Pneumatosis cystoides intestinalis is an uncommon condition characterized by the presence of submucosal and/or subserosal gas-filled cysts in the intestinal wall. These cysts, which may reach several centimetres in diameter, contain largely nitrogen or hydrogen and occur in the small bowel more commonly than in the colon and rectum.

Pneumatosis cystoides intestinalis was first reported as a post-mortem observation by Du Vernoi in the eighteenth century. The condition is commonly asymptomatic and discovered incidentally at laparotomy or on radiological investigation of an unrelated symptom, but it can also produce abdominal pain, subacute intestinal obstruction, intussusception, or rectal bleeding. Its aetiology remains obscure. Favoured theories include the intramural penetration of gas-producing organisms, excessive intraluminal fermentation, and the forcing of gas under high pressure into the bowel wall, either from the lungs via the mediastinum and mesentery in patients with pulmonary disease, or from the intestinal lumen after surgery or biopsy has left a mucosal breach. Each of these theories is supported by clinical and experimental observations. The condition is well recognized in pigs and some other animals.

Pneumatosis cystoides intestinalis is most common in men between the ages of 30 and 50 years, and has an association with peptic ulceration and pyloric stenosis, intestinal bypass surgery for morbid obesity, and chronic lung disease. A plain abdominal radiograph may show a linear arrangement of gas collections, or pneumoperitoneum, without clinical signs of peritonitis. Contrast studies distinguish this condition from polyposis by demonstrating radiolucent defects in the bowel wall which extend outside the column of barium (Fig. 1) 1007.

Accurate diagnosis prevents unnecessary surgery. The occasional familial occurrence of the condition increases the risk of confusion with familial polyposis coli and, therefore, of inappropriate colectomy. Biopsy should be performed, when the cyst will sometimes rupture with a hissing sound. Histology is diagnostic (Figs. 2 and 3) 1008,1009.

No treatment is necessary for the 85 per cent of patients who are asymptomatic. Oxygen therapy has been used successfully for symptomatic patients and is thought to work by inducing the exchange of inert gases from the cysts for oxygen, which is later absorbed. Good results have been reported after inhalation of 70 per cent oxygen, achieving a Po&sub2; of 250 mmHg for 5 days and after hyperbaric oxygen therapy at 2.5 atmospheres (252.5 kPa) for 150 min on each of 3 successive days. Dietary treatment has been successful in selected patients.

Intestinal resection should be reserved for patients with complications or severe refractory symptoms. The results of surgery in these cases are good.

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