Unilateral Grade 3 Microtia: An Anatomical Case Correlating Branchial Arch Embryology, Genetics, and Clinical Implications

Microtia is a spectrum of congenital auricular malformations ranging from mild hypoplasia to complete absence of the external ear. Grade 3 microtia (“peanut ear”) is characterized by a small lobule-type remnant with poorly formed or absent auricular subunits and is commonly associated with external auditory canal (EAC) atresia and conductive hearing loss. We report the case of a 7-year-old male child with unilateral right-sided Grade 3 microtia and EAC atresia, in whom the malformed lobular remnant and absent helix, antihelix, scapha, and tragus illustrate selective loss of first- and second-arch derivatives. The case is correlated with the normal development of the external ear from first and second branchial arch hillocks and failure of first-groove recanalization and is discussed in the context of known genetic factors such as HOXA2 and HMX1 and reported environmental risks. This anatomically detailed presentation, with a normal contralateral ear as internal control, provides a practical model for teaching branchial arch anatomy of the external ear, while briefly outlining key clinical implications for hearing and reconstruction.