MBS 208
Introduction to Basic and Clinical Anatomy
Radiology of the Abdomen and Pelvis
And
Cross-Sectional Anatomy
Overview
• Common imaging modalities for the
abdomen and pelvis
• How to read an abdominal plain film
• Visualizing anatomy through imaging –
•
•
•
•
Spaces in the abdomen and pelvis
The 4 abdominal quadrants
Vascular anatomy in the abdomen and pelvis
The colon, with attention to the right lower
quadrant
• The pelvis
Imaging Modalities for the Abdomen and Pelvis
• Commonly Utilized
Modalities
• Ultrasound
• CT (computed
tomography)
• Radiography
• Abdominal plain film
• Fluoroscopy
Other Modalities
• MRI
– Magnetic resonance
imaging
•
Nuclear medicine
– Gallium scan
• Positron Emission
Tomography (PET)
– Hysterosalpingography
Jeffrey B. Mendel, M.D. © 2007
X-ray
Basics
PA (anterior-posterior) view – X-rays enter through back
of chest and exit out front where they are detected
The detector (film or digital) captures the x-rays that
penetrate the target and an image is created
X-ray Basics
Attenuation of the x-ray
beam is affected by:
•Tissue density
•Tissue thickness
•X-ray energy (kV)
Structural elements that attenuate the beam to a greater
extent than air (black) or are less attenuating than bone
(white) show radiographically in various shades of gray
X - RAY --- FOUR BASIC DENSITIES
Air
Soft
Tissue
Fat
Bone
What is black, white, and gray?
•The spine, ribs,
scapulae, and ribs
attenuate the beam and
are white
•The heart and soft
tissues are gray
•The lungs and trachea
are filled with air and are
black
Why is there an air-fluid
level in the stomach
beneath the left
hemidiaphragm?
Answer: the patient was
imaged in the upright position
Approach to plain film interpretation
1) What is the normal and variant anatomy?
• Is something absent?
• Is there an additional finding?
2) Check for clues in the skin and soft tissues
3) Then evaluate the bones
•
position/alignment, cortex, density, internal
architecture, focal lesions
Cervical
rib
1
Additional Findings:
That ‘extra’ stuff
2
3
4
5
6
7
8
9
10
11
12
Bilateral cervical ribs
Polydactyly
What’s wrong with this radiograph?
The heart and
aortic arch are
also on the right
side (normally
left-sided
structures). This
is known as situs
inversus, a
congenital
variant.
Also note the
absence of both
clavicles.
Ultrasonography (ultrasound)
• Uses sound waves of frequencies 2
to 17 MHz. (Audible sound is in the
range of 20 Hz to 20 kHz.)
• Like SONAR, images result from the
propagation of sound waves through
the body and their reflection from
interfaces within the body
• The time it takes for the sound
waves to return to the transducer
provides information on the position
of the tissue in the body
Ultrasound
• No ionizing radiation
– Uses sound waves to visualize structures
• Very operator dependent
• Can not penetrate bone
• Mainstay of diagnosis for:
–
–
–
–
–
Ob-gyn (strong ‘foothold' in Ob)
Screening for vascular, abdominal & renal pathology
Palpable lesions: Breast and Musculoskeletal
Thyroid/neck pathology
Pediatric / Young women
Gray scale = anatomy
Gallstones
Colour Doppler = velocity and direction
Fetus in utero
CT – computed tomography
• Cross-sectional modality with
capabilities for multiplanar
reconstruction and dynamic
imaging to assess vascularity
•Tube rotates around the body
and a circle of stationary
detectors detects the penetrating
x-rays forming an image
CT – Computed Tomography
• X-ray tube and a semicircle
of detectors rotate around the
body
• Computer collects the data
from the detectors and
reconstructs a cross-sectional
image (back-projection)
• Tube and detectors spin
continuously allowing for
rapid imaging (helical CT) as
with CT angiography
CT - Limitations
• Ionizing radiation
• Requires contrast: IV and oral
– Oral contrast requires prep time (1-2 hours)
– Iodinated contrast is nephrotoxic
– Iodinated contrast has fatality rate 1:50,000
• even with low osmolar contrast
• Patient must be supine (prone)
• $$$
MRI -Magnetic Resonance Imaging
• Uses a high-field magnet
to image the body
• Rapidly switching
magnetic field gradients
align the precession of
the H protons (water and
fat)
• When the gradients are
turned off, a faint
radiofrequency signal is
produced
• Image is reconstructed
using Fourier transforms
• Multiplanar and vascular
assessment possible
Be
External Magnetic Field Be
High B
Spin
“flips”
Low B
Create a gradient in the magnetic field within the scanner so that it is
high in one corner, lowest in the opposite corner.
Protons in the high-field region produces highest frequency signal
Magnetic Resonance Imaging
•
•
•
•
•
•
•
•
•
•
Magnetic nuclei are abundant in the human body (H,C,Na,P,K) and spin randomly
Since most of the body is H2O, the Hydrogen nucleus is especially prevalent
Patient is placed in a static magnetic field
Magnetized protons (spinning H nuclei) in the patient align in this field like compass needles
Radio frequency (RF) pulses then bombard the magnetized nuclei causing them to flip around
The nuclei absorb the RF energy and enter an excited state
When the magnet is turned off, excited nuclei return to normal state & give off RF energy
The energy given off reflect the number of protons in a “slice” of tissue
Different tissues absorb & give off different amounts of RF energy (different resonances)
The RF energy given off is picked up by the receiver coil & transformed into images
MRI offers the greatest “contrast” in tissue imaging technology (knee, ankle diagnosis)
cost: about $1450 - $2000
time: 30 minutes - 2 hours, depending on the type of study being done
•
•
•
MRI: ‘Cadillac of soft tissue
imaging’
• Mainstay of diagnosis for
– Neurologic imaging
– Musculoskeletal imaging (after plain film)
– Magnetic Resonance Angiography
• Angiography without iodinated contrast*
– Expanding applications in chest, abdominal,
breast, and pelvic imaging
Visualizing
Anatomy:
Brain MRI
MRI of torn ACL
MRI of moderately torn rotator cuff
MRI - Advantages
•
•
•
•
True multiplanar imaging
Intravenous contrast not usually required
No ionizing radiation required
Newer scanners and well-trained technologists
minimize problems with claustrophobia
MRI - Limitations
• Ferromagnetic objects
cause artifacts that limit
imaging
• Contraindicated for
patients with
– Implantable devices:
cochlear implants,
pacemakers*
– Metal shavings in orbits
– Severe renal failure
• Still requires more
cooperation and longer
time than CT
• $$$$
How do you obtain 3D images
from 2D slices?
• Each image from CT, MR, PET, US or NM provides a 2D
image
• Stack enough thin sections together and you obtain a 3D
volume matrix
• If the width of the slices is similar to the size of the
elements in the 2D matrix you can reconstruct images in
any plane you choose or make 3D models of high
resolution
Coronary
Coronary CT Angiography – may eventually replace invasive angiography No arterial puncture = no risk of vascular damage
3D view of the arteries and the adjacent organs
The Axial(horizontal)
Section
• An axial section is
horizontal and
represents the plane
in which most CT is
acquired
Ao root
LV
LA
Right hemidiaphragm
liver
Ao
The Sagittal
Section
spine
Ao
PA
LA
• A sagittal section is in a plane
running longitudinally front-toback
• The mid-sagittal section
divides the body into two
symmetric halves
Bladder
The Coronal
Section
• Coronal sections are
in planes running
side-to-side
Ao
RV
liver
PA
LV
stomach
• A coronal section is
vertical perpendicular
to the sagittal section
Fluoroscopy
•
Dynamic radiography
– Permits real-time evaluation
of the gastrointestinal tract
– Barium Swallow (esophagus)
– Upper GI Series (stomach)
– Small Bowel Follow-through
– Barium Enema (colon)
•
Barium (& air) is introduced by
enema or swallowing
Barium appears white on the
images (high density attenuates
the x-ray beam)
Can assess both intrinsic
(mucosal) and some extrinsic
•
•
(mass-effect) abnormalities
Nuclear Medicine - GI Bleeding Scan
• Evaluates bleeding, particularly from the lower GI tract
• Radiopharmaceutical = Tc99m invitro labelled RBCs
• Sequential 5 minute images acquired over an hour
• Looking for progressive accumulation of tracer
Where is the bleeding on this scan ?
Answer: Cecum
Gallium Scan
• Used for lymphoma
staging & response
PET/CT
Initial Scan
Baseline
• Baseline
imaging
determines
whether the
tumor is
gallium-avid
• Serial scans
assess response
to treatment and
can distinguish
scar from
residual tumor
Injected Gallium-67 binds to transferrin &
enters the extracellular space of tumor cells
via permeable capillaries
9/03
6 Month Follow up
Response to Rx
11/03
Lymphoma recurs
7/04
Introduction
• The primary imaging modalities for the abdomen
and pelvis are plain film, ultrasound, and CT
• Most common indications for imaging include
pain, trauma, distention, nausea, vomiting,
and/or change in bowel habits
• Choice of modality depends upon clinical
symptoms, patient age & gender, and findings
on physical exam
• Mastery of the anatomy within each quadrant
can help explain particular symptoms, clinical
presentations, and/or imaging findings
Reading the Abdominal Plain Film
• Also known as the
“KUB” (kidney, ureter, &
bladder)
•
ach
m
Sto
Use a systematic approach to
interpretation
– Lung bases & diaphragms
– Bones
– Soft tissues
• Abnormal calcifications
• Organs
• Bowel
Plain film in 3 year old patient with pain
Reading the Abdominal Plain Film
• Also known as the
“KUB” (kidney, ureter, &
bladder)
•
ach
m
Sto
Colon
Use a systematic approach to
interpretation
– Lung bases & diaphragms
– Bones
– Soft tissues
• Abnormal calcifications
• Organs
• Bowel
Plain film in 3 year old patient with pain
AP SUPINE ABDOMEN X-RAY
GAS PATTERN
STOMACH
SM. BOWEL
COLON
Normal abdominal gas pattern with air in the stomach and scattered nondistended loops of large bowel and little small bowel gas present.
Transverse
colon
Descending
colon
Small intestinejejeunum & ileum
Ascending
colon
Small vs. Large Intestine
Horton KM et al, Radiographics. 2000
• Colon has sacculations called
haustra as teniae coli are
shorter than the colonic wall
• Colon is relatively peripheral
but can be very mobile
Small bowel had plica circulares & is
positioned centrally
>3 cm diameter and air/fluid levels on the upright suggests small bowel obstruction
Small bowel has
plicae circulares,
mucosal folds that
extend across the
entire diameter of the
bowel
The colonic
haustra indent
the margin but do
not extend across
the bowel
Gall bladder
Liver
spleen
stomach
Plain Film Soft tissues : Liver, Spleen, & Kidney
St
Sto
m
ac
h
Soft Tissue Structures: Subtle on KUB
Stomach
What’s Up on an Abdominal Film?
• Always check the lung bases for an infiltrate
• Look for free air on the upright film: commonly beneath the right hemidiaphragm
diaphragm
Free air under right hemidiaphragm due to
perforated duodenal ulcer
Liver edge
More Misplaced Air
• No gastric air bubble in left upper quadrant
• Air/fluid level superimposed on heart
HIATAL HERNIA
STOMACH
UPPER GI
ORAL BARIUM CONTRAST
WITHOUT CONTRAST
COLON
BARIUM ENEMA - RECTAL BARIUM
CONTRAST
47
NORMAL
ESOPHAGUS
DIAPHRAGM
HIATAL HERNIA
*Note distended
distal esophagus
with herniation of
gastric fundus into
chest through
esophageal hiatus.
DIAPHRAGM
This allows for reflux of gastric
contents into esophagus.
Calcifications, Metallic Surgical and Foreign Bodies
rectum
Surgical clips in RUQ from prior cholecystectomy
Appendicolith on plain film
Clinical-Anatomic
Approach
Divide and conquer !!!
• Median and
transumbilical planes
divide the abdomen
and pelvis into 4
quadrants
• Each quadrant has its
own particular
symptoms, clinical
presentations, and/or
imaging findings
The Right Upper Quadrant
What lives in the right upper
quadrant?
• Liver
• Gallbladder
• Hepatic Flexure of Colon
• Right kidney and adrenal gland
Clinically Important Hepatic
Anatomy
• Falciform ligament
defines right from left
lobe
• Blood supply:
– 70% via portal vein
– 30% via hepatic artery
• Left, middle, and right
hepatic veins converge
with IVC
• Each of 8 liver segments
have portal vein, hepatic
artery, and bile duct
(portal triad)
Normal Liver
on contrast
CT
Lt lobe
Portal Vein
Rt lobe
Sto
IVC
A
LK
Sp
Gall bladder
CBD
Crus of diaphragm
Sto
P
Falciform Lig.
– Serves as an
anatomical marker
between liver lobes
PORTAL VEIN
CT
Coronal and Axial images
US
Metastatic disease
• Lower attenuation foci
within the liver during portal
venous phase
• Liver is the most common
metastatic site after regional
lymph nodes
• Metastases from colon,
stomach, pancreas, breast and
lung primaries
Porta Hepatis – Portal Triad
Portal vein
Cystic artery
Hepatic duct
Common
hepatic artery
Splenic artery
Clinically Important Biliary Anatomy
• Hepatic cells secrete bile into
caniculi →
• Drain into interlobular bile
ducts →
•
•
•
•
Ducts merge into progressively
larger ducts, eventually R and L
hepatic ducts →
Merge in Porta Hepatis to form
common hepatic duct →
Joins with cystic duct to form
common bile duct →
Pass through pancreatic head to
empty into duodenum via sphincter
of Oddi
Ga
llb
la
dd
er
Common bile duct
Blocked Biliary System
Gallstone is compressing the common bile duct blocking the flow of bile
from the liver.
GALLSTONES
15-30% calcify
Cirrhosis: End-stage Liver
Disease
• The left lobe & caudate lobe hypertrophy
• Portal venous pressure rises causing
ƒ Reversed portal venous flow (hepatofugal)
ƒ Splenomegaly
ƒ Varices
ƒ Ascites
Liver
Spleen
Varices
Bowel loops are positioned centrally
due to the presence of ascites
The Left Upper Quadrant
What lives in the left upper
quadrant?
• Spleen
• Left lobe of liver
• Splenic flexure
• Left kidney and adrenal gland
liver
gall
bladder
T12
L1
Pylorus
stomach
L2
spleen
duodenum
Splenic rupture due to MVA
Blunt trauma
• The “left package”
– spleen, left kidney
• The “right
package” – liver,
right kidney
• “Midline” – left
lobe liver, pancreas
HEPATIC /
SPLENIC
LACERATION
Note rib fractures on x-ray
ENLARGED PALPABLE SPLEEN
Enlarged spleen raises issue of lymphoproliferative diseases or infection.
Midline Anatomy
What lives in the midline of
the abdomen?
• Pancreas
• Stomach
• Colon and small intestine
• Aorta and IVC
Pancreas
Normal pancreas on CT
liver
liver
Pancreatitis = Inflammation of the pancreas
Abdominal Wall
Midline:
• Rectus abdominis muscle
with linea alba at midline
Anterolateral
(Outer to Inner Layers):
• External oblique muscle
with aponeurosis joining
anterior layer of the rectus
sheath
• Internal oblique muscle
with rectus abdominis
muscle
• Transversis abdominis
muscle
• Transversalis fascia
• Peritoneum
Ventral Hernia
Hematoma in the Rectus Abdominis
Key arterial anatomy of the GI tract
Celiac artery (axis)
- arises form the ventral surface of the aorta,
just below the diaphragm, at the level of the
lower half of T12
Superior mesenteric artery (SMA)
- arises form the ventral surface of the aorta
approximately 1 cm below the origin of the
celiac at the level of the upper half of L1
Inferior mesenteric artery (IMA)
- arises from the ventral surface of the aorta at
the level of L3, approximately 3 cm above the
aortic bifurcation
Abdominal Aortic
Aneurysm (AAA)
• Aorta dilates causing loss of
laminar flow and intraluminal
thrombus (non-enhancing region)
• Aneurysms > 5cm in diameter are
at high risk for rupture
Infrarenal AAA with intraluminal thrombus
Normal caliber aorta
Images of AAA courtesy of A. Davidoff MD
MR Angiography
Right pelvic renal transplant
as seen on MRA
Celiac Artery
(Axis)
In most
Individuals
(~65%) the
celiac axis
divides into
three major
branches
1. Left gastric
2. Splenic
3. Hepatic
Diagnostic Angiography, Kadir, 1986.
Ashley Davidoff, MD
GI Vasculature:
Demand and
Supply
SMA
small bowel, right
and transverse
colon
IMA
left colon,
sigmoid colon
and part of
rectum
Clinically Oriented
Anatomy, Moore
et al., 1999
SMA & IMA
Middle colic
cHA
splenic
IMA
GDA
Lt colic
renal
SMA
IMA
Marginal
art of colon
Sigmoid and superior
rectal art
CT Mesenteric Angiography
This has virtually replaced diagnostic angiography
No arterial puncture = no risk of vascular damage
3D view of the arteries and the adjacent organs
Lower Intestinal Bleed
Extravasation of
contrast marking
site of bleeding
SMA
Right colic
• Bleeding scan
first, if positive:
Jejunal
Ileocolic
• Arteriogram
with possible
embolization of
bleeding vessel
Spaces in the Abdomen and Pelvis
• Potential spaces in the abdomen and pelvis
include:
– Intraperitoneal Spaces
• Greater and lesser omentum
– Retroperitoneal
– Extraperitoneal
• Potential spaces are difficult to appreciate on
dissection
• Best seen on imaging, especially when filled
with air or fluid
Peritoneal vs. Retroperitoneal Spaces
A
N
T
• Intra-peritoneal organs
are covered in a layer
of peritoneum, a double
layer of which
(mesentery) connects
them to the abdominal
wall
• Retroperitoneal organs lie behind
the posterior peritoneum
• Kidneys, adrenal glands, aorta & IVC,
duodenum, ascending and
descending colon, pancreas,
• Liver, stomach, spleen,
gallbladder, small bowel
& colon (cecum,
transverse, sigmoid)
Fluid in the peritoneal cavity
Omentectomy
clips
Greater sac
Liver
S
Panc
Scott Tsai, MD
Fluid in lesser sac
Not all fluid is free
flowing
Loculated ascites is
common in later stage
ovarian carcinoma
Greater and lesser
sacs communicate
via the epiploic
foramen
Fluid in peritoneal
cavity def: space
between visceral and
parietal peritoneum
•
Fluid accumulates in dependent
areas
• Morrison’s pouch (the peritoneal
reflection separating the liver
from the retroperitoneal kidney)
is the most dependent location
while supine
• The left and right paracolic
gutters are also dependent and
commonly accumulate fluid
Hepatorenal
recess (pouch of
Morison)
r. Paracolic gutter
l. Paracolic gutter
The Lower
Quadrants
Right: Cecum, ileocecal region,
and appendix; ovary (if female)
Left: descending colon and ovary
Most common clinical entities in the
lower quadrants are:
Right – Appendicitis, inflammatory
bowel disease (Crohn’s), colonic
malignancy
Left – Diverticulitis
Both – Pelvic abnormalities
Appendicitis
• Obstruction of appendiceal
lumen leads to inflammation
and/or rupture
• Typically present with fever,
nausea/vomiting, and
periumbilical/right lower
quadrant pain
• Presence of calcified
appendicolith (7-15%) and
abdominal pain = 90%
probability of acute
appendicitis
Appendicitis
Normal
Inflamed
Inflamed appendix
Appendicolith seen on bone window
Diverticulosis
Herniation of mucosa and submucosa through muscular layers
The Pelvis
What lives in the pelvis?
• Female:
• Uterus and ovaries
• Bladder
• Male:
• Bladder
• Prostate and seminal vesicles
Urinary System
CALYX
PELVIS
URETER
BLADDER
Perirenal Peril
Hydronephrosis
Non-obstructing stone
The right kidney appears swollen with
stranding in the perinephric fat and a
dilated collecting system (hydronephrosis)
A stone in the mid right ureter accounts for
obstruction of the collecting system
Nephrolithiasis
Perirenal space outlined
Extravasated
urine in the
right
perirenal
space due to
obstructive
kidney stone
Kidneys
Bladder stones or calculi
with obstruction of the
collecting system
Bladder
Stones
Imaging of the
Female Pelvis
• Ultrasound is the most common modality used to
image the uterus and ovaries
• Hysterosalpingography is exclusively used to
assess tubal patency (infertility evaluation)
• Pelvic MR is used selectively to evaluate the
uterus, ovaries and fetus
AP PELVIS
Sacrum
Sacro-iliac
joint
Greater
trochanter
Sacro- iliac
joint
Femoral head
Acetabulum
Superior
pubic
ramus
Lesser
trochanter
Symphysis pubis
Inferior pubic ramus
PELVIC VASCULAR TREE
1. ABDOMINAL
AORTA
2. INTERNAL
ILIAC
ARTERY
4
6
3. EXTERNAL
ILIAC
ARTERY
4. LUMBAR
ARTERY
5
5. COMMON
FEMORAL
ARTERY
6. COMMON
ILIAC
diaphragm
Psoas major m.
Quadratus
lumborum
Iliacus m.
Pelvic Viscera - Male
bladder
rectum
prostate
Descending, sigmoid
colon
Ascending
colon
PROSTATE
NOTE OBSTRUCTION
Benign Prostatic
Hyperplasia
This can obstruct the ureters entering the
bladder leading to hydronephrosis and renal
failure.
Pelvic Viscera - Female
bladder
uterus
ovary
rectum
Descending
colon
Ascending
colon
Rectouterine
pouch
uterus
Uterine (Fallopian) tube
fundus
body
cervix
ovary
Normal Uterus
on Sagittal MR
Myometrium:
(homogeneous, moderate
to low signal)
P
Image: St. Paul’s Hospital
Vancouver, BC
extracted from their website:
http://www1.stpaulshosp.bc.ca/
R
B
V
A
Endometrium: homogeneous intense signal
Uterus – Hysterosalpingography
Isthmic Segment
Ampullary segment
Contrast has been injected
through a canula placed
into the cervical os.
Iodinated contrast flows
retrograde with injection
filling the uterine cavity with
reflux into the fallopian
tubes.
Uterine cavity
Infundibulary Segment
Fimbriated
End
Normal
Catheter
Lower Uterine Segment
Imaging of the
Fetus
9 week pregnancy
US
30 week pregnancy
MRI
• US is the primary modality for imaging during pregnancy
• Gestational sac → yolk sac → fetal pole → cardiac activity at
5.5-6 weeks gestation
• Full fetal survey typically performed at 16-18 weeks
• MR used to evaluate specific developmental anomalies
Conclusions
• The primary imaging modalities for the abdomen
and pelvis are plain film, ultrasound, and CT
• Most common indications for imaging include
pain, trauma, distention, nausea, vomiting,
and/or change in bowel habits
• Choice of modality depends upon clinical
symptoms, patient age & gender, and findings
on physical exam
• Mastery of the anatomy within each quadrant
can help explain particular symptoms, clinical
presentations, and/or imaging findings