Micrognathia [K07.0] & Retrognathia [K07.0] , small jaw or retracted. Dfferentiate: Micrognathia [K07.0]: overall reduced size of mandible (lower jaw) and Retrognathia [K07.1]: decreased jaw size in the horizontal branch only; receding chin. Specify type of anomaly (Micro or retro-gnathia) and-Severity (severe or mild).
The ICD10 classified it outside from the chapter XVII with other malformations of branchial arches [K07.1 e K07.2] because the jaw is derived from the inferior branch of the first branchial arch.
That is why, ICD10 includes in the chapter XVI otocephaly [Q18.2] as other anomaly of brachial arches.