Giant cell tumors are commonly found over the flexor tendon sheath of the hand and wrist. However, giant cell tumors in the knee joint are rare, especially in children. We report an interesting case of an 11-year-old girl who presented with a painful lump on her right knee that enlarged over time. Clinically, she had fullness over the anterolateral part of her knee. Magnetic resonance imaging revealed an encapsulated mass inferior to the patella. The tumor measured 3 x 3.5 x 1.5 cm. Histopathological findings confirmed that it was a tenosynovial giant cell tumor. Because of initial mild symptoms, there was a delay of 2 years from the initial symptoms until tumor excision. Her follow-up period was 35 months, and her health to date is excellent with no recurrence. We believe that reporting this rare case will help clinicians update their knowledge on possible causes of lumps in the knee, and avoid diagnostic delay. It could also prove to be beneficial in arriving at a diagnosis in future cases.
Any medical diagnosis should take a multimodal approach, especially those involving tumour-like conditions, as entities that mimic neoplasms have overlapping features and may present detrimental outcomes if they are underdiagnosed. These case reports present diagnostic pitfalls resulting from overdependence on a single diagnostic parameter for three musculoskeletal neoplasm mimics: brown tumour (BT) that was mistaken for giant cell tumour (GCT), methicillin-resistant Staphylococcus aureus osteomyelitis mistaken for osteosarcoma and a pseudoaneurysm mistaken for a soft tissue sarcoma. Literature reviews revealed five reports of BT simulating GCT, four reports of osteomyelitis mimicking osteosarcoma and five reports of a pseudoaneurysm imitating a soft tissue sarcoma. Our findings highlight the therapeutic dilemmas that arise with musculoskeletal mimics, as well as the importance of thorough investigation to distinguish mimickers from true neoplasms.