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Gamma knife stereotactic radiosurgery of Nelson syndrome

¹ Department of Neurosurgery, Haukeland University Hospital, 5053 Bergen, Norway² Section for Endocrinology, Department of Medicine, Haukeland University Hospital, Bergen, Norway³ Centre for Clinical Research, Haukeland University Hospital, Bergen, Norway⁴ Department of Ophthalmology, Haukeland University Hospital, Bergen, Norway⁵ Institute of Surgery, University of Bergen, Bergen, Norway⁶ Institute of Medicine, University of Bergen, Bergen, Norway⁷ Department of Clinical Medicine, University of Bergen, Bergen, Norway⁸ Department of Biomedicine, University of Bergen, Bergen, Norway⁹ Department of Endocrinology, Internal Medicine, Norwegian National Hospital, Oslo, Norway

(Correspondence should be addressed to E O Vik-Mo who is now at Department of Neurosurgery, Ulleval University Hospital, 0407 Oslo and Institute for Surgical Research, Norwegian National Hospital, 0027 Oslo, Norway; Email: e.o.vik-mo{at}medisin.uio.no)

Objective: Gamma knife radiosurgery (GKR) can be used as primary or adjuvant therapy for the treatment of an ACTH-producing pituitary tumor after bilateral adrenalectomy, called Nelson syndrome (NS). We have examined the effect of GKR on tumor growth and ACTH-hypersecretion, and characterized the adverse events of this treatment in patients with NS.

Design: Cross-sectional follow-up study. First, retrospective data pre- and post-GKR were collected. Patients then underwent a predefined survey including radiological, endocrinological, ophthalmological, and neurosurgical evaluation.

Subjects: Ten patients treated with GKR for NS after previous bilateral adrenalectomy. The mean follow-up was 7 years. No patient was lost to follow-up.

Results: Tumor growth was stopped in all patients. The ACTH levels declined in eight patients, and normalized in one patient. There was a significant drop in ACTH levels, with a half-time of 2.8 years. No patient developed visual field defects or any other cranial nerve dysfunction as a result of treatment. Four patients started hormone substitution therapy during the follow-up period. The substitution therapy of three pituitary axes present at GKR treatment could be stopped during the same period. One patient developed a glioblastoma in the left parieto-occipital region 14 years after GKR, far from the field of treatment. As the radiation level was below 1Gy to this area, it is unlikely that the GKR treatment itself induced the malignant tumor.

Conclusion: In patients with NS, GKR is an effective adjuvant treatment, carrying relatively few adverse effects. Although the risk of developing a secondary neoplasia after GKR is present, it is probably extremely low.