IntroductionFemoral vein adventitial cystic disease is an exceedingly rare vascular disorder characterized by mucin-filled cysts within the venous wall, leading to potential luminal obstruction and clinical symptoms. This case highlights the diagnostic challenges and management of this uncommon condition.Case PresentationA 58-year-old male presented with a 2-month history of progressive left lower extremity swelling and discomfort. Physical examination revealed pitting edema along the calf. Duplex ultrasound demonstrated a hypoechoic cystic lesion compressing the femoral vein. Contrast-enhanced computed tomography (CT) and magnetic resonance imaging (MRI) confirmed a 3.1 cm × 1.4 cm × 2.1 cm cystic mass within the adventitial layer of the femoral vein, with partial luminal stenosis. No evidence of deep vein thrombosis or malignancy was observed.Intervention and OutcomeSurgical exploration via groin incision identified a translucent cyst arising from the femoral vein adventitia. Complete excision was performed with venous reconstruction. Histopathology confirmed a benign adventitial cyst with mucinous content and a single-layer endothelial lining. Postoperative recovery was uneventful, with resolution of symptoms and no recurrence at 3-month follow-up.ConclusionAdventitial cysts of the femoral vein, though rare, should be considered in patients with unexplained limb swelling. Multimodal imaging is critical for differential diagnosis, and complete surgical excision remains the definitive treatment. This case underscores the importance of recognizing atypical venous pathologies to prevent misdiagnosis and ensure optimal outcomes.
Song et al. (2026) studied this question.