Traditionally, the presence of gas in the portal venous system was interpreted as an ominous sign in the clinical setting of mesenteric ischemia in adults and necrotizing enterocolitis in infants. It was a surgical emergency, with a mortality rate of 75%-90%. Nowadays, mortality rates associated with portal venous system gas have declined to 29%-43%. This decline is due not to improved therapy but rather to new and better imaging techniques, which have allowed recognition of an increasing number of causes of gas in the portal venous system.
Recent reports have shown that portomesenteric vein gas is associated with several causes besides mesenteric ischemia. Portomesenteric vein gas is idiopathic in approximately 15% of cases. In some cases, such as those involving portomesenteric vein gas due to infectious and inflammatory abdominal diseases, interventional procedures, trauma (as in our case), and transplantation, the prognosis is favorable and surgery is not required.
Intravascular gas occurs in less than 1% of patients who sustain blunt abdominal trauma. In these patients, portomesenteric vein gas is thought to result from acute pressure changes that occur at the time of injury and force intraluminal gas into the bowel wall, where it is absorbed into the portal circulation. Portomesenteric vein gas in the setting of blunt trauma does not necessarily imply bowel necrosis or perforation, and the absence of peritonitis may allow observation of this finding.
On CT scans, air in the portal vein manifests as ramifying streaks with air attenuation that can reach the capsule at the periphery of the liver. Air has a propensity to accumulate in the intrahepatic radicals of the left portal vein due to its more ventral location. Intrahepatic portal vein gas should be differentiated from aerobilia. The distribution of hepatic gas in patients with aerobilia is central, around the portal hilum, and does not extend to within 2 cm of the liver capsule. Gas in mesenteric vein branches should be differentiated from pneumoperitoneum. Pneumoperitoneum does not have a linear, ramifying configuration and can be present in the antimesenteric border of the intestine. Findings of portomesenteric vein gas at CT should be carefully evaluated in the context of clinical findings before making decisions regarding diagnosis and therapy.
http://www.mypacs.net/cgi-bin/repos/mpv3_repo/wrm/repo-view.pl?cx_subject=6604325&cx_image_only_mode=off&cx_from_folder=92585&cx_repo=mpv4_repo
Sebastià C et al. Portomesenteric vein gas: pathologic mechanisms, CT findings, and prognosis. RadioGraphics 2000;20:1213-1224; discussion 1224-1226.
Carmen Gallego et al. Congenital and Acquired Anomalies of the Portal Venous System. RadioGraphics 2002; 22:141–159
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