Thrombi often form within vessels and develop into phleboliths. These phleboliths appear as calcified vessels under microscopic examination. Enchondromas develop from the mesodermal dysplasia associated with Maffucci syndrome. As the bones grow, some cartilage material is left behind and grows irregularly, developing into the characteristic bone deformities. Bone irregularities include shortened length of long bones, unequal leg length, pathological fractures and malunion of fractures.
Neoplastic changes occur in enchondromas.
The average age for neoplastic change is 40 years of age. Vascular neoplasms have occurred in four reported cases, two hemangiosarcomas and two lymphangiosarcomas. Less than 100 cases have been reported in the United States. Bone and skin abnormalities cease by the second to third decade. Patients have a good prognosis if no malignant degeneration occurs.