On gross examination, an enchondroma consists of bluish-gray lobules of fine translucent tissue. The degree of calcification of the lesion determines if the consistency is gritty. Under the microscope, a thin layer of lamellar bone surrounding the cartilage nodules is a positive sign that the lesion is benign. At low power, there are lobules of different sizes. Blood vessels are surrounded by osteoid.
Enchondromas have chondrocytes without atypia inside hyaline cartilage.
The nuclei are small, round and pyknotic. The cellularity varies between lesions and within the same lesion. Each potential enchondroma needs to be evaluated for cellularity, nuclear atypia, double nucleated chondrocytes and mitotic activity in a viable area without calcifications to distinguish it from low-grade chondrosarcoma. Small peripheral lesions are more likely to be benign than large axial lesions. The pathologic diagnosis is so difficult it always needs to be made in conjunction with the radiologist and the surgeon.