Complete Abdominal Ultrasound: Structures Evaluated
A complete abdominal ultrasound systematically evaluates the solid organs (liver, gallbladder, pancreas, spleen, kidneys), the abdominal aorta, the urinary bladder, and screens for free fluid or masses in the peritoneal cavity. 1, 2
Systematic Examination Approach
The examination should follow a standardized scanning protocol to ensure no organ is missed, typically proceeding through longitudinal, cross-sectional, and oblique planes 2:
Upper Abdomen - Right Upper Quadrant
- Liver: Evaluated for size, echogenicity, focal lesions, and parenchymal abnormalities 1, 2
- Gallbladder: Assessed for stones, wall thickening, and signs of cholecystitis 1, 3
- Right kidney: Examined in both short- and long-axis views for hydronephrosis, masses, and parenchymal changes 4, 5
- Morrison's space (hepatorenal recess): Screened for free fluid between liver and right kidney 6
Upper Abdomen - Left Upper Quadrant
- Spleen: Evaluated for size and focal lesions 1, 2
- Pancreas: Assessed for masses, inflammation, and pseudocysts 1
- Left kidney: Examined in both short- and long-axis views for hydronephrosis, masses, and parenchymal changes 4, 5
- Splenorenal recess: Screened for free fluid 6
Mid-Abdomen
- Abdominal aorta: Measured in anteroposterior diameter (normal up to 2 cm infrarenally) to detect aneurysm 7, 3
- Inferior vena cava: Assessed for patency and diameter 2
- Small intestine: Evaluated when clinically indicated for obstruction or wall thickening 1
- Stomach: Visualized when pathology is suspected 1
Lower Abdomen and Pelvis
- Urinary bladder: Assessed qualitatively for volume, overdistension, and wall abnormalities 4
- Pelvic pouch of Douglas: Screened for free fluid 6
- Uterus and adnexa (in females): Evaluated when gynecological pathology is suspected 8
- Prostate (in males): Assessed when indicated 1
Peritoneal Cavity Assessment
- Free fluid detection: The ability to detect hypo/anechoic free fluid in the peritoneal cavity is considered a basic skill for ruling in acute abdomen 4
- Masses: Any abnormal solid or cystic structures are documented and characterized 1, 9
Key Technical Considerations
Probe selection and positioning: Use a curvilinear abdominal transducer (2-5 MHz) for deep structures, with systematic sweeping in the same direction to avoid missing pathology 6, 2
Common pitfalls to avoid:
- A distended bladder can create artifactual hydronephrosis; ensure proper bladder status during renal imaging 5
- Perirenal fat can mimic free fluid in Morrison's space 6
- Fluid within stomach or bowel may be misinterpreted as free peritoneal fluid 6
- Always image both kidneys to identify bilateral disease or solitary kidney situations 5
Clinical Context
While ultrasound is highly sensitive for detecting structural abnormalities in solid organs (>95% for hydronephrosis 4, 95-100% for abdominal aortic aneurysm 7), it should not be used alone to identify the cause of a surgical abdomen, as it does not reliably characterize different etiologies such as infectious colitis, small bowel obstruction, or perforation 4. Integration with clinical assessment is essential 4.