In this study, we analyzed the correlation between CT findings and clinical outcome of PVG and PI to reveal which CT findings can be useful in predicting life-threatening cases. We confirmed that the existence of extrahepatic venous gas was the strongest prognostic factor correlated with bowel ischemia. We also reinforced the best practice that treatment strategy be based on the unique characteristics of the underlying disease.
PVG was first described by Wolfe and Evans in 1955 in infants with necrotizing enterocolitis [23]. Liebman et. al. reported that the mortality rate was 75% and that surgical resection was considered the solitary life-saving treatment [7]. PI was first described in autopsy specimens by Du Vernoi in 1783 [20, 24]. Like PVG, PI was also implicated in mesenteric ischemia, and carried a high mortality rate of 33–44% [6, 24]. As non-lethal cases of PVG are detected in recent years, the reported mortality of PVG is decreasing to 25–39% [3, 4, 7]. Benign PI cases have also been reported in the literatures [2, 6, 25].
Various diseases induce PVG and PI. The main causes of PVG and PI in our study were bowel ischemia, enteritis and constipation. We performed operations on the patients with bowel necrosis, gastrointestinal perforation, and cholecystitis, but the cases of bowel necrosis and perforation had a poor outcome. Koizumi et. al. reported in their large-scale data analysis that the major causes of PVG were bowel ischemia or necrosis (53%), gastrointestinal obstruction or dilatation (10.3%), and gastrointestinal infection (8.3%) [10]. The mortality rates identified for bowel ischemia (26.8%) and gastrointestinal perforation (33.3%) were similar to our findings [10]. On the other hand, enteritis, constipation, hemodialysis, bowel obstruction without bowel ischemia, gastric dilatation, iatrogenic disease, and recoverable bowel ischemia were addressed with conservative treatment. This suggests that both PVG and PI are not ominous signs by themselves, as there are non-fatal cases in which patients have recovered with conservative treatment [11, 26]. Diverticulitis, inflammatory bowel disease, post-abdominal trauma, post-transplant surgery, barium enemas, and colonoscopy were also reported as non-lethal causes of PVG and PI [11, 25, 27]. The appropriateness of surgery as a treatment strategy can be determined by analyzing the underlying disease, as the most effective treatment strategies are directed at root cause rather than secondary manifestations [4, 5, 11].
CT scans are highly-sensitive tools for detecting PVG and PI [3, 4, 7, 28]. Moreover, contrast-enhanced CT imaging is a useful investigative tool for identifying the underlying disease, especially bowel ischemia and gastrointestinal perforation [18, 28, 29]. We assessed representative CT findings of acute abdominal disease. Poor enhancement of the intestinal wall is a typical finding in bowel ischemia. Intestinal dilatation is the result of bowel obstruction, and sometimes accompanies aperistaltic bowel ischemia and enteritis. Intestinal wall thickness and disproportionate fat stranding are indicative of acute enteritis, inflammatory bowel disease, and gastrointestinal perforation [30, 31]. From the results of our study, we concluded that only the existence of extrahepatic venous gas was correlated with poor prognosis, while the other CT findings can aid in diagnosis of underlying disease. The detection of extrahepatic venous gas is relatively easy in a contrast-enhanced CT scan (Fig. 2). Some authors also reported that wide spread PVG was correlated with poor prognosis [5, 13, 17, 29]. From a pathophysiological standpoint, wide spread PVG often indicates progressive mucosal damage and can reflect the severity of the patient’s condition [32]. On the contrary, there are reports that the amount of gas was not related to patient prognosis at all [12, 33]. Notably, the cases with free air in our study were correlated with better outcome, although free air is a finding often representative of high-mortality gastrointestinal perforation. Perhaps this is because PI is one of the causes for extraluminal free air, and some cases of PI accompanied free air without gastrointestinal perforation. In a previous study, it was reported that free air could occur with long-standing PI and is rarely associated with peritonitis [17]. The frequency of extraluminal free air with PI was reported at 24.7% [30]. The combination of PVG and PI is not related to outcome in our study, although some authors reported that it related to worse outcome [6, 25]. Overall, we suggest that extra hepatic venous gas and poor enhancement of the intestinal wall are useful findings to predict bowel ischemia as well as determine the suitability of surgical treatment. Special caution should be used in cases with free air and PI in order to avoid futile laparotomy.
In addition to CT scan findings, data garnered from physical examinations, vital signs and laboratory tests were also prognostic factors for PVG and PI in previous literature. Higashizono et. al. reported that elevated levels of CRP, creatinine and lactate were correlated with bowel necrosis [1]. Abboud et. al. suggested that pre-existing chronic illnesses such as chronic renal failure, diabetes mellitus and hypertension affect the outcomes [11]. But the factors reported were numerous, and there is no consensus on which factor is the most reliable. In our study, advanced age and elevated CRP were significantly associated with severe cases in the univariate analysis.
PVG is considered to be an exacerbated form of PI with the same pathophysiology [2, 24, 34]. Since the liver is the drainage site in PI, PVG may indeed signal an advanced stage of PI [2]. Actually, PVG cases were related with group 1 more than with PI in this study. However, we should keep in mind that some cases of PI may include severe cases.
Our study was limited by a few factors: exclusion of data from institutions other than our own, relatively small sample size, and heterogeneity of patient conditions at first examination, as patients presented with variable physical manifestations after transfer to our hospital. There was also a degree of unfavorable selection bias of cases in regard to surgical treatment: some patients who required surgery could not receive the appropriate treatment due to their physical condition or advanced age.