Basilar invagination in a child with atlanto-occipital subluxation and suspected prenatal Dandy–Walker malformation

Although advances in imaging have allowed earlier and more accurate diagnosis of various fetal anomalies, Dandy–Walker malformation (DWM) remains one of the more challenging central nervous system anomalies to diagnose accurately before birth. Basilar invagination (BI), which is a dislocation of the dens in an upward direction, is occasionally accompanied by Klippel–Feil syndrome (KFS). We report a pediatric case of BI caused by atlanto-occipital subluxation (AOS) in KFS, suspected of having DWM prenatally but head magnetic resonance images (MRI) showed no evidence of that at 7 months of age.

At 28 weeks of gestation, fetal MRI study revealed a small cerebellar vermis, leading us to suspect a DWM. The patient was born at 40 weeks of gestation. Head CT showed inferior vermian hypoplasia without findings of hydrocephalus. Cervicothoracic CT showed cervical lamina assimilations, thoracic hemivertebrae, and cervicothoracic scoliosis. He was diagnosed with Dandy–Walker variant and KFS. At 7 months of age, head MRI showed near normal cerebellum and vermis and there was no evidence of the DWM. He did not have intellectual or developmental delay and imaging studies were performed periodically. At 9 years of age, an already existing cough headache deteriorated. Three-dimensional reconstructed images from CT scan showed C1 hypoplasia, fusion of C1 and C2, BI, and AOS. Sagittal T2-weighted MRI showed protrusion of cerebellar tonsils inferiorly to the level of the posterior arch of C2. Serum calcium, phosphate, and parathyroid hormone levels were normal. The diagnosis was tonsillar herniation related to BI following AOS in KFS. Posterior occipitocervical fixation was performed under traction.

We found out two important clinical issues: DWM findings after birth can be disappearing and BI can present sequential deterioration because of AOS in KFS. Our observation indicated the possible prognosis of pediatric BI with long follow-up and can help us decide on its surgical treatment timing when associated with AOS.