Answers

Short answers

1 This patient’s bowel obstruction could be caused by neoplasia, hernia, inflammatory stricture, volvulus, or congenital band adhesion.

2 Small bowel can be seen in the right obturator foramen on the computed tomogram.

3 This patient has an obstructed obturator hernia.

4 Female sex, old age, weight loss and malnutrition, chronic lung disease, prostatism, constipation, kyphoscoliosis, and multiparity can all predispose to an obstructed obturator hernia.

5 The patient has Howship-Romberg sign: pain in medial knee or thigh secondary to irritation of medial geniculate branch of the obturator nerve. You could also look for Hannington-Kiff sign—absent adductor reflex—or a mass palpable on vaginal examination.

Long answers
1 Differential diagnoses
The possible causes of small bowel obstruction in this patient are neoplasia, hernia, inflammatory stricture, volvulus, and congenital band adhesion. Given that this patient was elderly, had no surgical history, had "tinkling" bowel sounds (typical of mechanical bowel obstruction), and no detectable hernia on examination, the most likely cause of obstruction is a colonic cancer.

A retrospective study that looked at the aetiologies of 83 patients with intestinal obstruction but with no prior laparotomy or detectable hernia found the most common causes of enteric obstruction were hernias, congenital band adhesions, and volvulus .¹ Most of the hernias diagnosed in these patients were internal, and the remainder were mainly obturator or diaphragmatic. The most common causes of large bowel obstruction in this study were carcinoma, volvulus, and congenital band adhesions.

Neoplasia accounts for about 17% of all bowel obstructions but only 3% of small bowel obstructions.² The cause of small bowel obstruction is usually primary neoplasm, although secondary neoplasms from breast cancer, lung cancer, and melanomas can cause obstructions. Small bowel tumours account for approximately 5% of all gastrointestinal neoplasms and include gastrointestinal stromal tumours, lipomas, neurofibromas, lymphomas, or adenocarcinomas.²

Hernia is the causal factor in about 15% of bowel obstructions. Hernias are responsible for approximately 18% of all small bowel obstructions in developed countries; however, they are the most common cause in the developing world.² In general, the most common hernias in adults are inguinal hernias, followed by umbilical, incisional, femoral, and epigastric hernias.³ Other less common hernias that can cause obstructions are paraumbilical, obturator, spigelian, lumbar, gluteal, and internal hernias. Obturator and internal hernias are two of the few hernias that are not usually palpable, along with diaphragmatic hernias, which rarely obstruct.

Inflammatory stricture as a cause of small bowel obstruction has a prevalence of about 2%.² Inflammatory strictures in the small bowel are normally attributed to Crohn’s disease, which is a possibility in this patient despite her old age. More frequently, stricture in an elderly woman is secondary to diverticular disease. Inflammatory bowel disease causes approximately 5% of all small bowel obstructions in patients without prior laparotomy.¹

Volvulus is rare in the small bowel, causing only 1% of cases of obstruction.² Volvulus can occur at the caecum or sigmoid, the latter site being more common in the elderly.

Obstruction secondary to congenital band adhesion is, in general, very rare and accounts for 16% of small bowel obstructions in patients with no previous abdominal surgery.¹ Although these defects are present from birth, they may cause obstruction at any age—studies have shown an age range of 59-90 years old.⁴

2 Signs on the computed tomogram
The computed tomogram shows a mass between pectineus muscle anteriorly and the obturator externus posteriorly, which is characteristic of obturator hernia (fig 2).

View larger version (43K): [in this window] [in a new window] [PowerPoint Slide for Teaching]   Fig 2 Labelled computed tomogram of the patient’s abdomen, showing the trapped portion of small bowel, the pectineus muscle, the obturator externus, and the obturator internus

 
3 Diagnosis
The diagnosis in this patient is an obstructed obturator hernia, which is a hernia through the obturator canal. The route of the small bowel in this disorder is through the obturator foramen with the obturator artery and nerve as they exit the pelvis and the obturator vein as it enters the pelvis. A weakening of the membrane covering the foramen allows abdominal contents to be forced down between the pectineus and obturator externus muscles, usually anterior and medial to the neurovascular bundle.⁵ The hernial sac may contain small or large bowel, omentum, fallopian tube, or appendix. Obturator hernias are more common on the right side because sigmoid colon forms a barrier on the left.

Obturator hernias are rare—they comprise 0.073% of all hernias and are the cause of 0.4% of bowel obstructions.⁵ This type of hernia is important, however, because 90% of patients with obturator hernia present with obstruction, and strangulated hernias have a mortality of 25%.⁶ A retrospective study of 13 cases of obturator hernia showed that patients are usually female (85%) with a mean age of 82 years and a mean weight of 34.5 kg.⁵ A second retrospective study of 16 cases supports these characteristics, describing a female:male ratio of 7:1, a mean age of 79 years, and a mean weight of 39.5 kg.⁷ Computed tomography is usually diagnostic in these patients because symptoms and examination are often non-specific. Only one case in 10 is correctly diagnosed pre-operatively.⁵

A third of patients with obturator hernia report previous bouts of features of small bowel obstruction that resolve spontaneously. This factor may well account for the case patient’s symptoms over the preceding 18 months.⁵

4 Predisposing factors
Female sex predisposes to obturator hernia because the female pelvis is wider, so there is greater chance of a defect forming.⁵ Old age, weight loss, and malnutrition lead to loss of the protective peritoneal fat overlying the obturator canal, increasing the risk of herniation into the obturator canal.⁵ Other conditions that predispose to obturator hernia involve raised intra-abdominal pressure, including chronic lung disease, prostatic disease, constipation, kyphoscoliosis, and previous pregnancy.⁸

5 Diagnostic signs
The Howship-Romberg sign is characteristic of an obturator hernia but is present in only approximately 50% of patients.⁵ It can go unnoticed or be attributed to arthritis. Less well known, but more specific, is the Hannington-Kiff sign for obturator hernia—unilaterally absent adductor reflex in the thigh with a normal patella reflex on the same side.⁹ In addition, vaginal examination may reveal a palpable tender mass on the side of the lesion in patients with obturator hernia.¹⁰

Patient outcome
The patient underwent laparotomy, and the hernia was reduced and the defect closed with a mesh plug. The patient recovered well and was discharged home.

Cite this as: BMJ 2009;339:b3641