Teaching Case

A 57-year-old female patient was first admitted to hospital for a typical cerebral haemorrhage. During hospitalisation abdominal distension with light diffuse abdominal pain and constipation occurred with nausea and vomiting, but no fever. Haematological examination revealed a small increase of white blood cells (12, 000/mm3) and a PCR of 100mg/ML. Non important anamnestic details.

Abdominal LL radiograph showed a gross dilatation of the bowel, especially of colon (haustral markings), with multiple air-fluid levels (Fig.1).
CT showed a massive dilatation of caecum (9.8cm) and ascending colon filled with faeces. The main finding was the presence of gas between the wall and the intestinal content initially suggesting the diagnosis of pneumatosis intestinalis.
However, the gas collection did not extend proximally but stopped at the free gas-fluid level with an irregular punctuated pattern. No significant wall thickening and peri-intestinal soft-tissue stranding were detected (Fig.2). No other CT findings, such as mesenteric venous gas or artery thrombosis, were present. All these signs are in keeping with the diagnosis of pseudo-pneumatosis instead of pneumatosis intestinalis.
Colonoscopy confirmed a large mass of stool partially stuck to the mucosal folds and associated with moderate inflamed mucosa.
The patient received a conservative therapy and was dismissed with the diagnosis of unspecified colitis with intestinal subocclusion (Fig.3).

Pseudo-pneumatosis intestinalis is defined as the presence of intraluminal beads of gas trapped within or between faeces and the adjacent mucosal folds and may mimic the intramural gas of pneumatosis intestinalis [1].
The causes of pneumatosis intestinalis are traditionally divided into two categories: benign conditions (such as asthma, scleroderma and pyloric stenosis) and life-threatening conditions (such as bowel obstruction, necrotising enterocolitis, bowel ischaemia, cancer, trauma and drugs) [2, 3]. The most common life-threatening cause of pneumatosis intestinalis is bowel ischaemia [2]. Awareness of features that may differentiate between pneumatosis and pseudo-pneumatosis (an incidental imaging diagnosis) is critical for appropriate clinical management [4].
Patients with either pseudo-pneumatosis or benign causes of pneumatosis may be asymptomatic or present with mild-to-moderate symptoms [5]. Patients with life-threatening causes of pneumatosis may present with moderate to severe abdominal symptoms [4, 6, 7].
Abdominal radiography and CT are the most common imaging techniques used to detect the presence of gas collections. CT is the best imaging investigation because of its high sensitivity for detecting even small gas collections [8, 9] and its accuracy for detecting other findings suggestive of predisposing diseases.
CT findings useful for differentiating pseudo-pneumatosis versus pneumatosis include the location, distribution and pattern of gas. Pneumatosis intestinalis occurs focally or throughout the small bowel or colon [10]. Pseudo-pneumatosis is more frequently seen in the caecum and ascending colon (because of an admixture of liquid stool and gas) (Fig.2). The distribution of gas at the interface of the intestinal wall, which may reflect bowel wall alterations, is a useful tool because a gas collection against the bowel wall that stops at the free gas-fluid level within the bowel lumen suggests pseudo-pneumatosis (Fig.2), whereas gas along the bowel wall beyond the gas-fluid level is more consistent with pneumatosis intestinalis [11] (Fig.4). The pattern of gas may also be a helpful discriminator. An irregularly punctuated gas column pattern (from intact mucosal folds) is more commonly seen with pseudo-pneumatosis intestinali, while a relatively smooth contiguous gas column pattern (reflecting oedematous bowel wall) is suggestive of pneumatosis intestinalis [1] (Fig.2, 4).
Additional CT findings such as portomesenteric venous gas, mesenteric oedema and bowel wall thickening, vascular embolisation, bowel obstruction from a concomitant mass and pneumoperitoneum can be important signs indicative of the presence of pneumatosis intestinalis.
Although the clinical management of pneumatosis intestinalis should be ultimately made on the basis of multiple factors, including clinical symptoms, physical examination findings and laboratory test results [6], the knowledge of these key CT imaging findings may prevent an erroneous diagnosis of potentially life-threatening bowel ischaemia [1].