灰白区域是痛风石或由淋巴细胞、巨噬细胞、异物巨细胞浸润围绕的尿酸盐结晶的聚集物。痛风石是痛风的特征性病变，大多见于关节周围的软组织，包括肌腱与韧带，较少见于其它地方。沙粒状痛风是由急性痛风发作期尿酸钠盐结晶继续析出引起。
痛风性关节炎：大拇趾肉眼 X线 软组织内痛风石(低倍镜) 关节液查见尿酸盐结晶
The pale areas seen here are tophi, or aggregates of urate crystals surrounded by infiltrates of lymphocytes, macrophages, and foreign body giant cells. A tophus is the characteristic finding of gout. Tophi are most likely to be found in soft tissues, including tendons and ligaments, around joints. Less commonly tophi appear elsewhere. Tophaceous gout results from continued precipitation of sodium urate crystals during attacks of acute gout.