A bulge on the top of the foot may be caused by bony mass, epidermoid cyst, tendon sheath cyst, lipoma, gouty arthritis and so on. 1. Bone mass: mostly seen in the fracture displacement caused by trauma, if it occurs on the top of the foot, after the deformity heals, it can produce bone bulge locally, and the symptom of bulging on the top of the foot will appear. 2. Epidermoid cysts: also known as keratocysts, belonging to benign cysts, can be seen in the limbs, especially the back of the hand, foot and other parts. It can cause hemispherical bulges on the surface of the feet, with hard texture. 3. Tendon sheath cyst: the back of the foot injury or long-term strain caused by synovial fluid in the joint infiltration of the tissue, tendon sheath surrounding the tissue of the package, after repeated absorption as well as extrusion, can be localized on the top of the foot bulge, the surface is smooth, and there may be pressure and pain. 4. Lipoma: subcutaneous lipoma on the top of the foot can be manifested as the symptom of bulge on the top of the foot, which can be fluctuated when pressed, with soft texture and relatively clear boundary. 5. Gouty arthritis: due to the deposition of urate crystals on the dorsal joints of the feet, the formation of gout stones, which can be manifested as symptoms of bulging on the surface of the feet. If there is a bulge on the top of the foot and it does not disappear for a long time, it is recommended to consult a doctor in time to find out the cause of the bulge and its nature, and actively treat it after a clear diagnosis, so as to avoid delaying the condition.