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1.4 · Infl ammatory Bowel Diseases
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1
Signs on MRI and MR Enteroclysis
5 Fistula formation : the main advantages of MR
examination over CT are lack of radiation and high
soft-tissue details that make it ideal to detect
fistulas. Fistula is an abnormal tract between two
surfaces. In CD, fistulas are formed between the
organs (e.g., vesicoenteric fistula) or between the
internal organs and the skin surface (e.g.,
fistula-in-ano). Fistula-in-ano typically arises due to
rectal crypts infection and abscess formation, which
tunnels deep within the perineal tissues until it
opens into the skin surface. Fistula-in-ano is
identified as an abnormal longitudinal or linear tract
that typically runs parallel to the rectum and opens
into the skin surface. Thick granulation tissue line
may be found surrounding the fistula in chronic
cases. Active fistulas show signs of local
a
inflammation and enhancement after gadolinium
injection (
5 Thickening of the ileocecal valve can be nicely
demonstrated on coronal MR enteroclysis images
(
. Fig. 1.4.11 ).
5 Star sign : this sign is observed in MR enteroclysis and
represents multiple enteroenteric fistulae with
wall-to-wall adhesions (
attachment point between the intersected collapsed
bowel loops will result in a starlike configuration.
5 Mucosal polyp formation is seen in advanced stages of
CD as signs of mucosal regeneration (
5 Mesenteric lymphadenopathy : enlargement of the
mesenteric lymph node is a common sign in CD
(3–8 mm in size) (
nodes are >10 mm in size, carcinoma or lymphoma
should be suspected.
b
. Fig. 1.4.10 ).
. Fig. 1.4.12 ). The central
. Fig. 1.4.13 ).
. Fig. 1.4.14 ). When the lymph
. Fig. 1.4.10 Axial T1W postcontrasts with fat-saturation pelvic MRI in a patient with CD and fi stula-in-ano seen as abnormal tract
parallel to the anus in ( b ) and extends up to the rectum in ( a ) with contrast enhancement of the fi stula wall ( arrowheads )
. Fig. 1.4.11 Coronal MR enteroclysis image in a patient with
CD shows thickening of the mucosa of the ileocecal valve
( arrowhead )
. Fig. 1.4.12 Coronal MR enteroclysis image in a patient with
CD shows the star sign (Courtesy of Dr. K. Herrmann, Klinikum
Großhadern, Munich, Germany)
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Chapter 1 · Gastroenterology
by severe erosions that may lead to muscularis propria dam-
1
age, causing loss of the haustra and colonic dilatation.
Fulminant UC is seen in 15–20 % of cases.
CT is indicated in patients with UC when colonoscopy
and barium enema are not possible, for example, in cases of
sever in ammation, where the risk of perforation is high.
Both UC and CD carry the risk of malignant transformation. e risk of cancer in UC is 0.5–1 % a er 10 years of
universal colonic disease. Surveillance with CT or barium
enema is recommended for chronic patients with UC to
detect early colonic cancer that may present simulating strictures or in ltrative process.
Extraintestinal Manifestations of UC
5 Arthritis : it is the same as CD.
5 Sclerosing cholangitis : sclerosing cholangitis can be seen
in association with US in up to 70 % of patients with UC.
. Fig. 1.4.13 Coronal MR enteroclysis image in a patient with
CD shows mucosal polyp formation ( arrowheads ) and bowel
wall thickening ( arrows )
5 Central nervous system manifestations : neurological
manifestations of UC are rare and patient may present with
seizures. On brain MRI, multiple, periventricular,
intraspinal, and cerebellar hyperintense lesions may be seen
(. Fig. 1.4.15 ).
5 Pyostomatitis vegetans ( PV ): PV is a rare oral ulcerative
lesion seen in UC patients and less frequently in patients
with CD.PV is characterized by pustules (visible pus in a
blister), erosions, and vegetative plaques which appear on
the buccal and gingival mucosa forming a “snail-track”
appearance. PV is a speci c marker for IBDs
(. Fig. 1.4.16 ).
. Fig. 1.4.14 Coronal MR enteroclysis image in a patient with
CD shows periaortic lymphadenopathy ( arrowheads )
Ulcerative Colitis
UC is a chronic in ammatory disease of unknown origin,
characterized by rectal and colonic mucosal ulceration.
In contrast to CD, UC a ects only the inner wall of the
colon (super cial ulceration) and does not extend beyond
the muscularis propria layer and a ects the whole colon diffusely with no skip lesions. e rectum is involved in
95–100 % of cases. Patients commonly present with bloody
diarrhea with mucus. Lower abdominal pain, tenesmus, and
urgency are also common symptoms. Backwash ileitis refers
to mucosal in ammation of the terminal ileum in patients
with UC. Fulminant UC is a form of severe UC characterized
. Fig. 1.4.15 Axial FLAIR illustration demonstrates multiple T2
hyperintense signal intensity lesions in a patient with ulcerative colitis
( U C )
1.4 · Infl ammatory Bowel Diseases
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1
. Fig. 1.4.16 An illustration shows the clinical appearance of
pyostomatitis vegetans (PV)
Signs on Plain Radiograph
5 Dilated colonic segments with no haustration
( adult toxic dilatation of the colon )
5 Gasless abdomen : due to chronic diarrhea
5 Absence of fecal materials : because the bowel is not
functioning well
5 Toxic megacolon : abnormal distention of the colon
with air (
. Fig. 1.4.17 )
. Fig. 1.4.17 Plain abdominal radiograph shows toxic
megacolon ( arrowheads )
Signs on Barium Enema
5 Collar-button ulcer : it is a flask-shaped ulcer that is
commonly seen in intermediate stage of UC. This
type of ulcer is characterized by button-like shape
barium appearance. This appearance is seen
because UC causes erosions that extend until the
muscularis propria, with some intact mucosal layer
in between. The intact mucosal layer will have a
mushroomlike shape. In barium enema, the
barium will fill the erosion gaps between the intact
mucosal layers, giving this collar-button
appearance (
for UC, as it can be seen in duodenal and gastric
ulcers.
5 Pipe stem colon : this refers to rigidity and
narrowing of the colon due to longitudinal muscle
spasm and hypertrophy (
deformity is often seen in the mucosal
regenerative stage of the disease.
5 Toxic megacolon : toxic megacolon is one of the
devastating complications of UC and is seen in
<5 % of cases. Toxic megacolon is diagnosed when
the bowel wall shows dilatation >6 cm. Up to 30 %
of toxic megacolon develops during the first 3
months of the disease. Toxic megacolon is a
contraindication for barium enema because of the
risk of perforation during air inflation. A plain
. Fig. 1.4.18 ). This sign is not specific
. Fig. 1.4.19 ). This
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Chapter 1 · Gastroenterology
1
radiograph should be done in any patient with UC
planned for barium enema to exclude the
presence of megacolon (
. Fig. 1.4.17 ).
Signs on CT
5 The bowel wall thickness is diffuse and may affect
the entire colon. In contrast, bowel wall thickness
in CD may be eccentric and segmental with skip
lesions.
5 Perirectal fatty proliferation is seen as increased
fatty tissues around the rectum (
. Fig. 1.4.20 ).
. Fig. 1.4.20 Axial CT illustration demonstrates perirectal
fatty proliferation with fatty infi ltration of the rectal wall
( arrowhead )
. Fig. 1.4.18 Barium enema illustration demonstrates the
barium sign of collar-button ulcer ( arrowheads )
Signs on Colonic MRI (MRI Is Used to Diagnose and
Monitor UC when Endoscopy Cannot Be Performed
for Whatever Reason)
5 Hyperintensity and thickening of the colonic
mucosa and submucosa on T1W and T2W images,
caused by severe hemorrhagic changes.
5 T1W post-Gd images show enhancement of the
intestinal wall (
can be used to monitor the severity and the
activity of the disease; the stronger the signal, the
higher the severity of the disease.
5 Bowel wall thickening >10 mm with loss of the
normal haustration may be seen.
5 Increase in the perirectal fibro-fatty content with
widening of the presacral space as a sign of
long-standing disease.
5 Wall stratification is seen in 60 % of cases as a
hyperintense line on postcontrast T1W images
located between two hypointense stripes
(
. Fig. 1.4.22 ), representing edema and
inflammation between the mucosa and the
muscularis propria layers.
. Fig. 1.4.21 ). Postcontrast images
. Fig. 1.4.19 Barium enema examination in a patient with
chronic US shows marked stenosis and pipe-stem rigidity of the
sigmoid colon and the rectum ( arrowheads )
1.4 · Infl ammatory Bowel Diseases
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. Fig. 1.4.21 Axial T1W, fat-saturated, postcontrast MRI in a
patient with UC shows focal rectosigmoidal bowel wall enhancement indicating acute infl ammation ( arrowhead )
. Fig. 1.4.22 Axial T1W, fat-saturated, postcontrast MR
illustration of a female pelvis demonstrates the rectal wall
stratifi cation
D i ff erences Between Ulcerative Colitis
and Crohn’s Disease
5 CD commonly a ects the ileum and the ascending colon
and causes transmural (through the whole wall)
in ammation. In contrast, UC a ects the le colonic side
and causes only inner mucosal layer erosions. Also,
backwash ileitis is rare in CD.
5 Enlarged mesenteric lymph nodes are commonly seen
with CD.
5 e rectum is involved in 95 % of cases in UC, while only
15–20 % of cases in CD.
39
D i ff erential Diagnoses and Related Diseases
PAPA syndrome is a rare, pediatric, autosomic dominant
inherited auto-in ammatory disorder characterized by pyo-
genic aseptic arthritis , PG , and cystic acne . Patients present
with recurrent destructive arthritis. e synovial uid analysis shows purulent content with neutrophils accumulation,
but cultures are invariably negative. e cystic acne is seen in
the forehead, cheeks, nose, and chin. Humoral markers of
in ammatory diseases, including antinuclear antibodies and
erythrocyte sedimentation rate, can be negative. Up to 78 %
of patients presented with at least one additional in ammatory disorder like IBD, monoclonal gammopathy, acne conglobata, or hidradenitis suppurativa.
Further Reading
Al Roujayee A.Cutaneous manifestations of in ammatory
bowel disease. Saudi J Gastroenterol. 2007;13:159–62.
Cammarota T, etal. US evaluation of patients a ected by
IBD: how to do it, methods and ndings. Eur J Radiol.
2009;69:429–37.
Campa A, etal Management of a rare ulcerated erythema
nodosum in a patient a ected by crohn’s disease and
tuberculosis. J Plast Reconstr Aesthet Surg. 2008.
doi:10.1016/j. bjps.2008.11.024.
Dekker BJ, etal. Prevalence of peripheral arthritis, sacroiliitis
and ankylosing spondylitis in patients su ering from in ammatory bowel disease. Ann Rheum Dis. 1978;37:33–5.
Druschky A, et al. Severe neurological complications of
ulcerative colitis. J Clin Neurosci. 2002;9:84–6.
Furukawa A, etal. Cross-sectional imaging in Crohn disease.
Radiographics. 2004;24:689–702.
Giovagnoni A, etal. MR imaging of ulcerative colitis. Abdom
Imaging. 1993;18:371–5.
Herrmann KA, etal. e “star-sign” in magnetic resonance
enteroclysis: a characteristic nding of internal stulae in
Crohn’s disease. Scand J Gastroenterol. 2006;41:239–41.
Horton KM, etal. CT evaluation of the colon: in ammatory
diseases. Radiographics. 2000;20:399–418.
Javors BR, etal. Crohn’s disease: less common radiographic
manifestations. Radiographics. 1988;8:259–75.
Koulentaki M, etal. Ulcerative colitis associated with pri-
mary biliary cirrhosis. Dig Dis Sci. 1999;44:1953–6.
Lichtenstein JE, et al. e collar button. A radiographic-
pathologic correlation. Gastrointest Radiol. 1979;4:79–84.
Maccioni F, et al. Ulcerative colitis: value of MR imaging.
Abdom Imaging. 2005;30:584–92.
Maglinte DD, etal. Classi cation of small bowel Crohn’s sub-
types based on multimodality imaging. Radiol Clin North
Am. 2003;41:285–303.
Neye H, etal. Evaluation of criteria for the activity of Crohn’s
disease by power Doppler sonography. Dig Dis. 2004;22:
67–72.
Prassopoulos P, etal. MR enteroclysis imaging of Crohn dis-
ease. Radiographics. 2001;21:S161–72.
1
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Chapter 1 · Gastroenterology
Roggeveen MJ, et al. Ulcerative colitis. Radiographics.
1
2006;26:947–51.
Sun MR, etal. Current techniques in imaging of stula in
ano: three dimensional endoanal ultrasound and magnetic resonance imaging. Semin Ultrasound CT MR.
2008;29:454–71.
Wittenberg J, etal. Algorithmic approach to CT diagnosis of
the abnormal bowel wall. Radiographics. 2002;22:1093–9.
Yeon HB, etal. Pyogenic arthritis, pyoderma gangrenosum,
and acne syndrome maps to chromosome 15q. Am J Hum
Genet. 2000;66:1443–8.
systemic shock develops when >15 % of the circulation blood
volume is lost. Symptoms of upper GI bleeding include vomiting blood (hematemesis) and passing dark stool due to
blood digestion (melena). Severe lower GI bleeding may
present with passing fresh blood (hematochezia). In up to
75 % of upper GI bleeding cases and 80 % of lower GI bleeding cases, the bleeding will stop spontaneously with conservative treatment alone. In the remaining 20–25 % of cases,
further intervention is required.
In recent years, the role of multidetector CT in detecting the
source and the cause of bleeding has increased dramatically. CT
angiography is commonly performed to detect the source of
bleeding due to its fast scanning time and greater anatomical
1.5 Gastrointestinal Hemorrhage
coverage. Disadvantages of CT angiography include radiation
exposure and inability to perform intervention.
Gastrointestinal (GI) bleeding is classically divided into
upper and lower GI bleeding. Upper GI bleeding is de ned as
bleeding proximal to the ligament of Treitz, and lower GI
bleeding is bleeding distal to the ligament of Treitz.
Causes of upper GI bleeding include erosions or ulcers,
esophageal varices, Mallory–Weiss tear, and neoplasms.
Lower GI bleeding causes include diverticulitis, ulcerative
colitis, angiodysplasia, and neoplasms.
Patients with GI bleeding are o en asymptomatic until
blood loss exceeds 100mL per day. Tachycardia and hypotension occur when bleeding exceeds 500mL per day, and
In the classical catheter angiography, bleeding rates as low as
0.5mL/min can be detected with sensitivity of 63–90 % for
upper GI bleeding and 40–86 % for lower GI bleeding.
Conventional angiography speci city of up to 100 % is
established for both. Active bleeding is detected by extravasation of the contrast material into the bowel lumen (pathognomonic sign). Indirect signs of bleeding include detection
of aneurysms, arteriovenous stula, neovascularity, and
extravasation of the contrast material into con ned space.
CT angiography can detect active bleeding rate as low as
0.3mL/min.
Signs on CT Angiography
5 Active GI bleeding is detected in the arterial phase
of the scan when the contrast material is seen
within the bowel lumen (91–274 HU). The
extravasated contrast material may demonstrate
jet-like, linear, swirled, or pooled configuration
(
. Fig. 1.5.1 ).
5 The presence of hyperattenuated material within the
bowel lumen in postcontrast images that was not seen
a
. Fig. 1.5.1 Axial abdominal CTA illustration precontrast ( a ) and postcontrast ( b ). GI bleeding is detected in the arterial phase of the scan
as an extravasation of the contrast material within the bowel lumen ( arrowhead )
in the precontrast images is diagnostic of acute GI
bleeding (
5 For GI bleeding CTA, only intravenous contrast injection
is used. CTA is performed without prior oral
administration of water or contrast material. Water can
dilute the extravasated contrast material, causing
false-negative results.
5 Clotted blood attenuation is 28–82 HU, which can be
differentiated from active bleeding (>90 HU).
b
. Fig. 1.5.1 ).
1.6 · Pancreatitis
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Further Reading
Ernst O, et al. Helical CT in acute lower gastrointestinal
bleeding. Eur Radiol. 2003;13:114–7.
Ha HK, etal. Radiologic features of vasculitis involving the
gastrointestinal tract. Radiographics. 2000;20:779–94.
Jaeckle T, et al. Acute gastrointestinal bleeding: value of
MDCT.Abdom Imaging. 2008;33:285–93.
Laing CJ, etal. Acute gastrointestinal bleeding: emerging role
of multidetector CT angiography and review of current
imaging techniques. Radiographics. 2007;27:1055–70.
S c h e el H, etal. Acute gastrointestinal bleeding: detection of
source and etiology with multi-detector-row CT. Eur
Radiol. 2007;17:1555–65.
Yamaguchi T, etal. Enhanced CT for initial localization of
active lower gastrointestinal bleeding. Abdom Imaging.
2003;28:634–6.
Yoon W, et al. Acute gastrointestinal bleeding: contrast-
enhanced MDCT.Abdom Imaging. 2006a;31:1–8.
Yoon W, etal. Acute massive gastrointestinal bleeding: detec-
tion and localization with arterial phase multi-detector
row helical CT.Radiology. 2006b;239:160–7.
1.6 Pancreatitis
Pancreatitis is a disease characterized by in ammation of the
pancreatic parenchyma, either in acute or chronic forms.
Both acute and chronic pancreatitis have di erent etiologies
and radiological manifestations, which should be addressed
separately.
Acute Pancreatitis
Patients with acute pancreatitis typically present with abdominal pain that can be epigastric or located in the right or less
commonly le hypochondrial regions. e pain is described
as stabbing and commonly radiating to the back. Patients
with acute pancreatitis are partially relieved from the pain by
leaning forward, decreasing the retroperitoneal pressure on
the in amed swollen pancreas. Laboratory investigations
typically show highly elevated serum and urinary amylase
and lipase levels.
e most common causes of acute pancreatitis are gallbladder stones, alcoholism, mumps, and hypercalcemia. Acute
pancreatitis can be divided into two types according to severity: mild acute pancreatitis and severe acute pancreatitis. Mild
acute pancreatitis is characterized by reversible in ammation
and edema without pancreatic tissue necrosis. In contrast,
severe acute pancreatitis has the same symptoms as mild pan-
creatitis but associated with parenchymal necrosis and hemorrhage. Radiological imaging has an important role in detecting
and monitoring complications of acute pancreatitis which are:
(a) Hemorrhagic pancreatitis : it is a serious surgical emer-
gency of acute pancreatitis that occurs due to erosion of
the pancreatic vessels by the leaking pancreatic enzymes.
It occurs 4 % of cases with mortality up to 50 %. Patients
may present with discoloration of the anks ( Grey
Turner’s sign ) and/or the umbilicus ( Cullen’s sign ).
Cullen’s sign is a sign seen in cases of acute pancreatitis
or ruptured ectopic pregnancy. e sign is characterized
by the presence of uid seen around the porta hepatic
due to the spread of the in ammatory uid from the
subperitoneal space of the gastrohepatic and hepatoduodenal ligament through the Glisson sheath. e Glisson
sheath is the part of the Glisson capsule that surrounds
the intrahepatic portion of the hepatic portal system.
(b) Necrotizing pancreatitis : it is a pathologic condition
characterized by di use of focal areas of nonviable
pancreatic tissue due to in ammation. If the pancreatic
uid aspirated is sterile, then the condition is called
sterile pancreatic necrosis , and abdominal scan should
be repeated every 7–10 days to follow the evolution of
the pancreatic necrosis.
(c) Vascular thrombosis : it can arise due to the
in ammation around the vessels that will cause blood
stasis. e superior mesenteric artery and the splenic
vessels are the most common vessels a ected by
thrombosis due to acute pancreatitis.
(d) Pancreatic pseudocyst : it is a uid- lled cystic mass
con ned by a brous capsule. It is called pseudo because
its wall is not made of a true wall but a sac of
granulation tissue. It occurs in 10 % of cases and
maintains a communication with the pancreatic duct.
Pseudocyst can be mistaken with cystic pancreatic
tumor. Cystic pancreatic tumors, in contrast to
pancreatic pseudocysts, have normal amylase level,
while pseudocysts have high amylase level (typical
scenario); also, the presence of carcinoembryonic
antigen in the uid of the cyst a er aspiration to
con rm cystic cancers (tumor marker). Fate of
pancreatic pseudocyst will either (a) be resolved in 44 %
spontaneously within 6 months or (b) develop a brous
capsule a er 6 weeks and then needs drainage.
(e) Pancreatic abscess : it is an infected necrotic tissue or
uid collection that occurs usually a er 5 weeks with
unhealed acute pancreatitis. It is a surgical emergence
that occurs in 4 % of acute pancreatitis cases.
(f) Pancreatic pseudoaneurysm : it is a condition that occurs
when an eroded blood vessel opens and bleeds into an
adjacent pseudocyst. e pseudocyst will collect blood
inside it forming what is called a pseudoaneurysm. e
most common arteries involved are the pancreaticoduodenal artery and the gastroduodenal arteries.
(g) Bowel ileus : it can be focal a ecting regional small
bowel loops causing them to distend or di use a ecting
the entire intestine.
Diff erential Diagnoses and Related Diseases
A . Cholesterolosis ( strawberry gallbladder ): it is a rare
condition with unknown characterized by deposition of
lipid droplet saturated with cholesterol esters within the
gallbladder wall submucosa. e disease can occur with
or without the presence of gallbladder stones.
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Chapter 1 · Gastroenterology
Cholesterolosis is associated with recurrent attacks of
1
pancreatitis and acalculous cholecystitis.
B . Juxtapapillary duodenal diverticulum : it is de ned as
duodenal diverticulum located at peripapillary location.
e diverticulum can be asymptomatic or predispose to
choledocholithiasis, common bile duct dilatation, and
pancreatitis.
Signs on Plain Abdominal Radiograph
There are no reliable signs that can confi rm or exclude
acute pancreatitis in plain radiograph. However, one
sign that can be highly suggestive of pancreatitis is
the presence of signifi cant gas within the duodenum
due to adjacent infl ammatory process ileus ( sentinel
loop sign ).
3. Assessment of splenic vein patency by Doppler
sonography should be performed to exclude
thrombosis.
4. Pancreatic pseudoaneurysm can be diagnosed by
fi nding a mass with arterial fl ow within it (assessed
by Doppler sonography).
5. In cholesterolosis, highly echogenic foci are detected
within the gallbladder wall with posterior echogenic
shadow that forms a comet-like appearance (highly
specifi c) (
. Fig. 1.6.2 ) .
Signs on US
1. Normal ultrasound of the pancreas does not exclude
acute pancreatitis. The typical sign of pancreatitis in
ultrasound is thickening of the pancreas (head size
> 4.5 cm; neck, body, and tail > 3 cm in thickness),
associated with hypoechoic texture of the pancreas
due to edema (
2. Demonstration of fl uid collection in the
peripancreatic region may be seen.
. Fig. 1.6.1 ).
. Fig. 1.6.1 Ultrasound image of a patient with acute
pancreatitis showing hypoechoic, edematous head of the
pancreas ( arrowhead )
. Fig. 1.6.2 Ultrasound images showing cholesterolosis as hyperechoic foci within the gallbladder wall with “Comet-tail sign”
( arrowheads )
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1
Signs on CT (Method of Choice for Diagnosis)
1 . Peripancreatic fl uid : because the pancreas has no
capsule, the infl ammatory fl uid will roam free within
the abdomen and will collect mainly in the lesser sac
and the fl anks fi rst since the pancreas is
retroperitoneal structures. The presence of free fl uid
within the lesser sac and the anterior pararenal space
is diagnostic of acute pancreatitis (
2. There is diff use pancreatic swelling with blurring of
its margin due to edema. Enlargement of the
pancreas with reduction of its density and
peripancreatic fl uid collection in the lesser sac are
the classical radiological triad of acute pancreatitis.
3 . Dirty peripancreatic fat sign : due to infl ammation and
edema of the peripancreatic fat.
4 . Renal halo sign : the kidney is separated from the fl uid
in the abdomen by the Gerota’s fascia causing the
perinephric fat to appear as a hypodense halo
around it (
5 . Left - sided pleural eff usion : it may arise due to left
phrenic nerve irritation and can be seen in 30 % of
cases in chest radiographs.
6 . I n hemorrhagic pancreatitis , acute hyperdense blood
will be seen in 5 % (HU > 80).
7 . Necrotizing pancreatitis is diagnosed in CT by
decrease density of the pancreatic tissue (<30 HU or
less) and lack of enhancement after contrast
injection. Sometimes, air can be demonstrated in the
pancreatic body in CT confi rming necrotizing
pancreatitis (
width is necrotic, the gland is said to have undergone
central cavitary necrosis .
8 . Vascular thrombosis will be seen as lacking of
vascular enhancement after contrast injection on CT.
. Fig. 1.6.4 ).
. Fig. 1.6.5 ). If >90 % of the pancreatic
. Fig. 1.6.3 ).
9 . Pancreatic pseudocyst is detected as unilocular
pancreatic cyst full of fl uid-density material without
air with variable wall thickness (
material shows diff erent attenuations according to
the presence of necrotic material or hemorrhage. The
cyst wall characteristically shows uniform
enhancement after contrast administration. An
important tool in diff erentiating pseudocyst from
cystic neoplasms is evaluation of the lesion on serial
exams. Up to 60 % of pseudocysts will resolve
without intervention; besides the amylase levels are
usually high in cases with pseudocysts.
In Siemens dual-source SOMATOM Definition Flash
CT, a CT reconstruction technique known as iodine
window can be used to differentiate pancreatic
pseudocyst from pancreatic cystadenomas. In this
technique, imaging using the two different CT
. Fig. 1.6.6 ). The cyst
. Fig. 1.6.4 Axial abdominal, postcontrast CT image of a
patient with acute pancreatitis showing fl uid in the lesser sac
that surrounds the left Gerota’s fascia, showing the “halo sign”
( arrow )
. Fig. 1.6.3 Axial abdominal, postcontrast CT image of a
patient with acute pancreatitis showing fl uid in the lesser sac
( arrowhead )
. Fig. 1.6.5 Axial abdominal, postcontrast CT image of a
patient with acute pancreatitis aff ecting the body and tail
showing severe edema and air within the pancreatic
parenchyma, denoting necrosis; diff erential diagnosis includes
“pancreatic abscess with gas formation” ( arrow )
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Chapter 1 · Gastroenterology
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. Fig. 1.6.6 Axial abdominal, postcontrast CT image of a
patient with subacute pancreatitis that shows pseudocyst
formation ( arrow )
a
tubes voltage (e.g., at 80 kV and 120 kV) will show a
slight difference in tissue attenuation that can be
registered by the sensitive device. In the working
station, the user can separate this slight difference in
contrast enhancement and represent it as a digital,
yellow hue layer over the plain CT images. Therefore,
any small contrast uptake and enhancement can be
represented as a yellow hue/color over the plain
images. A pancreatic pseudocyst contains serous fluid;
therefore, no enhancement should be noticed. In
contrast, cystadenomas are cancerous cysts, so
iodinated contrast enhancement will be seen inside
the cyst, differentiating the cystadenoma from
pseudocyst.
10. Pancreatic pseudoaneurysm is detected as a pancreatic
pseudocyst with blood–fl uid inside it. Rarely, true
arterial aneurysm can arise from severe pancreatic
infl ammation (
b
. Fig. 1.6.7 ).
c
. Fig. 1.6.7 Sequential, coronal ( a – c ) and axial ( d ) abdominal, postcontrast CT images of a patient with acute pancreatitis who was
discovered to have aneurysmal dilatation of the gastroduodenal artery at the site of infl ammation in the pancreatic head ( arrowheads )
(Courtesy of Dr. Melvin D’Anastasi, Klinikum Großhadern (LMU), Munich, Germany)
d
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