Unilateral pes cavus caused by a thoracic intradural arachnoid cyst

Spinal arachnoid cysts (SAC) are rare causes of spinal cord compression. They can be found intra- and more often extradural. In a relationship of 2:1 intradural SAC are located in the posterior or anterior part of spinal canal, most in the area of thoracic spine. SAC can be idiopathic and congenital or the result of trauma or arachnoiditis. Their clinical picture varies between asymptomatic cases and symptoms typical for spinal cord compression. We report on an 8-year-old girl with a progredient, non congenital pes cavus (varus adductus) on the right side. Neurologic examination shows no pathologic findings. In MRI of spine a formation between the first and seventh thoracic vertebrae with a signal intensity like CSF was seen. It was located dorsal to spinal cord and lead to a shifting of spinal cord in a ventral position. By post myelography CT an arachnoid cyst with communication to spinal canal was assumed. The girl was operated by fenestration of the cyst to prevent further neurologic symptoms and progression of foot deformity. Because of skeletal fixation a reversal of pes cavus can not be expected. Probably an orthopedic surgical procedure will be necessary after puberty. Keywords: spinal arachnoid cyst, pes cavus, post myelography CT