The brownish color of the lesion specimen on visual inspection is due to extensive deposition of iron-containing hemosiderin. The disease is often accompanied by bloody effusions in the joints, leading some observers to believe that the condition is a vascular abnormality, whereas nodular synovitis is a true tumor or a reactive lesion, and thus the two are distinct. However, this difference is not obvious histologically, and some authors have used the name "hyperpigmented villous nodular synovitis" to include both synovial lesions. Clinically, the lesions appear as painless soft tissue masses, usually located in the fingers and toes. It can also be seen in other joints (especially the knee) and tendon sheaths. The pattern of single joint onset, combined with arthroscopic imaging and pathology can be diagnosed.