The Deceptive Nature of Pneumatosis Intestinalis: From Spontaneous Resolution to Bowel Ischemia

DISCUSSION

DuVernoy first described pneumatosis intestinalis in 1730.¹⁷ In 1995, the incidence in the general population was reported to be 0.03%¹⁸; however, advanced imaging techniques have led to greater detection rates, with Morris et al reporting an incidence of 0.37% in 2008.¹⁹ Pneumatosis intestinalis can occur at any age, with a higher incidence in older patients.⁹ Although the entire gastrointestinal tract can be affected, the small bowel is the most common location (42%), followed by the colon (36%).²⁰

Symptoms of pneumatosis intestinalis are not necessarily related to the presence or location of intramural gas in the gastrointestinal tract but rather to the underlying disorder.^2,21 Moreover, the extent of pneumatosis intestinalis does not correlate with the severity of symptoms or underlying disease.²² Presentation is variable, ranging from asymptomatic incidental radiographic findings to a variety of gastrointestinal signs and symptoms such as abdominal distention, pain, nausea, and vomiting.^10,11,21 In a retrospective analysis of 919 cases of pneumatosis intestinalis, diarrhea, bloody stools, abdominal pain, constipation, weight loss, and tenesmus were the most common related symptoms.¹³ Although pneumatosis intestinalis can arise from benign conditions that are neither obstructive nor ischemic,⁹ life-threatening conditions typically involve bowel ischemia.⁶ Delays in surgical intervention can result in high mortality rates, with reports showing that patients who undergo surgery within <6 hours tend to have a lower mortality rate.¹² Pneumatosis intestinalis in conjunction with a serum lactate concentration of ≥2.0 mmol/L, hypotension, metabolic acidosis, tachycardia, abdominal tenderness, and a thickened bowel wall has been associated with increased mortality.¹² Additionally, Hawn et al reported >80% mortality when serum lactate concentration was ≥2.0 mmol/L at the time of pneumatosis intestinalis diagnosis.²³

While primary pneumatosis intestinalis is rare, a considerable number of diseases and disorders have been implicated as a potential cause.^1,6 Although the definite pathogenesis of pneumatosis intestinalis remains unclear, mechanical, bacterial, and pulmonary causes have emerged as possible explanations among the various theories of underlying mechanisms behind this pathology.^9,10,11,24

The mechanical theory proposes that increased intraluminal pressure causes gas migration from the luminal space into the intestinal wall where the gas accumulates to form cysts.⁹ The bacterial hypothesis suggests that air-producing bacteria penetrate the intestinal mucosal barrier, causing gas to become trapped within the submucosa and lymphatic channels.²⁴ This theory is supported by the observation that pneumatosis intestinalis has resolved with the use of metronidazole.^15,25 The pulmonary theory attributes increased intraluminal pressure to the respiratory system.^10,11 Chronic lung conditions, such as chronic obstructive pulmonary disease, asthma, and interstitial pneumonia can cause alveolar rupture, allowing air to travel through the mediastinum into the perivascular spaces, ultimately reaching the intestinal wall.^10,11,26

The diagnosis of pneumatosis intestinalis is generally based on findings from plain radiographs or CT scans that demonstrate extraluminal gas in the bowel wall.^2,8 CT is regarded as the more sensitive diagnostic tool because it can detect important secondary signs that may indicate an underlying cause of pneumatosis intestinalis, including bowel wall thickening, altered mucosal enhancement, abnormally dilated bowel, soft tissue stranding, portal venous gas, and ascites.²⁷ Imaging commonly also reveals features suggestive of free intraperitoneal gas.⁸ Importantly, in the setting of pneumatosis intestinalis, pneumoperitoneum alone should not automatically suggest a perforated viscus, as free air can result from the perforation of individual gas-filled cysts.²⁸ CT imaging can help identify the distribution of gas and thereby assist in determining the cause of pneumatosis intestinalis.³

Useful laboratory tests include a complete blood count with differential, pH, serum bicarbonate, lactic acid, and serum amylase. Knechtle et al reported that the presence of metabolic acidosis, particularly lactic acidosis, and an elevated serum amylase level suggest ischemic bowel.²¹ In the Knechtle et al study correlating laboratory results with ischemic bowel, pH <7.3, serum bicarbonate <20 mmol/L, lactic acid >2 mmol/L, and serum amylase >200 IU/L were predictive of necrotic bowel and were associated with lower survival rates compared to patients with normal values.²¹

Management should be guided by a combination of radiographic findings, physical examination, and a carefully obtained medical history, primarily focusing on determining if the underlying pathology of pneumatosis intestinalis is benign or life-threatening.⁹ Patients with pneumatosis intestinalis on imaging and who present with abdominal pain, tenderness, diarrhea, fever, rectal bleeding, or hypotension are considered to have a severe clinical condition that requires surgery.²¹ However, patients negative for abdominal pain, leukocytosis (white blood cell count <12 mm³), sepsis, or acidosis would benefit from medical support and observation.¹²

Therapy is tailored to the suspected etiology. For as many as 50% of patients, treatment is largely supportive and nonspecific.¹¹ While infectious causes usually require urgent intervention, pulmonary causes can be managed conservatively.^29,30 However, because the overall mortality rate in patients with pneumatosis intestinalis ranges from 22% to 50%, nonsurgical management should be approached with caution.⁸

In our case, although the patient was not peritonitic during the physical examination, she continued to have persistent abdominal tenderness in the area of the small bowel pneumatosis intestinalis identified on CT scan. Additionally, despite the absence of acidosis in her laboratory results, the patient arrived with hypotension and leukocytosis, concerns that led us to opt for surgical management to rule out bowel ischemia. The patient had no lung pathology or other conditions that could explain her physical examination findings, laboratory abnormalities, or imaging results.

Conservative management includes observation, hyperbaric oxygen, and antibiotic therapy.³¹ Oxygen treatment is based on creating a high partial pressure of oxygen (PaO₂) gradient that promotes gas outflow through the cyst wall. The cysts release the gas in them and refill with oxygen, which is subsequently metabolized, leading to resolution.³¹ Antibiotic therapy primarily aims to reduce anaerobic bowel flora to mitigate gas production, and metronidazole is a commonly used agent.^15,25 Treatment typically continues until clinical and radiologic resolution is achieved.¹⁵ On the other hand, surgery is the preferred treatment for patients experiencing severe abdominal pain and metabolic derangements such as acidosis, which more likely indicate a state of ischemic or threatened bowel.^1,21,32

Although our patient ultimately did not benefit from surgical exploration, we believe that when a patient has an unclear clinical presentation, shows some signs of possible bowel ischemia, and does not have an obvious benign cause for pneumatosis intestinalis, a laparotomy may be beneficial.