NONIATROGENIC CAUSES OF PNEUMOBILIA
EMPHYSEMATOUS CHOLECYSTITIS
Emphysematous cholecystitis is a rare form of acute cholecystitis,
often associated with acalculous cholecystitis and perforation of the gallbladder.
Men are affected twice than women,
with a mean age of incidence around 50-70 years.
Often it correlates to diabetes and atherosclerotic disease; therefore the occlusion of cystic artery is considered a major cause of evolution towards the emphysematous form.
The most commonly involved bacteria belong to the family of Clostridium and Escherichia.
Clinically the onset is quite insidious and rapidly progressive,
often requiring a surgical intervention.
CT is the most sensitive and specific imaging modality for the diagnosis of the disease identifying even small air bubble in the gallbladder wall and in the biliary branches (intrahepatic and extrahepatic).
It could be frequent the relief of air in the portal branches or free air in the abdomen,
after the rupture of the wall,
by configuring the surgical emergency.
A CT scan without contrast medium is usually sufficient to arrive at a correct diagnosis (Fig.
2).
Fig. 2: 65 y.o man with acute emphysematous cholecystitis. (a-d) Unenhanced CT demonstrates intramural and intraluminal gas collections in gallbladder (green arrow) and in biliary duct (red arrow). (b-e) Post contrast phase confirm the diagnosis. (c) It is possible to see an air-fluid level in the gallbladder, sign of wall perforation.
ENTERIC BILIARY FISTULA
Especially in chronic conditions of cholelithiasis,
adhesions can establish between the gallbladder wall and gastro-intestinal segments,
especially with the duodenum and colon.
Adherence,
helped by the bowel peristaltic movement,
may result in a cholecysto-enteric fistula,
with passage of gallstones in the intestinal lumen; the stop of the calculus at the ileocaecal valve causes a biliary ileus,
a fairly rare event with an incidence of 1-4%,
and more common in the elderly.
Other possible causes of fistula are peptic ulcers and trauma.
CT is undoubtedly the most reliable imaging modality in the diagnosis,
with a sensitivity of 93% and a specificity of 100%.
The typical finding is the “Rigler triad” characterized by intestinal obstruction,
calculus in the intestinal lumen (often right iliac fossa) and air in the biliary branches.
Sometimes it is possible to see the fistula site.
Air in the portal vein or free air in the abdomen should always be sought as poor prognostic signs (Fig.
3).
Fig. 3: 82 y.o woman whit acute abdominal pain. (a) CT scan shows gas collection in biliary duct (red arrow). (b) A stone is found in the jejunum (green arrow). (c-d) It’s possible to identify the enteric biliary fistula (yellow arrow).
ASCENDING CHOLANGITIS
Ascending cholangitis or acute cholangitis is a clinical condition caused by the proliferation of bacteria in the biliary tree caused by an obstruction in the biliary system.
Bacteria can also arrive from the intestine through the portal venous system.
Bacteria (most often Gram negative,
in particular Escherichia coli) colonize the biliary system and biliary stasis allows their proliferation; because of the high biliary pressure they can pass the cellular barriers and penetrate into the blood system.
The main causes are choledocholithiasis (80%) and neoplastic lesions (20%); more rarely sclerosing cholangitis,
Oddi sphincter incontinence,
biliary tree endoscopic procedures (ERCP).
Classic clinical manifestation is the "Charcot's triad" with fever,
pain in the right upper quadrant of the abdomen and jaundice (in 40% of patients); less frequently shock with hypotension,
lethargy and mental confusion.
CT imaging is crucial in identifying the location and the type of obstruction; typically biliary tree is dilated and some areas of liver parenchymal are hyperdense only in the arterial phase (transient hepatic attenuation differences THADs).
Depending on the type of bacteria which support the infection,
gas in the biliary branches could be present (Fig.
4).
Fig. 4: 55 y.o man with fever who underwent Cholecistectomy and sphincterectomy 6 months before. The Ct scan shows gas collection in biliary tract.
NON IATROGENIC CAUSES OF PORTAL VENOUS GAS
The presence of gas in the portal branches is not still explained; there are two main hypotheses:
- the passage of gas produced by bacteria in the intestinal lumen through the bowel wall;
- the gas production by bacteria penetrated into the portal circulation.
The most characteristic finding on CT is the presence of air,
often with a linear morphology,
in the most peripheral portion of the liver within 2 cm from the capsule.
This allows distinguishing the portal gas from pneumobilia,
which tends to affect the central portion of the liver,
following the biliary branches.
BOWEL ISCHEMIA
It is a fairly common condition,
often associated with high mortality (75-90%) especially in the elderly.
It is caused by insufficient arterial or venous blood flow to the bowel.
We distinguish three stages:
- Ischemia of the mucosal layer (it is reversible);
- Ischemia of the mucosal and submucosal layer;
- Ischemia of the whole wall.
The wall damage,
in particular of the mucosa,
associated to the distension of the loops,
allows gas to pass on the venous system,
coming up through the portal circulation to the liver.
The intestinal ischemia is the main cause of gas in intrahepatic portal vein branches (70%) and,
when it is present,
it is associated with transmural bowel necrosis (91%) with increased mortality.
CT represents the most sensitive imaging modality (82%),
especially when an ANGIO CT is performed.
In addition to portal pneumatosis,
possible other findings are pneumatosis of the bowel wall,
pneumoperitoneum,
submucosal haemorrhage and peritoneal effusion.
The intestinal wall is never thickened (Fig.
5).
Fig. 5: 78 y.o. man with abdominal pain from 3 days. (a) Unenhanced CT scan shows gas collection within 2 cm from liver capsule, with linear and branched morphology (red arrow) (c) Air-fluid distension of intestinal loop and pneumatosis intestinalis is observed in lower abdomen (yellow arrow). (d) Gas bubble is found in mesenteric vein (white arrow).
The presence of air in the portal system however does not allow differentiating intestinal ischemia from other causes of portal pneumatosis.
As a matter of fact there is not a direct correlation between the extension of ischemia and the amount of intrahepatic gas.
Therefore,
CT findings should be always associated with the clinical and laboratory data.
NECROTISING ENTEROCOLITIS
Necrotizing enterocolitis (NEC) is a common cause of acute abdomen in preterm newborn; in 90% of cases it occurs in children of 36 weeks preterm,
in 10% of cases it affects children born at term with predisposing conditions to reduced mesenteric perfusion.
Etiology and pathogenesis of NEC are controversial,
but it seems to be mainly related to hypoxic ischemic damage of the gastrointestinal tract,
still immature,
combined with microbiological changes in the intestinal flora; a damage of the mucosa with intestinal ischemia and necrosis is the consequence.
Bacteria pass the bowel mucosa and proliferate; their metabolism leads to intramural gas (intestinal pneumatosis).
Through the mesenteric veins,
the gas embolises to the portal system and liver,
most commonly in the left lobe and the anterior segment of the right lobe.
The amount of portal pneumatosis is not always correlated to the quantity of intramural intestinal gas and also is not always associated with a poor prognosis.
In more than 30% of infants with NEC,
the X-ray detects portal pneumatosis.
Gas in the portal system is not an early sign of NEC,
as the intramural bowel gas.
The CT appearance of portal pneumatosis is characterised by gas with a linear distribution,
which extends from the main portal branches to the peripheral ones of both liver lobes.
It must be differentiated from pneumobilia,
which is not common in newborns and still localized preferentially in the ilum.
IBD
Crohn disease (CDs) is one of benign causes of portal pneumatosis.
Although rare,
it requires a surgical approach only if complicated by other adverse events,
such as intestinal perforation.
Usually it affects individuals under the age of 65 (in 95% of cases); we should think about this disease when portal pneumatosis is detected in a young patient without signs of intestinal ischemia.
Three main theories explain portal pneumatosis in CDs:
- Increased intraluminal pressure caused by colonoscopy follow-up with high inflation pressures;
- Enterovenous fistulisation,
an extremely rare complication that leads a direct communication between intestinal lumen and venous branches;
- Mucosal damage with sepsis,
related with intestinal inflammation and portal pyaemia.
CDs should be suspected on CT imaging in case of pneumatosis portal associated to the wall thickening of the intestinal loops affected by the disease.
The surgery in these patients is necessary only in case of intestinal perforation,
signs of peritonitis,
or in the cases the localisation of the enterovenous fistula is not possible.
NONIATROGENIC CAUSES OF PARENCHIMAL GAS
HEPATIC INFARCTION/LIVER TRANSPLANTATION
Hepatic infarction is an extremely rare condition as liver blood supply is guarantied by the hepatic artery and by the portal venous system; only when both systems are compromised infarction may occur.
The main causes are liver transplantation and hepatobiliary surgery.
Hepatic artery thrombosis is one of the most serious complications of transplantation with an incidence of 2-25%; since the bile ducts have an exclusively arterial blood supply,
it follows their necrosis.
Ischemia of hepatocytes and biliary epithelium leads to narrowing of the bile ducts,
biliary stasis,
abscess formation,
bacteraemia and sepsis.
Gangrene is another fatal complication of liver transplantation,
due to hepatic artery thrombosis.
Other less common causes of liver infarction are acute shock,
hypercoagulable states,
trauma,
pre-eclampsia.
Clinically it manifests with abdominal pain,
nausea,
vomiting and abnormal liver function.
On CT examination,
small infarcts appear as wedge-shaped peripheral areas of low attenuation; larger ones show geographical distribution with air in the portal and biliary branches.
In most cases the diagnosis is easy,
but sometimes it is necessary to be careful not to confuse them with abscesses,
focal steatosis areas or tumour.
LIVER ABSCESS
Thanks to the use of antibiotics,
the current incidence of liver abscesses is significantly reduced.
The number of lesions can help to identify the causes; in fact a unique pyogenic abscess is often cryptogenic while multiples are associated with haematogenous dissemination (either through the portal venous system from gastrointestinal diseases than through the hepatic artery in sepsis) and with ascending cholangitis.
Most abscesses are polimicrobial and the most frequently isolated bacteria are Escherichia coli and Klebsiella pneumoniae; staphylococci,
streptococci and anaerobes are less common.
Only in 20% of cases amoebas and fungi cause abscesses.
CT has a very high sensitivity (95-100%) in identifying abscesses (Fig.
6).
Fig. 6: 54 y.o. man with OLT and fever from 2 weeks. (a) Unenhanced CT scan shows a fluid collection with air-fluid level in 8th hepatic segment (c) Portal vein phase shows peripherally enhancing
Abscesses are classified in micro-abscesses (< 2 cm) and macro-abscesses (> 2 cm). Pyogenic abscesses appear as multiple small lesions scattered in the parenchyma with distribution similar to that of fungal abscesses in immunocompromised patients; however sometimes they tend to confluence.
The miliary spread pattern is typical in case of septicemia caused by staphylococcus while the cluster pattern is characteristic of coliforms and enteric bacteria.
On CT imaging abscesses appear as multiple small hypodense lesions,
well-defined,
with small peripheral enhancement and perilesional oedema; larger ones are generally unilocular with smooth margins,
but sometimes have internal baffles and irregular borders.
Approximately in 20% of abscesses gas is present,
both as small bubbles,
both as a fluid-air levels,
thus facilitating the diagnosis (Fig.7).
Fig. 7: An hepatic abscess with both bubble gas aspect (red arrow) and air-fluid level (green arrow)
The presence of gas in the amoebic abscesses is infrequent,
and linked to the presence of a fistula between the abscess and the stomach,
the duodenum or the colon,
or to a superinfection of the abscess by gas-forming bacteria.
COMPLICATED PARASITES CYST
Cystic hydatid disease is a worldwide spread zoonosis caused by the larval stage of Echinococcus granulosus and multilocularis.
It is particularly widespread in the Mediterranean area,
Africa,
South America and the Middle East.
The classic radiographic appearance is well known: a fluid density cyst with walls sometimes calcified and occasional daughter cysts or floating membranes within.
Complications such as superinfection and wall rupture may occur.
There are three major types of rupture:
- Contained: it occurs in case of intact pericyst with separation of endocyst.
- Communicating: when the cyst comes into direct communication with the biliary tree or,
more rarely,
with a bronchial branch; the latter case will occur only if the cyst in the upper segments of the liver,
with diaphragm erosion.
- Direct: in case of endocyst and pericyst rupture in the pleural cavity,
in the peritoneum or in a hollow viscera.
Superinfection complicated up to 25% of the cases of rupture.
TC features of complicated liver hydatid cysts include: interruption of the wall cyst (particularly evident in the presence of calcifications) and soft edges.
In case of superinfection or of communication with hollow viscera and bronchial tree,
an air fluid level is often evident (Fig.
8).
Fig. 8: 50 y.o man with a known story of hydatidosis. (a-d) A CT scan shows an hydatid cyst in the upper segment of liver (green arrow). (b) After admission in internal admission department for chest pain, cough and fever a CT unenhanced scan shows pleural effusion, lung fluid collection (e white arrow) and air-fluid level into the hydatid cyst (red arrow). Also pneumobilia is evident, especially in MinIP reconstruction (f yellow arrow)
EMPHYSEMATOUS CHANGES OF THE LIVER
Abdominal emphysematous infections include emphysematous cholecystitis,
emphysematous gastritis,
emphysematous pyelonephritis,
emphysematous pyelitis and emphysematous cystitis.
The emphysematous hepatitis,
unlike the other infection,
is an extremely rare event,
with only a few cases described in literature (21,
22,
23).
In all the cases described patients died within 7-24 hours after admission.
Even the case observed at our institution shows a rapid worsening of clinical condition,
until the death of the patient in less than 48 hours after admission.
The affected patients are usually diabetics.
The pathogenesis is still uncertain.
Possible factors are sepsis by forming gas bacteria (K pneumonie),
associated with intra-abdominal infection,
high levels of glucose in the blood and thrombus embolism.
CT is the most reliable method in the diagnosis of this condition,
and highlights extended collected air,
with bubble-like aspect,
with no fluid collections,
associated or not with pneumatosis portal.
It is also possible to observe pneumoperitoneum if air bubbles breaks in the abdominal cavity (fig 9).
Fig. 9: 79 y.o man with abdominal pain and fever from one day. The patient is diabetic since he was 55 y.o.. A CT unenhanced scan shows multiple bubble-like gas collection, spread all over the liver (red arrow). A lung HU level window shows the air nature of the inclusion, without fluid. Also portal pneumatosis (yellow arrow) and air in abdominal cavity (green arrow) is visible. The patient dies 24 hours after admission and in autopsy exam sepsis from Klebisella Pneumonie was found.
IATROGENIC CAUSES OF PNEUMOBILIA
BILIARY INTERVENTION
The presence of pneumobilia is a frequent iatrogenic condition caused by interventions on the bile duct; the main causes are sphincterotomy,
cholecystoenterostomy,
cholecystectomy, bile duct-duodenostomy and liver transplant (Fig.
10).
Fig. 10: Pneumobilia after ERCP procedure (red arrow)
A good anamnesis is fundamental to differentiate between air in the biliary tract or in the portal system.
CT with contrast media highlights included the presence of air with tubular aspect,
mainly in the central areas (while the portal pneumatosis is typically peripheral); the aerobilia prefers the left hepatic lobe.
IATROGENIC CAUSES OF PORTAL VENOUS GAS
CENTRAL VENOUS CATHETERISM/ENDOSCOPIC PROCEDURES
Portal pneumatosis is a rare complication of umbilical venous catheter placement procedures in the infant,
femoral central venous catheter or epidural catheter in adults; this type of procedures can sometimes be a result of introduction of air through the catheters,
with gas embolization into the systemic venous circulation.
In literature there are also several reported cases of air in portal system following a colonoscopy or barium enema procedures; the underlying mechanism seems to be little damages of the intestinal wall,
that allows the passage of air into the venous system during insufflation.
CHEMIOTHERAPY AND DRUGS
The presence of portal pneumatosis was observed in several patients in chemotherapic treatment.
Among the side effects of these drugs,
there are known complications on the gastrointestinal tract.
In particular,
peptic ulcers and pneumatosis intestinalis,
can be accompanied by gaseous embolization of portal branches.
Although this condition is often benign and not indicating a lethal risk for the patient,
it must be differentiated with more severe conditions,
such as the intestinal infarction.
The drugs most frequently responsible for this condition are the combinations of carboplatin and paclitaxel,
and the combination of irinotecan and cisplatin.
IATROGENIC CAUSES OF PARENCHIMAL GAS
TUMOR ABLATION
Various tumor ablation techniques percutaneous can cause gas inclusion in the liver parenchyma.
However,
the gas is not always present and does not represent a valid extension indicator of induced tumor necrosis.
In ablation using radiofrequency the tumor is destroyed by coagulation necrosis and the gas formed in the parenchyma and in the portal system disappears after about 20 minutes from the procedure; also it seems to have no clinical meanings.
The gas is not always present,
so that it can’t be used as an accurate indicator of tumor necrosis.
The combination of radio frequencies with the ethanol injection seems to be associated with increased presence of gas,
especially compared with a classic RF treatment,
probably because ethanol increases the conduction of heat (Fig.
11).
Fig. 11: Hepatic gas collection after a RFTA (red arrow). Pleural effusion and periepatic fluid collection are also visible. Ther is a small gas-bubble in abdominal cavity (white arrow).
Ethanol can also create problems in differential diagnosis,
because it has a low attenuation that simulate air density in TC.
In ablations using cryotherapy,
a tissue necrosis indicator is the presence of small bubbles of gas,
evident at the site of action for several days after the treatment.
HEPATIC ARTERY EMBOLIZATION
The embolization of the hepatic artery branches is a common practice in case of bleeding or tumor therapy.
The most commonly used methods involve the use of coils,
emboli and sponge material.
During the procedure it is possible the passage of small amounts of outside air into the circulation,
in spite of all possible precautions.
Therefore within 5-10 days of the procedure,
any control examinations,
and mainly in TC,
small gas bubbles in the treated liver can be observed.
It 'good to remember that these findings may also be associated with focal areas of necrosis of liver tissue (fig 12-13).
Fig. 12: CT scan 6 days after a TACE procedure shows small bubble gas within a necrotic area.
Fig. 13: CT scan 5 days after a TACE procedure shows small bubble gas in the area of treatment.