Manejo Metastasis Cerebrales

Leibel and Phillips Textbook of Radiation Oncology – Chapter 21 RT of CNS
BRAIN METASTASES Epidemiologic Statistics
Metastases to the brain occur in as many as 30% of patients with systemic cancer and outnumber primary brain tumors by 8 : 1. In the United states, approximately 170,000 cancer patients are expected to develop brain metastases every year.[95] Brain metastases exert a profoundeffect on the quality and length of survival, and despite the best current management, they represent the direct cause of death in one third to one half of affected patients.[96] Although brain metastases can arise from any primary cancer, certain tumors such as melanoma and carcinomas of the lung (especially small cell and adenocarcinoma), breast, and kidney have a propensity to metastasize to thebrain.[95] Approximately one half of patients present with only a single lesion, and an additional 20% have only two. Most brain metastases, particularly those that arise from primary sites other than the lung, occur at a late stage when metastatic dissemination is present elsewhere in the body.
Anatomy
Brain metastases arise from hematogenous spread to the white matter of the watershed area ofthe brain at the junction of the gray and white matter. Most metastatic tumors distribute themselves between the supratentorial and infratentorial compartments in proportion to the relative weight and blood supply of these structures; that is, 85% in the cerebral hemispheres, 10% to 15% in the cerebellum, and 1% to 3% in the brainstem.[97] Certain metastatic tumors, particularly small cell lungcancer and tumors arising in the prostate, uterus, or gastrointestinal tract, have a predilection to the cerebellum.
Most brain metastases grow as spherical, well-demarcated, solid masses that displace rather than destroy adjacent tissue. They may be surrounded by minimal to extensive edema. Some rapidly growing metastases undergo central necrosis or cystic change, and others, especially those frommelanoma, choriocarcinoma, and testicular carcinoma, may be hemorrhagic. Carcinomatous meningitis is a clinical syndrome caused by widespread invasion of the cerebral cortex by small or microscopic foci of tumor that may or may not be seen on imaging studies.[95]
Pathologic Conditions
The microscopic appearance of a brain metastasis resembles the primary tumor from which it arises. Thus, inpatients with an unknown primary cancer, extirpation of the metastasis with microscopic examination often provides an important clue as to the original site of the primary tumor.[96]

Clinical Presentation
The most common presenting signs and symptoms are summarized in Table 21-2. They usually begin insidiously and evolve over a period of days or a few weeks. The spread of edema through the whitematter frequently determines the speed of onset and progression of signs and symptoms.[95] Hemorrhage into a tumor may cause a more sudden onset or acute worsening of symptoms.
Diagnostic Studies
Gadolinium-enhanced MRI is the best diagnostic test for brain metastases.[98] MRI can detect small lesions not seen on CT, particularly in the cerebellum and brainstem. The T2-weighted image reveals anarea or areas of hyperintensity in the white matter, encompassing both the tumor and surrounding edema.
Although the clinical history combined with the results of MRI establish the diagnosis of brain metastasis with reasonable certainty, a definitive diagnosis of metastatic brain tumor cannot be made on scan results alone. Even a typical radiographically defined lesion may prove to be a primarytumor, an abscess, or another lesion.[98] A known systemic cancer increases the likelihood of brain metastases, and multiple lesions make the diagnosis even more likely. However, if doubt exists, a biopsy is required to establish the correct diagnosis.
Grouping
Although no generally accepted grouping system exists for brain metastases, one was proposed by investigators from the RTOG based on a...