Radiological anatomy of abdomen. Basic points.

1. RADIOLOGICAL
ANATOMY OF ABDOMEN

2. SYNOPSIS
Liver
Biliary tract
Spleen
Pancreas
Kidney
Adrenal gland
Gastrointestinal tract
Gross anatomy
Radiological anatomy –
USG / CT / MRI
Anatomical variants /
Congenital anamolies

3. LIVER

4. Liver - Anatomy
Largest of all abdominal organs, commands the right
upper abdominal quadrant
Great transverse measurement -20 to 26 cm
Vertically measurement- 15 to 21 cm
Greatest anteroposterior diameter (determined at
the level of the upper right kidney) - 7 to 12 cm.
The hepatic parenchyma is surrounded by a dense
layer of connective tissue forming the liver capsule.

6.  The liver’s
convex diaphragmatic surface
concave visceral surfaces.
 Bare area , Fossa of the gallbladder, fossa of the
inferior vena cava (IVC), and the suprarenal impression
are not covered by peritoneum.

8. • Two sagitally oriented fissures
linked centrally by transverse
porta hepatis , form the letter
H on visceral surface.
• Left fissure – Fissure for round
ligament anteriorly and
fissure for ligamemtum
venosum posteriorly.
• Right fissure – Fossa for GB
anteriorly and groove for IVC
posteriorly

9. Functional segmental anatomy
 Centrally located in each of the hepatic segments
 segmental branch of the portal vein
 hepatic artery
 segmental bile duct.
 The distal hepatic veins lie
between the individual
segments.

10. BISMUTH-COUINAUD SYSTEM
 Divides the liver into 8 functionally independent
segments.
 Each segment has its own vascular inflow ,
outflow and biliary drainage.
 Centre – Hepatic artery , portal vein and bile duct.
 Periphery – Vascular outflow through hepatic
veins.

11.  Segment I -caudate lobe.
 Receives branches from both the main portal vein
and its right and left branches - portal trinity.
 Does not drain into the hepatic veins but directly
into the IVC.
 All remaining liver segments (II to VIII) are defined
by their positions relative to branches of the portal
and hepatic veins.

13. Left portal vein
Gives off a caudate branch.
Divides into its terminal branches - left lateral
and left medial portal venous branches.
 The left lateral portal venous branch supplies
superior segment II, located lateral to the left
hepatic vein and above the portal venous plane.
 The left medial portal venous branch supplies
inferior segment III located laterally to the left
hepatic vein and beneath the portal venous plane
as well as segment IV.

14. • Segment IV is delineated
• Medially - middle hepatic vein and
• Laterally - left hepatic vein
• Subdivided into a superior segment IVa and an
inferior segment IVb in regard to the portal venous
plane.

15. Right portal vein
 The right anterior portal venous branch
 anterior-inferior segment V
 anterior-superior segment VIII
 The right posterior portal venous branch
 posterior-inferior segment VI
 posterior-superior segment VII

16. LIVER ANATOMY VARIANTS
• Horizontal elongation of the lateral segment
(bismuth-couinaud segment II) of the left
hepatic lobe, which can extend into the left
upper abdominal quadrant and eventually
abut or even wrap around the splenic contour.

17. • Riedel lobe - vertical
elongation of the right
lobe.
• Differentiated from
extracapsular extension
caused by a liver tumor (
hepatic adenoma or
metastasis).
Precontrast T1-weighted hepatic MRI in a
77-year-old woman with Riedel’s lobe
resulting from a prominent inferiorly
positioned narrow right lobe of the liver
that significantly extends the expected
confines of the liver.

18. BILIARY TRACT AND GALL BLADDER

19. Biliary
canaliculi
Segmental
bile duct
Common
hepatic duct
Common
bile duct
Ampulla of
vater
Cystic duct
Pancreatic
duct

20. IntraHepticDucts
 On computed tomography , normal intra hepatic bile ducts
appear as linear water-density structures accompanying the portal
vein branches.
 Normal IHDs measure less than 3 mm.
 They appear to be randomly scattered throughout the liver
but are confluent toward the hilum.
 The IHDs from each lobe unite to form the right and left main
hepatic ducts, which are located anterior to the portal veins .

22. Common hepatic duct
The right and left main hepatic ducts unite in
the hilum to form the common hepatic duct
(CHD).
 The CHD usually courses along a 45-degree
oblique plane with reference to the midline
sagittal plane, which lies to the right and
lateral to the proper hepatic artery.
 On CT the CHD usually measures 3 to 6 mm
in short-axis diameter

23. Common Hepatic Duct at hilum

24. Common bile duct
 The common bile duct (CBD) forms when the
cystic duct joins the CHD.
 This union occurs at varying levels, from high
in the porta hepatis to near the ampulla of
Vater.
 Because the union is usually not
demonstrated on CT, the term common duct
is used when the CHD and CBD cannot be
differentiated.

25. Intrapancreatic Common BileDuct

26. THE UNION IS USUALLY NOT DEMONSTRATED
ON CT, THE TERM COMMON DUCT IS USED
WHEN THE CHD AND CBD CANNOT BE
DIFFERENTIATED.

27. Ampulla of Vater
The CBD enters the pancreas and typically lies along the
posterior and lateral aspect of the pancreatic head.
The distal CBD and main pancreatic duct come into contact
on the medial side of the descending part of the
duodenum.
The two ducts pass separately
through the wall of the
duodenum and unite to form
a short dilated tube—the
ampulla of Vater

28. • The sphincter of Oddi is the circular muscle
complex around the CBD, pancreatic duct, and
ampulla of Vater; it consists of the
• sphincter choledochus
• sphincter pancreaticus and
• sphincter ampullae

29. On endoscopic retrograde cholangio pancreatography,
the ampullary segment is usually not visualized
because of the contraction of the sphincter of Odd.

30. Gall bladder
• The gallbladder is a blind
pouch lying along the
undersurface of the liver.
• The normal gallbladder
wall thickness ranges from
1 to 3.5 mm. On US, 3 mm
might be a reasonable
upper limit of normal.

31. USG anatomy
Normal GB wall appears s a pencil thin
echogenic line at sonography
Minimum 6 hrs fasting
Subcoastal or intercostal
approach
Supine – LLD
GB wall - <3mm
Transverse diameter - <4cm

32. CT Anatomy
• On transverse CT images, the gallbladder is a
rounded structure with a maximum diameter
of less than 4 to 5 cm in the distended state.
• Visualization of the gallbladder wall depends
on the degree of gallbladder distention and
the presence of abnormality.
• Enhancement of the gallbladder wall on CT
and MRI is normal after the intravenous
administration of contrast medium.

33. • The density of the gallbladder lumen is
generally that of water (0-20 Hounsfield units
[HU]).
• After intravenous contrast administration, an
increase in density is observed on CT.

34. Normal GB wall apperas as a thin
rim of soft tissue density that
enhances on contrast
administration.

35. Congenital anamolies
Phrygian Cap
 The most common anomaly of the entire
biliary tree
 Septation in the distal fundus of the
gallbladder, which results in the configuration
called a phrygian cap.

36.  In the retroserosal or concealed type, the
mucosal fold projecting into the lumen may
not be visible externally.
 In the serosal or visible type, the
peritoneum follows the bend in the fundus
and then reflects on itself as the fundus
overlies the body.

38. Ectopic gall bladder
 The gallbladder
can be located in
various positions

39. PANCREAS

40. PANCREAS
Retroperitoneal organ
Pancreas is an exocrine and endocrine organ
Approximately 15 cm long
Related to the stomach, duodenum, colon,
and spleen.

41. USG anatomy

42. CT ANATOMY - PANCREAS
The density of the nonenhanced pancreas is
normally the same as that of soft tissue, between
30 and 50 HU. It increases to 100 to 150 HU after
intravenous administration of iodine-based
contrast agents.
Homogeneous enhancement of the normal gland is
a useful sign for excluding necrosis in pancreatitis.

43. PANCREAS LIES OBLIQUE , HENCE ALL
PARTS ARE NOT AT THE SAME
TRANSVERSE LEVEL

44. MRI ANATOMY - PANCREAS
On T1-weighted images, the normal gland, owing to the
aqueous protein content, reveals higher signal
intensity than nonfatty tissue such as liver and
muscle.

45. On fat-suppressed T1-weighted sequences, the
relatively high signal intensity of the pancreas
increases

46. On T2-weighted sequences, the normal pancreas is
slightly hyperintense to muscle, whereas on fat-
suppressed T2-weighted images, the contrast
between the normal pancreas and surrounding
suppressed fat is minimal

47. Being a very vascular organ, the pancreas shows
intense contrast enhancement in the arterial
phase, followed by a rapid washout (

48. Variant anatomy
PANCREAS DIVISUM
• Failure of fusion of the dorsal and ventral ducts
• Separate drainage into duodenum - Predominant
drainage occurs through dorsal duct system (duct
of Santorini).
• Classified into three types
– I (classic form): complete lack of fusion between
dorsal and ventral duct systems
– II: absent duct of Wirsung
– III: small communicating branch connects dorsal and
ventral duct systems

50. Annular Pancreas
portion of pancreatic tissue in continuity with the
head that partially or completely circumscribes
duodenum.
encircles second portion of duodenum
associated with duodenal anomalies such as atresia,
atrophy, or stenosis .
discovered in childhood because of upper GI
obstruction

51. Agenesis of pancreas
Agenesis of
pancreas
Complete
agenesis
Incompatible
with life
Partial agenesis
Agenesis of
ventral pancreas
Agenesis of
dorsal pancreas
Complete
agenesis
Partial
agenesis

52. Complete agenesis of the dorsal pancreas: body and tail
of pancreas and whole dorsal duct system, including
minor papilla and accessory duct, are absent.
Partial agenesis of the dorsal pancreas: distal part of
pancreatic body or at least a remnant of accessory
duct and minor papilla are found.
the rounded head of the
pancreas (arrow) and the
absence of the neck and body.
the abnormal position of the bowel loops
(arrowheads) behind the stomach.
polysplenia

53. SPLEEN

54. SPLEEN
• Lies within the left upper
quadrant.
• Weighs 100 to 200 g
• The max craniocaudal
length is 12 cm.
• The normal spleen may have rib notching and
clefts that should not be confused with
lacerations in patients who have experienced
trauma.

55. The spleen is a network of
white and red pulp.
 The white pulp consists
of lymphocytes, plasma
cells, and macrophages.
The red pulp contains
splenic cords, splenic
sinuses, terminal
branches of the central
arteries, and pulp veins.

56. The visceral surface of the spleen is adjacent to
the stomach, left kidney, splenic flexure of the
colon, and tail of the pancreas.

57. Spleen – USG anatomy
Best assessed in left lateral
position with left arm
behind the head.
Visualised best obliquely in
9th or 10th intercostal space.
Higher echogenicity than
liver.

58. CT anatomy
On unenhanced CT
scans, the normal
splenic
parenchyma is
homogeneous - it
measures 40 to 60
Hounsfield units
(HU), usually 5 to
10 HU less than
the normal liver.

59. ROI measurement is placed within the liver and spleen.
If spleen measures 10HU or more than the liver – fatty
infiltrate is indicated.

60. VZAfter intravenous (IV)
contrast enhancement,
the spleen can have a
heterogeneous
appearance on early
arterial-phase images on
both CT and MRI.
This appearance is
believed to be due to
the differential
enhancement of red and
white pulp

61. Patterns of spleen enhancement in
arterial phase

62. MRI anatomy
 T1-weighted MRI the normal spleen has a
signal intensity equal to or less than that of
normal liver.
 T2-weighted images, the spleen has
uniformly high signal intensity.

63. Splenic Variants
Splenic cleft
 Easily recognized because of
their sharp, smooth borders.
 Typically located superiorly
and medially.
 Splenic clefts are not
associated with perisplenic
edema ,seen with splenic
laceration.

64. • Accessory spleen represents normal splenic tissue in
ectopic sites
• Arising from failure of fusion of some of the multiple buds
of splenic tissue in the dorsal mesogastrium during
embryologic life.
• They are typically located near the splenic hilum but can be
found anywhere in the peritoneal cavity

65. Wandering spleen - or ectopic
spleen is a rare entity
whereby the spleen migrates
from its normal site in the left
upper quadrant.
Nonunion of the peritoneum
of the lesser and greater sacs,
creating a longer splenic
mesentery and highly mobile
spleen.

66. IMAGING TECHNIQUES
Computed Tomography
 Single breath hold and IV administration of a contrast
agent.
 90-ml bolus of nonionic contrast agent is administered
at a rate of 2 to 3 ml/second.
Scanning is performed during the portal venous phase
at 60 seconds after the bolus is given. This approach
typically provides uniform enhancement of the spleen
and enhancement of the liver during the portal venous
phase.
In any patient being evaluated for trauma, delayed
scans taken 2.5 to 3 minutes after the bolus can often
exclude lacerations of the spleen or other abdominal
organs.

67. KIDNEY

68. Kidney - anatomy
Paired retroperitoneal organ.
Located on posterior abdominal wall.
Lies between T12 to L3.
Size
Adult male – 10 to 14cm
Adult female – 9-13cm

69. KIDNEYS
Anterior renal fascia
(gerota’s fascia)
Posterior renal fascia
(Zuckerkandl’s fascia)

70. The renal fascial layers divide the general retroperitoneal
space into three compartments extending from the
diaphragm to the pelvic brim—the anterior pararenal space,
the perinephric space, and the posterior pararenal space

71. PERINEPHRIC SPACE
 Contains the kidney, adrenal gland, renal
pelvis, proximal ureter, renal blood vessels,
renal capsular vessels, and perinephric fat.
 It is bounded by the anterior and posterior
renal fascial layers and is demarcated by their
sites of fusion.

72. Above -- two fascial layers fuse and adhere firmly to
the diaphragmatic fascia;
Laterally -- the layers fuse behind the ascending or
descending colon to form the lateroconal fascia
Medially -- the anterior renal fascia blends into the
connective tissue near the midline . posterior
renal fascia fuses with the psoas or quadratus
lumborum fascia.
Inferiorly -- fascial cone forming a caudal extension
of the main perinephric space containing the
proximal ureter and gonadal vessels

73. Lateroconal fascia
Anterior renal fascia
(gerota’s fascia)
Posterior renal fascia
(Zuckerkandl’s fascia)

74. Kidney – USG anatomy
 Cortex is less echogenic than
liver and more echogenic than
medulla.
Renal sinus consisting of
calyces , renal pelvis and fat
appears echogenic than cortex.

75. CT ANATOMY
• CT protocol for evaluation of the kidneys
consists of both non enhanced and contrast-
enhanced CT scans obtained in suspended
respiration to overcome the motion artifact.
• Non enhanced CT scans the normal renal
parenchyma has an attenuation value of 30 to
50 hounsfield units (HU), depending on
patient hydration, and the cortex and medulla
show no visible density differences.

76. • Nonenhanced scans
 permit contrast enhancement of a renal lesion to be
measured
 ensure that renal parenchymal calcifications, renal
calculi, renal and perinephric hemorrhage and fat,
and calcification in a renal mass will not be obscured
by contrast medium.
• The accuracy of attenuation values should also be
tested by measuring the attenuation value of the
gallbladder contents before and after IV
administration of contrast medium.

77. Corticomedullary phase
Corticomedullary phase occurs
between 25 and 70 seconds after
the start of contrast administration.
Renal cortex can be differentiated
from renal medulla at this stage
because (1) the vascularity of the
cortex is greater than that of the
medulla, and (2) contrast material
has not yet reached the distal aspect
of the renal tubules
Maximal opacification of the renal vein and arteries
occurs during this phase, allowing confident diagnosis of
tumor extension to the vein.
CORTICAL NEPHROGRAM

78. Nephrographic Phase.
The nephrographic phase
starts about 80 seconds and lasts
up to 180 seconds after the start
of injection.
Offers the best opportunity for
discrimination between the
normal renal medulla and a renal
mass
The nephrographic phase is the most valuable for detecting
renal masses and characterizing indeterminate lesions

79. Excretory Phase
Approximately 180 seconds after
the start of contrast injection, the
excretory phase begins.
 The contrast material is excreted
into the collecting system, so the
attenuation of the nephrogram
progressively .
 Delineate the relationship of a centrally located mass with the
collecting system.
 Evaluating urothelial masses.

80. Normal renal MRI.
A T1-weighted (gradient opposed-phase)
image
T2-weighted axial image (B) demonstrate
the normal appearance of the kidneys
T1-weighted axial Gd-enhanced image
reveals normal enhancing renal
parenchyma

81. Congenital anamolies
Horse shoe kidney : MC renal fusion anamoly.

82. Renal ectopia - Abnormal anatomical location of
one or both the kidney.

83. Adrenal gland
 Retroperitoneal structures
 Normal adrenal glands have a characteristic
inverted Y, V, or T shape
 Right adrenal gland is typically superior to the
right kidney.
 Left adrenal gland is usually anterior to the
superior pole of the left kidney.
 The adrenals are typically described as having
a central body and two (medial and lateral) limbs.
The body and limbs are typically smoothly shaped
and measure less than 10 mm in thickness; the
limbs can measure up to 4 cm in length

84. CT anatomy
Normal adrenal glands. Axial and coronal contrast-enhanced
CT demonstrates typical location and appearance of the right
and left adrenal glands

85. MRI anatomy
Axial contrast-enhanced T1-weighted MRI shows normal
thickness of the adrenal body and limbs (<1 cm) and normal
length (<4 cm).

86. GI Tract

87. Gastrointestinal Tract
Stomach These areas of the stomach
cannot always be well
demonstrated on axial CT or MRI,
so coronal or sagittal imaging
planes are very helpful to
understand the exact anatomic
location of the lesion .
Normal gastric wall is 2 to 5 mm
thick, with 10 mm being the upper
limit.
In an air-filled stomach - 3mm or
5mm

88. On CT or MRI, the normal gastric
wall enhances homogeneously
but shows a two- or three-
layered structure .
Inner layer- mucosal layer,
enhances markedly.
Intermediate layer - submucosal
layer low attenuation
Outer layer – muscular serosal
layer of slightly higher
attenuation
Normal gastric wall of the stomach (S) with
layered appearance.

89. In a suboptimally distended stomach, false-
positive gastric wall thickening can frequently
occur.
When air techniques are used
 the right decubitus position -proximal stomach
and GEJ
 the left decubitus position -distal stomach and
duodenum
[reverse of the patient’s position when barium
or water is used].
Left posterior oblique position - gastric antrum
Prone position - gastric fundus

90. SMALL INTESTINE
CT
 Normal small bowel wall thickness - 2 to 3
mm
 In the terminal ileum where 5 mm is
considered the upper limit of normal.
 The thickness of valvulae conniventes
should not exceed 3 mm.

91. Normal coronal CT enterography
image after oral administration of
Gastrografin as a positive oral
contrast.
Normal coronal CT enterography
image after oral administration of
water as a neutral oral contrast.

92. Colon and Rectum
 Colon is visualized on CT by its
anatomic location
typical haustral morphology
 Ringlike or tubular structure, depending on
the orientation and position relative to the
scanning plane.
 The wall of the normal colon measures 3
mm or less in thickness when the colon is
distended with oral contrast material.

93. • Caecum - Recognition of the cecum is
facilitated by visualization of the terminal
ileum, ileocecal valve, or appendix.

94.  Appendix - The appendix appears as a
small ringlike or tubular structure. The
presence of air or contrast material in the
appendix along with normal-appearing
surrounding fat may be indicative of absence
of appendicitis.

95. • The ascending and descending colons are
within the anterior pararenal space and
usually are surrounded by homogeneous fatty
tissue.

96. • The rectum is about 12 to 15 cm in length.
• The peritoneum covers the anterior surface of
the upper rectum
• Lower two thirds of the rectum are enveloped
by extraperitoneal connective and adipose
tissue.