Prevalence And Variations Of The Pyramidalis Muscle In Adults And Fetuses: Relevance And Clinical Implications

Abstract

Introduction: The pyramidalis muscle is a triangular shaped muscle that is located in the anterior abdominal wall, which originates from body of pubis and pubic symphysis and inserted into linea alba. The close relationship of pyramidalis with the rectus abdominis muscle has led to the belief that it develops embryologically as a doubling over the rectus abdominis muscle in the ventral portion.

Methods: Thirty-one adult cadavers (26 male and 5 female, embalmed in 10% formalin) and 30 fetuses (14-first trimester, 10-second trimester, and 6-third trimester; embalmed in 10% formalin) were dissected in the present study.

Results: The prevalence of muscle was found to be 87% in adult and 100% in fetus. In 77% of adult cadavers the muscle was present bilaterally and in 10% of adult cadavers the muscle was present unilaterally. In fetuses the muscle was present bilaterally. Few variations related to size and appearance of muscle were observed in both adult and fetus pyramidalis muscle.

Conclusions: The prevalence of pyramidalis muscle was 100% in fetus, whereas in adult it was 87%. The regression of muscle may be the reason behind this difference. In monkeys and prosimians, the pyramidalis tense the abdomen for compression of glands, helping in the expression of milk. Therefore it is speculated the pyramidalis muscle is atavistic owing to the loss of supernumerary nipples in humans.

The calculated Pyramidalis-pubo umbilical index was proportionately more in fetus than the adult pyramidalis muscle.