator hernias protrude through the obturator foramina, which are located in the anterolateral pelvic wall bilaterally immediately inferior to the acetabula (Figure 5). The obturator foramina are covered by the obturator membranes, except anterosuperiorly where the obturator canals are located. The obturator nerve and associated blood vessels are located in this canal and are surrounded by fatty tissue. Severe weight loss, aging, and malnutrition contribute to a loss of the surrounding fatty tissue, creating a space around the obturator nerve and vessels and predisposing to the development of an obturator hernia (4).

The most common symptom of obturator hernia is small-bowel obstruction (Figure 6), which produces varied clinical symptoms. Frequently, the initial symptom is mild, intermittent abdominal pain, which is secondary to intermittent, incomplete small-bowel obstruction. Related physical findings are rare since the incarcerated hernia is located posterior to the pectineus and adductor longus muscles (5). The Howship-Romberg sign, which is suggestive of an obturator hernia, consists of pain along the medial aspect of the thigh, extending to the knee, caused by irritation of the obturator nerve. However, this sign is present in only approximately 50% of cases of obturator hernia (4).

Because of such nonspecific presenting signs and symptoms, CT plays an important role in the diagnosis of obturator hernia by demonstrating incarcerated small bowel posterior to the pectineus muscle (Figures 5 and 6). In a recent study, CT provided an accurate preoperative diagnosis in 11 of 14 patients with obturator hernia (6). CT is noninvasive and rapidly performed and can lead to prompt diagnosis and treatment. Early treatment, which usually consists of laparotomy and repair of the hernia defect, is important to prevent incarceration, strangulation, and perforation, which are associated with high mortality rates.

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