Infantile Arachnoid Cyst Compressing the Sacral Nerve Root Associated with Spina Bifida and Lipoma

A 2-year-old boy presented with a rare sacral arachnoid cyst manifesting as gait disturbance. Neuroimaging revealed an intradural cyst in the sacral nerve root sheath associated with spina bifida occulta and a lipoma at the same level. At surgery, the conus medullaris was situated at the L-1 level and not tethered. The highly pressurized arachnoid cyst had exposed the dural sheath of the left S-2 nerve root and compressed the adjacent nerves. An S-2 nerve root pierced through the cyst. There was no communication between the cyst and spinal arachnoid space.