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Introduction
Retinal hemangioblastoma are rare benign tumours; the exact prevalence and incidence is unknown. Hemangioblastoma typically present as globular vascular tumours in the temporal peripheral retina, but can occur throughout the retina. 1 The tumours can be sporadic or part of the hereditary multi-tumour predisposition, von Hippel-Lindau disease (vHL). It is essential to distinguish between patients with sporadic tumours and those with vHL, as the latter group is at risk of developing a variety of benign and malignant tumours including CNS hemangioblastoma, renal cell carcinoma, pheochromocytoma, and pancreatic neuroendocrine tumours. 2 3 Due to their risk of severe and life-threatening complications, patients with vHL are recommended to undergo prophylactic surveillance to ensure early tumour diagnosis and treatment. 3 For retinal hemangioblastoma, the visual prognosis is significantly better when the tumours are diagnosed while still asymptomatic compared with when they have become symptomatic. 1 In contrast, patients with sporadic retinal hemangioblastoma have no known increased risk of additional tumours, and can be spared comprehensive surveillance.
The vHL diagnosis can often be confirmed genetically, as about 95% of patients who fulfil the clinical diagnostic vHL criteria, 3 have a detectable germline mutation in the tumour suppressor gene VHL, which regulates angiogenesis through controlled degradation of hypoxia inducible factors. 2
Retinal hemangioblastoma are the first manifestation in up to 77% of patients with vHL, 1 4-8 and may be the only sign of the disease. The ophthalmologist will often be the first doctor to meet a patient with potential vHL, and plays an important role in assessing his/her likelihood of having vHL. We aimed to determine the frequency of vHL as the underlying cause of retinal hemangioblastoma and to estimate retinal hemangioblastoma incidence and prevalence in a national study.
Materials and methods
In a national retrospective cohort study, we sought to identify all Danish individuals diagnosed with a retinal hemangioblastoma between 1977 and 2014. We used the national patient register, in which all residents' healthcare system contacts are registered, 9 as well as the national vHL research database of all families examined for vHL. 10 We searched the patient register for contacts occurring between 1 January 1977 (when registration started) and 3 March 2014 using the International Classification of Disease (ICD)-8 and ICD-10 diagnostic codes. As no...