A large air cyst in the peritoneal cavity can present diagnostic and therapeutic dilemmas.
CASE HISTORY
A man aged 82 was seen after a week of gradually increasing dull left upper quadrant abdominal pain, worsened by movement and associated with abdominal distension and constipation. There was no history of nausea, vomiting, change in bowel habit or weight loss. The medical history included rheumatoid arthritis and peptic ulcer disease. On examination he had a non-tender central abdominal mass, resonant on percussion. A plain abdominal X-ray showed a large central air-filled cyst, and air was seen throughout the colon and rectum. On contrast-enhanced CT (Figure 1) the cyst was 15 cm in diameter and did not seem to communicate with the bowel (no entry of contrast material taken orally).
Figure 1.
Contrast enhanced axial CT image confirming a thin-walled air-filled structure with no communication to the sigmoid colon (white arrows)
At laparotomy the cyst proved to be adherent to the bladder and sigmoid colon. It contained only gas—no urine, fluid or faeces—and no communication with the bowel wall or bladder wall was seen. The large bowel was free from diverticular disease but a few diverticula were noted along the mesenteric border of the jejunum.
The cyst was excised. Postoperatively, the obstructive symptoms completely resolved but the patient later developed pneumonia and died. On histological examination, faecal and food material was identified in granulation tissue within the lining of the cyst wall. In addition there was a small amount of colonic muscularis mucosa. The lesion was therefore categorized as a type I giant colonic diverticulum (Box 1).
Box 1.
Histological types of giant colonic diverticulum
| Type I | Pseudodiverticulum | Composed of granulation tissue and remnants of muscularis mucosa |
| Type II | Inflammatory diverticulum | Arises from local perforation and communicates with an abscess cavity |
| Type III | True diverticulum | Contains all the layers of bowel wall |
COMMENT
Preoperative diagnosis of a giant colonic diverticulum can be difficult even with the aid of contrast-enhanced CT and barium enemas. Most patients are in their 60s or over, and the presentation can be acute or chronic. In some the symptoms are due to complications such as volvulus, bowel obstruction, perforation, rectal bleeding or even carcinoma.3 Giant colonic diverticula are caused by entry of gas that cannot escape because of a ball-valve mechanism. Usually they originate from the sigmoid colon. The differential diagnosis includes duplication cysts and pneumatosis intestinalis. On CT, duplication cysts are usually fusiform and fluid filled, whereas giant colonic diverticula tend to be oval, central and gas-filled. Duplication cysts differ from types I and II giant colonic diverticula in including all four layers of the bowel wall. Type III (true diverticula) do show all four walls and are less easily distinguished. In pneumatosis intestinalis, multiple air-filled cysts arise on the mesenteric border of the intestine and their walls contain only smooth muscle.
Regarding treatment, successful needle aspiration has been reported, but without long-term follow-up.4 Some surgeons recommend diverticulectomy to prevent recurrences;5 others do not, because of the surrounding inflammation and the possibility of a wide diverticular neck.1,2 Colectomy is an alternative, and seems to have the same complication rate as diverticulectomy.2
References
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