ABSTRACT
EPIDEMIOLOGY Germ cell tumours of the nervous system (Table 38.1) are the morphological homologues of germinal neoplasms arising in the gonads and other extragonadal sites.65 There is considerable geographical variation in the incidence of these uncommon lesions, which occur at highest frequency among Far East Asians.35,50,82 In Western series, they collectively account for no more than 0.5 per cent of all primary intracranial neoplasms and approximately 3.0 per cent of those that are discovered in childhood and adolescence (the periods of greatest risk).6,10,22,26 By contrast, germ cell tumours constitute at least 2 per cent of all primary intracranial neoplasms and up to 15 per cent of paediatric examples in Taiwan and Japan, where they are most prevalent.21,35,40 One outlying analysis of tumor registries in Japan and the United States, however, documented similar incidence rates.43 A significantly increased incidence has also been noted in Koreans, children being preferentially affected.36,82 In fact, 90 per cent of these tumours
involve subjects below the age of 20 years (most occurring in the second decade) and case rates peak in 10-12 year olds.6,10,21,22,40,42,74 Congenital examples (typically teratomas) account for more than half of all fetal brain tumours,60,65 and exceptional cases come to attention in late adulthood.26 All sites considered, the male/female ratio is at least 2-2.5:1, but the sex distribution of central nervous system (CNS) germ cell tumours varies by region: a great excess of pineal examples affects boys, whereas girls predominate among patients with suprasellar lesions. Sex differences are also apparent in the distribution of histological subtypes: a male/female ratio of 1.5-2:1 for germinomas increases to over 3:1 for non-germinomatous tumour subtypes in some series.6,21,22,42,73
Pure germinomas are most frequently encountered, followed by mixed germ cell tumours and teratomas.6,10,21,22,34,42,67,73,74 One large series yielded the following percentages by histological subtype: germinomas, 41.1 per cent (including those with syncytiotrophoblastic giant cells, which accounted for 5.2 per cent of all cases); mixed germ cell tumours, 32 per cent; teratomas, 19.6 per cent (63.3 per cent of these being mature, 23.3 per cent immature and 13.3 per cent showing malignant transformation); embryonal carcinomas, 3.3 per cent; choriocarcinomas, 2 per cent; and yolk sac tumours, 2 per cent.42
