Pathogenesis of arachnoid cyst: congenital or traumatic?

For clarifying the pathophysiology of arachnoid cysts and reestablishing therapeutic criteria for such cases, we reviewed a series of 90 cases with arachnoid cysts focusing on the traumatic origin. Arachnoid cysts of congenital origin have been well known. But we suspected that 14 out of 90 patients (15.6%) with arachnoid cyst were closely related to head trauma. Seven of them suffered from head traumas in infancy. The episodes of head trauma included falling down in 4 patients, slipping down in 2 patients, and a motor vehicle accident in 1 patient. Traumatic arachnoid cysts had a latent period from head trauma to initial clinical manifestation. The mean latent period was 2.2 years, ranging from 10 months to 6.2 years. Six of 7 arachnoid cysts were located in the suprasellar area and 1 at the posterior fossa. An other 7 patients had a history of perinatal trauma. We postulate that head trauma in infancy may contribute to the pathogenesis of arachnoid cyst in some cases.