Diagnostic Ultrasound - Abdomen and Pelvis
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Diagnostic Ultrasound - Abdomen and Pelvis

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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 5

Liver Anatomy: Abdomen HEPATIC VISCERAL SURFACE Coronary ligament Diaphragm Right triangular ligament Left triangular ligament Falciform ligament Ligamentum teres Gallbladder Gallbladder Falciform ligament Porta hepatis Right renal impression Gastric impression Bare area Fissure for ligamentum venosum Inferior vena cava (Top) The anterior surface of the liver is smooth and molds to the diaphragm and anterior abdominal wall. Generally, only the anterior/inferior edge of the liver is palpable on a physical exam. The liver is covered with peritoneum, except for the gallbladder bed, porta hepatis, and the bare area. Peritoneal reflections form various ligaments that connect the liver to the diaphragm and abdominal wall, including the falciform ligament, the inferior edge that contains the ligamentum teres, and the obliterated remnant of the umbilical vein. (Bottom) This graphic shows the liver inverted, which is somewhat similar to the surgeon's view of the upwardly retracted liver. The structures in the porta hepatis include the portal vein (blue), hepatic artery (red), and the bile ducts (green). The visceral surface of the liver is indented by adjacent viscera. The bare area is not easily accessible. 6

Liver<br />

Anatomy: <strong>Abdomen</strong><br />

HEPATIC VISCERAL SURFACE<br />

Coronary ligament<br />

Diaphragm<br />

Right triangular ligament<br />

Left triangular ligament<br />

Falciform ligament<br />

Ligamentum teres<br />

Gallbladder<br />

Gallbladder<br />

Falciform ligament<br />

Porta hepatis<br />

Right renal impression<br />

Gastric impression<br />

Bare area<br />

Fissure for ligamentum<br />

venosum<br />

Inferior vena cava<br />

(Top) The anterior surface of the liver is smooth <strong>and</strong> molds to the diaphragm <strong>and</strong> anterior abdominal wall. Generally, only the<br />

anterior/inferior edge of the liver is palpable on a physical exam. The liver is covered with peritoneum, except for the gallbladder bed,<br />

porta hepatis, <strong>and</strong> the bare area. Peritoneal reflections form various ligaments that connect the liver to the diaphragm <strong>and</strong> abdominal<br />

wall, including the falciform ligament, the inferior edge that contains the ligamentum teres, <strong>and</strong> the obliterated remnant of the<br />

umbilical vein. (Bottom) This graphic shows the liver inverted, which is somewhat similar to the surgeon's view of the upwardly<br />

retracted liver. The structures in the porta hepatis include the portal vein (blue), hepatic artery (red), <strong>and</strong> the bile ducts (green). The<br />

visceral surface of the liver is indented by adjacent viscera. The bare area is not easily accessible.<br />

6

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