What Abdominal Ultrasound Evaluates
Abdominal ultrasound is the first-line imaging modality for evaluating biliary obstruction, gallbladder disease, and hepatic abnormalities, while also detecting liver abscesses, kidney pathology, ascites, appendicitis, and bowel inflammation. 1
Primary Diagnostic Targets
Hepatobiliary System (Highest Yield)
- Gallbladder pathology: Cholelithiasis, acute cholecystitis, acalculous cholecystitis, cholangitis, and gallbladder wall thickening 1
- Biliary tree obstruction: Dilated intrahepatic or extrahepatic bile ducts (sensitivity 32-100%, specificity 71-97% for detecting obstruction) 1
- Liver parenchymal disease: Diffuse hepatic hypoechogenicity, "starry sky" appearance, hepatomegaly, focal liver lesions, and liver abscesses 1, 2, 3
- Portal vein assessment: Increased portal vein wall thickness and vascular patency evaluation 2
Solid Organs
- Pancreas: Acute pancreatitis, pancreatic masses, and assessment of disease severity 1, 3
- Spleen: Splenic pathology and relevant abnormalities in critical care settings 3
- Kidneys: Renal abscesses, hydronephrosis, and urinary obstruction 1, 4
Bowel and Peritoneum
- Appendicitis: Particularly valuable as first-line imaging in pregnant patients 1
- Small bowel obstruction: Can have similar sensitivity to CT in specialized centers 1
- Bowel inflammation: Assessment of Crohn's disease activity and diverticulitis 1
- Free fluid: Ascites and intraperitoneal fluid collections 1, 5
Abdominal Collections
- Abscesses: Liver, kidney, and surgical wound abscesses 1
- Perforated bowel: Detection of free intraperitoneal air 3
Vascular Pathology
- Abdominal aortic aneurysm: 99% sensitive and 98% specific for detection in emergency settings 1
- Middle aortic syndrome: Elevated peak systolic velocities and abnormal waveforms 1
Clinical Context for Ordering
When Ultrasound is First-Line (Usually Appropriate)
- Right upper quadrant pain with suspected biliary disease 1
- Jaundice with suspected biliary obstruction 1
- Fever with abdominal symptoms or elevated liver enzymes 1
- Recent abdominal surgery with fever 1
- Pregnant patients with abdominal pain (primary modality before MRI) 1
- Palpable tender hepatomegaly (mandatory first-line imaging) 2
When Ultrasound Has Limited Utility
- Nonlocalized abdominal pain without fever in non-pregnant adults: CT with IV contrast is usually more appropriate 1
- Fever without abdominal symptoms or liver abnormalities: Routine use not recommended 1
- Retroperitoneal bleeding: Limited by patient positioning and acoustic windows 1
- Distal common bile duct stones: Sensitivity only 22.5-75% 1
Important Limitations
Ultrasound performance is operator-dependent and requires onsite experienced sonographers, which may increase costs despite being considered a low-cost procedure 1. Visualization is significantly impaired by increased bowel gas, large body habitus, and free intraperitoneal air 1. The modality cannot visualize the entire abdomen and may miss pathology outside the acoustic window 1.
Diagnostic Accuracy Compared to Other Modalities
When all three modalities (US, CT, MRI) were performed on the same patients, ultrasound correctly diagnosed 54% of abnormalities overall, with specific accuracy rates: gallbladder/biliary disease 100%, liver disease 25%, pancreatic disease 22%, renal disease 25%, and adrenal disease 0% 5. For gallbladder disease specifically, ultrasound provides the most accurate diagnoses compared to CT or MRI 5.