Signs of osteochondroma on imaging
The main diagnostic marker is the continuity of the medullary cavity of the lesion with the underlying bone. This feature is best visualized on CT or MRI. The tumor may be pedunculated and grow away from the joint, or it may be sessile on a broad base.
On MRI, the cartilage cap is clearly differentiated: on T2-weighted and proton-density-weighted (PDW) scans, the cartilage produces a bright (hyperintense) signal, contrasting with the darker muscles. In children, the thickness of this cap reaches 1–3 cm, whereas in adults it thins down to a few millimeters and normally should not exceed 2 cm in thickness.
On ultrasound, the cap is visualized as a hypoechoic layer over a bright bone surface.
Possible complications
Solitary osteochondroma rarely undergoes malignant transformation on its own (risk is less than 1%). However, in hereditary multiple exostoses, the probability of chondrosarcomatous transformation increases to 3–5%.
Complications are most frequently related to the mechanical impact of the tumor on adjacent tissues:
- Soft tissue impingement and neurovascular compression.
- Muscle edema or formation of an adventitious bursa, which on imaging can mimic sarcomatous transformation.
- Rarely, pseudoaneurysm formation.
- Deformation of the adjacent bone or even synostosis (when growing in the forearm or lower leg).
Subungual exostosis
This lesion is often mistaken for an osteochondroma due to a similar radiographic appearance (appearing as a spur under the nail). However, histologically it is a distinct pathology.
Main difference: subungual exostosis has no connection to the medullary cavity. MRI reveals a fibrocartilaginous cap that is typically more massive than the bony base. Most commonly, the exostosis appears on the dorsal aspect of the distal phalanx of the great toe following trauma or infection.
Enchondroma
An enchondroma is an intramedullary tumor composed of lobules of benign hyaline cartilage. It is very common (ranking second among cartilaginous tumors), with a peak incidence between the ages of 10 and 40 years.
Where to look:
- Hands and feet (especially proximal phalanges and metacarpals).
- Long tubular bones (femur, tibia, humerus).
Imaging appearance: On radiography, it is a well-circumscribed, lobulated, or oval lytic lesion, often located eccentrically in the metaphysis or diaphysis. It may cause endosteal scalloping and expansion of the cortex. Internal mineralization is frequently visible. On MRI, the tumor shows lobulated contours, a hyperintense signal on T2-weighted images, and areas of signal void corresponding to calcifications. Contrast enhancement occurs along the septa.
A large enchondroma is difficult to differentiate from a Grade 1 chondrosarcoma. Features favoring malignancy include a size greater than 5–6 cm and deep endosteal scalloping from the inside (deep endosteal scalloping).
Briefly: answers to topical questions
What is the difference between pedunculated and sessile forms of osteochondroma?
Pedunculated and sessile forms of osteochondroma differ in their type of attachment to the parent bone and the direction of growth.
| Morphology | Features |
|---|---|
| Pedunculated (pedunculated) | Typically directed away from the joint. A continuous connection of the medullary cavity with the parent bone is visualized. |
| Sessile (sessile) | Characterized by a broad base without the formation of a distinct stalk. |
What is Maffucci syndrome and how does it manifest on radiographs?
Maffucci syndrome is a rare disorder characterized by multiple enchondromatosis combined with multiple soft tissue hemangiomas (occasionally lymphangiomas). In 50% of cases, the pathology is unilateral.
On radiographs, the syndrome manifests with the following features:
- Multiple enchondromas — visualized within the bones (e.g., in the phalanges of the fingers).
- Phleboliths (phleboliths) — calcified thrombi within the venous spaces of hemangiomas, located in the soft tissues. This is a specific sign that reliably differentiates this syndrome from Ollier disease.
What syndromes of multiple exostoses exist and how do they differ?
There are two main subtypes of multiple enchondromatosis, which differ in the presence of extraosseous manifestations and the risk of malignant transformation.
| Syndrome | Characteristic |
|---|---|
| Ollier disease (Ollier disease) | Lesions are limited to bone tissue. The risk of malignant transformation ranges from 5% to 30%. |
| Maffucci syndrome (Maffucci syndrome) | Bone lesions are combined with soft tissue hemangiomas and, less commonly, lymphangiomas. The risk of malignant transformation is about 20%, and there is also an increased incidence of pancreatic carcinoma and gliomas. |
Radiographically, Maffucci syndrome is reliably differentiated from Ollier disease by the presence of phleboliths in the soft tissues.
Difference between osteochondroma and subungual exostosis: Osteochondroma is "open" to the bone (medullary continuity), whereas exostosis is "closed" (no continuity).
Class and exam questions
In adults, the cartilage cap of an osteochondroma should not exceed 2 cm. It is typically only a few millimeters thick.
In adults, the cartilage cap of an osteochondroma should not exceed 2 cm. It is typically only a few millimeters thick.
Both conditions manifest with multiple enchondromas. However, Maffucci syndrome is characterized by soft tissue hemangiomas, which are reliably identified on radiographs by the presence of phleboliths.
Both conditions manifest with multiple enchondromas. However, Maffucci syndrome is characterized by soft tissue hemangiomas, which are reliably identified on radiographs by the presence of phleboliths.
The main risk is an increased probability of malignant transformation of the cartilage cap into chondrosarcoma (up to 3–5%), as well as metadiaphyseal bone deformities.
The main risk is an increased probability of malignant transformation of the cartilage cap into chondrosarcoma (up to 3–5%), as well as metadiaphyseal bone deformities.
What else to study on this topic
- MRI semiotics of low-grade chondral tumors
- Periosteal chondroma and its differential diagnosis
- Ollier disease: clinical presentation and complications
- Maffucci syndrome: combination of enchondromatosis and hemangiomas
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