Pneumobilia is the presence of air within the biliary
tree. Air in the biliary tree is usually iatrogenic and is frequently
seen following procedures such as ERCP, sphincterotomy or biliary
surgery but may also occur after the passage of gallstones or distortion
of the lower common bile duct by local inflammation, tumor or duodenal
ulceration. Although it does not usually persist, the air can remain
in the biliary tree for months or even years and is not significant.
Air within the bile ducts is seen as densely echogenic lines with
shadowing along the course of the biliary system. It is characterized
by highly reflective linear echoes, which follow the course of the
biliary ducts. The air usually casts a shadow which is different
from that of stones, often having reverberative artifacts and being
much less well-defined or clear. This shadowing obscures the lumen
of the duct and can make evaluation of the hepatic parenchyma difficult.
Intrabiliary gas is occasionally indistinguishable from stones.
In most cases gas produces a brighter reflection and dirtier shadow
than do stones. A ring-down artifact is only seen behind gas and,
when found, can be used to confirm the diagnosis of pneumobilia.
Gas is also more likely to move.
* Portal venous : air In pneumobilia
the air is not carried peripherally to the same extent as portal
venous gas. The most difficult distinction lies between air within
the biliary tract and air within the portal system. They represent
two entirely different clinical entities. Pneumobilia is associated
with biliary-enteric fistula, incompetent sphincter of Oddi, and
emphysematous cholecystitis, and is commonly seen following biliary
bypass operations. The finding of portal venous air requires urgent
surgical exploration. The list of causes of portal venous gas is
long, but ischemic bowel with infarction and necrosis is by far
the most common etiology and carries a grave prognosis.
* stone : A similar pattern of echogenic
liver foci may be produced by calcifications. Calcifications within
the liver generally produce clearly definable acoustic shadows,
even with low-frequency transducers. Rarely, multiple biliary stones
form within the ducts throughout the liver and can be confused with
the appearances of air in the ducts. Finally, gas within the biliary
radicles often appears as linear echogenic foci. This appearance
is less common with calcifications. Gas is also more likely to move.
Causes of Pneumobilia
* Following ERCP (endoscopic retrograde cholangiopancreatographiy).
* Following surgery - biliary-enteric anastamosis.
* Biliary fistula: gastric or duodenal ulcer, gastric or colonic
carcinoma, bile duct carcinoma, gallstone ileus, following cholecystectomy,
carcinoma gallbladder, Crohn's disease.
* Abdominal trauma.
* Ruptured duodenal diverticulum's.
* Emphysematous cholecystitis.
* Patulous ampulla.
* Rupture of hydatid cyst into the bile ducts.
* Hepatobiliary ascariasis.
* Tracheobiliary fistula (congenital anomaly presenting with respiratory
distress in the newborn).
* Effect of drugs on the sphincter (magnesium, atropine, nitroglycerine