Petrous apex and subarcuate fossa maturation.

During the first year of life, the bone of the petrous apex grows rapidly. At birth, only 5 mm of bone separates the cochlea from Dorello's canal as compared to 2 cm in the adult. More than half this growth occurs during the first year of life. The subarcuate fossa is a cavity within the superior semicircular canal which reaches from the posterior fossa to the future mastoid in fetuses and nearly to the mastoid antrum in newborns. During the second year of left it is nearly obliterated to form a shallow depression or slit on the posterior aspect of the temporal bone and the variable petromastoid canal which contains the subarcuate artery and vein. Clinical petrositis of infants less that 1 year of age is rare, and provides a challenge for surgery. A case is reported and discussed.