Probe Positioning & Scanning Technique

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• Use a curved array transducer (e.g., 3–6 MHz) for general abdominal evaluation; for superficial zones (e.g., abdominal wall, anterior peritoneum), a linear probe (e.g., 7–12 MHz) may help detect subtle free air or echogenic peritoneal thickening. 

• Typical patient position: supine, with possible slight left tilt or elevation of head-end if needed to optimize fluid or gas detection.

• Standard windows to examine include:

  • Right upper quadrant (RUQ) — e.g., subcostal view between liver and kidney, to assess for fluid in Morrison’s pouch (hepatorenal recess). 

  • Left upper quadrant (LUQ) — splenorenal region.

  • Pelvis — pouch of Douglas in women, rectovesical pouch in men for free fluid.

  • Anterior abdominal wall or pre-hepatic space for free air (especially for suspected perforation). 

• Use gentle sweeping and sliding to assess the full peritoneal cavity; in suspected peritonitis look for indirect signs (fluid, peritoneal thickening, fat stranding/gas) rather than always expecting the disease to appear as a “mass”.

📸 Key Sonographic Findings in Peritonitis

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Here are common ultrasound findings suggestive of peritonitis:

✅ Normal Findings vs 🚨 Abnormal (Peritonitis) Comparisons

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Normal Ultrasound:

• Minimal or no free fluid in the hepatorenal or splenorenal recesses.

• Peritoneal stripe appears thin, uniform, with no significant thickening or enhanced echogenicity.

• Mesenteric fat appears homogeneous, not hyperechoic or thickened.

• No abnormal gas under abdominal wall or suspicious comet-tail artefacts.

Findings suggestive of Peritonitis:

• Significant free fluid, often in dependent portions of the peritoneal cavity (e.g., Morrison’s pouch, pelvis).

• Fluid may be complex (echogenic), especially in infectious or hemorrhagic cases.

• Peritoneal thickening/enhancement, fat hyperechogenicity.

• Evidence of free air if perforation: linear echogenic interface, dynamic shifting.

• Possibly localized fluid collections/abscesses or bowel loop changes pointing to source.

🧠 Practical Tips & Key Considerations

• Clinical correlation is essential: Peritonitis is usually a clinical diagnosis reinforced by imaging findings (pain, peritoneal signs, fever, lab markers) rather than imaging alone. 

• Ultrasound is operator-dependent; body habitus, bowel gas, patient cooperation affect image quality.

• Do not rely solely on absence of fluid to exclude peritonitis—small volumes of fluid or early disease may be missed.

• For suspected perforation, use anterior abdominal wall or sub-diaphragmatic windows to seek free air (ultrasound sensitivity is lower than CT but still useful). 

• When fluid is highly echogenic (as in infected ascites/septic fluid) it may be mistaken for soft tissue—beware and scan thoroughly. 

• Document images in at least two orthogonal planes, note location and character of fluid, any bowel/adnexal/organ abnormalities.

• In cases of suspected tubercular peritonitis the ultrasound may show ascites with fine septations, omental thickening, peritoneal nodules/strands