Abdominal CT scan made easy

Abdominal CT Scan
Crossing the barrier in bedside interpretation

DR. MASRUR AKBAR KHAN
MBBS, FCPS (Surgery)

Can a Clinician interpret CT scan
like a Radiologist?

• Introduction
• CT anatomy abdomen
• CT section with pathology
• Take home message

• Series of X-ray images taken from
different angles.
• Uses computer processing to create
cross-sectional images.

• Hyperdense
(more dense):
• When an
abnormality is
bright (white) on
CT.

• Isodense (the
same density):
• When an
abnormality is the
same density as
the reference
structure

• Hypodense
(less dense):
• When an
abnormality is
less dense than
the reference
structure

• Radiodensity on CT, Range from -1000 to
+1000.
• By definition water (CSF) = 0.

• Air is -1000 because it is the least dense
structure.
• Bone is the most dense and measures
+1000.

• Fat is less dense than water and therefore
measures -100.
• Brain parenchyma is more dense than water and
ranges from +20 to +40.
• White matter is less dense than gray matter due
to the fat within the myelin within the white
matter.

• Acute blood is bright on CT and measures +
55 to +75 HU. C
• Calcification is more dense than blood and
will measure in the low 100's.

• Reductions in intensity of x-ray beam as
it traverses matter either by absorption
or deflection.

• High attenuation
– Absorption of x-ray photon
– Presented as white on image
• Low attenuation
– Free passage of photon
– Presented as black on image

• It is a mode of
operating a CT
system.
• Used to display slice
locations rather than
for direct diagnosis.

• Different “Windows" can be created to
highlight specific structures.
• Adjustments in gray scale/shade according to
the specific attenuation properties of tissue

• Brain windows
are useful to
evaluate the
parenchyma

• Bone
windows are
useful for
evaluating
fractures and
the paranasal
sinuses.

PHASIC SCAN/
CONTRAST ENHANCED SCAN

• Iodinated intravenous contrast
– Increases the density of blood vessels and
organs
– Lymph nodes distinguished from blood
vessels
– Abnormal lesions in solid organs become
easier to distinguish from normal
surrounding parenchyma

• Iodinated oral contrast
– During abdominal CT
– Opacify the small bowel
– This makes it easier to distinguish normal
bowel from pathological lymph nodes or
other mesenteric masses

• Standard 64 slice gives cross section with 0.5
mm thickness
• 256 and 320 slices provide higher accuracy

Read the information on the CT scan

Hold the film in the proper orientation

• Always begin cranial and gradually
move caudally.
• Assess structures from superficial to
deep, first analyze tissues of abdominal
wall and then progress to internal
structures

• Begin by following one organ
• Track it through entire sequence.
• With experience, follow organs that lie
in same transverse plane.

Follow the IV contrast filled Aorta as we descend caudally.
Branches and points of interest will be noted.

Azygous Vein. Hemiazygous Vein

This is an excellent image of the right, middle and left hepatic veins draining into the
Inferior Vena Cava. Don’t confuse this structure with the IVC, this is the esophagus at
the level of the Lower esophageal sphincter, page up and down to confirm this.

The outline of the Inferior Vena Cava is more
distinct in this image.

Portal Vein Branching into the Liver
Liver
Stomach

More portal vein branching into
the liver lobes

Splenic Artery. Splenic Vein.
Scroll up and down to confirm.
Spleen

Proper Hepatic Artery. Splenic Vein
Portal vein
Adrenal
Glands

You can see the Celiac artery starting to branch from the Aorta. You can follow
this down in the next four images Proper Hepatic Artery is labeled in the upper
right The splenic vein and artery are in the lower left

Proper Hepatic Artery and Splenic Artery (the splenic
artery is the circle). Splenic Vein

Here the Splenic Vein is emptying into the portal vein.
Follow this up and down.
Pancreas

This is the Superior Mesenteric Artery
Branching off the Aorta.

Rt. and Lt. Kidneys
Pancreas Head

Renal Veins emptying into the IVC.
We also see the right renal artery branching off the Aorta,
follow it down till you see it enter the right kidney.
The Superior Mesenteric Vein is outlined on the top of this image.
If you follow the SMV up, you will see it empty into the Portal Vein.

Here we see the right and left renal vein entering into the Inferior Vena Cava. We
Also see the left renal artery branching off the aorta and heading toward the left
kidney. Page up and down to trace these vessels.

Superior Mesenteric Vein – follow it up as it joins
the Splenic Vein to form the Portal Vein

Note inferior mesenteric artery emerging from aorta
Inferior mesenteric vein extends cephalad to join smv.

Aorta bifurcates into common illiac arteries
Appendix is noted coiling in Rt. Lower quadrant
Note air in lumen on adjacent scans
Psoas
muscles

CT SECTION FEMALE (NOT LABELED)

Coronal
reconstruction
( anterior to
posterior)
1, liver
2, body of stomach.
3, transverse colon.

1, Ileal loop
2, Right and left lobe of
liver.

• 1, GB.
• 2, Pyloric antrum.
• 3, Liver.
• 4, Body of
stomach.
• 5, crus of
diaphragm.
• 6, Transverse colon.
• 7, Small bowel.

• 1, small bowel.
• 3, transverse colon.
• 4, external oblique.
• 5, internal oblique
• 6, transverse
abdominis

• 1, Body and neck of
pancreas
• 2, pyloric antrum.
• 3,sigmoid colon.
• 4, descending colon.
• 5, cecum.

• 1, portal vein.
• 2,. splenic vein
• 3, superior
mesentric vein
• 4, superior
mesentric artery
• 5,spleen

• 1, jejunal loop
• 2, SMA
• 3, Descending colon.
• 4, spleen.
• 5, Iliac wing.
• 6,UB

• 1, duodenal- descending,
horizontal, ascending
part.
• 2, spleen and splenic vein.
• 3, fundus of stomach.
• 4, tail of pancreas.
• 5, left colic and right colic
vein.
• 6, ascending and
descending colon.
• 7, right and left external
iliac vein
• 8, inferior mesentric vein.
• 9,IVC

• 1, caudate lobe of
liver
• IVC and left renal
vein.
• 2, abdominal aorta
and right common
iliac aretry.
• 3, splenic vein.
• 4,celiac trunk and
superior mesentric
artery.
• 5,inferior mesentric
vein.
• 6, right colic vein

• 1,.abdominal aorta and
renal artery
• 2, IVC.
• 3, Spleen
• 4,Right and Left kidney.
• 5, Gluteus medius and
minimus muscle.
• 6, Iliac and psoas
muscle.
• 8, Asc. and Desc. colon.
• 9, UB.

• Right and left crus
of diaphragm.
• Both kidneys
• Right lobe of liver
• Spleen
• Psoas and iliac
muscle.
• Right and left
common iliac artery
and vein.

• Liver ,spleen
,kidneys
• Rectum
• Anal canal

• Spinal cord
• Lumbar vertebrae
• Quadratus
lumborum
• Sacrum

Sagittal
reconstruction
(left to right)
• Spleen
• Ext. ,Int. oblique and
transverse
abdominis muscle.

• Left kidney
• Splenic flexure
• Descending colon
• Iliac muscle

• Transverse colon
• Body of stomach
• Jejunal loops
• Left kidney
• Erector spinae and
quadratus
lumborum.
• Iliac and psoas
muscle.
• Gluteus medius
• Gluteus maximus

• Splenic vessel
posterior to the tail
of pancreas.
• Left lobe of liver.
• Pyloric antrum
• Jejunal loop.
• Left common iliac
artery ,
• Left external iliac
artery
• Left common iliac
vein
• Left external iliac vein

• Abdominal aorta
• Celiac trunk
• SMA
• Pyloric antrum
• Body of pancreas
with splenic artery
and vein behind it.
• Duodenum

• IVC
• Head of pancreas
• Horizontal part of
duodenum
• Portal vein
• Left lobe of liver
• Jejunal loop
• Sigmoid colon
• Rectum
• UB

• IVC
• Portal vein
• Psoas muscle
• Common iliac vessel
• Rectus abdominis
muscle

• GB
• Right kidney
• Hepatic flexure of
colon
• Quadratus
lumborum
• Erector spinae
muscle

• Ascending colon

Can an isolated slice of CT scan
confirm diagnosis?

• Be competent in interpretation of CT scan
• Beware of superiority complex
• Never underestimate your Radiologist
colleague.

Don’t let a CT scan replace you
clinical acumen

Abdominal CT scan made easy

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