Osteitis fibrosa is a form of high-turnover bone disease, characterized by a marked increase in the number of BRU. The result is an increase of resorption lacunae with active osteoclasts. Likewise, it is accompanied by increased osteoblast activity and predominantly non-lamellar or “woven osteoid”. The increase in osteoid thickness is modest given that it is a consequence of high turnover and not due to a mineralization delay, as is the case with osteomalacia. The activation of fibroblast-like mesenchymal cells gives rise to the production of peritrabecular fibrosis. In cortical osteons, increased porosity usually occurs with a tendency to reduced bone mass, whereas in trabecular bone, the accumulation of woven bone may leave the bone mass unchanged or even increased. Tetracycline labeling is usually widespread, with increased separation between bands.