Self-Limited Pneumoporta in the Era of Computed Tomography: A Case Report and Review of the Literature

Pneumoporta in patients with abdominal pain has been thought to be suggestive of fatal underlying conditions, such as mesenteric infarct, requiring emergency treatment. Widespread use of computed tomography (CT) has increased the frequency of detection of pneumoporta in patients with diseases other than mesenteric infarct. The natural course of resolution of pneumoporta has been rarely discussed in the literature and mainly focused on patients with iatrogenic diseases. Herein, we report the case of a 64-year-old woman who presented at our emergency department with positive peritoneal signs and pneumoporta. A 10 cm long segment of resolved ischemic bowel was detected on exploratory laparotomy, and bowel resection was not performed. Follow-up CT performed 62 hours later revealed complete resolution of pneumoporta. The patient was discharged uneventfully and was administered short-term prophylactic therapy with enoxaparin for thromboembolism. The epidemiology, etiology, and resolution of pneumoporta are also reviewed.


Background
Pneumoporta has been thought to be an ominous radiological sign.However, the etiology is associated with various diseases ranging from severe fatal conditions requiring rapid surgical intervention to medical diseases with a benign course.Treatment of pneumoporta should be based on the etiology of the condition.The natural course of resolution of pneumoporta has rarely been discussed in the literature.Here, we report a case of a 64-year-old woman with spontaneously resolved ischemic bowel and pneumoporta, and the epidemiology, etiology, and resolution of pneumoporta are reviewed.

Case Presentation
A 64-year-old woman presented at our emergency department with intermittent abdominal pain for 3 days without vomiting or dysentery.The patient was otherwise healthy, but had a history of spinal surgery and was a carrier of the hepatitis B virus.She did not have a history of hydrogen peroxide ingestion.Upon arrival at the emergency department, her vital signs were stable and consciousness was clear.Physical examination revealed distended abdomen and diffuse peritoneal sign.Laboratory examination showed no leukocytosis, but a mild left shift.Lactic acid levels were within the normal range.Abdominal CT scan showed the presence of air in the portal venous tree in the left hepatic lobe, patent superior mesenteric artery (SMA), and superior mesenteric vein, and bowel wall thickening and distension of the ileum were noted (Figures 1 and 2).The patent SMA, as detected by the abdominal CT scan, was also observed.The patient underwent emergency exploratory laparotomy.Intraoperative examination revealed a 10 cm long segment of the resolved ischemic ileum with a thickened wall and no transmural infarction.The liver surface was noncontributory.Follow-up abdominal CT performed 62 hours after laparotomy revealed complete resolution of hepatic portal venous gas (Figure 3).A series of workups for the thromboembolic event, including cardiac echography and coagulation studies for autoantibodies, factor VIII, protein C, and protein S, yielded no abnormal data except elevated levels of D-D dimer and factor VIII.The patient was discharged uneventfully and was administered shortterm prophylactic therapy with enoxaparin for thromboembolism.

Discussion
Pneumoporta has been considered to be an ominous radiological sign.However, pneumoporta may be associated with conditions ranging from severe fatal diseases requiring urgent surgical intervention to medical diseases that follow a benign course, such as gastroenteritis, which can be managed with only conservative treatment [1,2].A mortality rate as high as 75-90% has been reported, mainly owing to the occurrence of mesenteric infarction [3][4][5].Nowadays, the widespread utilization of CT scan has increased the frequency of detection of pneumoporta in the clinical scenario [6,7].Indeed, mesenteric infarctions are the main etiological factors that lead to potentially fatal outcomes and should always be considered when diagnosing the cause of pneumoporta [8,9].In addition, because of the increased frequency of occurrence of benign diseases [2,6], prompt clinical evaluation and surgical decision are paramount in cases of pneumoporta.
CT scan enables early detection due to high sensitivity for pneumoporta and is superior to other radiological modalities, including ultrasound and abdominal plain film, in diagnosis of underlying abdominal diseases [7].Since the 1970s, the introduction of the CT scan has gradually advanced the ability of physicians to accurately diagnose pneumoporta, and pneumoporta can now be detected at less advantaged stages [7].More than half of the etiologies of pneumoporta were mesenteric infarct, reported to account for 61-75% of cases [3,8,10].Other etiologies include gastrointestinal dysmotility, infectious/inflammatory processes, toxicity-related conditions, and iatrogenic lesions [11,12].Notably, the appearance of pneumoporta in relation to iatrogenic causes increase in frequency over recent decades [8].
The correlation of outcomes and the presence of pneumoporta, as well as the duration of pneumoporta, have not been clearly elucidated [3,9].The appearance of pneumoporta is associated with poor outcomes in patients experiencing cardiac arrest outside of the hospital [13].Nevertheless, the notoriously high mortality generally encountered in patients with pneumoporta has decreased to 25-29% in recent reports, mainly due to early detection and incidental findings during the diagnosis of other diseases [9,14,15].Furthermore, the resolution of pneumoporta has been shown to be associated with the improvement of the underlying diseases.
In order to investigate the clinical characteristics of pneumoporta resolution in the era of CT scan, we reviewed the English literature by searching for the keyword "portal venous gas" or "hepatic portal venous gas" in PubMed.The age, sex, etiology, diagnostic modality (including conventional roentgenography, ultrasound, and CT scan), duration of pneumoporta, and patient outcomes were reviewed.Patients who were diagnosed as pneumoporta on CT scan were included in the study.The exclusion criteria were listed as following: the patients died of fulminant mesenteric infarct without CT followup, the unclear recording about resolution of pneumoporta, or the detection of pneumoporta by the radiological modalities other than CT scan.A total of 61 cases were eligible and are listed according to the etiology (Table 1).Several classifications have been proposed in literature, and the system we used here was based on  -: not mentioned in the literature.* whether the causes were iatrogenic or not because the classification conveyed clinical usefulness and prognostic prediction [12,16].For demography available in the literature, the male/female ratio was 1.5, with a mean age of 53.4 years (range, 10 to 94 years).Iatrogenic etiologies were the main causes of pneumoporta (61%).The resolution of pneumoporta was associated with the improvement of underlying diseases, and the reported duration of pneumoporta ranged from 20 min to 2 months.
The correlation between lethal potentiality and pneumoporta is unclear.The risk of hepatic flow compromise by air accumulating in the portal systems may be taken into consideration.However, pneumoporta itself rarely affected hepatic flow in both animal and human studies.The observation might be explained by the anatomy of the dual blood supply of liver [17,18].Accordingly, researchers have assumed that the pathophysiological mechanism responsible for the onset of pneumoporta is the cause of death, not the air bubbles themselves [17].The detailed mechanism necessitated further study.

Noniatrogenic Causes
For noniatrogenic causes, improvement of pneumoporta in patients with mesenteric infarct was rarely reported, possibly because of the fulminant course of these underlying conditions.The appearance of pneumoporta in mesenteric infarct is associated with high mortality and morbidity [53].Other diseases in which pneumoporta has been noted include gastrointestinal dysmotility, infection/inflammation, and medication/toxicity-related conditions.The outcomes in these situations were satisfactory following prompt surgical intervention.Notably, various medical diseases are predisposing factors for pneumoporta and do not mandate surgical intervention.In these cases, pneumoporta is usually noticed incidentally, and the course is usually self-limited.Transient ischemic enteritis has been reported to be a cause of pneumoporta and can also be successfully managed conservatively [54].

Iatrogenic Causes
The course of pneumoporta after iatrogenic events is generally benign and transient, lasting no more than 1 day in the majority of cases.Incidental discovery of pneumoporta usually urges clinicians to repeat the imaging examination and followup with the patients closely, as shown in the literature.The appropriate treatment for iatrogenic cases seems to "wait and see," except in one patient who died of portal vein thrombosis and sepsis after cryotherapy [43].
Diffuse peritoneal signs and wall thickening of the small bowel revealed by physical examination and CT scan, respectively, in the presence of pneumoporta is a condition that requires urgent surgical intervention [6].The condition may be suggestive of an underlying clinical condition, such as mesenteric ischemia/infarction.However, in our case, only one segment of the thickened small bowel, which seemed to be the resolved ischemic bowel, was observed during the intraoperative examination.This patient is alive, and bowel resection was not required.
The natural course of pneumoporta is rarely discussed systemically in the literature and is only sporadically reported in patients with iatrogenic diseases [24,29,44].In our case, sequential CT scan performed 62 hours after laparotomy revealed complete resolution of pneumoporta.This observation implies that pneumoporta may be a paraphenomenon that disappears when the underlying pathology is improved.
There were some limitations in our review.First, the duration of pneumoporta was ambiguous, lacking a clear definition and strict control.Actually the duration recorded in the paper indicated a potential period that the pneumoporta may exist.Second, the appearance of pneumoporta was regarded as a paraphenomenon in benign diseases; therefore, the follow-up modalities depended on clinicians' judgment in the absence of standard protocol.Third, the real incidence of self-limited pneumoporta might be underestimated because the "benign" pneumoporta would disappear spontaneously.We believed the occurrence of pneumoporta would outnumber the cases recorded in the literature.In despite of the above-mentioned limitations, we are convinced that our study offers a general description of current self-limited pneumoporta reported in the English literature.The overall survey pointed out some undiscovered issues concerning the pathophysiology and clinical outcomes of pneumoporta.

Conclusion
Mesenteric infarct should always be considered when diagnosing the cause of pneumoporta accompanied by positive peritoneal signs.The diagnosis of pneumoporta merely based on radiological findings is an intriguing possibility, and the management of pneumoporta should be based on etiological findings.In our case, spontaneous resolution of pneumoporta was observed.

Figure 1 :
Figure 1: Computed tomography (CT) scan showed the presence of gas in the portal vein, mainly in the left hepatic lobe.

Figure 3 :
Figure 3: CT performed 62 hours after laparotomy showed complete resolution of hepatic portal vein gas.

Table 1 :
Clinical characteristics and outcomes of pneumoporta resolution in reported cases in the literature.