Asymptomatic tonsillar herniation in a neonate with cleidocranial dysplasia.

A male neonate was antenatally diagnosed with cleidocranial dysplasia on the basis of prenatal ultrasound findings and molecular testing of the RUNX2 gene. The patient presented with urosepsis at 24 days of life and subsequently developed apneas after endoscopic examination of the vocal cords. Computed tomography and MRI studies of the head revealed crowding of the posterior fossa with tonsillar and uncal herniation. Apneas were initially thought to be related to brainstem compression; however, the patient responded immediately to caffeine and subsequently stabilized with antibiotic therapy. To our knowledge, this is the first published MRI study of the brain of a neonate with cleidocranial dysplasia to demonstrate the striking posterior fossa findings seen secondary to the reduced bony skull structures. However, despite the dramatic herniation, brainstem function was not compromised.