Pneumatosis cystoides intestinalis (PCI) is a condition in which multiple gas-filled cysts occur under the serosa or mucosa of the gastrointestinal tract. PCI is uncommon but increasingly is being recognized and reported. PCI was described by Du Vernoi in 1730 during cadaver dissection, and it has long been noted in animals. PCI occurs in two clinical settings: fulminant, which usually requires immediate surgery, and benign, an incidental finding at colonoscopy or laparotomy.
PCI has several possible causes, the most notable of which are mechanical and bacterial. The mechanical theory suggests that gas is forced into the bowel wall by one or more mechanisms: (1) pulmonary action, (2) trauma, (3) mucosal injury, (4) anastomoses, (5) obstruction, (6) increased pressure, or (7) increased peristalsis. Chronic obstructive pulmonary disease may be associated with PCI. Because coughing, artificial insufflation of the lungs, straining, and alveolar ectasia lead to alveolar rupture, air is thought to dissect into the mediastinum, along the great vessels to the retroperitoneum, and along the perivascular space, through the mesentery, to the bowel serosa. Experiments in the early 1960s showed that injection of air into a catheter inserted into the mediastinum of animals resulted in subserosal PCI of the colon and sigmoid. The distribution of PCI is related to the bowel vascular pattern and has been reported after such procedures as sigmoidoscopy, colonoscopy, and mucosal biopsy. Breaks in mucosal integrity, such as ulcerations, also may permit entry of intraluminal gas into the bowel wall. PCI has been reported after end-to-end anastomosis and with increased frequency in patients who have undergone a jejunoileal bypass. In these patients, the condition affects the bypassed small bowel—usually the midjejunum. Some investigators believe that the ileosigmoid anastomosis permits large bowel flora to enter the ileum, with subsequent increased gas production and cyst formation. Other researchers believe that the absence of bile may increase bacterial growth, leading to increased hydrogen production and cyst formation.
A bacterial origin of PCI is supported by several analyses of cyst gas. Normal luminal gas is approximately 15% hydrogen, compared with 50% hydrogen found in PCI cysts. Common species in the gut microbiome are known hydrogen producers. The bacterial cause of PCI is also supported by breath-hydrogen analyses of affected patients. Many patients with PCI have increased breath hydrogen levels, leading some investigators to postulate that the high amount of hydrogen produced by bacteria may be responsible for the persistence of cysts. Several investigators have injected organisms such as Escherichia coli, Enterobacter aerogenes, and Clostridium perfringens into intestinal submucosa in animals during experiments and were able to induce PCI. It is thought that a functional break in the mucosa, with penetration of bacteria into the submucosa or subserosa or both, may be involved in this formation of intestinal gas cysts. Interestingly, the phenomenon of PCI persists independent of the bacteria undergoing translocation. Decreased intestinal mucosal resistance to infection or ulceration also may lead to severe fulminant PCI, which occasionally is seen in adults.
PCI is still a relatively uncommon finding. It can be classified as either adult or infantile and can be benign or fulminant. Infantile PCI is usually submucosal and fulminant, as acute necrotizing enterocolitis, with edema of the bowel wall and dilatation of lymphatics. In adults, PCI is usually benign. However, fulminant PCI can occur with a high mortality rate despite surgery. The benign form can be divided into primary (idiopathic) and secondary forms. The cysts are submucosal, subserosal, or both, and are usually found incidentally. The secondary form of the disease accounts for approximately 85% of cases. PCI affecting the small bowel and ascending colon is thought to be secondary, whereas that affecting the descending colon is idiopathic or primary. Secondary PCI can be associated with a proximal gastrointestinal lesion such as pyloric stenosis or with chronic obstructive pulmonary disease. Box 69-1 illustrates some conditions associated with secondary PCI.
Intestinal obstruction or strangulation
Refractory celiac sprue
Neurogenic bowel dysfunction
Peptic ulcer disease, including pyloric channel lesion
Chronic obstructive pulmonary disease, including emphysema and asthma
Collagen vascular diseases
Exposure to alkyl halides, including chloral hydrate and trichloroethylene
Acquired immune deficiency syndrome
Histology and Gross Pathology
The histologic changes observed in PCI can be replicated by injecting air into subcutaneous tissue. After several days a foreign body reaction occurs with inflammation, development of a histiocytic lining, and pericyst fibrosis. The intestinal gas cysts of PCI are also surrounded by foreign body giant cells and macrophages ( Fig. 69-1 ). Serosal cysts usually occur near the mesenteric border, with only a few on the antimesenteric margin. Cysts are frequently located on loops of dilated bowel and range in size from a few millimeters to several centimeters. They can occur singly or in clusters, occasionally appearing like soap bubbles on the serosa ( Fig. 69-2 ). Submucosal cysts, although not visible, give the bowel a spongy consistency; cyst gas is under pressure and “hisses” when the cysts are punctured.