Morphological effects in pituitary tumours following radiotherapy.

Seven cases with different endocrinological types of pituitary tumours were subject to open surgery 6-25 years after fractionated and 2 months - 9 years after single dose irradiation. Two cases had been treated with both types of irradiation. Tumour tissue was analyzed at the light and electron microscopic levels. Hyalinization around blood vessels occurred independent of type of irradiation but required some time to develop. This was not found in one tumour analyzed 2 months after single dose treatment. Single dose treatment (30-70 Gy) caused extensive fibrosis and few surviving cells in the primary target area. Tumours treated with fractionated dose irradiation (26-45 Gy) showed a large number of tumour cells present 6-8 years after treatment. Many of these cells revealed morphological damage. The morphological findings of the presently available material may indicate that a single dose treatment causes rapid and extensive tumour damage at the site of the primary target but that surviving tumour cells are present outside this area. Fractionated irradiation results in an initial dysfunction with persistence of more or less structurally altered cells for several years.