Keywords
fistula - gallstone - ileus - obstruction
Introduction
Gallstone ileus (GSI) is a rare form of bowel obstruction that occurs in 0.4 to 1.5%
of patients with cholelithiasis.[1] Gallstones (>2 cm) are thought to enter the duodenum through a cholecystoduodenal
fistula.[2] GSI is an important complication of gallstone disease since it is often underreported
and poorly managed. The terminal ileum or the ileocolic junction is usually the common
location for mechanical obstruction as a result of gallstone due to its reduced diameter.
Patients present with small bowel obstruction symptoms including severe abdominal
pain, nausea, vomiting, and abdominal distention. Computed tomography (CT) scan will
show obstructed bowel; however, the impacted gallstone, especially the cholesterol
ones, may not be detected due to their radiolucent nature. The important clues to
look for include air in biliary tree, subtle increased density of the impacted calculus,
and specks of rim calcification if any.
We report an interesting case of GSI that was not detected on preliminary plain CT
scan but got detected on a follow-up CT scan, and discuss the subtle clues that led
to its diagnosis.
Case Report
A 66-year-old male, a known case of chronic medical renal disease, presented to the
emergency department with one day complaints of abdominal pain and four episodes of
vomiting. Patient had no prior history of abdominal surgery, cholecystitis. On examination,
his abdomen was soft, distended. Patient was dehydrated with raised serum creatinine
levels; hence, he was started on intravenous fluids and antibiotics.
Ultrasonography abdomen revealed a contracted gallbladder and gaseous distension of
bowel loops. Plain anteroposterior radiograph of the abdomen in erect position revealed
no evidence of bowel dilatation or air-fluid levels.
He was managed conservatively. Two days later, he developed breathlessness with increased
abdominal distension for which a plain CT scan of the abdomen was done. The CT scan
revealed dilated jejunal and proximal ileal loops. Abrupt transition zone was identified
at the level of mid-ileum and distal ileal loops were collapsed. However, no cause
of obstruction could be detected. No intramural air foci, pneumoperitoneum, or free
fluid in the abdomen was seen. The gallbladder was contracted in the present scan.
Ryle's tube was inserted and patient was put on Bilevel Positive Airway Pressure support.
The patients general condition improved; however, clinically the obstruction did not
resolve. A repeat CT scan of the abdomen was performed 4 days after the initial scan.
The CT scan demonstrated contracted gallbladder with air foci and pneumobilia ([Fig. 1]). A small communication of the gallbladder could be seen with the first part of
duodenum. Persistent small bowel dilatation with an abrupt transition point was seen.
However, the transition zone that was earlier visualized in the mid-ileal loops now
had moved further into the distal ileum ([Fig. 2]). Upon careful examination, a 5 × 3cm radiolucent, oval-shaped density was identified
at the transition zone having a subtle density difference with the fluid in the bowel
loops ([Figs. 3] and [4]). Small specks of rim calcification were seen in it. These findings could be better
appreciated on narrow window settings ([Fig. 5]). This was likely to be a radiolucent gallstone. The patient was taken up for exploratory
laparotomy with removal of impacted gallstone ([Figs. 6] and [7]) and decompression of intestines. Cholecystectomy and repair of cholecystoduodenal
fistula using omental patch were done with feeding jejunostomy. The patient's condition
improved postoperatively.
Fig. 1 Coronal section of contrast-enhanced follow-up computed tomographic scan shows increased
air pocket in the gallbladder lumen (thin blue arrow). It also shows the obstructed
gallstone in the pelvic region that is radiolucent with a few calcific specks in periphery
(thick blue arrow). Note that its contour is conforming with the lumen of the ileal
wall.
Fig. 2 (A) Axial section of unenhanced computed tomographic (CT) scan shows a radiolucent gallstone
in the ileum conforming with the contour of the ileum (blue arrow). Notice the specks
of rim calcification. (B) Axial section of contrast-enhanced follow-up CT scan shows that there is a change
in transition zone as the gallstone has moved further distally within the ileum (blue
arrow). The enhanced bowel wall makes visualization of the peripheral rim calcifications
difficult.
Fig. 3 Coronal section of follow-up enhanced computed tomography shows the obstructing gallstone
(thin blue arrow) and the abrupt transition point (thick blue arrow) distal to which
the ileal lumen is collapsed.
Fig. 4 Axial section of follow-up enhanced computed tomography shows that the density of
the gallstone (straight blue arrow) and the adjacent fluid (curved blue arrow) within
the bowel lumen is almost similar thus making it difficult to identify.
Fig. 5 Coronal section of unenhanced computed tomography. The gallstone is better visualized
after the narrowing the window settings and its size can be measured.
Fig. 6 Intraoperative image of removal of obstructed gallstone from the ileum.
Fig. 7 Gallstone removed from the ileum.
Review of earlier CT scan showed that both the gallstone and the gallbladder air were
present ([Figs. 8] and [9]). However, the air focus was very tiny at that time and hence not reported.
Fig. 8 Axial section of unenhanced computed tomography shows a speck of air within the gallbladder
lumen (thin blue arrow). An incidental rounded hypodense nonenhancing lesion is seen
in the right anterolateral abdominal wall (thick blue arrow) likely to be an epidermoid
inclusion cyst.
Fig. 9 Comparative scans of axial unenhanced computed tomography with narrow window settings
in the left sided image. The gallstone is better visualized in narrow window settings
(blue arrow). Note the collapsed ileal loop distal to it.
Discussion
GSI is an uncommon presentation of gallstone disease. It refers to obstruction of
the small bowel due to impaction of one or more gallstones that have passed into intestines
through a bilioenteric fistula. Most common fistula is a connection from the gallbladder
to the duodenum (85% of cases) formed following chronic erosion by a stone or recurrent
calculous cholecystitis.[1] The impacted stones are usually greater than 2 to 2.5 cm in diameter.[1]
[3]
[4] Smaller stones pass through the lumen of the bowel as “rolling stones” and rarely
cause obstruction.
Common places for gallstones to be lodged include the ileum and ileocecal valve due
to the anatomical narrow lumen in 60% of cases, jejunum in up to 16%, stomach in 15%,
and colon (gallstone coleus) in 2 to 8% of cases.[5]
[6]
Gallstones are notoriously difficult to visualize on plain film radiography, with
only 10 to 20% of stones containing enough calcium to be radiopaque.[7]
[8] Contrast-enhanced CT for GSI has a much higher sensitivity of 90 to 93%,[1]
[9]
[10]
[11]
[12] specificity of 100%,[9]
[12] and accuracy of 99%[9]
[12] as it has a higher sensitivity for the detection of air in gallbladder and subtle
calcification seen in gallstones. Rigler's triad described on plain films comprising
of air in biliary tree, small bowel obstruction, and ectopic radiopaque gallstones
is pathognomonic for GSI. In the literature, only 14 to 53% of cases present with
the full criteria and in most cases, only two signs out of the triad are present.[1]
[9]
[13]
[14]
[15] Since then, two further signs have been described: change in the location of a previously
noted gallstone (Rigler's tetrad)[10] and a dual air-fluid level in the right upper quadrant, the medial one being in
the duodenal bulb, and the lateral one in the gallbladder (herein Rigler's pentad).[1] CT scan in addition will show abnormal inflamed gallbladder with wall thickening
and presence of bilioenteric communication suggestive of fistula. The transition point
of bowel caliber is well seen on the CT scan and a close evaluation will reveal even
the lucent obstructing calculi.
Plain CT scan is found to be helpful as the small specks of calcification in the rim
of calculi are better seen. On intravenous contrast-enhanced CT scanning, there can
be difficulty in defining some radiolucent stones or rim-calcified stones[9]
[16] due to a lack of differentiation from the enhanced small bowel wall.
In our case, there were three challenges that prevented the diagnosis in the first
place—air focus was tiny and the calculus was lucent, almost conforming to the shape
and density of the fluid filled bowel loop. On analyzing the reasons, it was felt
that GSI being a rare cause of intestinal obstruction, careful attention to gallbladder
was not a routine practice in such cases. More so, the patient did not have any history
of gallbladder disease. In subsequent scan, the air focus became larger and air appeared
in bile ducts as well. What helped in identifying the calculus in the subsequent scan
was the distal shift in the position of the obstructing point from proximal to distal
ileum. We realized only a mobile intraluminal cause of obstruction like a gallstone
could cause this. Also, though the stone was largely lucent, it could be visualized
upon narrowing the window settings of image on the workstation. It is well known that
subtle density difference between the normal and abnormal in CT scans can be often
appreciated upon change in the window width and center settings. Subtle calcific specks
were also present in the rim of the calculus but were discounted as nonspecific hyperdense
bowel content as GSI was not a consideration in the first scan. Hyperdense specks
are often seen in the bowel lumen due to the use of certain oral medication and they
can mask the subtle rim calcification of the calculus.[17] Overall, a combination of above imaging factors combined with lack of clinical suspicion
led to the missed diagnosis in the first scan. But attention to details and more obvious
findings helped us in making the correct diagnosis in the second scan.
To conclude, GSI is a rare cause of intestinal obstruction. Close evaluation of gallbladder
and biliary tree is needed in cases of intestinal obstruction for presence of air.
Careful evaluation of intestinal lumen with appropriate window settings at the transition
point to look for a lucent gallstone is needed. If follow-up CT scan shows a change
in level of obstruction, a mobile intraluminal cause must be considered.
