Crystals commonly encountered by color compensated polarized light microscopic examination of synovial fluid aspirated from inflamed joints or irrigated from tophi of patients with gout. The four panels show: needle-shaped urate crystals without inflammatory cells from a tophus (upper left); intra- and extracellular urate crystals during acute gouty arthritis (upper right); an intracellular calcium pyrophosphate (CPP) crystal during an episode of acute CPP crystal arthritis (pseudogout) (lower left); and cholesterol crystals from a chronic joint effusion aspirated from a patient with rheumatoid arthritis (lower right). Note the characteristic needle-shaped urate crystals, rhomboid-shaped CPP crystal, and notched shield-shaped cholesterol crystals.
