Normal Anatomy
Appendix
Normal appendix
 A thin walled tubular structure
that may be collapsed or filled
with air, fluid or contrast.
 Normally does not exceed 6mm
diameter and has a sharp
contour defined by homogeneous
low-density mesenteric fat.
 Originates between the ileocecal
valve and the cecal apex on the
same side as the valve. (1/3
course inferomedially from the
cecum and 2/3 are retrocecal).
 Tips for finding the appendix: trace
the colon from the anus to the
cecum. The appendix will be located
along the cecum on the opposite
side of the ileocecal valve from the
ascending colon.

Normal air-filled appendix (arrow)
Appendicitis

Demographics:
 Any age, most commonly
10-30 years old
 Slightly more common in
males (1.4 : 1)

Clinically:
 Abdominal pain, often RLQ
 Nausea
 Vomiting
 Fever
Note enlargement of the appendix (arrows),
intraluminal fluid, and adjacent inflammatory
stranding
Possible findings in acute
appendicitis

Enlarged appendix, > 6 mm in
diameter





Appendiceal wall thickening
Appendiceal wall enlargement
Periappendiceal fat stranding
Focal cecal apical thickening
Detection of an appendicolith - appearing
as a ringlike or homogeneous calcification
(viewing the CT with bone windows aids in
detection).
Normal Bowel Imaging
Large bowel has haustra
scattered all along the colon.
The colon also has epiploicae
(fat filled tags) on its surface.
These haustra and epiploicae
separate the large from the
small intestine.
Colon is filled with feces which
has bubbly appearance
The small bowel is located in
the center of abdomen
Fairly narrow about 2.5 cm
tube like structure winds
compactly back and forth
within the abdominal cavity
The small intestine is
identified by valvulae
circulares or circular folds on
oral contrast study.
SBO: Postop and paralytic ilues

Demograpics:
 Patients who are postop, have
a malignancy, Crohn’s, or
hernia.
 Patients on narcotics

Clinically:
 Constipation, Nausea, and
vomiting
 Abdominal fullness/excessive
gas
 Pain and cramps in stomach
area
Axial CT scan through the lower abdomen
shows multiple fluid-filled and dilated loops of small
bowel (white arrows) and collapsed right colon (red
arrow) consistent with a mechanical small bowel
obstruction.
SBO: Radiograph




Multiple dilated small
bowel loops are seen
(white arrowheads).
There is fecal material in
the right and left
colon (arrows).
Air is seen in the rectum.
The surgical staples
indicate recent
abdominal surgery.
(black arrowheads).
Upright Abdominal Film
Air - Fluid Levels
Dilated Small Bowel
Large Bowel Obstruction
Dilated bowel loops proximal to the obstruction.
Arrow points to the etiology of obstruction.
Diverticulosis
Small saclike
outpouchings of mucosa
and submucosa through
the muscular layers of
the wall of the colon.
 Most common in the
sigmoid colon
 Small rounded
collections of air, feces,
or contrast outside the
lumen. Ranging from
1mm to 2 cm.
 Thickening of the
muscular wall of the
colon is common

No itis here, this is moderate
diverticulosis of the sigmoid colon
Diverticulosis

Demographics:
 Rare before age 40
 Incidence increases with age
 May be associated with low-
fiber diet

Clinically:
 Most often asymptomatic,
diagnosed incidentally
 May be associated with lower
abdominal discomfort,
bloating, constipation
Arrowheads point to multiple diverticula
arising from the recto sigmoid. The contrast in
diverticula is left over from previously
administered GI contrast.
Diverticulosis- Radiograph
This radiograph shows scattered diverticula throughout the abdomen.
On the right is a magnified view of the left lower quadrant of the
same radiograph. Notice the many scattered diverticula throughout
the sigmoid and descending colon (arrows).
Diverticulitis
• Demographics:
• See Diverticulosis
• Clinically:
•
•
•
•
•
Abdominal pain, often LLQ
Nausea
Vomiting
Constipation or diarrhea
Fever
Note wall thickening in the sigmoid colon (arrows)
and adjacent inflammatory changes in the pericolic
fat
Colitis: UC vs Crohn’s



UC – Inflammation and
diffuse ulceration of the
colon mucosa starting in the
rectum and extending
proximally.
Wall thickening (7-8mm)
with lumen narrowing
Outer wall is smooth
Crohn’s – Transmural
inflammation usually effects the
terminal ileum and proximal colon.
-Wall thickening 10-20mm
-Outer wall is irregular
-Active disease shows layering of
the colon (target and halo signs)
-Chronic disease with fibrosis show
homogeneous enhancement of the
colon wall
-Fibrous and fat proliferation
separate bowel loops
--Additional findings – lymph nodes
up to 1cm in mesentary, fistulas,
sinus tracts, abscesses, phlegmons
Ulcerative Colitis

Demographics:
 Peak incidence between
15 – 30 years old
 Equal incidence in
males and females

Clinically:
 Diarrhea (can be > 10





loose stools / day), often
bloody
Rectal bleeding
Passage of mucus with
defecation
Abdominal pain
Constipation
Fever
Note diffuse thickening of the sigmoid colon (arrows) and
minimal adjacent inflammatory stranding
Example of Ulcerative colitis

CT scan of a patient
with long-standing
ulcerative colitis
shows a
submucosal halo of
fat within the rectum
(arrow). There is
also perirectal
fibrofatty
proliferation (*).
Crohn’s Disease

Demographics:
 Two peaks of incidence:
15 – 30 and 50 – 80
years old
 Equal incidence in
males and females

Clinically:
 Abdominal pain
 Diarrhea (usually non-
bloody)
 Steatorrhea
 Fatigue
 Oral ulcers
Note thickening of the terminal ileum (curved
arrow) and cecum (straight arrow) and
inflammatory changes in the adjacent fat
Example of Crohns

White attenuation:
enhancement in ileal Crohn
disease. On an intravenous
contrast-enhanced CT scan,
the enhanced thickened
wall of the small bowel
(solid arrows) is slightly
higher attenuation than the
inferior vena cava (open
black arrow). The vasa recta
are dilated (arrowhead) and
separated by increased fat
deposition ("creeping fat
sign"). Open white arrow =
enlarged mesenteric node.
Colitis: Infectious

Pseudomembranous colitis (C. Diff) –
Cytotoxic entertoxin ulcerates the mucosa
and creates pseudomembranes of mucin,
fibrin and inflammatory cells
 Pancolitis or segmental with irregular wall thickening up to 30
mm with shaggy endoluminal contour.
 Submucosal edama creates an “accordian pattern”
Colitis: Ischemic
Usually occurs in setting of low cardiac
output in pts w/ extemsove. But
nonocclusive vascular disease.
 Affects watershed areas most: splenic
flexure and rectosigmoid region.
 Produces halo sign in postcontrast scans,
stranding and inflammation in pericolic fat
 Complications: hemorrhage, pneumatosis,

Example of Diffuse ischemic
colitis

CT scan obtained with
oral and intravenous
contrast material shows
diffuse, low-attenuation
thickening of the
colonic wall (arrows).
This is an example of
the water halo sign.
Water halo sign: diffuse, low-attenuation
thickening of the colonic wall (arrows)
Pseudomembranous colitis

Demographics:
 Most commonly caused
by C.diff overgrowth
following treatment with
antibiotics
 Advanced age is risk
factor

Clinically:
 Watery diarrhea (5-10x
per day)
 Abdominal cramps
 Hematochezia
 Fever
Note diffuse wall thickening throughout the
colon (arrows), and pericolic inflammation
Return to Table of Contents
Pseudomembranous colitis- cont’d
(Left) Axial CT scan of the midabdomen utilizing oral but not intravenous contrast
demonstrates marked thickening of the colonic wall (white arrows) producing the so-called
"accordion sign." There is a small amount of pericolonic stranding (red arrow) and ascites
(green arrow). (Right) Axial CT scan through the pelvis shows marked thickening of the wall
of the rectum (yellow arrows) indicating this is a pan-colitis.
Adenocarcinoma (Colon)

Demographics:
 Uncommon before age
40; 90% of cases are
after age 50
 In the US, male
incidence is 25% higher
than female

Clinically:
 Abdominal pain
 Change in bowel habits
 Hematochezia or
melena
 Iron deficiency anemia
Note circumferential thickening of the cecum (curved arrows)
and a hypodense focus within the wall which is due to
necrosis (straight arrow)
Major complication of many
types of colitis: Toxic megacolon

Dilation> 5cm w/
thinning of colon wall,
pneumatosis and
perforation
Colonic volvulus
(Usually diagnosed on x-ray)
Twisting of folding of an intraperitoneal
segment of the colon
 Sigmoid volvulus – apex points toward the left
lower quadrant
 Cecal volvulus – apex points toward the right
lower quadrant.

Swirl sign of Sigmoid
Volvulus in a 5 yo >
Liver- Anatomy
The Couinaud classification of
liver anatomy divides the liver
into eight functionally
indepedent segments. Each
segment has its own vascular
inflow, outflow and biliary
drainage. In the center of each
segment there is a branch of
the portal vein, hepatic artery
and bile duct. In the periphery
of each segment there is
vascular outflow through the
hepatic veins.
Couinaud classification of liver anatomy
http://www.ctisus.com/
Segment 1: The caudate lobe
The caudate lobe is anatomically different from other lobes in
that it often has direct connections to the IVC through hepatic
veins, that are separate from the main hepatic veins.
 The caudate lobe may be supplied by both right and left
branches of the portal vein.

Identifying segments
The first step in correctly
identifying the remaining
segments is to is to
locate the portal vein.
The arrow is pointing to the portal vein and, in this image, is
at the junctions between the upper and lower segments.
Identifying segments
Above the portal vein will
be segments 2, 4a, 8 and
7
Identifying Segments
Below the portal vein
will be segments: 3,4b,
5 and 6
Identify the branches of the hepatic vein



Right hepatic vein: divides the right lobe into anterior and
posterior segments.
Middle hepatic vein: divides the liver into right and left lobes. This
plane runs from the inferior vena cava to the gallbladder fossa.
Left hepatic vein: divides the left lobe into a medial and lateral part.
Right lobe

Identify the right hepatic vein which divides
the right lobe into anterior (segment 8 & 5)
and posterior segments ( segment 6 & 7).
 Anterior lobe:
○ Segment 8 is located superior to the the portal
vein.
○ Segment 5 is Located inferior to the portal vein
 Posterior Lobe :
○ Segment 7 is located superior to the portal vein
○ Segment 6 is Located inferior to the portal vein
Left Lobe

The left lobe is divided into medial and
lateral segments by the left hepatic vein.
 To the left of the left hepatic vein are segments 2
& 3.
○ Segment 2 is located superior to the portal vein.
○ Segment 3 is located inferior to the portal vein.
 To the right of the left hepatic vein are segments
4a & 4b
○ Segment 4a is located superior to the portal vein.
○ Segment 4b is located inferior to the portal vein.
Normal liver, unenhanced CT
Note the areas of hypodensity (arrows), which are
normal hepatic and portal veins coursing through the
liver.
Photo, Armstrong et al, 2004
Normal liver CT, enhanced
Note the increased density of the hepatic and portal veins. Also note the
adjacent stomach, which is filled with contrast.
Photo, Armstrong et al. 2004
Homogeneity – Hepatic Neoplasms

Knowing which lesions are hypervascular
(hyperintense) and which are hypovascular
(hypodense) can help identify the type of
neoplasm, but the key thing is that they are of a
different density than the surrounding liver
parenchyma.
 Hypervascular examples: carcinoid tumor mets,
hepatocellular carcinoma
 Hypovascular examples: colon cancer mets,
cholangiocarcinoma

Most mets, as opposed to primary tumors, are
rounded and well demarcated from surrounding
parenchyma on enhanced scans.
Appearance of various liver neoplasms
during early arterial phase
Hypovascular metastasis
due to colon cancer
Carcinoid tumor metastasis
is hypervascular
Hypovascular primary
cholangiocarcinoma
Primary hepatocellular
carcinoma is hypervascular
(hypodense area is necrosis)
Homogeneity – Cysts and Abscesses
Contrast also helps identify cysts and abscesses,
which contain collections of fluid

Cysts: Have well-defined margins and are low
density (attenuation similar to water), unenhancing
lesions
 Note: cysts below ~ 1cm in size cannot be reliably
distinguished from neoplasms

Abscesses: appear similar to cysts, but usually
their walls are thicker (due to surrounding edema)
and more irregular
 May not be able to distinguish from a necrotic tumor
Hepatic Cyst vs. Abscess
Photo, Novelline et al, 2004
Photo Lee et al, 1998
Left, hepatic cyst; right, hepatic abscess. Note the thickened wall of
the abscess.
Homogeneity – Liver Trauma

Trauma can cause hepatic parenchymal
lacerations, subcapsular and intrahepatic
hematomas

All are low-density areas relative to
contrast-enhanced parenchyma

Leakage of contrast = active bleeding
Hepatic Laceration
Photo, www.e-radiography.net
Gallbladder

Ultrasound is the
preferred initial
modality in the
investigation of right
upper quadrant pain.
Normal gallbladder on US
Cholecystitis

Demographics:
 "fat, forty, female and fertile ”
 Incidence increases with age
 May be associated with low-
fiber diet

Clinically:
 Fever, Nausea, and vomiting
 Positive Murphy’s Sign
 Elevated WBC
US findings: Thick GB wall, stones in GB,
absence of echoes posterior to the calculi
"Shadowing"
Gallstones on CT

Although less sensitive
than ultrasound, CT
findings include :
• Cholelithiasis
• Gallbladder distension
• Gallbladder wall
thickening
• Mural or mucosal
hyperenhancement
• Pericholecystic fluid and
inflammatory fat
stranding
• Enhancement of the
adjacent liver
parenchyma due to
reactive hyperaemia
hyperattenuating calculi (arrow) in gallbladder
Pancreas
The head of the pancreas is
surrounded by the duodenum
as it makes a C-loop around
the pancreas. The tail is in the
hilus of spleen.
 With contrast enhancement it
has the same density as liver
and spleen.
 It is recognizable by the
splenic vein running along
posterior inferior groove.
 The common bile duct
traverses through the head of
the pancreas and joins with
the pancreatic duct at the
ampulla of Vater to empty bile
into the second or descending
part of the duodenum.

Normal pancreas
Pancreatitis


Demographics
 Any age, however
less common <45
years
Clinically:
 Abdominal pain,
fever, nausea, and
vomiting
Acute Pancreatitis

Excepted findings:
 Enlargement of pancreas due
to edema
 Peripancreatic inflammation:
linear strands in the
peripacreatic fat
 Phlegmon
 Hemorrhagic: Enlarged
pancreas with increased
density due to hemorrhage
 Necrosis: On contrast
enhanced phases the necrotic
pancreatic parenchyma will
Diffusely enlarged pancreas with low density
show decreased or no
enhancement when compared from edema
C: Colon St: Stomach P: Pancreas
with normally enhancing viable
tissue
Chronic Pancreatitis
May show dilated duct,
enlarged pancreas,
pseudocyst, calcification
 Optimal visualization
with helical CT using
pancreas-optimized
protocol - water as oral
contrast agent, initial
scan without IV contrast,
then contrast infusion
using pancreatic cancer
Mass density in pancreas
protocol
White arrow: Psudocyst
 Limited usefulness in
Black arrow: Calcifications
early chronic
pancreatitis

Acute Pancreatitis on KUB

Radiographic findings:
 Cut off sign and Ileus
 Cut off sign: abrupt
termination of gas within
the proximal colon at
the level of splenic
flexure, seen on
abdominal radiographs,
CT, and barium enema
in patients with acute
pancreatitis.
White arrowpoints to Transeverse colon cut off at Splenic flexure. No air
in descending colon.
TC: Transverse colon
I: Represents small bowel loops with air suggestive of Ileus
Chronic Pancreatitis on KUB
Radiographic findings:
• Calcifications in the
pancreas
• Pseudocysts: As
necrotic pancreatic
tissue liquefies, it forms
a "pseudocyst”.This
may be in the region of
the pancreas or extend
beyond the pancreatic
region.