Primary Brain Lymphomas
Primary brain lymphomas originate in neural tissue and are usually B-cell tumors. Diagnosis requires neuroimaging and sometimes CSF analysis (including Epstein-Barr titers) or brain biopsy. Treatment includes corticosteroids, chemotherapy, and radiation therapy.
Incidence of primary brain lymphomas is increasing, particularly among immunocompromised patients and the elderly. Lymphomas tend to infiltrate the brain diffusely, often as multicentric masses adjacent to the ventricles, but may occur as solitary brain masses. Lymphomas may also occur in the meninges, uvea, or vitreous humor. Most are B-cell tumors, often immunoblastic. The Epstein-Barr virus may contribute to development of lymphomas in immunocompromised patients. Most patients do not develop subsequent systemic lymphoma.
MRI can suggest the diagnosis. MRI may be unable to distinguish cerebral toxoplasmosis (which is common among patients with AIDS) from lymphoma.
If there are meningeal signs, CSF is examined; it may contain lymphoma cells. In immunocompromised patients, Epstein-Barr virus DNA may be detected in CSF. If CSF does not contain lymphoma cells or Epstein-Barr virus DNA, guided-needle or open biopsy is required. Because lymphoma is initially highly sensitive to corticosteroids, giving these drugs just before biopsy may cause the lesion to disappear, resulting in a false-negative biopsy.
Most primary brain lymphomas are difficult to cure because they infiltrate the brain diffusely. Usually, corticosteroids result in rapid improvement initially. Many chemotherapy regimens, particularly those containing methotrexate (delivered as high-dose IV infusions), are effective; with methotrexate, median survival may approach 4 yr. Methotrexate can also be delivered intrathecally, usually via an sc intraventricular device (Ommaya reservoir). The drug is sometimes infused into the carotid artery after general anesthesia is induced and 25% mannitol is given IV to open the blood-brain barrier.
Chemotherapy regimens may be followed by radiation therapy, usually after 12 to 16 wk but sometimes delayed until the tumor recurs. The delay helps reduce radiation toxicity.