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(Radiographics. 2000;20:1213-1224.)
© RSNA, 2000

SCIENTIFIC EXHIBIT

Portomesenteric Vein Gas: Pathologic Mechanisms, CT Findings, and Prognosis1

Carmen Sebastià, MD, Sergi Quiroga, MD, Eloy Espin, MD, Rosa Boyé, MD, Agustí Alvarez-Castells, MD and Manel Armengol, MD

1 From the Departments of Radiology I.D.I. (C.S., S.Q., R.B., A.A.C.) and Surgery (E.E., M.A.), Hospital General Universitari Vall d'Hebron, Pg Vall d'Hebron 119-129, Barcelona 08015, Spain. Recipient of a Certificate of Merit award for a scientific exhibit at the 1999 RSNA scientific assembly. Received February 28, 2000; revision requested March 15 and received May 4; accepted May 4. Address correspondence to C.S.


   Abstract
Top
 Abstract
LEARNING OBJECTIVES FOR TEST...
 Introduction
 CT Manifestations
 Pathogenic Mechanisms
 Conclusions
 References
 
Portomesenteric vein gas is a rare condition whose pathogenesis is not fully understood. Portomesenteric vein gas is most commonly caused by mesenteric ischemia but may have a variety of other causes. The primary factors that favor the development of this pathologic entity are intestinal wall alterations, bowel distention, and sepsis. Portomesenteric vein gas is idiopathic in approximately 15% of cases. Advanced imaging techniques such as computed tomography (CT) have increased the sensitivity for detection of portomesenteric vein gas. At CT, portal vein gas appears as tubular areas of decreased attenuation in the liver, predominantly in the left lobe. Gas in the great mesenteric veins can easily be demonstrated with contrast material–enhanced CT, whereas gas in the small mesenteric veins appears as tubular or branched areas of decreased attenuation in the mesenteric border of the bowel. Findings of portomesenteric vein gas at CT should be carefully evaluated in the context of clinical findings. In the majority of cases, the prognosis is favorable and surgery is not required. However, when CT demonstrates portomesenteric vein gas and clinical findings suggest the presence of mesenteric ischemia, surgery is mandatory.

Index Terms: Mesentery, CT, 95.1291 • Mesentery, diseases, 95.75, 95.761 • Mesentery, gas, 792.719 • Mesentery, ischemia, 95.761 • Portal vein, CT, 957.1291 • Portal vein, gas, 957.75


   LEARNING OBJECTIVES FOR TEST 1
Top
 Abstract
 LEARNING OBJECTIVES FOR TEST...
Introduction
 CT Manifestations
 Pathogenic Mechanisms
 Conclusions
 References
 
After reading this article and taking the test, the reader will be able to:


   Introduction
Top
 Abstract
 LEARNING OBJECTIVES FOR TEST...
 Introduction
CT Manifestations
 Pathogenic Mechanisms
 Conclusions
 References
 
Portal vein gas and mesenteric vein gas are rare conditions that have been associated with extended bowel necrosis and fatal outcome (1). Portal vein gas was first described in children by Wolfe and Evans (2) in 1955 and in adults by Susman and Senturia (3) in 1960.

Portal vein gas and mesenteric vein gas are generally treated separately in the radiology literature and may, in fact, appear as separate findings. Mesenteric gas is absent in cases of portal vein gas secondary to portal pylephlebitis or hepatic transplantation, and portal vein gas may not be present in cases of intestinal disease that is detected early before the gas reaches the portal venous system. However, the two entities are usually found together and in this article will be referred to corporately as portomesenteric vein gas.

Recent reports have shown that portomesenteric vein gas is associated with several causes besides mesenteric ischemia. In some cases, such as those involving portomesenteric vein gas due to infectious and inflammatory abdominal diseases, interventional procedures, trauma, and transplantation, the prognosis is favorable and surgery is not required.

Reports describing the significance of portomesenteric vein gas are usually based on findings at conventional radiography. However, advanced imaging techniques such as computed tomography (CT) have increased the sensitivity for detection of portomesenteric vein gas. In cases of mild pneumoperitoneum, CT has allowed visualization of small amounts of intraabdominal air that could not be seen at conventional abdominal radiography (4). Although to our knowledge no study has been conducted comparing the effectiveness of the two modalities in portomesenteric vein gas, it seems reasonable that CT would also be more sensitive than radiography in the detection of this disease entity (5).

In this article, we review the CT manifestations of portomesenteric vein gas and the causes of this pathologic condition in adults. On the basis of our experience and descriptions in the literature, we have divided these causes into four groups: (a) intestinal wall alterations (inflammatory bowel disease, mesenteric ischemia), (b) bowel distention (gastric and bowel dilatation due to spontaneous, traumatic, and iatrogenic causes), (c) intraabdominal sepsis (eg, diverticulitis, abdominal wall gangrene, pylephlebitis), and (d) unknown causes (transplantation, pneumatosis intestinalis, corticosteroid therapy, chronic pulmonary disease). In addition, we discuss and illustrate the evolution, differential diagnosis, and prognosis of portomesenteric vein gas as well as the causes and CT manifestations of mesenteric ischemia.


   CT Manifestations
Top
 Abstract
 LEARNING OBJECTIVES FOR TEST...
 Introduction
 CT Manifestations
Pathogenic Mechanisms
 Conclusions
 References
 
Portal Vein Gas
At CT, portal vein gas appears as tubular areas of decreased attenuation in the liver, predominantly in the left lobe (Fig 1). These low-attenuation areas are caused by the accumulation of gas in the intrahepatic portal veins, from where it is carried by centrifugal blood to the hepatic periphery. Portal vein gas can be visualized at conventional radiography, but substantial amounts must be present for detection (5). The radiographic criterion for portal vein gas is a branching area of low attenuation extending to within 2 cm of the liver capsule (1). Modalities such as CT and ultrasonography can help detect smaller amounts of portal vein gas, making it possible to demonstrate portomesenteric vein gas earlier in the course of the disease and implement early aggressive treatment, which may decrease mortality (6).



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  		Figure 1a.   Portal vein gas. Contrast material-enhanced CT scans obtained at the top (a) and in the middle (b) of the liver show tubular areas of decreased attenuation in the periphery of the liver (arrows), findings that are consistent with gas in the intrahepatic portal veins.

 


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  		Figure 1b.   Portal vein gas. Contrast material-enhanced CT scans obtained at the top (a) and in the middle (b) of the liver show tubular areas of decreased attenuation in the periphery of the liver (arrows), findings that are consistent with gas in the intrahepatic portal veins.

 
Intrahepatic portal vein gas must be differentiated from air in the biliary tree (pneumobilia). In the latter condition, the air is located centrally (ie, it does not extend to within 2 cm of the liver capsule) (Fig 2), and a confluence of air is seen in the common hepatic duct. Pneumobilia also has a left lobe predilection at CT because of its more ventral location. In contrast, collections of portal vein gas are smaller and more numerous and are seen in the liver periphery. However, it is possible for pneumobilia and portal vein gas to coexist.



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  		Figure 2a.   Pneumobilia. Contrast-enhanced CT scans obtained at the top (a) and in the middle (b) of the liver show tubular areas of low attenuation in the biliary tree (arrows). Note the central location of the air, which does not extend to within 2 cm of the liver capsule (cf Fig 1).

 


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  		Figure 2b.   Pneumobilia. Contrast-enhanced CT scans obtained at the top (a) and in the middle (b) of the liver show tubular areas of low attenuation in the biliary tree (arrows). Note the central location of the air, which does not extend to within 2 cm of the liver capsule (cf Fig 1).

 
Mesenteric Vein Gas
Gas from the intestinal lumen can pass through the intestinal wall and travel via the small mesenteric veins and the superior or inferior mesenteric vein to the portal vein and into the liver. The presence of gas in the superior or inferior mesenteric vein depends on the vascular supply to the affected intestine. Gas in the great mesenteric veins can easily be demonstrated with contrast-enhanced CT (Fig 3a, 3b). Gas in the small mesenteric veins appears as tubular or branched areas of decreased attenuation in the mesenteric border of the bowel (Fig 3c). Mesenteric vein gas should not be confused with pneumoperitoneum or air in the appendix. Pneumoperitoneum does not have a tubular or branched appearance and can be found in the interface between the antimesenteric border of the bowel and the parietal peritoneum (peritoneal cavity) (Fig 4). An appendix with air in the lumen can be recognized by its visible wall, a finding that distinguishes the appendix from the small mesenteric veins, and by its attachment to the cecum (Fig 5), although in many cases it is difficult to track the air all the way to the cecum, especially when it is in a retrocecal location.



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  		Figure 3a.   Mesenteric vein gas. (a) Contrast-enhanced CT scan depicts gas in the gastrocolic venous trunk (arrow) and superior mesenteric vein (arrowhead). The marked enhancement of the vein demonstrates the vascular nature of the affected structure. (b) Contrast-enhanced CT scan obtained in a patient with diverticulitis of the sigmoid colon demonstrates gas in the inferior mesenteric vein (arrow). (c) Contrast-enhanced CT scan demonstrates multiple tubular areas of low attenuation in the mesentery (arrows), findings that are consistent with gas in the small mesenteric veins.

 


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  		Figure 3b.   Mesenteric vein gas. (a) Contrast-enhanced CT scan depicts gas in the gastrocolic venous trunk (arrow) and superior mesenteric vein (arrowhead). The marked enhancement of the vein demonstrates the vascular nature of the affected structure. (b) Contrast-enhanced CT scan obtained in a patient with diverticulitis of the sigmoid colon demonstrates gas in the inferior mesenteric vein (arrow). (c) Contrast-enhanced CT scan demonstrates multiple tubular areas of low attenuation in the mesentery (arrows), findings that are consistent with gas in the small mesenteric veins.

 


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  		Figure 3c.   Mesenteric vein gas. (a) Contrast-enhanced CT scan depicts gas in the gastrocolic venous trunk (arrow) and superior mesenteric vein (arrowhead). The marked enhancement of the vein demonstrates the vascular nature of the affected structure. (b) Contrast-enhanced CT scan obtained in a patient with diverticulitis of the sigmoid colon demonstrates gas in the inferior mesenteric vein (arrow). (c) Contrast-enhanced CT scan demonstrates multiple tubular areas of low attenuation in the mesentery (arrows), findings that are consistent with gas in the small mesenteric veins.

 


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  		Figure 4.   Pneumoperitoneum. Contrast-enhanced CT scan depicts extraluminal air in the peritoneal cavity due to a perforated hollow viscus. The air is located between the antimesenteric border of the bowel and the parietal peritoneum (arrows). Air in this location cannot be seen in cases of venous mesenteric air.

 


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  		Figure 5.   Air in the appendix. Contrast-enhanced CT scan shows air in the appendix mimicking mesenteric vein gas (thick arrow). The walls of the appendix and its attachment to the cecum (thin arrow) are clearly seen.

 

   Pathogenic Mechanisms
Top
 Abstract
 LEARNING OBJECTIVES FOR TEST...
 Introduction
 CT Manifestations
 Pathogenic Mechanisms
Conclusions
 References
 
The precise mechanism for the formation of gas in the portomesenteric venous system is still uncertain. The primary factors that favor the development of portomesenteric vein gas are intestinal wall alterations, bowel distention, and sepsis (1). In many cases, two or all three conditions are present (1,6). In other cases, the cause of portomesenteric vein gas is not known.

Intestinal Wall Alterations
Several disease processes can cause ulceration of the gastric, duodenal, and bowel wall, permitting the passage of intraluminal air into the portomesenteric venous system. Enhanced mucosal permeability may also promote the formation of vessel lumen gas in the absence of demonstrable ulceration of the mucosa. Some severe conditions such as Crohn disease result in actual sloughing of the epithelial lining, allowing gas to enter mural vessels. The most common causes of intestinal wall alterations are intestinal ischemia with bowel necrosis, perforated gastric carcinoma or ulcer, and inflammatory bowel disease (ulcerative colitis, Crohn disease).

The most common cause of portomesenteric vein gas is bowel ischemia. Portomesenteric vein gas resulting from bowel ischemia has been shown to have a poor prognosis, with a mortality rate of 75%–90% (1,7). However, more recent articles have suggested that portomesenteric vein gas is not in itself a predictor of mortality (5). The causes of mesenteric ischemia include arterial and venous mesenteric thrombosis, aortic dissection, hypoperfusion associated with nonocclusive vascular disease, embolic disease, and disease processes leading to intestinal obstruction (Fig 6) (8).



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  		Figure 6a.   Causes of mesenteric ischemia. (a) Contrast-enhanced CT scan demonstrates a thrombus in the superior mesenteric artery (arrow). (b) Contrast-enhanced CT scan obtained in a different patient shows a thrombus in the superior mesenteric vein (arrow). Gas is also seen in other mesenteric veins (cf Fig 7d). (c) Contrast-enhanced CT scan obtained in yet another patient depicts gas in the mesenteric veins (white arrow) due to mesenteric ischemia secondary to abdominal aortic dissection (black arrow).

 


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  		Figure 6b.   Causes of mesenteric ischemia. (a) Contrast-enhanced CT scan demonstrates a thrombus in the superior mesenteric artery (arrow). (b) Contrast-enhanced CT scan obtained in a different patient shows a thrombus in the superior mesenteric vein (arrow). Gas is also seen in other mesenteric veins (cf Fig 7d). (c) Contrast-enhanced CT scan obtained in yet another patient depicts gas in the mesenteric veins (white arrow) due to mesenteric ischemia secondary to abdominal aortic dissection (black arrow).

 


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  		Figure 6c.   Causes of mesenteric ischemia. (a) Contrast-enhanced CT scan demonstrates a thrombus in the superior mesenteric artery (arrow). (b) Contrast-enhanced CT scan obtained in a different patient shows a thrombus in the superior mesenteric vein (arrow). Gas is also seen in other mesenteric veins (cf Fig 7d). (c) Contrast-enhanced CT scan obtained in yet another patient depicts gas in the mesenteric veins (white arrow) due to mesenteric ischemia secondary to abdominal aortic dissection (black arrow).

 
CT findings in mesenteric ischemia include occlusion of the splanchnic vasculature, bowel distention, bowel wall thickening, either marked or absent enhancement of the bowel wall, intestinal pneumatosis, mesenteric edema, ascites, portomesenteric vein gas, and infarction of other organs (Fig 7) (9). However, most of these signs are nonspecific and must occur in association with clinically suspected acute mesenteric ischemia to be considered significant for this disease entity.



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  		Figure 7a.   Mesenteric ischemia. (a) CT scan demonstrates bowel dilatation (arrowheads) and mesenteric infiltration (arrows). (b) CT scan shows pneumatosis intestinalis (arrow) and venous mesenteric gas (arrowhead). (c) CT scan demonstrates absence of enhancement of the bowel wall (arrow). (d) CT scan obtained in the same patient as in Figure 6b shows mesenteric edema (straight arrow), bowel wall thickening (curved arrow), and air in the small mesenteric veins (arrowheads). (e) CT scan demonstrates renal and hepatic infarcts (arrows) and hepatic portal vein gas (arrowhead).

 


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  		Figure 7b.   Mesenteric ischemia. (a) CT scan demonstrates bowel dilatation (arrowheads) and mesenteric infiltration (arrows). (b) CT scan shows pneumatosis intestinalis (arrow) and venous mesenteric gas (arrowhead). (c) CT scan demonstrates absence of enhancement of the bowel wall (arrow). (d) CT scan obtained in the same patient as in Figure 6b shows mesenteric edema (straight arrow), bowel wall thickening (curved arrow), and air in the small mesenteric veins (arrowheads). (e) CT scan demonstrates renal and hepatic infarcts (arrows) and hepatic portal vein gas (arrowhead).

 


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  		Figure 7c.   Mesenteric ischemia. (a) CT scan demonstrates bowel dilatation (arrowheads) and mesenteric infiltration (arrows). (b) CT scan shows pneumatosis intestinalis (arrow) and venous mesenteric gas (arrowhead). (c) CT scan demonstrates absence of enhancement of the bowel wall (arrow). (d) CT scan obtained in the same patient as in Figure 6b shows mesenteric edema (straight arrow), bowel wall thickening (curved arrow), and air in the small mesenteric veins (arrowheads). (e) CT scan demonstrates renal and hepatic infarcts (arrows) and hepatic portal vein gas (arrowhead).

 


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  		Figure 7d.   Mesenteric ischemia. (a) CT scan demonstrates bowel dilatation (arrowheads) and mesenteric infiltration (arrows). (b) CT scan shows pneumatosis intestinalis (arrow) and venous mesenteric gas (arrowhead). (c) CT scan demonstrates absence of enhancement of the bowel wall (arrow). (d) CT scan obtained in the same patient as in Figure 6b shows mesenteric edema (straight arrow), bowel wall thickening (curved arrow), and air in the small mesenteric veins (arrowheads). (e) CT scan demonstrates renal and hepatic infarcts (arrows) and hepatic portal vein gas (arrowhead).

 


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  		Figure 7e.   Mesenteric ischemia. (a) CT scan demonstrates bowel dilatation (arrowheads) and mesenteric infiltration (arrows). (b) CT scan shows pneumatosis intestinalis (arrow) and venous mesenteric gas (arrowhead). (c) CT scan demonstrates absence of enhancement of the bowel wall (arrow). (d) CT scan obtained in the same patient as in Figure 6b shows mesenteric edema (straight arrow), bowel wall thickening (curved arrow), and air in the small mesenteric veins (arrowheads). (e) CT scan demonstrates renal and hepatic infarcts (arrows) and hepatic portal vein gas (arrowhead).

 
When CT demonstrates portomesenteric vein gas and clinical findings suggest the presence of mesenteric ischemia, surgery is mandatory. However, extensive portomesenteric vein gas does not necessarily indicate a poor prognosis (Figs 8, 9).



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  		Figure 8a.   Portomesenteric vein gas due to mesenteric ischemia. (a) Contrast-enhanced CT scan depicts mural thickening of the colon (arrows), mesenteric edema, and gas in the mesenteric vessels (arrowheads). Note also the presence of polycystic renal disease. (b) Contrast-enhanced CT scan demonstrates portal vein gas (arrows), a finding that caused suspicion for mesenteric ischemia. At surgery, the right side of the colon demonstrated necrosis, and hemicolectomy was performed. Follow-up CT performed 15 days later demonstrated resolution of the portomesenteric vein gas. The patient's recovery was uneventful.

 


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  		Figure 8b.   Portomesenteric vein gas due to mesenteric ischemia. (a) Contrast-enhanced CT scan depicts mural thickening of the colon (arrows), mesenteric edema, and gas in the mesenteric vessels (arrowheads). Note also the presence of polycystic renal disease. (b) Contrast-enhanced CT scan demonstrates portal vein gas (arrows), a finding that caused suspicion for mesenteric ischemia. At surgery, the right side of the colon demonstrated necrosis, and hemicolectomy was performed. Follow-up CT performed 15 days later demonstrated resolution of the portomesenteric vein gas. The patient's recovery was uneventful.

 


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  		Figure 9.   Mesenteric vein gas due to mesenteric ischemia. Contrast-enhanced CT scan demonstrates gas in the mesenteric veins (arrow) and thickening of the cecum (arrowhead). Although only a small amount of portomesenteric vein gas was found at CT, the patient had massive mesenteric ischemia and died immediately after surgery.

 
Bowel Distention
Bowel distention can produce minimal mucosal disruption that allows intraluminal gas to become intravascular. Portomesenteric vein gas secondary to bowel distention can occur in association with (a) iatrogenic gastric and bowel dilatation (gastrostomy, sclerotherapy for gastric varices, endoscopic retrograde cholangiopancreatography, colonoscopy, barium enema); (b) spontaneous paralytic ileus, mechanical obstruction, and acute gastric dilatation; (c) blunt trauma; and (d) barotrauma.

To help guide the clinical management of portomesenteric vein gas, Hong et al (6) categorized patients as either "iatrogenic" or "noniatrogenic." Their findings indicated that more widespread use of invasive techniques has changed the clinical manifestation of portomesenteric vein gas. Iatrogenic portomesenteric vein gas can be managed medically in most cases and does not mandate urgent laparotomy (Fig 10) (6,10).



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  		Figure 10a.   Portomesenteric vein gas in a patient who presented with abdominal pain and distention. The patient had undergone colonoscopy 10 hours earlier. CT was performed for suspected colon perforation. (a) Scanogram shows marked distention of the colon. (b) Unenhanced CT scan demonstrates portomesenteric vein gas (arrows). The nasogastric tube can also be seen. The patient was treated conservatively and had an uneventful recovery.

 


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  		Figure 10b.   Portomesenteric vein gas in a patient who presented with abdominal pain and distention. The patient had undergone colonoscopy 10 hours earlier. CT was performed for suspected colon perforation. (a) Scanogram shows marked distention of the colon. (b) Unenhanced CT scan demonstrates portomesenteric vein gas (arrows). The nasogastric tube can also be seen. The patient was treated conservatively and had an uneventful recovery.

 
Bowel dilatation due to paralytic or obstructive ileus is another cause of portomesenteric vein gas. Paralytic ileus can be managed medically (Fig 11) (11). Patients with bowel obstruction but no accompanying signs of mesenteric ischemia are treated on the basis of clinical findings and laboratory results (5,12).



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  		Figure 11a.   Portomesenteric vein gas associated with paralytic ileus secondary to bronchial artery embolization in a patient who presented with abdominal pain and distention. CT was performed 24 hours after embolization. (a) Contrast-enhanced CT scan shows intrahepatic portal vein gas (arrows). (b) Contrast-enhanced CT scan depicts bowel distention with mural air (arrowheads). Mesenteric ischemia was suspected, and the patient underwent surgery. No ischemic bowel was found. Contrast-enhanced follow-up CT performed 20 days later demonstrated resolution of the hepatic portal vein gas.

 


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  		Figure 11b.   Portomesenteric vein gas associated with paralytic ileus secondary to bronchial artery embolization in a patient who presented with abdominal pain and distention. CT was performed 24 hours after embolization. (a) Contrast-enhanced CT scan shows intrahepatic portal vein gas (arrows). (b) Contrast-enhanced CT scan depicts bowel distention with mural air (arrowheads). Mesenteric ischemia was suspected, and the patient underwent surgery. No ischemic bowel was found. Contrast-enhanced follow-up CT performed 20 days later demonstrated resolution of the hepatic portal vein gas.

 
Intravascular gas occurs in less than 1% of patients who sustain blunt abdominal trauma (13). 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 (13). 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 (14).

Intraabdominal Sepsis
Several infectious abdominal processes have been associated with portomesenteric vein gas, including diverticulitis, abdominal abscess and gangrene, cholecystitis and cholangitis, appendicitis, colitis (inflammatory, pseudomembranous, secondary to Candida infection in human immunodeficiency virus–related disease), and abdominal tuberculosis.

The pathogenesis of portomesenteric vein gas associated with infectious gastrointestinal diseases is not fully understood. Three theories have been put forward: (a) portomesenteric vein gas results from septicemia in branches of the mesenteric and portal veins (pylephlebitis) (15,16); (b) portomesenteric vein gas results from increased intraluminal fermentation of carbohydrates due to bacteria (17); and (c) mesocolic abscess causes inframesocolic perforation that dissects between the peritoneal leaflets of the mesocolon, thereby creating access to the mesocolic veins (18).

Portomesenteric vein gas is a rare complication of colonic diverticulitis (Fig 12), but the combination of the two conditions can lead to hepatic abscess. Inflammatory involvement of the inferior mesenteric vein complicating diverticulitis of the sigmoid colon can result in septic thrombophlebitis and the presence of gas within the vein (19). If no synchronous liver abscesses are present, portomesenteric vein gas is not associated with a poor prognosis.



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  		Figure 12a.   Portomesenteric vein gas associated with diverticulitis and mesocolic abscess. (a) Contrast-enhanced CT scan shows branched areas of decreased attenuation in the left hepatic lobe (arrows), findings that are consistent with portal vein gas. (b) Contrast-enhanced CT scan depicts sigmoid bowel thickening (arrowhead) and a mesosigmoid abscess (arrows). Surgical findings confirmed acute diverticulitis and abscess. Colostomy and abscess drainage were performed. Contrast-enhanced follow-up CT demonstrated resolution of the portal vein gas.

 


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  		Figure 12b.   Portomesenteric vein gas associated with diverticulitis and mesocolic abscess. (a) Contrast-enhanced CT scan shows branched areas of decreased attenuation in the left hepatic lobe (arrows), findings that are consistent with portal vein gas. (b) Contrast-enhanced CT scan depicts sigmoid bowel thickening (arrowhead) and a mesosigmoid abscess (arrows). Surgical findings confirmed acute diverticulitis and abscess. Colostomy and abscess drainage were performed. Contrast-enhanced follow-up CT demonstrated resolution of the portal vein gas.

 
Intraperitoneal and retroperitoneal abscesses and gangrene (Fig 13) can also cause portomesenteric vein gas.



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  		Figure 13.   Abdominal wall gangrene with portomesenteric vein gas. Contrast-enhanced CT scan shows subcutaneous and mesenteric gas (arrows), a finding that is consistent with abdominal wall gangrene. Note also the presence of gas in the mesenteric vein (arrowhead). Surgical findings confirmed the diagnosis, and the patient died 3 days later in the intensive care unit.

 
Portal phlebitis triggered by Mycobacterium tuberculosis is a very rare vascular disease (Fig 14), with few cases described in the literature (20). When clinical measures are not effective, surgical resection of the vein is indicated.



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  		Figure 14a.   Pylephlebitis due to tuberculosis in a man with non-Hodgkin lymphoma who presented with fever and abdominal pain. (a) Contrast-enhanced CT scan depicts peripancreatic nodes with a hypoattenuating center (arrows). (b) Contrast-enhanced CT scan demonstrates gas in the extrahepatic portal vein (arrow). CT-guided biopsy of the nodes was performed, and Mycobacterium tuberculosis was cultured. Follow-up CT performed 6 months later after completion of treatment for tuberculosis demonstrated decreased peripancreatic adenopathy and resolution of the portal vein gas.

 


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  		Figure 14b.   Pylephlebitis due to tuberculosis in a man with non-Hodgkin lymphoma who presented with fever and abdominal pain. (a) Contrast-enhanced CT scan depicts peripancreatic nodes with a hypoattenuating center (arrows). (b) Contrast-enhanced CT scan demonstrates gas in the extrahepatic portal vein (arrow). CT-guided biopsy of the nodes was performed, and Mycobacterium tuberculosis was cultured. Follow-up CT performed 6 months later after completion of treatment for tuberculosis demonstrated decreased peripancreatic adenopathy and resolution of the portal vein gas.

 
The indication for surgery in portomesenteric vein gas is based on the underlying cause of the disease entity; treatment with broad-spectrum antibiotics is sufficient in most cases.

Unknown Causes
Portomesenteric vein gas is idiopathic in approximately 15% of cases (16) and has been observed in organ transplantation (liver, kidney, bone marrow), pulmonary diseases (chronic obstructive pulmonary disease, bronchopneumonia, asthma) (Fig 15), steroid and cytostatic therapy, and seizures.



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  		Figure 15a.   Pneumatosis intestinalis with portomesenteric vein gas in a patient with asthma and non-Hodgkin lymphoma who was undergoing corticoid therapy. Routine abdominal radiography demonstrated intramural bowel gas, and CT was performed. (a) Scanogram demonstrates pneumatosis intestinalis (arrows). (b) Contrast-enhanced CT scan (lung window) shows intramural bowel gas (arrowhead) and mesenteric vein gas (arrows). The patient had no abdominal symptoms and made a full recovery without having to undergo surgery.

 


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  		Figure 15b.   Pneumatosis intestinalis with portomesenteric vein gas in a patient with asthma and non-Hodgkin lymphoma who was undergoing corticoid therapy. Routine abdominal radiography demonstrated intramural bowel gas, and CT was performed. (a) Scanogram demonstrates pneumatosis intestinalis (arrows). (b) Contrast-enhanced CT scan (lung window) shows intramural bowel gas (arrowhead) and mesenteric vein gas (arrows). The patient had no abdominal symptoms and made a full recovery without having to undergo surgery.

 
Portomesenteric vein gas is a common finding in the first 2 weeks after hepatic transplantation and may not have prognostic significance (Fig 16). In a series by Chezmar et al (21), seven of 39 liver transplant recipients (18%) had portomesenteric vein gas, but none had bowel infarction or necrosis. Portomesenteric vein gas has also been associated with venovenous bypass, sepsis, and primary graft failure.



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  		Figure 16.   Portomesenteric vein gas associated with hepatic transplantation. Contrast-enhanced CT scan obtained 10 days after surgery demonstrates portal vein gas (arrow). There were no complications at that time. Unenhanced CT performed 10 days later showed resolution of the portal vein gas.

 

   Conclusions
Top
 Abstract
 LEARNING OBJECTIVES FOR TEST...
 Introduction
 CT Manifestations
 Pathogenic Mechanisms
 Conclusions
References
 
The most serious and most frequent cause of portomesenteric vein gas in adults is mesenteric ischemia. However, the association of portomesenteric vein gas with this disease process does not imply a worse prognosis; thus, surgical treatment should not be excluded when this sign is present. Several other disease processes have been described recently as causes of portomesenteric vein gas. In the majority of cases, particularly when portomesenteric vein gas is secondary to invasive procedures, surgery is not required and the prognosis is favorable. Findings of portomesenteric vein gas at CT should be carefully evaluated in the context of clinical findings before making decisions regarding diagnosis and therapy.


   Footnotes
 
See the commentary by Baker.


   References
Top
 Abstract
 LEARNING OBJECTIVES FOR TEST...
 Introduction
 CT Manifestations
 Pathogenic Mechanisms
 Conclusions
 References
 

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