In this patient who most likely has a primary central nervous system (CNS) lymphoma with evidence of mass effect, high-dose glucocorticoids should be administered immediately. Because the brain is enclosed in a fixed space, mass effect within the brain causes progressively increased intracranial pressure (ICP) that, if untreated, can lead to diffuse brain injury, permanent disability, and death. Headache is typically the first presenting symptom and is followed by nausea and vomiting; as ICP increases, more advanced findings include altered mental status, focal neurologic deficits (such as papilledema), and loss of consciousness. Because progression can be rapid, emergent CT or MRI imaging of the brain followed by immediate treatment are essential to avoid the late adverse consequences of increased ICP that lead to permanent neurologic dysfunction and death. Glucocorticoids remain the initial therapy of choice because of their rapid anti-inflammatory effect that decreases the edema associated with malignant mass lesions. Intravenous administration of dexamethasone is standard for later stages of increased ICP (impaired mentation, uncontrolled seizures) with a recommended dose of 8 to 10 mg every 6 hours. Higher-dose dexamethasone (100 mg/d) does not improve the response rate and is associated with more adverse effects.

Metastatic tumors originating from lung cancer and cutaneous melanoma are the most common malignancy-related causes of increased ICP. These tumors, particularly melanoma, are also associated with intracerebral hemorrhage. Other less common causes of increased ICP related to malignancy include lymphoma, primary brain tumors, and germ cell tumors. Because treatment of ICP varies markedly depending on the cause, a tissue diagnosis of the mass lesion is important in guiding subsequent therapy. A primary CNS lymphoma is the most likely diagnosis in this young patient with a brain mass and HIV infection that is not optimally treated. Because lymphomas are extremely glucocorticoid sensitive, early administration may make obtaining a tissue sample difficult by distorting histologic findings; it is therefore preferable to obtain a biopsy in a stable patient with possible or likely CNS lymphoma prior to glucocorticoid therapy if there are minimal sequelae of increased ICP. However, in all patients with more advanced complications of increased ICP such as this patient, immediate glucocorticoid treatment is indicated.

Combination chemotherapy is appropriate only after initial steps are taken to lower the ICP and a tissue diagnosis is established, which has not yet been done in this patient.

Intracranial pressure monitoring is used to follow the effectiveness of therapies intended to decrease pressure in the cranial space and is most often used in association with severe traumatic brain injury. Although the benefit of pressure monitoring needs to be evaluated in an individual patient, it would not be appropriate to delay administration of glucocorticoids while assessing this patient for monitoring.

Either whole brain or stereotactic radiation therapy may be appropriate for some tumors causing increased ICP, but this therapy would be indicated only after the patient receives acute treatment and a tissue diagnosis is established.