BASILAR INVAGINATION IN OSTEOGENESIS IMPERFECTA AND RELATED OSTEOCHONDRODYSPLASIAS - MEDICAL AND SURGICAL-MANAGEMENT

Osteogenesis imperfecta (OI) is a heritable disorder of bone developme nt caused by defective collagen synthesis. Basilar invagination is an uncommon but devastating complication of this disease. The authors pre sent a comprehensive strategy for management of craniovertebral anomal ies associated with OI and related osteochondrodysplasias. Twenty-five patients with congenital osteochondrodysplasias (18 OI, four Hajdu-Ch eney syndrome, and three spondyloepiphyseal dysplasia) and basilar inv agination were evaluated between 1985 and 1995. The male/female ratio in this cohort was 1:1. The mean age at presentation was 11.9 years (r ange 13 months-20 years). Fourteen patients (56%) presented during ado lescence (11-15 years of age). Symptoms and signs included headache (7 6%),lower cranial nerve dysfunction (68%), hyperreflexia (56%), quadri paresis (48%), ataxia (32%), nystagmus (28%), and scoliosis (20%). Fou r patients (16%) were asymptomatic. Seven (28%) had undergone previous posterior fossa decompression; one had also undergone ventral decompr ession. Imaging findings included basilar invagination (100%), ventral brainstem compression (84%), hydrocephalus (32%), hindbrain herniatio n (28%), and syringomyelia/syringobulbia (16%). Patients with hydrocep halus underwent ventricular shunt placement. Reducible basilar invagin ation (40%) was treated with posterior fossa decompression and occipit ocervical fusion. Those with irreducible ventral compression (60%) und erwent transoral-transpalatopharyngeal decompression followed by occip itocervical fusion. All patients improved initially. However, basilar invagination progressed radiographically in 80% (symptomatic in 24%) d espite successful fusion. Prolonged external orthotic immobilization w ith the modified Minerva brace afforded symptomatic improvement and ar rested progression of the deformity. The mean follow-up period was 5.9 years (range 1.1-10.5 years). Ventral brainstem compression in OI sho uld be treated with ventral decompression, followed by occipitocervica l fusion with contoured loop instrumentation to prevent further squamo occipital infolding. Despite fusion, however, basilar invagination ten ds to progress. Prolonged immobilization (particularly during adolesce nce) may stabilize symptoms and halt further invagination. This study represents the largest series to date addressing craniovertebral anoma lies in OI and related congenital bone softening disorders.