Paraplegia induced by mild trauma in a child with thoracic spinal arachnoid cyst

•Acute onset of symptoms from spinal arachnoid cysts are rare.•Progressive symptoms from spinal arachnoid cysts require surgical intervention.•Relatively innocuous trauma can be a nidus for progression in asymptomatic lesions.

Spinal arachnoid cysts are rare entities that often present with progressive myelopathy and are treated via surgical excision and fenestration. The acute onset of symptoms from these lesions is not well described in the literature. We report an 18-month-old child with acute onset of paraplegia following a mild trauma, who was found to have a compressive dorsal thoracic intradural spinal arachnoid cyst and emergently treated via surgical decompression and cyst resection. After several months of physical therapy the child achieved meaningful neurologic recovery. Spinal arachnoid cysts can cause acute decompensation in children with serious neurological injury following mild trauma, this risk should be weighed when managing asymptomatic lesions.