The second patient, a 42 year old female, underwent a frontal craniotomy in 1968 because of a suprasellar pituitary adenoma. The optic nerves and the optic chiasm were embedded in the tumour, but pre- and postoperatively the visual acuity of both eyes was normal and there were no visual field defects. Six months later radiation therapy was started, because of persistence of GH hypersecretion. The radiation schedule was 50 Gy in 2 Gy daily fractions in 42 days. Eight megavolt photons and a three-field-technique were used. Five months later, she complained about progressive visual loss, occurring within a few weeks. At ophthalmological examination the visual acuity of the left eye was 0.1 and was accompanied by a temporal hemianopsia. The visual acuity of the right eye was 1.0 with an altitudinal visual field defect in the upper quadrant. On fundoscopy there was bilateral optic atrophy. The visual field defect of the left eye did not change, but the visual acuity deteriorated gradually in a time span of 2 years to 1/60. The visual field defects of the right eye worsened in 1983 and 1988. In this eye the visual acuity changed to 0.7 in 1992 and 0.5 in 1995.
A pneumoencephalogram made in 1979 showed limited suprasellar extension of the pituitary adenoma with the optic system well demarcated in the suprasellar air thus excluding tumour recurrence. This finding strongly suggest that the visual deterioration in the left eye was due to radiation treatment. We assume by reviewing of all ophthalmologic data and exclusion of other causes, that the gradually worsening of vision in the right eye is also due to RON.
In the present series, two out of 63 irradiated patients (3.2%) developed RON. A total radiation dose greater than 50 Gy and/or a radiation fraction size greater than 2 Gy are suggested to be risk factors for RON1,9. One of the presently reported cases had a total radiation dose of 50 Gy and a radiation fraction size of 2 Gy. This would suggest the presence of other risk factors, associated with the development of RON after radiation therapy in GH-secreting pituitary adenoma. Apart from the probable risk attribu-table to vascular compromise6,9, GH-secreting pituitary adenoma as such may confer an increased risk for RON development as previously suggested1-3,5. In case 2 of the present series the optic nerves and optic chiasm were embedded in the tumour, which may have been contributed to the development of RON.
It is generally proposed, that most cases of RON occur within 18 months after radiation therapy7. Case 1 of the present series well illustrates, that late development of RON can occur, indicating that the clinician should remain alert of this complication, even many years after radiation therapy.
RON is a rare complication after external beam radiation therapy for acromegaly, which may occur after a considerable latency period.