CASE SUMMARY:

A 56-year-old man presented with acute onset of abdominal pain. The patient had

no history of inflammatory bowel disease or recent trauma and no recent interventions, such as endoscopy or contrast enema. An abdominal CT scan was performed (figures 1 to 3).

DIAGNOSIS:

Portal venous gas.

In this patient, it was associated with nonfatal, nonhemorrhagic pancreatitis. The differential diagnosis for portal venous gas includes necrotizing enteritis, arterial and venous mesenteric occlusions, bowel obstruction, perforated gastric ulcer, hemorrhagic pancreatitis, sigmoid diverticulitis, and various iatrogenic causes.

DISCUSSION:

The CT demonstrated air in the peripheral segments of the intrahepatic portal vein radicles, in the extrahepatic portal vein, in the superior mesenteric vein, and in the splenoportal junction. The differential diagnosis for portal venous gas includes necrotizing enterocolitis with mesenteric arterial thrombosis, other arterial and venous occlusions, bowel obstruction, perforated gastric ulcers, sigmoid diverticulitis, iatrogenic causes, and hemorrhagic pancreatitis. At the level of the head and uncinate process, the pancreas was enlarged, with stranding of the adjacent fat. Clinically, there was no evidence of bleeding; the hematocrit was stable, and, on the nonenhanced CT scan of the abdomen, no high-attenuation soft-tissue density was noted in or adjacent to the pancreas to suggest hemorrhage. Moreover, there was no evidence of intramural bowel gas, and no peripancreatic pseudoaneurysms were identified. An ultrasound of the abdomen did not identify any gallstones. A follow-up CT scan of the abdomen with IV contrast was performed approximately two weeks later and showed peripancreatic fluid collections, the largest of which was noted in the lesser sac, and resolution of the portal venous gas (figure 4). The peripancreatic fluid collection was drained percutaneously and the patient survived this episode with an extended ICU and hospital course.

Gas within the portal venous system was first reported in 1955 by Wolfe and Evans in a series of six pediatric cases with necrotizing enteritis associated with mesenteric arterial thromboses.1 The first report of portal venous gas in adults was by Susman and Senturia in 1960;2 since then, multiple causes of portal venous gas have been described. These include arterial and venous mesenteric occlusions, bowel obstruction, perforated gastric ulcers, hemorrhagic pancreatitis, sigmoid diverticulitis, and various iatrogenic causes.3 This report is the first description of a case of nonfatal portal venous gas associated with nonhemorrhagic pancreatitis.

The detection of portal venous gas is not a specific disease but rather a feature common to many serious illnesses, which may be diagnosed with plain films, ultrasound,4 or CT.5 Portal venous gas is diagnosed radiographically by the appearance of tubular lucencies branching from the porta hepatis to within two centimeters of the peripheral liver margin. The appearance arises from the accumulation of gas in the distal portal system, which is carried in a hepatopedal direction by the flow in the portal vein, as documented with real-time ultrasound studies. Portal venous gas must be differentiated from pneumobilia, which tends to accumulate in the large central bile ducts near the liver hilus, due to the hepatofugal biliary flow.

The actual origin and composition of the portal venous gas itself are unclear. One possible mechanism involves elevated intraluminal pressures in conjunction with mucosal ulcerations; a second theory suggests luminal bacterial overgrowth with later submucosal and intravenous invasion by gas-producing bacteria. The morbidity and mortality associated with portal venous gas were once thought to be related to the underlying pathologic process causing the gas. Recent theories suggest that the portal venous gas may limit hepatic blood flow, thus reducing the detoxifying effectiveness of the liver for bacteria and toxins. Alternatively, the portal venous gas may denature proteins within the blood, activating either the hemostatic or fibrinolytic mechanisms. The breakdown of the protective intestinal mucosa and the decreased hepatic reticuloendothelial function are both possible explanations for the high rate of sepsis seen with portal venous gas.

Portal venous gas has been previously reported as being associated with hemorrhagic pancreatitis.2 The first description was in a 19-year-old female, who also had gastric pneumatosis and who expired at surgery.6 In a surgical series of the clinical significance of portal venous gas, the incidence of hemorrhagic pancreatitis causing this finding was 1 in 64 cases.7 Hemorrhage in the setting of pancreatitis is common; the majority of patients tend to bleed from nonpancreatic sources, such as ulcers and Mallory-Weiss tears.8 Bleeding directly from major pancreatic or peripancreatic arteries or veins is caused by the exposure to proteolytic enzymes from the pancreatic inflammatory process. The bleeding usually occurs in the GI tract, the peritoneal space, or the retroperitoneal space.

Pseudoaneurysms may develop and can also rupture and bleed. Alternatively, thrombosis of the portal vein or proximal tributaries may cause segmental portal venous hypertension, with development of mesenteric or gastric varices, which also may bleed. It is uncertain why this case was not associated with hemorrhage. Perhaps the amount of bleeding was too small to be detected by imaging or by laboratory studies. Possibly, the prior reported case of portal venous gas was associated with inflammatory erosion of a peripancreatic artery. If the inflammatory process only involved erosion in the lower-pressured portal venous system, the incidence of bleeding would be expected to be reduced.

Portal venous gas in adults is associated with necrotic bowel in 74% of cases; it has a dismal prognosis, with a mortality rate of 85%.3 Intestinal mucosal ulceration, bowel distention, and positive blood cultures are seen in approximately 85% to 88% of cases, with many patients presenting with two (50%) or more (35%) of these findings. The amount of necrotic bowel varies from a single small segment to almost total bowel-wall necrosis.

Because the diagnosis is nonspecific, the treatment of portal venous gas must be directed at the primary cause. In the setting of abdominal catastrophe with suspected necrotic bowel, surgery is required. More recently, iatrogenic cases of portal venous gas have been reported, and they are associated with endoscopic retrograde cholangiopancreatography (ERCP), barium enema, or endoscopy in patients with inflammatory bowel disease and in those who have undergone catheterization of the umbilical vein. Iatrogenic causes of portal venous gas have a much better prognosis and are treated with supportive measures, such as antibiotics and IV fluids.

In summary, this case report illustrates a rather unusual complication, that of nonfatal portal venous gas in association with a relatively common disease process such as pancreatitis.

References

1. Wolfe JN, Evans WA: Gas in the portal veins of the liver in infants: A roentgenographic demonstration with postmortem anatomic correlation. AJR 74:486-489, 1955.

2. Susman N, Senturia HR: Gas embolism of the portal venous system. AJR 83:847-850, 1960.

3. Griffiths DM, Gough MH: Gas in the hepatic portal veins. Br J Surg 73:172-176, 1986.

4. Nachtegaele P, Afschrift M, Vandendreissche M: Sonographic diagnosis of gas embolism in the portal vein. Gastrointest Radiol 7:375-377, 1982.

5. Fisher JK: Computed tomography of colonic pneumatosis intestinalis with mesenteric and portal venous gas. J Comput Assist Tomogr 8:573-574, 1984.

6. Sisk PB: Gas in the portal venous system. Radiology 77:103-107, 1961.

7. Liebman PR, Patten MT, Manny J, et al: Hepatic-portal venous gas in adults: Etiology, pathophysiology, and clinical significance. Ann Surg 187:281-287, 1978.

8. Vujic I: Vascular complications of pancreatitis. Radiol Clin North Am 27(1):81-91, 1989.