目的 提高临床医师对原发性中枢神经系统恶性黑素瘤临床病理和影像学特征的认识。 方法 回顾性分析1例原发性中枢神经系统恶性黑素瘤患者的临床诊疗资料，包括临床症状、MRI和PET-CT特征以及脑脊液细胞学和脑组织活检的病理学诊断结果，并结合相关文献进行诊疗思路探讨。 结果 本例患者为老年男性，以快速进展性痴呆和行走平衡障碍为主要临床表现。头颅核磁共振成像（magnetic resonance imaging， MRI）检查结果显示广泛大脑皮质、右侧小脑半球及双侧脑沟裂区呈T1和T2加权像高信号并伴明显强化和小脑幕上脑积水。脑脊液细胞学检测发现含黑素颗粒的异型细胞，最终经脑组织活检确诊为原发性中枢神经系统恶性黑素瘤。 结论 以弥漫性软脑膜受累及脑积水为影像学特征的原发性中枢神经系统恶性黑素瘤患者可表现为快速进展性痴呆，其特征性MRI影像学异常和脑脊液细胞学改变是早期诊断的重要线索，确诊仍需依赖病理学检查。

Objective To improve clinician's understanding of the clinicopathological and imaging features of primary central nervous system malignant melanoma. Methods The clinical diagnosis and treatment data of one patient with primary central nervous system malignant melanoma were retrospectively analyzed, including clinical symptoms, magnetic resonance imaging (MRI) and PET-CT findings, as well as cerebrospinal fluid cytology and brain biopsy pathology. The diagnostic and therapeutic approaches were discussed in conjunction with relevant literature. Results The patient in this paper was an elderly male presenting with rapidly progressive dementia and gait imbalance as the main clinical manifestations. Cranial MRI demonstrated hyperintensities on T1- and T2-weighted imaging with significant contrast enhancement in extensive cortical involvement, lesions in the right cerebellar hemisphere, and bilateral sulcal, along with supratentorial hydrocephalus. Cerebrospinal fluid cytology revealed the presence of atypical cells containing melanin granules, and the diagnosis of primary central nervous system malignant melanoma was finally confirmed through pathological examination of a brain biopsy. Conclusion Patients with primary central nervous system malignant melanoma, characterized by diffuse leptomeningeal involvement and hydrocephalus on imaging, may present with rapidly progressive dementia. The characteristic MRI findings and cerebrospinal fluid cytological changes serve as key clues for early diagnosis, while definitive confirmation still relies on pathological examination.