Macrodystrophia lipomatosa

a nonhereditary form of localized gigantism of unknown cause marked by congenital and progressive overgrowth of all the mesenchymal elements of a digit and disproportionate increase in the fibroadipose tissue. The increase in adipose tissue involves bone marrow, periosteum, muscles, nerve sheaths and subcutaneous tissues. Nerves may also be enlarged and irregular. Both endosteal and periosteal depositions of bone are responsible for phalangeal enlargement. This developmental disorder is recognizable at birth.

The foot is affected more commonly than the hand. Usually involvement is unilateral, with the favoured sites in both upper and lower extremities being the second and third digits. Local anomalies (syndactyly, polydactyly, clinodactyly) are very frequent.

On radiographs abnormalities are observed in both soft tissues and bone (Fig.1). Overgrowth of soft tissues is most prominent in the distribution of the median and plantar nerves, at the distal end of the digit and along its volar aspect. Small lucent areas may be present where overgrowth of fat occurs in the soft tissues. Late in childhood, secondary degenerative joint disease develops.

Other imaging techniques such as CT scanning and MR imaging may demonstrate large linear radiolucent bands of fat within the affected muscle.

Neurofibromatosis produces the most difficulty in differential diagnosis, but generally the radiographic findings can allow differentiation of macrodystrophia lipomatosa from neurofibromatosis.