Which of the following is NOT a recognised cause of ACQUIRED micrognathia?

Correct answer: A. Infection of the inner ear

• A. CORRECT — this is the exception. The INNER EAR (cochlea and vestibular apparatus) sits within the petrous temporal bone and has NO anatomic continuity with the temporomandibular joint. Inner ear infection produces vertigo and sensorineural hearing loss, but it does not reach the condyle and therefore cannot damage the mandibular growth centre.
• B. TRAUMA to the TMJ in a growing child is the single most common cause of acquired micrognathia. Condylar fracture or intracapsular haemorrhage leads to ANKYLOSIS and loss of the condylar growth site, producing a small, retruded mandible with an antegonial notch.
• C. MASTOIDITIS is a direct extension of middle ear infection into the mastoid air cells, adjacent to the joint, with the same potential for TMJ involvement and growth arrest.
• D. MIDDLE EAR infection (otitis media) lies immediately posterior to the TMJ, separated only by a thin plate of bone. Suppurative middle ear infection can spread directly into the joint, causing septic arthritis and subsequent ankylosis — a well-documented cause in the pre-antibiotic era.

Note: Separate CONGENITAL micrognathia (Pierre Robin sequence, Treacher Collins, hemifacial microsomia — present at birth) from ACQUIRED micrognathia (condylar trauma, TMJ infection, juvenile idiopathic arthritis, irradiation of the condyle in childhood).