Incidence of brain tumours in two English counties: a population based study

Objective-To define the incidence of brain tumours in Devon and Cornwall an d to discover which case finding methods are the most fruitful. To examine what happens to patients after the diagnosis of a brain tumour. Methods-The primary method of case ascertainment was a review of all CT wit h contrast and MRI of the head performed on the population of Devon and Cor nwall between 1 April 1992 and 31 March 1997. Secondary sources included re gistrations with the South and West Cancer Intelligence Unit and a search f or all patients either admitted to hospital with a brain tumour or operated on for a brain tumour during the same period. Results-16 923 scans were reviewed of which 8774 (52%) were normal. The sca n review found 2483 incident intracranial tumours, of which 861 were metast ases. Secondary sources of case ascertainment disclosed 46 further cases. C ases were missed by the scan review mainly for technical reasons and only t hree patients were found who were diagnosed by nonimaging methods. The inci dence of primary intracranial tumours standardised to the population of Eng land and Wales was higher than any previously reported (21.04 (17.18-25.62) /100 000 person-years). Overall, 21% of cases were not admitted to hospital . The categories least likely to be admitted were those with sellar and cra nial nerve tumours. Those not admitted to hospital were significantly older than those who were. Conclusion-One fifth of patients are not admitted to hospital after the dia gnosis of a brain tumour and incidence studies must use case finding method s which will capture these cases. An audit of imaging results provides almo st complete case ascertainment. This study shows that the incidence of prim ary brain tumours is considerably higher than previously thought. Official figures from the cancer intelligence units significantly underestimate brai n tumour incidence, especially for benign tumours.