[A case of intrathoracic perineurial cyst].

A 67-year-old man was referred to our surgical clinic for evaluation of an abnormal shadow on the chest X-ray examination. CT scan and MRI revealed a tumor in the posterior mediastinum and destruction of the pedicle and intraspinal invagination by the tumor. The tumor in a paravertebral area are linked with a vertebral canal through a destructed intervertebral foramen. MRI showed that the tumor was a cyst which contained fluid. On thoracotomy a hen's egg sized cyst was found in the posterior mediastinum, the cyst was excised. Pathological diagnosis was a perineurial cyst. This case was clearly differentiated from an intrathoracic meningocele and a neurilemmoma microscopically. This case is the first intrathoracic perineurial cyst in Japan.