Patient with hip pain.
A patient presented with atypical hip pain. Therefore plain radiographs of both hips and knees were ordered. The anteroposterior radiograph of the right hip revealed large exostoses of the femoral neck. Continuity of the cortex and marrow of the lesion with the underlying femur were suggestive for osteocartilaginous exostoses. Beneath the exostosis, a few rounded calcifications were visible in the soft tissues. To clarify the origin of these calcifications and to exclude malignancy, an MRI of both hips and thighs was ordered. The anteroposterior radiograph of the right knee also revealed several osteocartilaginous exostoses. The multiplicity of these lesions suggest the diagnosis of Hereditary Multiple Exostoses. The MR examination confirmed the diagnosis of HME, and also showed a large bursa filled with calcifications, suggesting secondary synovial osteochondromatosis.
An osteocartilaginous exostosis, also known as osteochondroma, is the most frequent benign bone tumor, in fact rather a developmental disorder than a real neoplasm. These lesions are caused by a herniation of the epiphyseal growth plate through the periost resulting in the separation of a cartilage fragment. This cartilage cap acts like an enchondral plate and is responsible for a progressive ossification. Continuation of cortical and medullary bone with the underlying bone can be seen on the radiographics. The most common site of involvement is the metaphyseal and/or diaphyseal area. They occur most often in the femur, tibia and humerus. If multiple, they are more suggestive for Hereditary Multiple Exostoses (HME), a hereditary autosomal dominant disorder. In most cases, no symptoms are present, but pain can develop due to a mechanical conflict. Other complications are cosmetic/ osseus deformity, fracture and vascular or neurologic compromise. Formation of large bursa is a rarely described complication. It is most frequently related to sites with motion where friction develops. In our case, friction between the exostosis at the posteror side of the femoral neck and the ischial tuberosity may have induced the bursa formation. Because of this chronical irritation, the bursa has enlarged as a result of increased synovial fluid production. Within the synovium of these bursae, secondary synovial osteochondromatosis ( SOC) can occur, due to a metaplastic condition. SOC is an uncommon disorder characterised by the formation of multiple cartilaginous nodules, who can become calcified or ossified and may detach from the synovium to become loose bodies. These calcifications should not be confused with a calcified cartilaginous cap. In our patient the calcifications were located 10cm below the exostosis: this was also suggestive for calcified loose bodies in SOC. The occurance of SOC within a bursa associated with an osteochondroma is very rare with only 6 cases reported to date. Peh et al. stated that shedding of osteochondroma fragments into the bursal cavity could lead to changes in the bursal synovial lining, contributing to further development of osteochondral nodules. The cartilage cap can transform into a malignant chondrosarcoma. Suggestive findings for malignant degeneration are: a cartilage cap more than 2cm ( significant soft tissue mass containing particular scattered or irregular calcification), irregular or indistinct surface, growth of previously unchanged osteochondroma in a skeletally mature patient, focal regions of radiolucency in the interior of the lesion, and erosion or destruction of the adjacent bone. Patients with HME are at greater risk to develop a malignancy. Malignant transformation is seen in 1% of solitary osteochondroma and in 3%-5% of patients with HME. In our patient, the cartilaginous cap of the femoral exostosis was less than 2 cm.
Osteocartilaginous exostoses with large bursa formation and secondary synovial osteochondromatosis.
Considering the patient is a 41-year-old male with hip pain and imaging findings of an osteochondroma-like protrusion and multiple calcifications in adjacent cystic lesions, the likely diagnosis is: “Osteochondroma of the right femoral neck with secondary bursa formation and synovial osteochondromatosis changes.”
The cartilage cap is currently less than 2 cm and shows no obvious signs of malignant transformation; thus, chondrosarcoma is not strongly considered at this time.
Disclaimer: This report provides a reference based on imaging and clinical information and cannot replace in-person consultations or professional medical advice. If you have any concerns or experience any progression of symptoms, please consult a specialist or visit a medical facility promptly.
Osteocartilaginous exostoses with large bursa formation and secondary synovial osteochondromatosis.
