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Histological changes in the pituitary gland and adenomas following radiotherapy

To elucidate histological changes in the pituitary gland and adenomas following radiotherapy, two irradiated pituitary glands and seven irradiated non‐functioning adenomas were studied. The latter included four cases with conventional radiation (CR) and three cases with radiosurgery: two with gamma knife radiosurgery (GKR) and one with stereotactic fractionated radiotherapy (SRT). The specimens were obtained 10 months to 10 years (mean 58 months) after the radiotherapy. Irradiated pituitary glands showed diffuse fibrosis in the adenohypophysis, whereas irradiated adenomas showed either mild or no fibrosis in five CR/SRT cases and diffuse thick hyaline deposits in two GKR cases. No necrosis was observed. Stellate‐shaped S‐100 protein‐positive cells were greater in number in the irradiated pituitary glands than in the normal glands. Pituitary cells with dense granular reactivity for mitochondrial protein, cytochrome oxidase, and Mn‐SOD, mimicking oncocytes, were greater in number in the irradiated adenohypophysis but did not show any change in cell size. Many irradiated pituitary cells and some irradiated adenoma cells were densely positive with anticytokeratin 1,5,10,14 antibody whereas non‐irradiated counterparts were negative. In adenomas, MIB‐1 labeling index remained unchanged after the radiation. The results may indicate that radiation‐induced fibrosis was associated with an increased number of folliculo‐stellate cells, mitochondrial dysfunction, and squamous metaplasia. These findings were prominent in irradiated pituitary cells and may participate in delayed pituitary hypofunction following radiotherapy. In irradiated adenoma cells, similar findings were observed but diffuse fibrosis was absent. The histological changes were more intensive in adenomas following GKR than those following CR.