Pre-patellar Tumoral Calcinosis of Knee with Intra-articular Extension: An Index Case Study

Tumoral calcinosis is a rare hereditary condition characterized by the deposition of calcium phosphate and hydroxyapatite in periarticular soft tissues. First described by Giard and Duret in 1898 and later detailed by Inclan in 1943, this condition has often been confused with other forms of periarticular calcification. Tumoral calcinosis predominantly affects young males and is typically found around major joints, such as the shoulder, elbow, hip, ankle, and wrist.

We present a unique case of tumoral calcinosis in a 12-year-old boy, exhibiting intra-articular extension within the knee - an unprecedented finding in the literature. The patient had a 2-year history of progressive, nodular swelling around the left knee, initially presenting as painless nodules that later became painful and ulcerated. Radiographic and CT imaging revealed a massive, lobulated calcific mass extending from the superior patella to the pre-patellar region, including an intra-articular component.

The diagnosis was confirmed through imaging and histopathological examination following surgical excision. Histology showed calcified masses surrounded by giant cells, epithelioid cells, and fibrosis. Treatment involved complete surgical excision of the calcific masses, followed by lavage of the knee joint. The patient showed no recurrence at a 3-year follow-up.

Tumoral calcinosis is often misdiagnosed due to its similarity to other conditions involving soft-tissue calcification. This case underscores the importance of differentiating tumoral calcinosis from other disorders like calcinosis cutis and soft-tissue sarcomas. Genetic studies have identified mutations in GALNT3 and FGF23 genes, which contribute to the disorder's pathogenesis by disrupting phosphate metabolism. Effective management requires a combination of surgical excision and phosphate regulation.

Tumoral calcinosis, though rare, should be considered in differential diagnoses for periarticular calcifications, especially in younger patients. This case highlights the need for a multi-modal diagnostic approach and emphasizes that tumoral calcinosis can present with intra-articular involvement, a feature not previously reported in the knee joint. Long-term follow-up is essential due to the potential for recurrence.