Pathogenic mechanisms of intestinal pneumatosis and portal venous gas: should patients with these conditions be operated immediately?
© Mitsuyoshi et al. 2015
Received: 15 June 2015
Accepted: 1 October 2015
Published: 15 October 2015
We aimed to histologically observe portal venous gas (PVG)-causing intestinal pneumatosis (IP) and evaluate pathogenic mechanisms and therapeutic strategies, including decisions on whether emergency surgery should be performed. Autopsy was performed in two cases of nonocclusive mesenteric ischemia (NOMI). We directly histologically observed the pathogenic mechanisms of IP caused by gas-producing bacteria and IP considered to be caused by mechanical damage to the intestinal mucosa. IP can be classified hypothetically into the following types according to pathogenesis: (1) infection, (2) rupture (damage) of the intestinal mucosa + increased intestinal intraluminal pressure, and (3) mixed type. In cases of IP caused by gas-producing bacteria or IP associated with intestinal wall damage extending beyond the mucosa to the deep muscular layer, emergency surgery should be considered. However, it is highly possible that patients who test negative for infection with gas-producing bacteria whose intestinal wall damage remains only in the mucosa can be conservatively treated.
For a long time, portal venous gas (PVG) has been considered to be a sign of poor prognosis in abdominal diseases [1, 2]. Especially when PVG is caused by intestinal necrosis due to ischemia, the mortality rate is high even after emergency laparotomy with intestinal resection [1, 3]. Although PVG-causing intestinal pneumatosis (IP) can be broadly classified into IP caused by intestinal wall infection with gas-producing bacteria and IP caused by mechanical rupture of the intestinal mucosal wall [4, 5], no report has clearly described the actual processes of the conditions by using histological findings. In the two cases of nonocclusive mesenteric ischemia (NOMI) that we experienced, we directly observed IP from a histopathological perspective. We report a summary of the pathogenic mechanisms and primary diseases, as well as therapeutic strategies and prognosis, in these two cases, along with a brief literature review.
PVG was first reported in neonatal cases by Wolfe et al. in 1955 , while the first adult cases were reported by Susman et al. in 1960 . Since then, PVG and IP have often been reported in cases of severe necrotizing enterocolitis associated with ischemia, such as SMA embolism and NOMI. In the past, PVG and IP were regarded as signs of poor prognosis [1, 2] and pathological conditions for which emergency surgery such as intestinal resection should first be considered. In recent years, with wide adoption of multidetector-row computed tomography (MDCT), the number of cases diagnosed in the relatively early stage or cases without severe infection has also increased , and a number of conservatively treated cases have also been reported [7–9]. However, in our literature search, we did not find any report of a detailed morphological analysis of the actual mechanisms; thereby, IP was caused by infection, without infection, or by mechanical mucosal damage.
In the two cases of NOMI that we recently experienced, we made the hypothesis about the pathogenic mechanisms of IP from a histological perspective. In cases of not only NOMI but also intestinal ischemia, damage due to these conditions first occurs in the mucosa and then gradually spreads to all muscular layers. However, in case 1, the mucosal necrosis and consequent mucosal rupture (laceration) were mild, and no damage caused by the ischemia was observed in the submucosal layer, muscular layer, or serosa. Intestinal gas was observed that might have migrated to the lacerated mucosa and seeped into the deep muscular layer and then further into wall-damaged blood vessels; no bacterial infection was observed in the intestinal wall. Unfortunately, the patient in this case died of heart failure. However, we assume that the NOMI in this case could have been treated conservatively without performing surgery.
In case 2, although the autopsy findings were consistent with findings in NOMI, the findings in intestinal infection associated with necrosis were histologically more apparent than those in necrosis caused by intestinal vascular insufficiency. We observed that gas was directly produced in the intestinal wall and migrated into blood vessels. This pathological condition would ultimately lead to perforation and was normally indicated for emergency surgery aimed at intestinal resection. However, the patient rapidly went into shock, because of which we missed the timing of surgery. This case characteristically showed that a Gram-negative bacillus formed colonies around the pneumatosis, while a Gram-positive bacillus tended to form colonies in areas slightly away from the pneumatosis. In order to determine whether these findings are universal trends, future research reports are needed.
Our hypothesis about classification of IP
Gas-producing bacteria infect and colonize the intestinal wall. Mucosal rupture is not always involved.
Sepsis caused by acute mesenteric ischemia and others.
Highly likely to have severe infection or to have already developed sepsis, and a fatal outcome is likely.
Emergency surgery should first be considered.
② Mucosal rupture + increased intraluminal pressure
Intestinal gas seeps into the damaged mucosa and gradually migrates to the deep layer; infection does not always occur concomitantly.
Inflammatory bowel disease, gastric cancer or ulcer, ileus, severe constipation, blunt abdominal trauma, and so on.
The risk of perforation is low when the extent of mucosal rupture is limited. If the rupture persists for a long time, it will be complicated by bacterial infection and progress to the above “infection.”
Emergency surgery is not always required.
③ Mixed type
① + ②
Regarding NOMI associated with IP, we have histopathologically made the hypothesis about the pathogenic mechanisms, summarized the diseases that can cause NOMI, and discussed therapeutic strategies and prognosis, along with a brief literature review.
In addition to NOMI are many other gastrointestinal diseases that cause PVG and IP. In gastrointestinal diseases associated with intestinal necrosis, the incidence rates of concomitant PVG and IP are high and fatal outcome is highly likely. Thus, whether PVG and IP are caused by infection or mechanical mucosal rupture should be definitively determined, and treatment should be applied based on pathological conditions. Even in patients with conditions complicated by PVG and IP, the chance of survival is good depending on the causative factors. Thus, treatment should not be easily abandoned.
Written informed consent was obtained from the patient for publication of this case report and any accompanying images. A copy of the written consent is available for review by the Editor-in-Chief of this journal.
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