19 y.o. man with known problem, referred to Orthopedic Clinic for further management.
Multiple hard nodular masses near extremity joints. They are somewhat deep to soft tissues and are non-tender.
Multiple well-defined pedunculated exophytic lesions project from the metaphyseal region of the distal femur and proximal tibia, oriented away from the left knee joint. There is medullary continuity with the bone of origin. The epiphyses and joints are uninvolved.
Well-defined osseous excrescence of the right fibular head which has medullary continuity with the fibula, and very little if any osteoid matrix. The lesion wraps around the tibia posteriorly, and causes deformity of the tibia but no invasion/destruction. Similar lesions are found in the distal tibiae bilaterally, causing deformity of the adjacent fibulae.
These imaging findings are diagnostic for Multiple Hereditary Exostoses. For less clear-cut cases, or when only a single lesion is identified, see the TF topic discussion for other diagnostic considerations.
Additional information to supplement the Topic Discussion:
* Though HME is rare in the general population, the prevalence is much higher in two isolated ethnic communities; The Chamorros of Guam (1/1000), and the Pauingassi of Manitoba Canada (1/100).
* HME should be differentiated from Dysplasia Epiphysealis Hemimelica, which also consists of multiple exostoses, but involves the epiphysis, often destroying the joint. It is usually unilateral.
* Multiple exostoses of the tibiae are also associated with Turner's Syndrome, and Fetal Alcohol Syndrome.
* Surgical treatment is on a symptomatic basis, and is usually delayed until after skeletal maturity, unless malignant degeneration occurs.
Hereditary multiple exostoses (HME) is an autosomal dominant condition resulting in multiple osteochondromas. In western populations the prevalence is approximately 1:50,000-100,000. Common clinical presentations include pain and cosmetic deformity.
Osteochondromas may be sessile or pedunculated and are the result of a separated cartilaginous fragment of the epiphyseal growth plate, which has herniated through the normal periosteal bone cuff (notch of Ranvier). This fragment continues to grow, resulting in an osseous protuberance with direct medullary continuity and a cartilaginous cap. Consequently, these lesions are typically found in a juxta-epiphyseal distribution.
Complications of osteochondromas include fracture, mass effect (vascular compromise and neurologic sequelae), bursa formation/inflammation (secondary to abnormal frictional forces), and malignant transformation. Malignant transformation occurs in approximately 1% of solitary osteochondromas and has been reported in approximately 3-5% of HME patients. The most commonly associated malignancy is chondrosarcoma but osteosarcoma is another possibility, albeit less likely.
There are several concerning radiographic findings which may suggest malignant transformation:
â€¢ Continued growth in a skeletally mature patient
â€¢ Irregular/indistinct surface
â€¢ Focal radiolucency
â€¢ Erosion/destruction of adjacent bone
â€¢ Soft tissue mass (with scattered irregular calcifications)
Finally, and perhaps the most important criterion, is a cartilaginous cap thickness greater than 1.5cm. This can be measured with ultrasound, CT and MRI.
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