Rare Cause of Congenital Unilateral Facial Palsy: High-Resolution Computed Tomography (HRCT) Findings of Isolated Facial Canal Hypoplasia and Aplasia.

Congenital facial nerve palsy (CFNP) is an uncommon medical condition conventionally grouped into acquired (traumatic) and developmental (isolated or syndromic) categories depending on the cause. Distinction between the two etiological mechanisms is mandatory for determining further prognosis and selecting the treatment method. High-resolution computed tomography (HRCT) of the temporal bone currently remains the gold-standard diagnostic technique used to examine the complex osseous architecture of the Fallopian canal and reveal congenital abnormalities. In this report, we describe the case of a four-year-old girl who had right-sided congenital facial nerve palsy in the form of asymmetric facies and deviation of the angle of the mouth to the left side since birth. Her perinatal history was unremarkable, with no evidence of birth trauma or prolonged labor. To rule out anatomical anomalies, HRCT of the temporal bones was performed. The study revealed a selectively hypoplastic labyrinthine segment of the right facial canal, progressing to severe hypoplasia and complete aplasia of the tympanic and mastoid segments. Notably, the adjacent middle ear ossicles, bony labyrinth, and contralateral temporal bone structures were entirely normal, ruling out broader syndromic association. Isolated congenital agenesis and hypoplasia of the facial nerve canal, without associated external, middle, or inner ear anomalies, is an extremely rare embryological aberration causing CFNP. This case clearly illustrates the key role of HRCT in establishing a definitive diagnosis of developmental facial palsy, thereby preventing unnecessary surgical decompressions and guiding parental counseling.