Emilio Farfán; Oscar Inzunza; Mark Echeverría; Verónica Inostroza; Jaritza Tramolao & Natalia Sánchez

The sternal muscle is an anatomic variation characterized by the presence of an accessory muscle in the ventral thoracic wall. Its occurrence is more prevalent in anencephalic fetuses or newborns, although the underlying reason remains unclear. Anencephaly results from a failure in the neural tube closure, leading to brain tissue protrusion and subsequent degeneration. Here, we report the presence of a sternal muscle in an anencephalic newborn. A white male anencephalic newborn was dissected to expose the ventral thoracic muscular wall. Morphometric analysis of the sternal muscle was performed. We identified a bilateral sternal muscle in an anencephalic newborn, with an unusual presentation: the right hemithorax contained a simple fascicle, whereas the left hemithorax presented a double fascicle, whit the superior fascicles bifurcating again in two fascicles. All the fascicles originated from the contralateral pectoralis major muscle. Innervation and vascularization could not be determined. The findings meet the criteria to be considered an uncommon bilateral sternal muscle. We discuss possible associations between the sternal muscle and anencephaly, considering genetic components such as PAX3, CXCR4, and PCP/non-canonical Wnt pathway. This hypothesis is based on the embryologic origin of thoracic ventral muscles and the process of neural tube closure. We also propose investigating the presence of sternal muscle in adults as a potential indicator of less severe neural tube closure defects.

KEY WORDS: Muscle development; Anencephaly; Embryology.

FARFÁN, E.; INZUNZA, O.; ECHEVERRÍA, M.; INOSTROZA, V.; TRAMOLAO, J. & SÁNCHEZ, N. Relationship between neuraltubeclosuredefectsandthepresenceofsternalmuscle:Acasereportandanembryologicalhypothesis. Int.J.Morphol.,44(1):206- 210, 2026.