Human temporal bone study on the postnatal ossification process of auditory ossicles.

Abstract

OBJECTIVE: In infancy the head of the malleus and body of the incus normally contain bone marrow, which is gradually replaced by bone and converted into vascular channels with age. This study was carried out to clarify the age at which ossification of the ossicles is complete and to examine factors influencing the ossification process. STUDY DESIGN: Human temporal bone sections from 32 infants and children with or without congenital anomalies, aged 1 day to 9 years, who were born at term were studied. METHODS: The percentage bone marrow area occupying the head of the malleus and body of the incus was calculated in three horizontal temporal bone sections for each case, using computer-aided digital processing of images. RESULTS: Bone marrow was observed in both the malleus and incus in children until 25 months of age, while after the age of 25 months no bone marrow tissue was present in either of the ossicles. It appeared that the bone marrow space disappeared somewhat earlier in the malleus than in the incus. The bone marrow space around the otic capsule disappeared much earlier than that within the ossicles. The age at completion of ossification was correlated with neither the presence of congenital anomalies nor the presence of residual mesenchyme in the middle ear. CONCLUSIONS: Ossification of the ossicles seems to occur steadily throughout fetal life and after birth during development of the middle ear. Although the clinical significance of postnatal residual bone marrow within the ossicles is not known, it possibly plays a role as a blood-forming organ in early infancy.