Primary Glomus Tumor of the Inferior Vena Cava Diagnosed by Endovascular Biopsy: A Rare Incidental Finding

Glomus tumors are uncommon mesenchymal neoplasms with modified smooth muscle differentiation that classically arise in the subungual region but may occur at extradigital, visceral, and intravascular sites.Although primary intravascular glomus tumors have been reported, apparent primary origin within the inferior vena cava (IVC) represents an unusual presentation and must be distinguished from secondary caval involvement by an extravascular tumor.A 44-year-old man with hypertension, diabetes mellitus, and osteoarthritis underwent musculoskeletal imaging for persistent right shoulder and upper back pain following a fall.Imaging incidentally demonstrated a 1.7-cm infrarenal IVC intraluminal abnormality initially interpreted as bland thrombus, while PET-CT showed no 18F-fluorodeoxyglucose (FDG)-avid malignancy.Endovascular evaluation demonstrated an obstructive intraluminal mass, and biopsy revealed uniform round-to-oval cells arranged around branching vascular channels.Immunohistochemistry demonstrated strong diffuse smooth muscle myosin heavy chain positivity with negative CAM 5.2 and chromogranin staining, supporting the diagnosis of glomus tumor.Subsequent surgical resection confirmed a 2.5-cm glomus tumor with smooth muscle actin (SMA) and caldesmon positivity and a low Ki-67 proliferative index (<1%).This case demonstrates the diagnostic challenge of an indeterminate intraluminal IVC lesion and emphasizes the importance of distinguishing apparent primary caval origin from secondary IVC tumor involvement.Endovascular tissue sampling can provide a minimally invasive means of establishing a diagnosis when imaging findings are inconclusive, and the integration of imaging, histomorphology, immunohistochemistry, and surgical pathology is essential for definitive classification.