Long-term follow-up monitoring with multimodal ultrasound in a case of suspected renal angiomyolipoma with renal vein/inferior vena cava thrombus: a case report.

Surgical intervention is typically recommended for renal angiomyolipoma (AML) complicated by inferior vena cava (IVC) thrombus, given the potential risk of cardiopulmonary embolism. However, the natural history and corresponding imaging progression in such cases are not well understood. We describe a female patient with an imaging-based diagnosis of renal AML and an associated IVC tumor thrombus (Mayo Grade II), who presented to our center in December 2021. The initial suspicion raised by renal ultrasound (US) was subsequently confirmed via contrast-enhanced abdominal computed tomography (CT). Due to concerns regarding surgical risks, the patient declined operative management. A nearly four-year follow-up protocol was therefore initiated, utilizing multimodal ultrasound (grayscale, color Doppler, and contrast-enhanced ultrasound [CEUS]) to monitor disease behavior. Serial assessments revealed a distinct biphasic pattern of “progression followed by stabilization” in the tumor thrombus. Specifically, a trend of centripetal extension was observed over the first 19 months, after which the thrombus remained radiologically stable for the subsequent 18 months. Throughout this period, no aggressive features were identified, and the size of the primary renal lesion was unchanged. This case illustrates that a fat-containing renal tumor with IVC thrombus, presumed to be an AML based on imaging characteristics, may undergo a phase of progression before entering a period of spontaneous stabilization. It further highlights the clinical utility of multimodal US in tracking the course of such lesions. For asymptomatic patients with similar imaging findings who are unwilling or unsuitable for surgery, and in whom serial imaging demonstrates eventual stabilization, an active surveillance strategy may represent a reasonable management option.