Named after the British surgeon James Rutherford Morison, Morison’s pouch is also known as the hepatorenal recess or the subhepatic recess (the space that separates the liver from the right kidney). This recess is free of fluid under normal circumstances, but can fill with fluid under certain conditions such as hemoperitoneum or ascites. This space can best be visualized via ultrasound. According to the Textbook of Pediatric Emergency Medicine, “The amount of intraperitoneal fluid needed for detection by ultrasound has been reported to be as little as 100 mL and will depend on the source of the bleeding and patient positioning.” In adults, any low frequency probe is adequate to visualize the space. However, in pediatric trauma patients who have small intercostals spaces a microconvex probe should be used to avoid rib shadowing. Morison’s Pouch is one of the 4 views of the FAST exam.
References: Textbook of Pediatric Emergency Medicine 6th Edition pages 1732-1733. Edited by Gary Robert Fleisher and Steven Ludwig