Osteopetrosis

The precocious type is inherited as an autosomal recessive trait and is usually lethal. Affected infants fail to thrive and have hepatosplenomegaly, cranial nerve dysfunction (especially blindness and deafness) and hydrocephalus. The marrow cavity is obliterated by abnormal bone, which leads to anaemia and thrombocytopenia and predisposes the patient to recurrent infections. On radiographs this type of osteopetrosis exhibits generalized osteosclerosis (Fig.1) (Fig.2) (Fig.3). Tubular bones show defective modeling with longitudinal or transverse striations. The appearance may resemble that seen in rickets. Other findings include periostitis and fractures, which generally heal. In the skull, the site affected most frequently and severely is the cartilaginous portion at the base of the skull. In addition, malformed teeth and poorly developed mastoid regions and paranasal sinuses may be present. Vertebral bodies have a prominent anterior vascular notch and tend to be uniformly radiodense.

The delayed type is an autosomal dominant variety, also known as Albers Schonberg disease. Pathologic fracture, problems after tooth extraction, mild anaemia or cranial nerve palsies may lead to a diagnostic search that reveals osteopetrosis. Radiographic findings are similar to but less severe than those in the precocious form. Diffuse osteosclerosis with defective tubulation and a thickened cortex are typical, and sometimes a bone within bone appearance is seen.

An intermediate recessive type represents a milder form of osteopetrosis. Among the features are short stature, pathologic fractures, anaemia and hepatomegaly. On radiographs typical findings are diffuse bone sclerosis, interference with normal bone modeling, and a bone within bone appearance.

Osteopetrosis with tubular acidosis, also termed marble brain disease or Sly's disease, is an automsomal recessive disorder consisting of osteopetrosis, renal tubular acidosis and cerebral calcifications. Mental retardation and a deficiency in carbonic anhydrase are present in some affected persons. Other features are a failure to thrive, symptoms related to renal tubular acidosis, muscle weakness, and hypotonia. Radiographic findings include osteosclerosis, obliteration of the medullary cavity and pathologic fractures.

DR/RB