Lymphangioma is a congenital vascular malformation arising from aberrant lymphatic deve-lopment, with a reported incidence of approximately 1 in 4 000. The condition predominates in the pedia-tric population, with the head and neck representing the most frequently affected anatomical regions. By contrast, scrotal lymphangioma in adults is exceedingly rare and remains highly susceptible to misdiagnosis or diagnostic omission in clinical settings. Here, we report a case of cystic lymphangioma of the penis in a 42-year-old male who presented with a mass at the penile root persisting for over 30 years, with marked enlargement over the preceding six months. Physical examination revealed a cystic mass measuring approximately 7 cm×4 cm×5 cm on the left aspect of the penile root, with a positive transillumination sign. Bilateral testes, epididymides, and spermatic cords were unremarkable. Ultrasonography demonstrated an irregular cystic anechoic lesion at the penoscrotal junction with well-defined margins. Magnetic resonance imaging (MRI) revealed a multilocular cystic lesion at the scrotal root measuring approximately 5.6 cm×3.8 cm×6.3 cm. Both imaging modalities were consistent with cystic lymphangioma. The patient underwent complete surgical resection under epidural anesthesia. Intraoperatively, the mass was confirmed to be multilocular and contained taupe-colored fluid. Histopathological analysis revealed endothelial cell lining of the cyst wall, and immunohistochemical staining was positive for CD31, establishing the definitive diagnosis of cystic lymphangioma. Genomic profiling identified a somatic heterozygous missense mutation in the PIK3CA gene at codon E545 (GAG>GCG), consistent with the established pathogenic mechanism underlying lymphangioma. Mechanistically, somatic PIK3CA mutations activate downstream signaling cascades, driving aberrant proliferation of lymphatic endothelial cells and culminating in cystic lesion formation. Clinically, lymphangioma typically manifests as a painless, slowly enlarging cystic mass. Definitive diagnosis relies on integrated imaging and histopathological evaluation, with differential diagnoses encompassing indirect inguinal hernia, hydrocele, and varicocele. Complete surgical resection remains the first-line therapeutic strategy and is associated with a substantially reduced recurrence rate. For patients deemed ineligible for surgery, sclerotherapy or molecularly targeted agents, including sirolimus and alpelisib, represent viable alternatives. The patient achieved an uneventful postoperative recovery with no evidence of recurrence at one-month follow-up. Although adult scrotal cystic lymphangioma is a rare clinical entity, it exhibits characteristic clinical, radiological, and pathological features that, in conjunction with molecular genetic analysis, enable accurate diagnosis. Early complete resection confers a favorable prognosis. Heightened clinical awareness and standardized management of lymphangioma at atypical anatomical sites are warranted.

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作者贡献声明  杨庆凯、卢剑：提出研究思路，设计研究方案，收集、分析、整理数据，撰写论文；陆敏：收集、分析、整理数据；洪锴：提出研究思路，总体把关及审定论文。所有作者均参与论文修改，并对最终文稿进行审读和确认。