Case Report: Primary inferior vena cava leiomyosarcoma with hepatic metastases initially misinterpreted as primary hepatic leiomyosarcoma - ultrasonographic features and diagnostic insights.

Background: Leiomyosarcoma of the inferior vena cava is a rare and malignant soft tissue tumor. Diagnosis is often delayed due to non-specific symptoms. Imaging is crucial, yet preoperative differentiation remains challenging. Case presentation: A 59-year-old woman presented with a two-year history of right upper quadrant pain. Initial ultrasound revealed a large, well-defined, hypoechoic hepatic mass (10.6 × 7.8 cm) with heterogeneous echotexture featuring multiple strip-like hyperechoic regions and irregular anechoic areas. Contrast-enhanced ultrasound showed a malignant enhancement pattern. Chest CT indicated pulmonary metastases. Initial ultrasound diagnosis was primary hepatic leiomyosarcoma. Ultrasound-guided biopsy confirmed leiomyosarcoma. Subsequent targeted comprehensive imaging re-evaluation, including retrospective review of ultrasound cine loops and MRI sequences, demonstrated tumor continuity with the IVC lumen, leading to the final diagnosis of primary inferior vena cava leiomyosarcoma with hepatic extension and pulmonary metastases. Conclusions: This case demonstrates that targeted ultrasound re-evaluation is valuable for clarifying the tumor-IVC relationship. The sonographic finding of multiple strip-like hyperechoic regions may be a characteristic feature of inferior vena cava leiomyosarcoma. We propose that leveraging imaging similarities between smooth muscle tumors across different anatomical sites (e.g., uterus, peripheral veins) can foster a cross-organ diagnostic mindset. Furthermore, exploring cross-organ, cross-modality transfer learning models could address data scarcity and enhance diagnostic capabilities for rare entities like inferior vena cava leiomyosarcoma.