[Anatomo-radiologic correlations in spontaneous hematoma of the rectus abdominis muscles]

Rectus sheath hematomas are a frequent but sometimes misdiagnosed disease in patients under anti-coagulative drugs, hemodialysis, or simply in the elderly. The most frequent localization is in the lower part of the abdomen: the explanation lies in the anatomy of the abdominal wall, especially in the arcuate line of the rectus sheath. Aim of this work is to explain the reason of the almost constant location correlating the anatomy with the CT features.

The rectus abdominis muscle lies between the aponeuroses of the transverse and oblique muscles which form the so called rectus sheath. This arrangement is found from the costal arch to a level approximately between the umbilicus and the pubic symphisis, where the rear layer of the rectus sheath ends with a curved edge, called the arcuate or semicircular line of Douglas. Beneath this line the aponeuroses of the three muscles pass in front of the rectus which is separated from the peritoneum only by the fascia trasversalis, a thin connective layer between the rectus and the preperitoneal fat. In this lower aspect of the muscle the perforating branches of the inferior epigastric artery running in the preperitoneal fat may rupture causing a large hematoma widely spreading in this loose space.

11 cases of rectus sheath hematoma diagnosed over 5 years were reviewed. They were referred to US because of a rapidly growing palpable mass or painful swelling of the abdominal wall with acute anemia. Sonography was performed in 11 patients and CT in 7.

10 hematomas were located in the lower third of the rectus muscle below the arcuate line in the pelvis, 1 was in the upper third of the muscle: the vast majority of pelvic hematomas is easily accounted for by the peculiar anatomy of the region.

The diagnosis of hematoma of the rectus abdominis, sometimes misleading, should be included as a differential in all the patients who present with acute abdominal pain and blood loss. The anatomy of abdominal wall correlates well with CT findings and explains the reason why most hematomas are found in the lower third of the muscle.

The diagnosis, whether clinical or based on imaging findings, needs accurate pathoanatomic knowledge of the anterior abdominal wall. Once the diagnosis has been confirmed (by US or CT) patients should be treated conservatively as those that are operated are at risk of developing complications, mainly hemorrhagic.