Cervicothoracic extradural arachnoid cyst: possible association with obstetric brachial plexus palsy.

The association of cervicothoracic extradural arachnoid cysts and obstetric brachial plexus palsy has not previously been reported. We report two patients with this association. The first patient is a 9-month-old boy with left obstetric brachial plexus palsy that developed bilateral leg weakness at 6 months of age owing to compression of the spinal cord by a C6 to T8 left cervicothoracic extradural arachnoid cyst.