Ultrasound-based multimodal diagnosis and endovascular therapy for phlegmasia cerulea dolens secondary to May–Thurner syndrome in a middle-aged male patient

Rationale: This study explores the value of ultrasound in the diagnosis of patients with phlegmasia cerulea dolens (PCD). The enrolled patient suffered from PCD secondary to iliac vein compression syndrome (IVCS) and complicated by extensive lower-limb deep vein thrombosis (DVT). We analyzed an atypical case in a middle-aged male. We summarized the advantages and limitations of ultrasound. We aimed to provide practical references for multimodal diagnosis and emergency management of critical DVT patients. Patient concerns: A 54-year-old male patient was diagnosed with IVCS. The condition was complicated by extensive left lower-limb DVT and subsequent PCD. We retrospectively collected his clinical data, imaging findings, and interventional records. We summarized the typical ultrasound features. We combined computed tomography angiography (CTA) and venography results. We further clarified the clinical role of ultrasound in such life-threatening vascular emergencies. Diagnoses: Based on clinical manifestations and multimodal imaging examinations, the final diagnoses were phlegmasia cerulea dolens (PCD) secondary to iliac vein compression syndrome (IVCS), complicated by extensive left lower-limb deep vein thrombosis. Interventions: The patient received emergency endovascular interventional therapy, including thrombus aspiration, catheter-directed thrombolysis, and iliac vein stent implantation. Anticoagulant therapy was administered perioperatively. Serial ultrasound examinations were performed before and after intervention to dynamically evaluate venous hemodynamics. Outcomes: Ultrasound rapidly detected extensive thrombosis in the left femoral vein, popliteal vein, and calf intermuscular veins. It clearly displayed thrombus location, scope, and echogenic features. It provided critical imaging evidence for emergency intervention. However, ultrasound could not directly visualize iliac vein stenosis. Pelvic anatomical depth and intraluminal thrombus obstruction mainly accounted for this limitation. CTA and venography successfully confirmed the underlying IVCS etiology. Postoperative ultrasound hemodynamic parameters objectively evaluated vascular recanalization efficacy. Combined interventional treatment effectively restored limb blood flow. Lower-limb edema and pain were significantly relieved after treatment. Lessons: Ultrasound serves as the first‑line screening tool for PCD. It allows rapid and real‑time evaluation of thrombus burden in the emergency department. Routine postoperative hemodynamic ultrasound can objectively assess vascular recanalization for therapeutic monitoring. However, ultrasound carries a high risk of missed diagnosis of primary iliac vein stenosis. For highly suspected IVCS cases, CTA and venography are essential for etiological confirmation. A multimodal collaborative diagnosis and treatment strategy is strongly recommended for critical PCD patients.