Two rare intra-articsular knee disorders with overlapping symptoms: separate case reports of tenosynovial giant cell tumour and lipoma arborescens and literature review

BACKGROUND: Tenosynovial giant cell tumour (TGCT) and lipoma arborescens (LA) are both rare intra-articular lesions of the knee. Despite their distinct pathological nature, they often present with similar clinical manifestations such as joint swelling, pain, and limited motion, which makes differential diagnosis challenging. CASE PRESENTATION: We report two patients who presented with progressive knee swelling and discomfort and were admitted within the same clinical session, offering a unique opportunity for direct comparison. Magnetic resonance imaging (MRI) revealed intra-articular soft-tissue masses in both cases. Both patients underwent arthroscopic synovectomy, with histopathological examination confirming the diagnosis of TGCT in one case and revealing the characteristic villous proliferation of adipose tissue within the synovium diagnostic of LA in the other. Both patients underwent surgical resection and experienced significant improvement in symptoms during follow-up. CONCLUSION: Although uncommon, TGCT and LA should be considered in the differential diagnosis of unexplained knee joint swelling or effusion. MRI provides valuable clues, but definitive diagnosis relies on histopathological confirmation. Awareness of these rare conditions may help avoid misdiagnosis and guide appropriate management.