The hepatorenal recess (Morison's pouch) is the most dependent posterior peritoneal space in the supine patient, located between the inferior surface of the liver (right lobe) superiorly and the upper pole of the right kidney and right adrenal gland inferiorly. It is bounded medially by the hepatoduodenal ligament and the lesser omentum, and laterally by the right lateral abdominal wall. Free peritoneal fluid preferentially accumulates here in the supine patient.
The hepatorenal recess (Morison's pouch) is the first site examined in the FAST (Focused Assessment with Sonography in Trauma) ultrasound protocol for free intraperitoneal fluid: the probe is placed in the right mid-axillary line at the level of the 11th rib to visualise the liver-kidney interface. As little as 100-200 mL of free fluid can be detected as an anechoic stripe between the liver and kidney. A positive FAST in a haemodynamically unstable trauma patient is an indication for emergency laparotomy without CT. The recess also collects fluid in peritonitis, ascites, and ruptured ectopic pregnancy.
FAST ultrasound demonstrates free anechoic fluid in Morison's pouch in a haemodynamically unstable trauma patient with blunt abdominal injury; this positive FAST finding combined with haemodynamic instability (systolic BP below 90 mmHg unresponsive to resuscitation) is an indication for immediate damage control laparotomy without CT delay.
