Introduction

Brain (ICD-9 191) and nervous system (ICD-9 192), cover a range of neoplasms arising from glial tissue and the meninges.

Histology, classification and diagnosis

Histological classification is based on the presumptive cell of origin (Rubinstein, 1972), but there are often diagnostic difficulties in determining type. Glial tumors show wide variations in aggressiveness, some being highly malignant whereas others grow relatively slowly. There are also differences in the age distribution of the various histological types, medulloblastoma being found exclusively in children (Table 51.1 and 51.2). Signs and symptoms depend on the size, rate of growth and anatomical location of the tumors. Clinically, tumors of the meninges and brain may present with similar findings, so that earlier statistics on different types may be biased. While glial tumors never metastasize, many other tumors frequently metastasize to the brain, notably bronchogenic carcinoma, and breast cancer in females. Metastases may also be present in the bones of the skull and vertebral column and thus indirectly mimic CNS lesions.

The availability of medical care clearly influences the likelihood of diagnosis, and in the past intracranial tumors were underdiagnosed. A full autopsy is often necessary for accurate diagnosis. Given the difficulty of obtaining biopsy material there may be an element of uncertainty about the diagnosis in several registries. Newer imaging procedures should increase the accuracy of registration statistics. Helseth et al. (1988) provide an excellent discussion of these problems.