The Nelson Syndrome: A Reappraisal

The historical definition of Nelson syndrome is the association of a large corticotroph adenoma arising after total bilateral adrenalectomy (TBA), associated with high ACTH levels. Whether TBA accelerates tumor growth is not demonstrated. Today small corticotroph adenomas can be detected using pituitary MRI, and their progression can be closely monitored. Fast- and slow-growing tumors have been reported, and the delay between adrenalectomy and the corticotroph tumor progression is also variable, usually within the first 3 years. The high level of ACTH following TBA is the best validated factor predicting corticotroph tumor progression. The corticotroph tumor progression does not seem accelerated during the pregnancy. Complications are either related to the treatment - mainly pituitary failure -, or to the tumor burden. Surgery and radiotherapy can control the corticotroph tumor progression in a majority of situations. TBA is very efficient to control the deleterious hypercortisolism, but the exact indications remain to be determined. Prolonged follow-up is necessary.