Psoas haematomas can occasionally occur after trauma, where a build up of blood occurs in the retrofascial space. The psoas muscles are placed posterior to the transversalis fascia, so technically sits outside the peritoneum.
Psoas haematoma is usually associated with direct blunt trauma to the back and flank. They can be associated with a large degree of haemorrhage which is clinically difficult to detect, due to the retrofascial site of the haemorrhage. It is recommended that the patient's haemoglobin level be monitored for at least 2 days post trauma1, as a large amount of blood can be lost within this large muscle.
Injuries associated with psoas haematoma include ureteral compression and nerve compression. In these cases, operative decompression would be undertaken. Usually, conservative monitoring is the treatment of choice.
In this patient, note the bulky right psoas muscle which is much more heterogeneous in comparison the left sided psoas. This is due to the extravasation of blood from the original traumatic event.
Case contributed by A/Prof. Pramit Phal.