This is a classic example of gout. This 74-year-old man developed a painful nodule over his olecranon bursa. He also had elevated serum uric acid. Tophaceous gout results from abnormalities in purine metabolism, leading to elevated serum uric acid and deposition of monosodium urate crystals. These deposits usually are in the ear, elbows, fingers, and toes. The crystals are painful, but interestingly have little inflammation by histology. Foreign-body giant cells often line the deposits. When stored/fixed in ethanol, as opposed to formalin, the crystals become birefringent under polarized light, as in this case.
Using a polarizer (perpendicular to plane), the crystals glow a brilliant blue. They are yellow when parallel to plane (not shown). This feature of gout is only well developed when stored/fixed in alcohol, not formalin.