Introduction

Brain metastases are the most common intracranial tumors among adults, with a reported incidence of 20–40% in patients with cancer. In descending order, lung, breast, malignant melanoma, renal, and gastrointestinal are the most common tumors giving rise to brain metastases. Metastases can be single, solitary, or multiple. “Single” metastases refers to the presence of only one brain metastasis and implies nothing about the extent of cancer that may or may not be present elsewhere; “solitary” refers to a single metastasis that is the only known site of metastatic cancer in the body; and “multiple” refers to the presence of more than one metastasis and makes no distinction regarding the presence of systemic cancer. Approximately two-thirds to three-quarters of patients with brain metastases have multiple lesions. Single metastasis is more common with breast, renal, and colon cancer. Multiple lesions are more commonly seen with malignant melanoma and lung cancer.

This chapter will address the pathophysiology, clinical features, radiographic diagnosis, and treatment of brain metastases.

Pathophysiology

Intracranial metastases may involve the brain parenchyma, the blood vessels (including the dural sinus), the cranial nerves, the dura, the leptomeninges, and the inner table of the skull (Figure 58.1). Most brain metastases are the result of hematogenous spread, usually through the arterial circulation, and are distributed throughout the brain in proportion to the cerebral blood flow, with approximately 80% being located in the cerebral hemispheres, 15% in the cerebellum, and 5% in the brain stem.