abdominal ct

1. Basics of abdominal CT scan

2. ABDOMINAL TRAUMA
 CT is the study of choice in abdominal trauma.
 Intravenous contrast CT is always used
 If head CT is to be done, it should be done first
before contrast material is injected for the
abdomen.
 Oral contrast is usually not administered for
abdominal trauma.

3.  Rectal contrast is occasionally administered in
penetrating trauma to search for a bowel
laceration.

4. Liver
 The liver receives its blood supply from both
hepatic arteries and portal veins and drains to the
inferior vena cava via the hepatic veins.

5.  Evaluation of liver masses is usually done with a
combination of scans obtained before and after
intravenous contrast injection .
 Postcontrast scans are obtained in two phases:
one is done quickly (hepatic arterial phase) and
then a second is done about a minute later (portal
venous phase); the combination helps to best
define and characterize liver masses.

6.  This combination of three separate scans done
without contrast and then during the arterial
phase followed by the venous phase is called a
triple phase scan.

10. Recognizing fatty infiltration of the
liver on CT
 When diffuse, the liver is usually slightly enlarged.
 The blood vessels stand out prominently but are
usually neither obstructed nor displaced.
 The spleen is denser than the liver with or
without intravenous contrast
 Normally, the liver is equal to or greater than the
density of the spleen.
 Focal fatty infilttation can produce an appearance
that mimics tumor, but fatty infiltration usually
produces no mass effect

12. Recognizing cirrhosis of the liver on
CT
 Early in the disease, the liver may demonstrate
diffuse fatty infiltration.
 As the disease progresses, the liver contour
becomes lobulated.
 The liver shrinks in volume with the right lobe
characteristicallybecoming smaller while the
caudate lobe and left lobe become
disproportionately larger.

13.  Portal hypertension may develop and can lead to
dilated vessels around the stomach, splenic
hilum, and esophagus representing varices.
 Splenomegaly may develop
 Ascites may be present.

14.  Patients may have a combination of ascites and
pleural effusion for a number of reasons,
including cirrhosis, ovarian tumors, metastatic
disease, hypoproteinemia, and congestive heart
failure.

17. Differentiating pleural effusion
from ascites.

18. SPACE-OCCUPYING LESIONS OF
THE LIVER
 CT studies are best at demonstrating liver
masses when performed both with and without
contrast, as either study alone may fail to reveal
an isodense mass, i.e., one that has the identical
attenuation as the surrounding normal tissue

19. Recognizing liver metastases on
CT
 They are usually multiple, low attenuation masses
 Larger metastases may demonstrate areas of
necrosis that can be recognized as mottled areas
of low attenuation within the mass.
 Mucin-producing carcinomas, such as might
originate in the stomach, colon, or ovary, can
calcify both the primary tumor and the
metastases

21. Recognizing hepatocellular
carcinoma on CT.
 Solitary mass, frequently large
 Multiple nodules
 Diffuse infiltration throughout a segment,
lobe, or entire liver

22.  Most are low density (hypodense) or the same
density as normal liver (isodense) without
contrast
 enhance on the arterial phase with IV contrast
(hyperdense), and then return to hypodense
or isodense on the venous phase
 Low attenuation areas from necrosis are
common.
 Calcification occurs relatively frequently.

23. Diffuse hepatocellular carcinoma
of the liver.

24. Recognizing cavernous
hemangiomas of the liver on
CT
 Usually hypodense lesions on unenhanced
scans, hemangiomas have a characteristic
nodular enhancement from the periphery
inward following injection of intravenous
contrast and become isodense in the venous
phase.
 Contrast tends to be retained within the
numerous vascular spaces of the lesion so that ir
characteristically appears denser than the rest
of the liver on delayed (lO-minute) scans

25. Hemangioma of the liver, triple
phase study.

28. CT findings in hepatic trauma
 Lacerations-irregularly marginated, low
attenuation branching defects
 Hematomas-focal, high attenuation lesions first
caused by blood; may progress to low attenuation
mass-like lesions filled with serous fluid
 Subcapsular hematomas-lenticular fluid
collections that conform to the shape of the outer
contour of the liver but which frequently flatten the
adjacent liver parenchyma

29. Hepatic and splenic lacerations,
hepatic
contusion.

30. ACUTE CHOLECYSTITIS AND
GALLSTONES
 CT findings in acute cholecystitis include
thickening and enhancement of the gallbladder
wall (>3 mm) and pericholecystic fluid or air in the
wall or lumen of the gallbladder (emphysematous
cholecystitis)

31.  A gallstone is visible
(closed white arrow)
in a
 distended gallbladder
that demonstrates
pericholecystic
infiltration of the
surrounding fat (open
white arrow).
Enhancement of
gallbladder wall
 (dotted white arrow) is
also seen.

32.  A small dot of air is in
the lumen of
gallbladder (closed
white arrow), a sign of
emphysematous
cholecystitis.
 There is enhancement
and thickening of the
wall

33. Spleen
 The liver should always be denser than or equal
to the density of the spleen.
The spleen is usually about 12 cm long, does not
project substantially below the margin of the 12th
rib, and is about the same size as the left kidney.

34. SPLENIC INFARCTION
 Splenic infarctions are best seen on contrast-
enhanced scans in patients with such
abnormalities as sickle cell disease, emboli
originating on the left side of the heart in patients
following acute myocardial infarction,
polycythemia, lymphoma, and leukemia.

35.  Classically, a splenic infarct appears as a low
attenuation, wedge-shaped lesion at the
periphery of the spleen that causes no mass
effect

37. CT findings in splenic tranma
 Contusion-
 Hematoma
 Laceration
 Subcapsular hematoma-
 Intraperitoneal fluid or blood-

38. Intrasplenic and perisplenic
hematomas.

39. URINARY TRACT CALCULI
 Unenhanced, multislice spiral CT scans have
replaced conventional radiography in the search
for renal and ureteral calculi and their
complications.
 A negative stone search study has a negative
predictive value of 98%.

40.  The direct finding is a calcific density in the ureter,
at the ureterovesical junction, or in the bladder

44. Renal cysts
Simple renal cysts are a very common finding
on CT
 scans of the abdomen occurring in more than half
o the population over 55 years of age.
 Simple cysts are benign, fluid-filled structures
that are frequently multiple and bilateral.
 They tend to have a sharp margin where they
meet the normal renal parenchyma.

46.  A laceration of the left
kidney is manifested
by the low
 attenuation linear
defect (closed white
arrow).