Benign pneumatosis: Importance of patient history, symptoms and imaging

A 60-year-old asymptomatic male patient with dermato-polymyositis-associated interstitial lung disease was admitted for pre-lung transplant workup. A chest CT was performed showing interstitial lung disease patterns (ground-glass opacities and reticulations). Slices passing through the superior abdomen showed intestinal parietal pneumatosis and extra-visceral gas. An abdominal CT was performed subsequently.

Abdominal CT scan (pre and post-intravenous contrast injection in venous phase) showed parietal pneumatosis of the ascending colon extending until the hepatic flexure. Extra-visceral gas was seen in the pericolic anterior pararenal space, spreading along the Toldt fascia through de ascending mesocolon in the retroperitoneal retromesenteric plane. No abnormal bowel distention or contrast enhancement defect was seen within the intestinal walls. There was no gas within the vascular structures, and no significant peritoneal abnormalities were observed. There was no clinical or biological acute abnormality, so the patient was released after imaging.

CT scan identification of pneumatosis intestinalis is not to be taken lightly as it is a pathological state of intestinal wall seen in life-threatening conditions such as acute mesenteric ischaemia, intestinal obstruction, trauma, ingestion of corrosive agents, colitis/enteritis and organ transplantation. In less common occasions, it is associated with relatively benign conditions and is known as benign pneumatosis or pneumatosis cystoides intestinalis when the amount of air is conspicuous. It may be associated with a wide variety of etiologies, including ileal surgery, colonoscopies, chronic pulmonary diseases, connective tissue disorders and ingestion of sorbitol or lactulose [1].

Connective tissue disease as dermato-polymyositis was the most probable aetiology for our patient. The mechanism leading to gas within the intestinal wall is unclear but some theories have been proposed: mechanical theory (a mucosal defect allowing bowel gas to travel into lymphatic channels and redistributed by peristalsis)[2], bacterial theory (submucosal localization of fermenting Clostridia and E.Coli releasing gas within the submucosa and lymphatic channels)[3] and pulmonary theory (pulmonary conditions leading to rupture of alveoli frees gas into the mediastinum into the retroperitoneal space and via the perivascular spaces into the intestinal wall)[4].

In all conditions, air can also be found extramurally as in the present case.

Identifying features that allow the differentiation between the more common life-threatening pneumatosis and the rare and innocuous condition of benign pneumatosis is therefore important. Clinically, patients with the former usually describe abdominal pain (moderate or severe) and distension as well as diarrhoea and/or bloody stools. Patients with benign pneumatosis are usually asymptomatic but may present mild respiratory and abdominal symptoms (shortness of breath or chronic abdominal pain and constipation for instance)[5].

Imaging features[6] also help in differentiating pneumatosis from its pitfall of pseudo-pneumatosis, corresponding to intraluminal beads of gas trapped within or between stools and intestinal mucosa folds. Topography of pneumatosis is usually focal or throughout the small bowel or colon, while pseudo-pneumatosis is common in the caecum and ascending colon. Distribution of the gas within the intestinal wall that stops at the same level as the free gas-fluid level is more likely to be pseudo-pneumatosis while if it continues beyond this level is more likely to be pneumatosis. The pattern of gas is usually irregular and punctuated in pseudo-pneumatosis, while a smoother gas column pattern is more consistent with pneumatosis. Findings such as portomesenteric venous gas, vascular embolization, cancer and pneumoperitoneum can also tip the balance in favour of pneumatosis.

Mistaking the two conditions may be potentially life-threatening as the management is radically different and depends on the underlying causes of each one. Patient clinical history, symptoms and imaging features are necessary in the distinction between the two seemingly similar yet drastically different conditions.