Recurrent multiloculated cystic variant of Lhermitte-Duclos disease managed with cyst fenestration and Ommaya reservoir placement: illustrative case.

backgroundLhermitte-Duclos disease (LDD), or dysplastic gangliocytoma of the cerebellum, is a rare benign lesion typically characterized by slow growth and absence of cystic changes. Cyst formation in LDD is distinctly uncommon, and detailed clinical courses of such cases are rarely documented. OBSERVATIONS: The authors describe a case of a young male with multiloculated cystic LDD in the right cerebellar hemisphere. The lesion recurred with progressive cyst enlargement, ultimately causing brainstem compression. Despite multiple resections and fenestrations, histopathological analysis consistently revealed characteristic features of LDD, including thickened cerebellar folia with reduced Purkinje and granular cells, dysplastic neurons, and a very low Ki-67 index (≤ 1%). Final management, including cyst fenestration and placement of an Ommaya reservoir, successfully restored CSF communication, preventing further enlargement and stabilizing neurological symptoms. LESSONS: Although LDD generally follows a benign course, multiloculated cystic variants can present with progressive recurrence and neurological deterioration. This case emphasizes the importance of recognizing cystic changes in LDD and demonstrates that adequate fenestration with communication to cisternal spaces, supplemented by Ommaya reservoir placement when necessary, can provide durable disease control. https://thejns.org/doi/10.3171/CASE25907.