RESUMO
Introduction Metastatic tumours are the most common neoplasms seen in the central nervous system (CNS) and continue to be the major systemic cause of cancer morbidity and mortality. The survival of metastasis in the CNS depends upon interaction between tumour cells and brain microenvironment during its development at this new site. Macroscopic features and corresponding radiological findings can be diagnostic in majority of cases. However, microscopic evaluation could be necessary when the differential diagnosis includes a primary CNS tumour or a primary tumour of unknown origin. The first step in the diagnosis of a metastatic brain lesion is to exclude a primary CNS tumour. Although general approach to a metastatic lesion from an unknown primary tumour is the same everywhere else, there are slight variations for the metastatic lesions in the CNS. Additional studies like immunohistochemical stains may be useful. Aim To evaluate the clinicopathological features of metastatic deposits in CNS and to differentiate them from primary CNS lesions. Materials and Methods Out of 4500 specimens, 112 were CNS biopsy specimens of which 64 were benign and 48 were malignant; 18 of them were CNS metastatic deposits. Haematoxylin and eosin (H&E) stained sections of these lesions were studied for their morphological features. When morphological features were not enough to establish definitive diagnosis, immunohistochemical stains were applied to arrive at a definite diagnosis. Diagnostic approach to CNS metastasis, immunohistochemical assessment of neoplasm of unknown primary (NUP) and primary CNS lesions entering in the differential diagnosis of metastases were analysed. Results Most CNS metastatic deposits in our study were adenocarcinomas from aerodigestive tract. Conclusion In the diagnosis of CNS metastatic lesions, the exclusion of the primary CNS tumour falling in the various differential diagnoses considered is the most important step followed by identification and verification of the site and type of unknown primary tumour.