Periosteal chondrosarcoma, also known as paracortical chondrosarcoma and parachondrosarcoma, is a benign hyaline cartilage tumor arising from the periosteum or subperiosteal connective tissue and occurring on the bone surface. Periosteal chondrosarcomas are quite rare, accounting for less than 2% of chondrosarcomas. It can develop in both adults and children, but is more common in young adults or adults between the ages of 20 and 40. There is no significant gender difference in the incidence. Site of disease Periosteal chondrosarcomas are most common in long tubular bones, especially the humerus and femur, and account for about 70% of cases. Short tubular bones (e.g., bones of the hand and foot) account for about 25% of cases. Periosteal chondrosarcoma mainly affects the epiphysis. Typical sites are the proximal ends of the humerus and tibia and the distal and proximal ends of the femur, often located at the attachment points of tendons and ligaments. Clinical manifestations Prolonged localized swelling of the limb may be associated with mild to moderate intermittent pain. Clinical examination may reveal a slow growing irregular hard mass on the limb. Imaging Diagnosis Imaging shows a clear or well-defined soft tissue mass with calcification near the surface of the bone cortex. The tumor may compress the surrounding bone cortex into a superficial defect with clear borders (“butterfly” sign). The bone surface is often rough and uneven, and may be associated with periosteal reaction and sclerosis, which does not communicate with the medullary cavity. The bone cortex close to the tumor may show reactive hyperplasia, forming a crater-like elevation. CT and MRI can clearly show the boundaries of the tumor and the invasion of the medullary cavity. The typical periosteal chondrosarcoma is a round or ovoid mass of various sizes located outside the bone cortex. Most of them do not exceed 4 cm in diameter and are covered by a fibrous envelope. The tumor is lobulated in section and is a light blue or grayish-white transparent cartilage; it has yellowish-white calcified spots or streaks. The tumor usually does not invade the soft tissue and medullary cavity. Microscopic examination Periosteal chondromas are composed of hyaline cartilage lobules. In some periosteal chondromas, the microscopic appearance is typical of that seen in endophytic chondromas, i.e., small, scattered cells with dense nuclei, or some cells are large and clustered with atypical or binucleated nuclei. The margins of the tumor often have numerous thin-walled vessels and foci of reactive new bone formation. The new bone may form a thin shell at the edge of the tumor growth. The base of the lesion is sclerotic new bone and is attached to the bone cortex. It is difficult to distinguish chondrosarcoma from periosteal soft tissue based on histologic examination alone. Treatment If a periosteal chondrosarcoma is asymptomatic and non-persistent (usually no further growth after the body growth has ended), the patient should be followed up without surgical treatment. If surgery is required, the tumor should be removed in its entirety, either marginally or extensively, to ensure a cure. However, transcatheter resection within the lesion also has a high success rate. Prognosis Periosteal chondrosarcoma can be treated by intra-lesion, marginal, or extensive resection. The recurrence rate is low regardless of the surgical approach used.