This was a cross-sectional descriptive study, with data collection over a 24-month period from July 2014 to July 2016.

The study took place in the medical imaging department of the EL RAPHA private Polyclinic in Libreville, Gabon.

We carried out an exhaustive sampling by systematic census of all HIV-positive patients referred for MRI on suspicion of CNS involvement on the basis of clinical (infectious syndrome, confusional or cerebellar syndrome, or deficiency) and/or biological arguments, and who may or may not have had a previous brain scan.

After collecting epidemiological and clinical information’s, an MRI examination was carried out with a high field machine (1.5 Tesla). The protocol included morphological sequences (FLAIR, T1, T2, T2*), diffusion sequences, as well as a 3D T1 Vibe sequence after injection of 10 ml of gadolinium. Two Radiologists carried out the interpretation of the images. In case of discrepancies, the opinion of a third radiologist was required.

All the data was recorded on a survey form filled in by us.

The parameters studied were demographic data (age, sex), clinical signs of orientation, lesions observed on brain CT scan (if applicable), those found on MRI and the diagnoses retained.

The diagnosis was retained globally on the basis of a cluster of clinical, biological and radiological arguments:

· Cerebral Toxoplasmosis: Evocative aspect (annular elevation within an important edema, topography) in imaging associated with Toxoplasma gondii positive serology in serum IgG and regression of radiological signs under specific treatment.

· Tuberculosis: Typical appearance in “grape clusters” in imaging. Active lesions or squeal of pulmonary tuberculosis if present have guided the diagnosis. Concerning, clinical improvement under specific treatment of tubercular abscesses and meningitis was of great help in confirming the diagnosis.

· Cortical atrophy: Dilatation of the cortical grooves with absence of parenchymal or meningeal lesions associated in imaging.

· HIV encephalitis and Progressive Multifocal Leukoencephalopathy (PML): The signal in T1 and T2, the absence of elevation, the topography, number, bilaterally and symmetry of lesions on MRI, and the regression of viral load after the introduction or modification of triple ARV therapy.

· Lymphoma: The signal in T1 and T2, the topography, number and, annular or nodular enhancement of the lesions on MRI, as well as the absence of improvement under anti-toxoplasma treatment after 10 days and a good response under corticosteroid therapy.

The data were treated using Epi info 7 software version 2.2.6. The percentages were calculated to describe the qualitative variables. In order to investigate the performance of cerebral tomodensitometry compared to MRI under our practice conditions, the sensitivity, specificity, positive and negative predictive values of the said examination were determined using MRI as reference standard.

A total of 39 patients were included during the study period. Their mean age was 37.6 ± 15 years with extremes of 18 and 85 years, and their sex ratio was (M/F) 0.6. They all had a plasma Cluster of Differentiation 4 (CD4) lymphocyte count ≤ 200/mm³. The main findings of the MRI are summarised in Table 1. Neurological deficit, convulsions and headaches were the most frequent indications in 34.28%, 25.71% and 17.14% cases respectively. Among the 39 patients, 35 (89.74%) had pathological MRI; and toxoplasmosis was the most common diagnosis, 37.14% (Table 2).