Posterior Fossa Ring-Enhancing Lesions in the Adult Immunocompetent Host: Illustrative Cases, Systematic Review, and Proposed Diagnostic Algorithm.

Posterior fossa ring-enhancing lesions (PFREL) in immunocompetent adults represent a diagnostic challenge. We conducted a retrospective institutional analysis combined with a systematic literature review (PRISMA 2020) to describe the etiological spectrum of PFREL and to develop a diagnostic algorithm. Among 116 cases reviewed, infectious causes were most common (52%), followed by tumoral (38%) and inflammatory (2%) etiologies. Headache was the most frequent symptom, and 36% of patients presented with multiple lesions. Reported outcomes varied, with complete symptom resolution in 36% of cases and a mortality rate of 16%. Based on clinical and radiological features, we proposed a diagnostic algorithm, which was validated on an independent cohort of 16 patients and provided correct classification in each case. This algorithm may support the diagnostic process in PFREL and help to guide further investigations and management.