Adult osteopetrosis: study of two brothers.

Bone biopsies from 2 adult cases of benign osteopetrosis have been studied histologically and under the electron microscope. The most important findings were a high degree of osteosclerosis, narrowing and fibrosis of medullary spaces, and the presence of abundant uncalcified osteoid tissue with an osteomalacia-like appearance. The osteoclasts were not numerous. All of them lacked the brush border and many showed wide cytoplasmic vacuoles containing amorphous and filamentous material. This picture, which is not different from that found in cases of fetal osteopetrosis, has not been modified by ethydronate therapy.