Combined Diagnostic Approach to AIDS-Related Primary CNS Lymphoma Using EBV-DNA Polymerase Chain Reaction in CSF, Thallium-201 Single-Photon Emission Computed Tomography, and Toxoplasma gondii Serologies. Is a Brain Biopsy Always Necessary?

Focal brain lesions (FBL) in HIV-infected patients remain a diagnostic dilemma. Approximately 30-40% of all patients with AIDS show central nervous system (CNS) disease [1,2]. This number increases to 75% or more in autopsy studies. Approximately 10% of AIDS patients with CNS disease have one or more mass lesions [2]. The differential diagnosis of these mass lesions is broad and can include primary CNS lymphoma (PCNSL), Toxoplasmosis, progressive multifocal leucoencephalopathy (PML), HIV encephalopathy, cytomegalovirus (CMV)-encephalitis, herpes simplex virus (HSV)encephalitis, tuberculoma, cryptococcoma, vasculitis, and abscess [3]. Toxoplasmosis and PCNSL account for over 50% of FBL [2], with toxoplasmosis being the most common cause. Lesions caused by toxoplasmosis and PCNSL are often difficult to distinguish from each other by radiographic appearance on CT or MRI [4,7,8,9,10,11]. Toxoplasmosis typically causes > 2 ringenhancing lesions, often with associated edema, and lesions commonly occur in frontal, basal ganglia, and parietal regions [9]. PCNSL classically causes a single or multiple hypodense lesions that enhance homogenously; however, central necrosis can cause a ring-enhancing appearance. Lesions are often located in the cerebrum, basal ganglia, cerebellum, and, occasionally, the brain stem, and are typically periventricular. Subependymal spread is pathogonomic for PCNSL. However, there is considerable overlap between the appearance of these two entities. For example, 21% of toxoplasmosis lesions are single lesions on MRI, and PCNSL causes multiple lesions in 50% of cases. Brain biopsy is the gold standard for the diagnosis of FBL. Serious complications due to brain biopsy have been reduced with the use of stereotactic biopsy procedures [1, 10]. Complications from stereotactic brain biopsy include hemorrhage, neurological impairments, which may be transient or permanent, and, rarely, infection at the biopsy site. In one study, perioperative morbidity after stereotactic biopsy was 12%, while perioperative mortality was 2% [6]. Hemorrhage was the most common complication and, interestingly, all hemorrhages occurred in patients found to have PCSNL [3]. The diagnostic yield of stereotactic biopsy is high, often >90% [1, 2, 4, 6, 12]. Many diagnostic algorithms have been developed in order to identify HIV-infected patients, presenting with neurological signs or symptoms, who would most likely benefit from a brain biopsy [1, 6, 12]. Figure 1 and Figure 2 [12] show the most commonly used alorithms.