Osteopetrosis is a rare generalized dysplasia of the skeleton. It is a hereditary condition that results in extremely dense bones throughout the skeleton. Osteopetrosis is essentially a failure of osteoclastic activity within the bone. There are congenita and tarda forms, which can vary in severity of disease.
It is characterized by the persistence of the calcified cartilaginous matrix that is normally destroyed during growth. The marrow spaces are diminished in volume and are replaced by calcified cartilaginous matrix. The cortex is hypoplastic and there is little room in the marrow for blood formation in the skeleton. This type is unusually presents at birth and is often fatal. Patients typically present with anemia, throbocytopenia and hydrocephalus.
The form of this disease with precocious manifestations is known as the malignant form. This typically presents in infancy with hepatosplenomegaly, anemia, increased incidence of infection and failure to thrive. The diagnosis is made when radiographs taken for other reasons demonstrate marked sclerosis of the skeleton, which has been described as "marble bones". The bones are very dense but are extremely brittle resulting in multiple fractures. Anemia, thrombocytopenia and recurrent infections with severely enlarged lymph nodes often lead to early fetal death.
Cranial manifestations are most prominent at the skull base due to cranial nerve pareses from small cranial neuroforamina and hydrocephalus. Optic atrophy is secondary to such constriction and therefore, eye tests are included in the evaluation of all cases of osteopetrosis.
This form is generally in seen in older children and adults and presents with milder clinical manifestations. The characteristic finding is the "bone in bone" appearance often seen in the vertebral bodies and metacarpals. These have also been described as endobones. These are sclerotic osseous inserts resembling miniature models of the bones containing them. They have been found in nearly every bone in the body but most notably in the metacarpal, metatarsal and vertebral bodies. This appearance of "bone in bone" is pathognomonic of classic osteopetrosis.