Osteochondroma is a cartilaginous abnormality of bone development, also known as osteochondral ectoplasia, which can be solitary or multiple, and is called hereditary multiple osteochondroma because it runs in families. The age of onset is more than 5 years old, more males than females, and the ratio of males to females is 1.5 to 2:1. Most of the cases are found in the epiphysis of the long bones of the limbs and the pelvic bones and scapulae.
Etiology and pathology
Solitary osteochondroma is a misshapen tumor located on the bone surface. The heredity and multiplicity of hereditary multiple osteochondromas suggest a congenital malformation tumor in origin.
Clinical manifestations
Solitary osteochondroma presents clinically as a slow-growing, painless, hard, fixed mass that originates on the bone surface without adhesion to the surrounding soft tissues. Sometimes the osteochondroma rubs against the muscles and tendons that cover its surface and forms a synovial cyst. Symptoms are caused by mechanical compression of the surrounding soft tissues and may occasionally affect joint function.
In hereditary multiple osteochondromas, the symptoms are multiple bony end masses, which are often asymmetrical on palpation. In severe cases, the limbs may be shortened, often with forearm bowing, radial head dislocation, knee valgus, and foot drop due to compression of the common peroneal nerve by the proximal fibular mass. In adults, the sudden onset of pain and enlargement of the mass is a sign of malignancy.
Auxiliary examination
1.X-ray: It is an outward bony protrusion attached to the epiphysis, growing in the same direction as the muscle traction, connected with the affected bone cortex and cancellous bone, and the cartilage cap is not visible, and there are long-tipped type and broad-based type.
Multiple osteochondroma shows thickening of the epiphysis, thinning of the cortex, different shapes of the tumor, and often deformity of the affected bone and joint. When the tumor is malignant, the cartilage part on its surface grows rapidly, and when there is a large amount of calcification, the x-ray performance is obvious.
2.Radionuclide scan: the junction of bony part and cartilage cap of osteochondroma is concentrated with radionuclide, when there is malignant change, the radionuclide uptake at the lesion will be suddenly increased.
3.CT examination: It can clearly show that the tumor is connected with the affected bone cortex and cancellous bone, and the cartilage cap part shows soft tissue density, sometimes irregular calcification and ossification can be seen.
4.MRI examination: the signal of bony part is the same as that of cancellous bone in adjacent epiphysis, and the cartilage cap shows low signal in T1-weighted image and high signal in T2-weighted image; MRI examination can clarify the thickness of cartilage cap, if it is more than 25mm, it should be considered as possible malignant change.
5, pathological examination: the surface of the bony mass seen by the naked eye is covered with a thin layer of translucent blue-gray cartilage. It pushes the surrounding soft tissue and forms a thin layer of loose tissue with the adjacent muscle tissue, making it easy to perform blunt peeling. Below the cartilage cap is a thin band of chalky calcified cartilage and below this is cancellous bone with yellow bone marrow between them. In adults, the average thickness of the cartilage cap is 3 to 5 mm. When there is malignancy, the cartilage cap of osteochondroma grows into the surrounding soft tissue, and if it exceeds 25 mm, malignancy is highly suspected.
Microscopically, the cartilage cap is composed of hyaline cartilage with a columnar arrangement of outer cells, under which a mast cell layer and a degenerated matrix calcified layer as well as primary trabecular bone are clearly visible. The growth mechanism of the cartilage cap is similar to that of the epiphyseal plate in all respects.
Diagnostic points
1. The clinical manifestation is a slow-growing, painless, hard, fixed mass.
2. X-ray shows a bony protrusion outward from the epiphyseal cortex of the affected bone, which is connected to the affected bone cortex and cancellous bone.
Pathological examination shows a thin layer of translucent blue-gray cartilage covering the surface of the bony mass, a thin layer of loose tissue covering the cartilage surface, and a cartilage cap composed of chondrocytes arranged in a columnar pattern, under which a mast cell layer and a degenerated matrix calcification layer as well as the primary trabecular bone are clearly visible.
Differential diagnosis
Parosteal osteosarcoma is a primary malignant tumor in the soft tissue adjacent to the bone surface that tends to grow around the bone. In the early stage, there may be a narrow translucent gap between the lesion and the bone, mostly without periosteal reaction. The main points of differentiation from osteochondroma are long history of the latter, no clinical pain when it is not malignant, no venous expansion on the surface, no high skin temperature, clear margins on X-ray and CT examination, no translucent gap between the lesion and bone, and clear differentiation on pathological examination.