A 12-year-old girl came to our centre for occasional knee pain related to physical activity.
There was no history of trauma, night pain or fever.
On physical examination a firm, fixed mass, mildly tender to palpation was located at the medial aspect of the right thigh.
On plain radiograph (Fig. 1), a solitary sessile exostosis was identified at the medial aspect of the distal femoral metaphysis.
An MR examination (Fig. 2) revealed the cortical and medullary continuity of the lesion with the original bone.
Treatment options were discussed and surgical excision was recommended, however, the family chose to observe the lesion.
At three-year follow-up, plain X-rays and MR (Fig. 3) showed disappearance of the lesion.
Osteochondroma represents the most common bone tumour and constitutes 20%-50% of all benign bone tumours. [1]
It most commonly occurs in the metaphyseal region of the long bones. [2]
Most lesions appear in children and adolescents, and tend to be painless, slow-growing masses that may go unnoticed. Additional symptomatic complications include osseous deformity, fracture, vascular compromise, neurologic sequelae, overlying bursa formation, and malignant transformation [3].
The radiographic appearance of this tumour is often diagnostic and reflects its pathologic characteristics, a lesion composed of cortical and medullary bone with an overlying hyaline cartilage cap. The presence of this hyaline cartilage cap thickness is an important criterion in determining malignant transformation of the lesion. Additional imaging modalities frequently employed in the evaluation of this lesion include bone scintigraphy, US, CT and MR [4].
There are few cases of spontaneous regression of solitary osteochondromas reported in the literature and many theories have been proposed. One of them says that the active resorption and metaphyseal remodelling caused by altered vascular supply due to fractures may lead to cessation of the cartilage cap and subsequent tumour regression [5]. It is also described that osteochondroma resorption occurs as a result of an accompanying pseudoaneurysm [6]. Other authors have proposed that osteochondroma growth ceases before somatic growth ceases, followed by incorporation of the lesion into the cortex by appositional growth of the adjacent bone [7]. This last theory relates to our case. We attributed the spontaneous disappearance to a physiological mechanism, probably the osteochondroma growth ceased because our patient was near to her somatic growth cessation period.
Spontaneous regression of others benign bone tumours or tumour-like lesions have been also reported, for example eosinophilic granuloma, fibrous dysplasia, fibrous cortical defect, non-ossifying fibroma, osteoid osteoma and bone island [8]. In inflammatory-related lesions such as eosinophilic granuloma, cessation of inflammation may be the mechanism of growth arrest. Necrosis within the tumour and/or local changes in hormonal control, plus remodelling of the sclerotic area may lead to tumour regression.
Treatment of osteochondroma is individualized, with small asymptomatic or minimally symptomatic lesions requiring only supportive management and close follow-up. Larger symptomatic lesions may be resected, although surgical resection of benign osteochondromas is not without complications [9]. As the patient had already developed clinical manifestations, surgical approach was recommended. However, the possibility of regression of solitary osteochondromas should be taken into account when considering surgical excision [10].
Evanescent osteochondroma
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Based on the provided X-ray and MRI images, the following observations can be made:
Based on these imaging characteristics, this suggests a benign bony exostosis originating from the metaphyseal region of a long bone.
Combining the patient’s age, clinical presentation, and imaging findings, the following are the potential diagnoses or differentials:
Considering the patient’s age, occasional knee pain, the palpable fixed mass on clinical exam, and imaging findings showing a bony outgrowth continuous with the cortex and marrow, with a normal-appearing cartilaginous cap and no signs of malignancy, the most likely diagnosis is:
Osteochondroma
If there is still clinical doubt or a need to evaluate the thickness of the cartilaginous cap, further MRI sequences or follow-up can be considered. If symptoms worsen or the cartilaginous cap thickens, malignant transformation should be ruled out.
For this patient, if symptoms are not severe and conservative follow-up is chosen, moderate exercise is advised to maintain joint and muscle function while minimizing stress on the knee joint. The FITT-VP principle is recommended:
If surgical treatment is performed, postoperative rehabilitation should be carried out under the guidance of a professional rehabilitation therapist, focusing on:
This report provides a reference analysis based on the presented clinical and imaging data. It does not replace an in-person specialty consultation, further diagnostic tests (such as pathology or lab tests), or professional face-to-face advice from a qualified physician. If you have any questions, please consult an orthopedic specialist or related professional for a more comprehensive and individualized medical guidance.
Evanescent osteochondroma
