Osteochondroma is also known as osteochondral exophytic warts. Osteochondroma is a warty bony bump that occurs on the surface of bone and is covered with cartilage cap. Osteochondroma is the most common bone tumor, accounting for about 35% of benign bone tumors and 8% of all bone tumors. It is divided into two types: solitary (isolated) and multiple. Multiple cases, also known as hereditary osteochondromatosis, is an autosomal dominant disease that can involve multiple long bones and is associated with bone dysplasia and bending or shortening deformities. However, there are no significant differences in age of onset or gender, whether solitary or multiple. Some osteochondromas occurring in specific locations have specific names. For example, osteochondromas that occur near the joint are called epiphyseal osteochondromas, and those that occur under the nail at the end of the finger (toe) bone are called subungual osteochondromas. Osteochondromas rarely become malignant. However, if the tumor grows rapidly within a short period of time, especially in adults, the possibility of malignancy should be highly suspected. Malignant osteochondroma is called chondrosarcoma. The most common sites of involvement are the distal femur, proximal tibia and proximal humerus epiphysis. Involvement of flat bones is uncommon, most often in the ilium and scapula. Clinical manifestations Most often seen in adolescents. Most patients do not have significant symptoms. The most common symptom is a localized, slow-growing, hard mass. It is usually seen as a result of incidental palpation of the mass or x-ray finding of the tumor. Some patients can develop symptoms due to compression of blood vessels, nerves and internal organs. Medial lesions on the lower femur or upper tibia can be painful due to direct impact on the mass or fracture of the tip due to tendon slippage. Larger tumors can compress nerves and cause symptoms. Compression of the cauda equina nerve can occur with lumbar spine lesions. Swellings in the foot and ankle can make walking and shoeing difficult. Some patients can have complications such as bursae or bursitis. Progressive pain and/or sudden enlargement of the mass is a sign of osteochondroma malignancy. Diagnostic imaging The characteristic structure of osteochondroma is a bony protrusion that is continuous with the basal bone and appears on X-ray as a bony lesion protruding from the basal bone (mainly the epiphysis). The bony prominence may have a narrow base with a long tip or a broad base with a short tip, and in a few larger tumors the tip may be expanded like a cauliflower. However, regardless of the morphology of the bony prominence, it always points toward the diaphysis and away from the epiphysis. The margins can be neat but can also be uneven, depending on the amount of apical cartilage. Irregular calcification may occasionally be seen at the tip. If it is in the shape of an ink stain on blotting paper, it indicates that the cartilage in it has not yet calcified. Because the cartilage cap and secondary synovium of an osteochondroma are not visualized on x-ray, the bony prominence is often smaller than the actual tumor. If extensive irregular intrachondral flocculent and speckled calcifications are seen, one needs to be alert for malignancy. CT can better show irregular tumors in the mid-axis of the backbone, and there can be round or cauliflower-shaped irregular high-density shadow at the tip, which is due to calcification of the cartilage cap. MRI can show the relationship between tumor and basal bone from multiple directions and angles, and the special cartilage signal can directly show the cartilage cap, and the change of cartilage cap is an important sign of malignancy. MRI can also show the bursal changes around the tumor, and these are the advantages of MRI examination. The cartilage cap is low signal on T1-weighted images and significantly high signal on fat-suppressed T2-weighted images, with signal characteristics similar to those of articular hyaline cartilage. The thickened cartilage cap needs to be alerted for malignant changes. Pathologic diagnosis Gross examination Osteochondroma is a tipped or broad-based bony protrusion with cortical and medullary cavities that are continuous with the basal bone. The tumor varies in size and is generally 3 cm to 4 cm in diameter, with larger ones reaching 10 cm or more. Thickening (>2cm) and irregular cartilage cap suggest the possibility of malignant transformation. The thickness of the cartilage cap varies with the age of the patient, and the younger the patient, the thicker the cartilage cap is; in adults, the cartilage cap is very thin or almost disappears, and its thickness is mostly between 1 and 5 mm. In adults, the cartilage cap is thin or almost disappears, and its thickness is mostly between 1 and 5 mm. Microscopically, it is similar to the normal cartilage epiphyseal plate, the surface chondrocytes and stromal tissue are less mature, the closer to the base, the more mature, the mature chondrocytes at the junction are arranged in columnar shape, and calcification and ossification are seen. The base of the tumor is the main body of the tumor, which often accounts for most of the tumor and is composed of spongy cancellous bone, with fibrous tissue between the trabeculae and rich capillary network. The diameter of the tumor is usually 3-4 cm, and the larger ones can be more than 8 cm. In adults, if the diameter of osteochondroma exceeds 8 cm, the possibility of chondrosarcoma should be alerted. A secondary bursa may form at the tip of the osteochondroma, especially if the larger tumor is against a muscle or tendon, which often rubs back and forth against the tip of the osteochondroma. The inner surface of the bursa may be covered with synovial membrane, and the bursa cavity can sometimes contain free bodies. Treatment Asymptomatic people can be treated without considering surgery, and close observation is sufficient. However, surgery should be considered if the following conditions occur: the tumor is too large and affects the appearance; symptoms appear (pain, affect joint function, compression of blood vessels, nerves or other important tissues, etc.); it continues to grow in adulthood; malignant tendency is suspected; it is located in the medial bones, such as pelvis, scapula, spine, etc. The scope of resection during surgery should include part of normal bone tissue around the base of the tumor to avoid missing and causing recurrence. Prognosis After cessation of development, most osteochondromas stop growing and no special treatment is needed. After surgical resection, the tumor can be cured in general. Recurrence is usually seen in those with incomplete resection. However, multiple recurrences or recurrence after complete resection should indicate the possibility of malignancy.