Macrodystrophia lipomatosis is a rare, congenital form of localized gigantism of fingers or toes. Almost always unilateral and can involve both the upper extremities (usually in the distribution of the median nerve with the index and middle fingers most commonly involved) and in the lower extremities (usually in the distribution of the plantar nerves). Predominantly fibroadipose tissue produced in association with arteriovenous fistulas or localized hyperplastic vascular and lymphatic elements. Can be associated with neurofibromatosis type I or Klippel Trenaunay syndrome. Radiographically, it appears as hypertrophy of soft tissues and bones. The pathologic findings are infiltration and hypertrophy of adipose tissue in subcutaneous tissue, nerve sheaths, and periosteum. Macrodystrophia lipomatosa is usually diagnosed at birth or during the neonatal period.
Proposed etiologies include a variable form of neurofibromatosis, lipomatous degeneration, disturbed fetal circulation, trophic influence of a tumified nerve, in utero disturbance of growth-limiting factor or an error in segmentation.
The exact mechanism causing Klippel-Trénaunay-Weber Syndrome is not known. A mesodermal defects affecting angiogenesis and associated with persistent of the embryonic vascular network might explain the vascular anomalies.
Some believe that a disturbance in the regulation of tissue growth factors is the underlying mechanism.