SCIENTIFIC EXHIBIT 1213 Portomesenteric Vein ... - RPH Doctorrphdoctor.org/wp-content/uploads/2016/08/CT-Portomesenteric-Vein-gas.pdf · of decreased attenuation in the mesenteric

1213SCIENTIFIC EXHIBIT

Portomesenteric VeinGas: Pathologic Mecha-nisms, CT Findings,and Prognosis1

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

Portomesenteric vein gas is a rare condition whose pathogenesis is notfully understood. Portomesenteric vein gas is most commonly causedby mesenteric ischemia but may have a variety of other causes. Theprimary factors that favor the development of this pathologic entity areintestinal wall alterations, bowel distention, and sepsis. Portomesenter-ic vein gas is idiopathic in approximately 15% of cases. Advanced im-aging techniques such as computed tomography (CT) have increasedthe sensitivity for detection of portomesenteric vein gas. At CT, portalvein gas appears as tubular areas of decreased attenuation in the liver,predominantly in the left lobe. Gas in the great mesenteric veins caneasily be demonstrated with contrast material–enhanced CT, whereasgas in the small mesenteric veins appears as tubular or branched areasof decreased attenuation in the mesenteric border of the bowel. Find-ings of portomesenteric vein gas at CT should be carefully evaluated inthe context of clinical findings. In the majority of cases, the prognosisis favorable and surgery is not required. However, when CT demon-strates portomesenteric vein gas and clinical findings suggest the pres-ence 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 • Portalvein, CT, 957.1291 • Portal vein, gas, 957.75

RadioGraphics 2000; 20:1213–1224

1From 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 scientificassembly. Received February 28, 2000; revision requested March 15 and received May 4; accepted May 4. Address correspondence to C.S.

©RSNA, 2000

See the commentary by Baker following this article.

LEARNINGOBJECTIVESFOR TEST 1After reading thisarticle and takingthe test, the reader

will be able to:

� Summarize thepossible causes ofportomesenteric veingas.

� Discuss the CTmanifestations, dif-ferential diagnosis,and prognosis ofportomesenteric veingas.

� Describe the causesand CT manifesta-tions of mesentericischemia.

CME FEATURESee accompanying

test at http://www.rsna.org

/education/rg_cme.html

1214 September-October 2000 RG � Volume 20 • Number 5

IntroductionPortal vein gas and mesenteric vein gas are rareconditions that have been associated with ex-tended bowel necrosis and fatal outcome (1).Portal vein gas was first described in children byWolfe and Evans (2) in 1955 and in adults bySusman and Senturia (3) in 1960.

Portal vein gas and mesenteric vein gas aregenerally treated separately in the radiology lit-erature and may, in fact, appear as separate find-ings. Mesenteric gas is absent in cases of portalvein gas secondary to portal pylephlebitis or he-patic transplantation, and portal vein gas maynot be present in cases of intestinal disease thatis detected early before the gas reaches the portalvenous system. However, the two entities areusually found together and in this article will bereferred to corporately as portomesenteric veingas.

Recent reports have shown that portomesen-teric vein gas is associated with several causesbesides mesenteric ischemia. In some cases, suchas those involving portomesenteric vein gas dueto infectious and inflammatory abdominal dis-eases, interventional procedures, trauma, andtransplantation, the prognosis is favorable andsurgery is not required.

Reports describing the significance of porto-mesenteric vein gas are usually based on findingsat conventional radiography. However, advancedimaging techniques such as computed tomogra-phy (CT) have increased the sensitivity for detec-tion of portomesenteric vein gas. In cases of mildpneumoperitoneum, CT has allowed visualiza-tion of small amounts of intraabdominal air thatcould not be seen at conventional abdominal ra-diography (4). Although to our knowledge nostudy has been conducted comparing the effec-tiveness of the two modalities in portomesentericvein gas, it seems reasonable that CT would alsobe more sensitive than radiography in the detec-tion of this disease entity (5).

In this article, we review the CT manifestationsof portomesenteric vein gas and the causes of thispathologic condition in adults. On the basis of ourexperience and descriptions in the literature, wehave divided these causes into four groups: (a) in-testinal wall alterations (inflammatory bowel dis-ease, mesenteric ischemia), (b) bowel distention(gastric and bowel dilatation due to spontaneous,traumatic, and iatrogenic causes), (c) intraab-dominal sepsis (eg, diverticulitis, abdominal wallgangrene, pylephlebitis), and (d) unknown causes(transplantation, pneumatosis intestinalis, corti-costeroid therapy, chronic pulmonary disease).In addition, we discuss and illustrate the evolu-tion, differential diagnosis, and prognosis of por-tomesenteric vein gas as well as the causes andCT manifestations of mesenteric ischemia.

CT Manifestations

Portal Vein GasAt CT, portal vein gas appears as tubular areas ofdecreased attenuation in the liver, predominantlyin the left lobe (Fig 1). These low-attenuation ar-eas are caused by the accumulation of gas in theintrahepatic portal veins, from where it is carriedby centrifugal blood to the hepatic periphery.Portal vein gas can be visualized at conventionalradiography, but substantial amounts must bepresent for detection (5). The radiographic crite-rion for portal vein gas is a branching area of lowattenuation extending to within 2 cm of the livercapsule (1). Modalities such as CT and ultraso-nography can help detect smaller amounts ofportal vein gas, making it possible to demonstrateportomesenteric vein gas earlier in the course ofthe disease and implement early aggressive treat-ment, which may decrease mortality (6).

Intrahepatic portal vein gas must be differenti-ated from air in the biliary tree (pneumobilia). Inthe latter condition, the air is located centrally(ie, it does not extend to within 2 cm of the livercapsule) (Fig 2), and a confluence of air is seenin the common hepatic duct. Pneumobilia alsohas a left lobe predilection at CT because of itsmore ventral location. In contrast, collections ofportal vein gas are smaller and more numerous

RG � Volume 20 • Number 5 Sebastia et al 1215

a. b.

and are seen in the liver periphery. However, it ispossible for pneumobilia and portal vein gas tocoexist.

Mesenteric Vein GasGas from the intestinal lumen can pass throughthe intestinal wall and travel via the small mesen-teric veins and the superior or inferior mesenteric

vein to the portal vein and into the liver. The pres-ence of gas in the superior or inferior mesentericvein depends on the vascular supply to the affectedintestine. Gas in the great mesenteric veins caneasily be demonstrated with contrast-enhanced

a. b.

Figure 1. Portal vein gas. Contrast ma-terial–enhanced CT scans obtained at thetop (a) and in the middle (b) of the livershow tubular areas of decreased attenua-tion in the periphery of the liver (arrows),findings that are consistent with gas in theintrahepatic portal veins.

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


a. b.Figure 3. Mesenteric vein gas. (a) Con-trast-enhanced CT scan depicts gas in thegastrocolic venous trunk (arrow) and su-perior mesenteric vein (arrowhead). Themarked enhancement of the vein demon-strates the vascular nature of the affectedstructure. (b) Contrast-enhanced CT scanobtained in a patient with diverticulitis ofthe sigmoid colon demonstrates gas in theinferior mesenteric vein (arrow). (c) Con-trast-enhanced CT scan demonstratesmultiple tubular areas of low attenuationin the mesentery (arrows), findings that areconsistent with gas in the small mesentericveins.

CT (Fig 3a, 3b). Gas in the small mesenteric veinsappears as tubular or branched areas of decreasedattenuation in the mesenteric border of the bowel(Fig 3c). Mesenteric vein gas should not be con-fused with pneumoperitoneum or air in the appen-dix. Pneumoperitoneum does not have a tubularor branched appearance and can be found in theinterface between the antimesenteric border of thebowel and the parietal peritoneum (peritoneal cav-ity) (Fig 4). An appendix with air in the lumencan be recognized by its visible wall, a finding thatdistinguishes the appendix from the small mesen-teric veins, and by its attachment to the cecum(Fig 5), although in many cases it is difficult totrack the air all the way to the cecum, especiallywhen it is in a retrocecal location.

Pathogenic MechanismsThe precise mechanism for the formation of gasin the portomesenteric venous system is still un-certain. The primary factors that favor the devel-opment of portomesenteric vein gas are intestinal

wall alterations, bowel distention, and sepsis (1).In many cases, two or all three conditions arepresent (1,6). In other cases, the cause of porto-mesenteric vein gas is not known.

Intestinal Wall AlterationsSeveral disease processes can cause ulceration ofthe gastric, duodenal, and bowel wall, permittingthe passage of intraluminal air into the portomes-enteric venous system. Enhanced mucosal per-meability may also promote the formation of ves-sel lumen gas in the absence of demonstrable ul-ceration of the mucosa. Some severe conditionssuch as Crohn disease result in actual sloughingof the epithelial lining, allowing gas to enter mu-ral vessels. The most common causes of intesti-nal wall alterations are intestinal ischemia withbowel necrosis, perforated gastric carcinoma or ul-cer, and inflammatory bowel disease (ulcerativecolitis, Crohn disease).

The most common cause of portomesentericvein gas is bowel ischemia. Portomesenteric veingas resulting from bowel ischemia has been shownto have a poor prognosis, with a mortality rate of

c.


4. 5.Figures 4, 5. (4) Pneumoperitoneum. Contrast-enhanced CT scan depicts extraluminal air in the peritoneal cav-ity due to a perforated hollow viscus. The air is located between the antimesenteric border of the bowel and the pari-etal peritoneum (arrows). Air in this location cannot be seen in cases of venous mesenteric air. (5) Air in the appen-dix. Contrast-enhanced CT scan shows air in the appendix mimicking mesenteric vein gas (thick arrow). The wallsof the appendix and its attachment to the cecum (thin arrow) are clearly seen.

75%–90% (1,7). However, more recent articleshave suggested that portomesenteric vein gas isnot in itself a predictor of mortality (5). Thecauses of mesenteric ischemia include arterial andvenous mesenteric thrombosis, aortic dissection,

hypoperfusion associated with nonocclusive vascu-lar disease, embolic disease, and disease processesleading to intestinal obstruction (Fig 6) (8).

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


CT findings in mesenteric ischemia includeocclusion of the splanchnic vasculature, boweldistention, bowel wall thickening, either markedor absent enhancement of the bowel wall, intesti-nal pneumatosis, mesenteric edema, ascites, por-tomesenteric vein gas, and infarction of other or-gans (Fig 7) (9). However, most of these signs

d. e.

a. b. c.

Figure 7. Mesenteric ischemia.(a) CT scan demonstrates bowel di-latation (arrowheads) and mesenter-ic infiltration (arrows). (b) CT scanshows pneumatosis intestinalis (ar-row) and venous mesenteric gas (ar-rowhead). (c) CT scan demon-strates absence of enhancement ofthe bowel wall (arrow). (d) CT scanobtained in the same patient as inFigure 6b shows mesenteric edema(straight arrow), bowel wall thicken-ing (curved arrow), and air in thesmall mesenteric veins (arrow-heads). (e) CT scan demonstratesrenal and hepatic infarcts (arrows)and hepatic portal vein gas (arrow-head).

are nonspecific and must occur in associationwith clinically suspected acute mesenteric ische-mia to be considered significant for this diseaseentity.

When CT demonstrates portomesenteric veingas and clinical findings suggest the presence ofmesenteric ischemia, surgery is mandatory. How-ever, extensive portomesenteric vein gas does notnecessarily indicate a poor prognosis (Figs 8, 9).


8a. 8b.

9.

Bowel DistentionBowel distention can produce minimal mucosaldisruption that allows intraluminal gas to becomeintravascular. Portomesenteric vein gas secondaryto bowel distention can occur in association with(a) iatrogenic gastric and bowel dilatation (gas-trostomy, sclerotherapy for gastric varices, endo-scopic retrograde cholangiopancreatography,colonoscopy, barium enema); (b) spontaneousparalytic ileus, mechanical obstruction, and acutegastric dilatation; (c) blunt trauma; and (d) baro-trauma.

Figures 8, 9. (8) Portomesenteric vein gas due to mesentericischemia. (a) Contrast-enhanced CT scan depicts mural thick-ening of the colon (arrows), mesenteric edema, and gas in themesenteric vessels (arrowheads). Note also the presence of poly-cystic renal disease. (b) Contrast-enhanced CT scan demon-strates portal vein gas (arrows), a finding that caused suspicionfor mesenteric ischemia. At surgery, the right side of the colondemonstrated necrosis, and hemicolectomy was performed. Fol-low-up CT performed 15 days later demonstrated resolution ofthe portomesenteric vein gas. The patient’s recovery was un-eventful. (9) Mesenteric vein gas due to mesenteric ischemia.Contrast-enhanced CT scan demonstrates gas in the mesentericveins (arrow) and thickening of the cecum (arrowhead). Al-though only a small amount of portomesenteric vein gas wasfound at CT, the patient had massive mesenteric ischemia anddied immediately after surgery.

To help guide the clinical management of por-tomesenteric vein gas, Hong et al (6) categorizedpatients as either “iatrogenic” or “noniatrogenic.”Their findings indicated that more widespread useof invasive techniques has changed the clinicalmanifestation of portomesenteric vein gas. Iatro-genic portomesenteric vein gas can be managed


medically in most cases and does not mandateurgent laparotomy (Fig 10) (6,10).

Bowel dilatation due to paralytic or obstruc-tive ileus is another cause of portomesenteric veingas. Paralytic ileus can be managed medically(Fig 11) (11). Patients with bowel obstructionbut no accompanying signs of mesenteric ische-mia are treated on the basis of clinical findingsand laboratory results (5,12).

Intravascular gas occurs in less than 1% of pa-tients who sustain blunt abdominal trauma (13).In these patients, portomesenteric vein gas isthought to result from acute pressure changesthat occur at the time of injury and force intralu-minal gas into the bowel wall, where it is ab-sorbed into the portal circulation (13). Portomes-enteric vein gas in the setting of blunt traumadoes not necessarily imply bowel necrosis or per-foration, and the absence of peritonitis may allowobservation of this finding (14).

Intraabdominal SepsisSeveral infectious abdominal processes have beenassociated with portomesenteric vein gas, includ-ing diverticulitis, abdominal abscess and gan-grene, cholecystitis and cholangitis, appendicitis,colitis (inflammatory, pseudomembranous, sec-ondary to Candida infection in human immuno-deficiency virus–related disease), and abdominaltuberculosis.

The pathogenesis of portomesenteric vein gasassociated with infectious gastrointestinal dis-eases is not fully understood. Three theories havebeen put forward: (a) portomesenteric vein gasresults from septicemia in branches of the mesen-teric and portal veins (pylephlebitis) (15,16);(b) portomesenteric vein gas results from in-creased intraluminal fermentation of carbohy-drates due to bacteria (17); and (c) mesocolicabscess causes inframesocolic perforation thatdissects between the peritoneal leaflets of the mes-ocolon, thereby creating access to the mesocolicveins (18).

b. a.Figure 10. Portomesenteric vein gas in a patient who presented with abdominal pain and distention. Thepatient 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 portomesenter-ic vein gas (arrows). The nasogastric tube can also be seen. The patient was treated conservatively and had anuneventful recovery.


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

Portomesenteric vein gas is a rare complicationof colonic diverticulitis (Fig 12), but the combina-tion of the two conditions can lead to hepatic ab-scess. Inflammatory involvement of the inferiormesenteric vein complicating diverticulitis of thesigmoid colon can result in septic thrombophlebi-

tis and the presence of gas within the vein (19). Ifno synchronous liver abscesses are present, porto-mesenteric vein gas is not associated with a poorprognosis.

a. b.Figure 11. Portomesenteric vein gas associated with paralytic ileus secondary to bronchial artery embolization in apatient who presented with abdominal pain and distention. CT was performed 24 hours after embolization. (a) Con-trast-enhanced CT scan shows intrahepatic portal vein gas (arrows). (b) Contrast-enhanced CT scan depicts boweldistention with mural air (arrowheads). Mesenteric ischemia was suspected, and the patient underwent surgery. Noischemic bowel was found. Contrast-enhanced follow-up CT performed 20 days later demonstrated resolution ofthe hepatic portal vein gas.


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

Figure 13. Abdominal wall gangrene with portomes-enteric vein gas. Contrast-enhanced CT scan shows sub-cutaneous and mesenteric gas (arrows), a finding that isconsistent with abdominal wall gangrene. Note also thepresence of gas in the mesenteric vein (arrowhead). Surgi-cal findings confirmed the diagnosis, and the patient died3 days later in the intensive care unit.

Intraperitoneal and retroperitoneal abscessesand gangrene (Fig 13) can also cause portomes-enteric vein gas.

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

The indication for surgery in portomesentericvein gas is based on the underlying cause of thedisease entity; treatment with broad-spectrumantibiotics is sufficient in most cases.

Unknown CausesPortomesenteric vein gas is idiopathic in ap-proximately 15% of cases (16) and has been ob-served in organ transplantation (liver, kidney,bone marrow), pulmonary diseases (chronic ob-structive pulmonary disease, bronchopneumonia,


a. b.Figure 15. Pneumatosis intestinalis with portomesenteric vein gas in a patient with asthma and non-Hodgkin lym-phoma 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 CTscan (lung window) shows intramural bowel gas (arrowhead) and mesenteric vein gas (arrows). The patient had noabdominal symptoms and made a full recovery without having to undergo surgery.

Figure 16. Portomesenteric vein gas associated withhepatic transplantation. Contrast-enhanced CT scanobtained 10 days after surgery demonstrates portal veingas (arrow). There were no complications at that time.Unenhanced CT performed 10 days later showed reso-lution of the portal vein gas.

asthma) (Fig 15), steroid and cytostatic therapy,and seizures.

Portomesenteric vein gas is a common findingin the first 2 weeks after hepatic transplantationand may not have prognostic significance (Fig16). In a series by Chezmar et al (21), seven of39 liver transplant recipients (18%) had porto-mesenteric vein gas, but none had bowel infarc-

tion or necrosis. Portomesenteric vein gas hasalso been associated with venovenous bypass,sepsis, and primary graft failure.

ConclusionsThe most serious and most frequent cause of por-tomesenteric vein gas in adults is mesenteric ische-mia. However, the association of portomesentericvein gas with this disease process does not imply aworse prognosis; thus, surgical treatment shouldnot be excluded when this sign is present. Severalother disease processes have been described re-cently as causes of portomesenteric vein gas. Inthe majority of cases, particularly when porto-mesenteric vein gas is secondary to invasive pro-cedures, surgery is not required and the prognosisis favorable. Findings of portomesenteric vein gasat CT should be carefully evaluated in the contextof clinical findings before making decisions regard-ing diagnosis and therapy.

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SCIENTIFIC EXHIBIT 1213 Portomesenteric Vein ... - RPH Doctorrphdoctor.org/wp-content/uploads/2016/08/CT-Portomesenteric-Vein-gas.pdf · of decreased attenuation in the mesenteric