Physiological pelvic intraperitoneal fluid refers to the presence of a small volume of free fluid in the pelvis, particularly the pouch of Douglas. It occurs in young females of reproductive age and can be a mimic of traumatic free fluid in abdominal trauma.
Unfortunately, pelvic free fluid may be the only sign of traumatic bowel or mesenteric injury.
In the trauma patient, free pelvic fluid isolated to the pouch of Douglas that is low in density (below 15 HU) and does not extend more superiorly than the S3 body can be regarded as non-traumatic in nature 1.