Differential Diagnosis for a Growing Bump on the Knee

Single Most Likely Diagnosis

• Osteochondroma: A common benign bone tumor that can grow over time, causing a bump on the knee. It can be painful, especially when pressed, and is consistent with the described symptoms.

Other Likely Diagnoses

• Ganglion Cyst: A lump under the skin that occurs when fluid accumulates, often near joints or tendons. While it can be painful when pressed, it typically doesn't grow significantly over years unless it's a large cyst.
• Bursitis: Inflammation of a bursa, which are fluid-filled sacs that cushion bones, tendons, and muscles near joints. Chronic bursitis can cause a painful swelling that might resemble a growing bump.
• Lipoma: A benign tumor composed of fat tissue. It can grow over time and cause discomfort, especially if it presses on nearby structures.

Do Not Miss Diagnoses

• Soft Tissue Sarcoma: Although rare, sarcomas can present as a growing lump. Missing this diagnosis could be fatal, making it crucial to consider, especially if the lump is rapidly growing or accompanied by systemic symptoms.
• Osteosarcoma: A type of bone cancer that can cause a painful lump on the knee. Early detection is critical for effective treatment.

Rare Diagnoses

• Synovial Chondromatosis: A rare condition where cartilage grows in the synovium (the lining of the joints), leading to multiple small bumps or a single large mass. It's usually associated with joint pain and swelling.
• Hemangioma: A benign vascular tumor that can occur under the skin and, in rare cases, near the knee. It might cause a growing, painful lump, especially if it involves deeper tissues.