Evidence of posterior fossa hypoplasia in the familial variant of adult Chiari I malformation: Case report

OBJECTIVE AND IMPORTANCE: A case of familial Chiari I malformation and a review of the literature are presented. Recent posterior fossa morphological studies suggest that the sporadic variant of adult Chiari I malformation may be caused by occipital dysplasia and overcrowding of posterior fossa contents. This analysis was applied retrospectively for two of the three members of this familial variant. CLINICAL PRESENTATION: A family is described in which symptomatic Chiari I malformation occurred in two generations: monozygotic twin sisters and the daughter of one sister. The monozygotic twins developed symptoms within I year of each other, and both had associated syringomyelia. The daughter of one of the twins presented with symptomatic tonsillar herniation alone at a young age. INTERVENTION: All three family members underwent surgical decompression of the craniovertebral junction, with or without syringosubarachnoid shunting, with good results. CONCLUSION: Cases of familial Chiari I malformation are rare, although they are probably under-reported. An evaluation of posterior fossa morphology in these patients suggests that occipital dysplasia and overcrowding of posterior fossa contents may be the substrate for both familial and sporadic cases of Chiari I malformation and suggests a unifying concept of origin.