Intra-Articular Extra-Synovial Venous-Type Synovial Haemangioma of the Knee in a Young Adult: Case Report and Literature Review of This Frequently Misdiagnosed Lesion

Abstract

Objective To report a rare lesion, an intra-articular extra-synovial venous-type synovial haemangioma of the knee in a young adult and to review the relevant literature on this frequently misdiagnosed entity. Case report A 21-year-old man presented with recurrent knee effusions and pain over several years. Imaging studies revealed a well-defined, intra-articular, extra-synovial soft-tissue mass located in the anteromedial compartment of the knee. Magnetic resonance imaging (MRI) demonstrated multiple tubular structures with high signal intensity on T2- and short tau inversion recovery (STIR)-weighted images and intense, homogeneous contrast enhancement, consistent with a vascular lesion. Surgical excision was performed, and histopathological analysis confirmed a venous-type synovial haemangioma, characterized by large-calibre vascular channels lined by bland endothelial cells and containing organizing thrombi. The postoperative course was uneventful, and the patient remained disease-free at 6 months of follow-up. Conclusion Synovial haemangioma, though rare, should be considered in the differential diagnosis of recurrent knee effusions in young patients. It may mimic other benign or malignant periarticular lesions. MRI plays a key role in the evaluation, and the diagnosis can be strongly suggested by imaging, but histopathological confirmation remains essential for accurate characterization and appropriate management.

The authors' abstract, as published at the source. International Journal of Surgical Pathology, 2026 · DOI ↗