Pachyostotic

Pachyostotic is an adjective relating to pachyostosis, a condition characterized by abnormal thickening of bone tissue, usually by periosteal deposition that enlarges the cortical bone and often narrows the medullary cavity. It may occur with or without increased bone density (osteosclerosis).

In paleontology and zoology, pachyostosis is common in certain aquatic reptiles and fossil mammals, where thickened and dense bones, such as ribs or limb bones, function as ballast to aid buoyancy control. The condition is sometimes termed pachyosteosclerosis when both thickening and density increase are present.

In medicine, pachyostosis is used descriptively to denote thickened bones due to periosteal bone growth. It can occur as part of developmental variation or in association with metabolic or genetic disorders; it is not a disease in itself but a descriptive feature that may require clinical correlation.

Diagnosis and interpretation depend on context. Radiographs or CT in living individuals reveal a thick cortex and often a reduced or altered medullary cavity, while in fossils the presence of pachyostosis can affect estimates of body mass and implications for the animal’s ecology.