A Mimic in the Frontal Lobe: CNS Histiocytosis Masquerading as a Glial Neoplasm in a Young Adult

Purpose This case describes an unusual presentation of central nervous system (CNS) histiocytosis in a 19-year-old male, presenting with imaging features initially suggestive of a glial tumor, but further work-up redirected the diagnosis toward a condition of non-glial origin. Also it highlights how evolving clinical and radiologic data can uncover an unexpected diagnosis. Methods A 19-year-old male presented with acute neurological symptoms. Serial MRI examinations with contrast administration were performed to this patient. Imaging characteristics were reviewed in correlation with clinical progression and histopathological findings. Results Initial MRI revealed a T2/FLAIR hyperintense mass in the right frontal operculum with associated perilesional leptomeningeal enhancement in the adjacent sulci. No diffusion restriction was seen. Over two weeks, the lesion nearly doubled in size, with increased patchy enhancement, leptomeningeal spread to temporal and parietal regions, and new infundibular thickening. Mild midline shift developed. Biopsy confirmed CNS histiocytosis. Partial regression was noted after steroid treatment. Conclusion This case emphasizes the possible radiologic overlap between glial tumors and rare mass like presentation with parenchimal involvement of CNS histiocytosis. Recognition of leptomeningeal involvement, infundibular thickening and steroid responsiveness can aid differentiation and prompt biopsy.