A. Brief Descriptions：
Rheumatoid nodule within the substance of the synovial membrane in a patient with rheumatoid arthritis.
Rheumatoid nodules are present in approximately 20% to 25% of patients with rheumatoid arthritis.
B. Gross Findings：
Solitary or multiple, nontender, firm, freely movabile, large subcutaneous nodules.
C. Micro Findings：
Center: homogenous eosinophilic fibrinoid degeneration of collagen.
Periphery: peripheral palisade of histiocytes and lymphocytes.
Robbins Pathologic Basis of Disease, 6th ed. P1248-1251.
【 Fig. 208-1 (LP)】
【 Fig. 208-2 (LP)】A typical serpiginous zone (top) of amorphous, eosinophilic, fibrinoid material surrounded by palisading histiocytes and lymphocytes.