[Natural history and staging of brain metastases]

Intracranial metastases represent 7-17% of all brain tumours, their incidence at autopsy varying between 5.8 and 22% in different series. The neoplasms most commonly metastasizing to the brain are those of lung, breast, renal and skin (melanoma) origin. In two-thirds of cases, intracranial metastases are located within the brain parenchyma, while the remaining third involves the pachymeningeal envelopes. Leptomeningeal metastases are rare and develop mainly from leukemia, lymphomas and breast carcinoma. The route of spread to the central nervous system is usually hematogenous but occasionally direct involvement from adjacent bone or pachymeningeal metastases can occur. Median survival from clinical presentation usually doesn't exceed a few months. However brain metastases are the cause of death only in about 15% of patients. This is probably due because they occur late in the course of the natural history of the disease, when metastatic deposits in other viable organs have already developed. Due to this reason, systematic assessment of metastases to the brain is not advisable in all patients but it should be restricted to symptomatic patients and to asymptomatic patients affected by small cell carcinoma and adenocarcinoma of the lung, who could benefit from prophylactic brain irradiation. In symptomatic patients, plain skull X-ray, electroencephalography and computed tomography represent appropriate diagnostic tools to provide accurate informations about number, size, site and morphological characteristics of brain metastases.