Diagnostic Ultrasound - Abdomen and Pelvis

Liver
○ Appear as echolucent defects within liver parenchyma
with no reflective wall: Large sinusoids with thin or
absent wall
○ Branches enlarge and can be traced towards IVC
○ Flow pattern has a triphasic waveform
– Resulting from transmission of right atrial pulsations
into veins
□ A wave: Atrial contraction
□ S wave: Systole (tricuspid valve moves toward apex)
□ D wave: Diastole
○ Right hepatic vein
– Runs in coronal plane between anterior and posterior
segments of right hepatic lobe
○ Middle hepatic vein
– Lies in sagittal or parasagittal plane between right and
left hepatic lobe
○ Left hepatic vein
– Runs between medial and lateral segments of left
hepatic lobe
– Frequently duplicated
○ 1 of 3 major branches of hepatic veins may be absent
– Absent right hepatic vein ~ 6%
– Less commonly middle and left hepatic vein
• Hepatic artery
○ Flow pattern has low-resistance characteristics with large
amount of continuous forward flow throughout diastole
– Normal velocity 30-70 cm/s
– Resistive index ranges 0.5-0.8, increases after meal
○ Common hepatic artery usually arises from celiac axis
○ Classic configuration: 72%
– Celiac axis → common hepatic artery →
gastroduodenal artery and proper hepatic artery →
latter gives rise to right and left hepatic artery
○ Variations from classic configuration
– Common hepatic artery arising from SMA (replaced
hepatic artery): 4%
– Right hepatic artery arising from SMA (replaced right
hepatic artery): 11%
– Left hepatic artery arising from left gastric artery
(replaced left hepatic artery): 10%
• Bile ducts
○ Normal peripheral intrahepatic bile ducts are too small to
be demonstrated
○ Normal right and left hepatic ducts measuring a few
millimeters are usually visible
○ Normal common duct
– Most visible in its proximal portion just caudal to porta
hepatis: Less than 5 mm
– Distal common duct should typically measure < 6-7
mm
– In elderly, generalized loss of tissue elasticity with
advancing age leads to increase in bile duct diameter:
< 8 mm (somewhat controversial)
ANATOMY IMAGING ISSUES
Imaging Recommendations
• Transducer
○ 2.5-5 MHz curvilinear or vector transducer is generally
most suitable
○ Higher frequency linear transducer (i.e., 7-9 MHz) useful
for evaluation of liver capsule and superficial portions of
liver
• Left lobe
○ Subcostal window with full inspiration generally most
suitable
• Right lobe
○ Subcostal window
– Cranial and rightwards angulation useful for
visualization of right lobe below dome of
hemidiaphragm
– Can sometimes be obscured by bowel gas
○ Intercostal window
– Usually gives better resolution for parenchyma
without influence from bowel gas
– Right lobe just below hemidiaphragm may not be
visible due to obscuration from lung bases
– Important to tilt transducer parallel to intercostal
space to minimize shadowing from ribs
Imaging Pitfalls
• Because of variations of vascular and biliary branching
within liver (common), it is frequently impossible to
designate precisely boundaries between hepatic segments
on imaging studies
CLINICAL IMPLICATIONS
Clinical Importance
• Liver ultrasound often first-line imaging modality in
evaluation for elevated liver enzymes
○ Diffuse liver disease, such as hepatic steatosis, cirrhosis,
hepatomegaly, hepatitis, and biliary ductal dilatation, are
well visualized with ultrasound
○ Documentation of patency of portal vein, hepatic vein
waveforms, and hepatic arterial velocities are helpful in
evaluation for etiologies of elevated liver function tests
• Liver metastases are common
○ Primary carcinomas of colon, pancreas, and stomach are
common
– Portal venous drainage usually results in liver being
initial site of metastatic spread from these tumors
○ Metastases from other non-GI primaries (breast, lung,
etc.) commonly spread to liver hematogenously
• Primary hepatocellular carcinoma
○ Common worldwide
– Risk factors include chronic viral hepatitis B or C,
alcoholic cirrhosis, or nonalcoholic steatohepatitis
– Ultrasound commonly used for screening and
surveillance in patients at risk for development of
hepatocellular carcinoma (HCC) typically at 6 month
intervals
SELECTED REFERENCES
1. Heller MT et al: The role of ultrasonography in the evaluation of diffuse liver
disease. Radiol Clin North Am. 52(6):1163-75, 2014
2. McNaughton DA et al: Doppler US of the liver made simple. Radiographics.
31(1):161-88, 2011
3. Kruskal JB et al: Optimizing Doppler and color flow US: application to
hepatic sonography. Radiographics. 24(3):657-75, 2004
Anatomy: Abdomen
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