Congenital malformed posterior arch of atlas with fusion defect: a case of developmental canal stenosis causing cervical myelopathy.

Congenital anomalies of the posterior arch of the atlas (PAA) are usually asymptomatic and diagnosed incidentally. Very rarely, they present with cervical myelopathy, usually being associated with partial aplasia or agenesis of PAA. We describe a 44-year-old lady with cervical myelopathy secondary to a malformed PAA with developmental atlas-level spinal stenosis and a congenital posterior fusion defect with persistent midline cleft showing significant non-osseous fibro-cartilaginous hypertrophy, causing critical cord compression. Spinal decompression by en-bloc wide excision of anomalous arch with occipito-cervical fusion was performed. Post-operatively, the patient's neurology improved gradually over 12 months, with radicular symptoms being the earliest and gait disturbance being the last symptom to resolve. At 24 months, she was asymptomatic with imaging showing good spinal cord decompression at the level of atlas. Developmental atlas stenosis with hypertrophic posterior arch fusion defect is an unusual cause of cervical myelopathy, which can be effectively treated with decompression with/without stabilization. Being aware of such an entity can avoid diagnostic dilemma and facilitate prognostication of outcomes, accurate surgical planning in the stenotic segment thereby ensuring effective management of these patients.