Radiation-induced nerve root degeneration and hypertrophic neuropathy in the lumbosacral spinal cord of rats: the relation with changes in aging rats.

Three-month-old WAG/Rij rats were irradiated with 300 kV X-rays on the lumbar region of the spinal column with doses below the level for causing paralysis due to radiation radiculomyelopathy. 8--9 months after irradiation, degeneration of predominantly the ventral nerve roots of the cauda equina was boserved. Three stages were distinguishable: I) Demyelination and proliferation of Schwann cells; II) Local swelling of ventral nerve roots, with concentric layers of Schwann cells resembling hypertrophic neuropathy; III) Malignant Schwannoma, invading roots and spinal cord. It is concluded that the degenerative and proliferative lesions represent a continuous series of stages of slowly progressive lesions. The ventral nerve root degeneration (1st stage) is similar to that observed in aging, unirradiated rats, normally developing at the age of 18--20 months.