Answer: a) Pneumatosis intestinalis
Pneumatosis intestinalis (PI) refers to the observation of intramural gas within the small or large intestine. It can be seen in a linear or cystic fashion and may be found in the subserosa or submucosa of the intestinal wall.¹ Clinically, PI can be associated with a spectrum of illnesses, ranging from intestinal ischemia to benign causes. When symptoms are present, they typically include abdominal pain, diarrhea, abdominal distention, and hematochezia.¹ Now that CT imaging has become more common, PI is encountered more frequently in asymptomatic patients. Common clinical settings where PI is found include infants with necrotizing enterocolitis; adults suffering from chronic obstructive pulmonary disease (COPD); immunosuppressed individuals; patients with bowel ischemia due to various etiologies; and, occasionally, asymptomatic adults with benign clinical findings.¹ Although PI can be spotted endoscopically or grossly during surgery, it is usually encountered on plain radiographs or CT scans. PI is visualized best when viewed using the lung window setting on CT imaging.² Barium contrast may confirm the presence of intramural gas and often indicates the amount of gas that is present; however, this modality is contraindicated if the patient is known to have PI. Ultrasonography is another sensitive, commonly used imaging modality that is beneficial because of its ability to depict gas in the portal venous system.¹

There are three major hypotheses to explain the pathogenesis of PI. The mechanical theory states that tears along the bowel wall allow gas to dissect through it and form collections of gas in the submucosa.¹ Additionally, air could dissect into the venous drainage and travel into the portal venous system (Figure 2). When this occurs, the prognosis is grave, and the mortality rate reaches approximately 75%.³ The mechanical theory also explains how pulmonary illnesses like COPD can lead to PI. This occurs when air from ruptured alveoli tracks along the pulmonary vasculature into the mediastinum and then travels through the mesentery, ending up in the subserosal tissue.² The second theory states that the intramural cysts are caused by gas-producing bacteria in the bowel, such as Clostridium perfringens, which enter the mucosal layer due to breaks in the mucosal wall.¹ The third theory suggests that certain bacteria located in the intestinal lumen produce an excessive amount of hydrogen during food metabolism, which increases intraluminal pressure and causes gas to dissipate into the submucosa, resulting in PI. Interestingly, certain drugs, such as alpha-glucosidase inhibitors, can suppress carbohydrate digestion and cause excessive bacterial fermentation, which increases the production of hydrogen gas.^4,5

To help manage patients with PI appropriately, various clinical features should be monitored. These include careful observation of blood pressure, arterial blood gas, lactic acid and amylase levels, and routine examination of the abdominal area to rule out an acute abdomen. Patients who present with hypotension, metabolic acidosis, and elevated lactic acid and amylase levels, should undergo emergency exploratory laparotomy, because these findings suggest bowel necrosis, which could rapidly escalate to death.²

The prognosis of PI varies greatly, depending on the underlying illness. The treatment ranges from emergent surgery in cases where bowel necrosis is present to conservative medical management with antibiotics, oxygen therapy, and an elemental diet in cases where COPD or other non-life-threatening conditions are the cause.¹ Common antibiotics used to treat PI are metronidazole, tetracycline, ampicillin, and vancomycin.¹ Oxygen therapy is given to patients to decrease the intestinal hydrogen concentration and subsequently lower the intraluminal pressure in the bowel.¹ A study investigating the use of an elemental diet for PI treatment showed that symptoms can be alleviated in as little as 3 days and intestinal cysts can be removed within 2 weeks if patients are placed on a diet consisting of amino acids, simple sugars, fats, vitamins, minerals, and trace elements.⁶

References

1. Heng Y, Schuffler MD, Haggitt RC, et al. Pneumatosis intestinalis: a review. Am J Gastroenterol. 1995;90(10):1747-1758.
2. Pear BL. Pneumatosis intestinalis: a review. Radiology. 1998;207(1):13-19.
3. Knechtle SJ, Davidoff AM, Rice RP. Pneumatosis intestinalis. Surgical management and clinical outcome. Ann Surg. 1990;212(2):160-165.
4. Hisamoto A, Mizushima T, Sato K, et al. Pneumatosis cystoides intestinalis after alpha-glucosidase inhibitor treatment in a patient with interstitial pneumonitis. Intern Med. 2006;45(2):73-76.
5. Yanaru R, Hizawa K, Nakamura S, et al. Regression of pneumatosis cystoides intestinalis after discontinuing of alpha-glucosidase inhibitor administration. J Clin Gastroenterol. 2002;35(2):204-205.
6. Johnston BT, McFarland RJ. Elemental diet in the treatment of pneumatosis coli. Scand J Gastroenterol. 1995;30(12):1224-1227.