Teaching NeuroImages: platybasia and basilar invagination in osteogenesis imperfecta.

A 15-year-old girl with osteogenesis imperfecta (OI) and multiple bone fractures since early childhood presented with occipital headache. She had blue sclera and short neck (figure 1), right hypoglossal palsy, bilateral pyramidal tract signs, and gazeevoked nystagmus. Cervical MRI showed platybasia, basilar invagination, brainstem/high cord compression, and narrowing of upper cervical canal (figure 2). Cervical traction relieved headache. OI is characterized by diffuse osteopenia and bone fragility.1 Platybasia (flattening of the skull base) with secondary basilar invagination (developmental anomaly of the craniovertebral junction in which the odontoid process abnormally prolapses upward through the foramen magnum)2 in OI results from abnormally soft bone at the cranio-cervical junction and the odontoid process protruding through the foramen magnum.3 Appropriate screening may prevent severe neurologic consequences.