Atypical Lhermitte-Duclos Disease Presenting as a Malignant Cerebellar Tumor: NeuN-Positive Neuronal Differentiation as a Diagnostic Clue.

Lhermitte-Duclos disease (LDD), or dysplastic cerebellar gangliocytoma, is a rare benign cerebellar lesion that may present with atypical imaging and histopathological features, resulting in diagnostic uncertainty and potential overtreatment. We report a 32-year-old woman who presented with progressive headache, vomiting, vertigo, and right-sided cerebellar ataxia. Magnetic resonance imaging revealed a large right cerebellar lesion extending into the vermis, middle cerebellar peduncle, and hemipons, with inhomogeneous contrast enhancement and diffusion restriction, closely mimicking a malignant posterior fossa tumor. The patient underwent suboccipital craniotomy and decompression. Histopathology demonstrated distorted cerebellar folia with depletion of the Purkinje cell layer and expansion of the granular layer by neurocytic cells, raising a diagnostic dilemma with medulloblastoma. Immunohistochemistry showed NeuN and synaptophysin positivity with a very low K i -67 index, supporting LDD. Postoperative imaging demonstrated subtotal resection, and the patient had an uneventful recovery. This case highlights the importance of recognizing atypical presentations of LDD and the critical role of immunohistochemistry in establishing the diagnosis.