Hyperplasia

Among the types of hyperplasia with effects on the musculoskeletal system, congenital adrenal hyperplasia, bone marrow hyperplasia and various types of skeletal hyperplasia are of importance.

Hyperplasia of the bone marrow is common in numerous types of anaemia. In sickle cell anaemia, red marrow extends into all of the bones, even those of the hands and feet in infants. It leads to widening of the medullary cavities and thinning of the remaining trabeculae. Radiographic abnormalities in this situation include increased osteopenia with cortical thinning, especially in the axial skeleton. In addition, widening of the diploic space is associated with thinning of the tables of the skull. Involvement of the spine is manifested by increased radiolucency of the vertebral bodies, prominent vertical trabeculae, and fish vertebrae or H vertebrae. Marrow hyperplasia in bones of the thorax and extremities may also lead to osteoporosis and cortical thinning. The findings in the appendicular skeleton are not as prominent in the adult as in the child because of the normal fatty conversion of the marrow of the extremities that occurs with advancing age. In beta thalassaemia, bone proliferation on the outer table of the vault leads to a hair on end appearance (dense radial striations traversing the thickened calvaria that appear to extend beyond the outer table). Maxillary alterations can lead to hypertelorism, malocclusion of the jaws and displacement of teeth (rodent facies). The cranial vault and facial changes are much more severe in thalassaemia than in other anaemic disorders.

Congenital adrenal hyperplasia, an endocrine disorder resulting from the secretion of excessive amounts of adrenocorticotropic hormone (ACTH), is caused by loss of one of the enzymes involved in the conversion of cholesterol to normal hormonal steroids. The clinical picture varies, but most frequently female pseudohermaphroditism occurs. Initially the affected person shows accelerated growth, but premature closure of the physes may eventually result in short stature. Dental maturation may also be accelerated, and the costal cartilages may undergo premature calcification.

Congenital enlargement of a single bone, a limb or other portion of the skeleton may be idiopathic or accompany numerous disorders, such as neurofibromatosis, Proteus syndrome, Wilms' tumour, cerebral gigantism, lymphangiomatosis and arteriovenous malformation.

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