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We report the youngest recorded example of a fibrocartilagenous mesenchymoma of bone, with an age at presentation of 1 year and 7 months. The youngest previously recorded cases have been in 9 year old patients.
A male infant aged 1 year and 10 months originally presented to the orthopaedic clinic with a three month history of limping and pain in the left leg. There was no history of trauma and there were no localising signs in the left leg. An x ray showed a lucent area with surrounding sclerosis involving the proximal left tibial metaphysis. He had originally been brought to the accident and emergency unit two days after the initial onset of symptoms (aged 1 year and 7 months) and radiographs taken at that time had shown no significant abnormalities. Therefore, the lesion had progressed rapidly over three months (fig 1).
Because of the presence of symptoms and the rapid progression radiologically, open biopsy and currettage of the lesion were carried out. At surgery the cavity contained reddish brown fluid. Microbiological examination of the tissue removed showed no subsequent bacterial growth. After surgery the child’s symptoms resolved, and radiographs taken four months later showed a decrease in the size of the lucent area.
The specimen received consisted of multiple small fragments of tissue, which included bone.
Histologically, it contained bland but quite cellular fibrous tissue within which there were islands of hyaline cartilage, some of which were possibly metaplastic. Most of the cartilage had large nuclei and it was neither reactive nor part of the growth plate. A tiny focus of growth plate-like tissue was seen. The histological features were those of a fibrocartilagenous mesenchymoma of bone (fig 2).
The term fibrocartilagenous mesenchymoma with low grade malignancy was first described by Dahlin et al for a rare bone tumour that had a specific clinical behaviour, radiological features, and morphological features.1 The differential diagnosis of this lesion involves several entities, including chest wall hamartoma (mesenchymoma) and dedifferentiated chondrosarcoma.2,3 The most important differential diagnosis is fibrous dysplasia with cartilaginous differentiation. The tumour usually occurs in the metaphyses of the long bones and commonly presents with pain. Other sites have been documented, such as the metatarsal bones, vertebrae, and the pubis.4
Radiologically, this tumour often abuts an open growth plate. These tumours are predominantly radiolucent, although some mineralisation is often seen. Cortical destruction is an additional common finding.1
This lesion is generally treated by surgical resection. Local recurrences have been recorded. On review of the current limited literature, no distant spread has been recorded and there is no associated mortality. This entity is thought to represent a true neoplasm rather than a hamartoma.
There have been four previously published series describing fibrocartilagenous mesenchymoma of bone comprising, in total, 20 patients. Our patient is more than 7 years younger than the youngest previously recorded case. The light microscopic features together with the clinical presentation and radiological appearance are characteristic. The most important histological feature is cartilage with the appearance of epiphyseal plates.
Some cases recur locally, but no metastasis or death was caused by these lesions. Dahlin thought that this lesion was of low grade malignancy.1 A more recent series suggests that the term malignant is not warranted.4
In summary, the average age of occurrence of this tumour in previous published series is calculated to be 14 years and 10 months. The youngest previously recorded cases were in 9 year old patients.1,4 Therefore, our patient, who is more than 7 years younger than these individuals, is the youngest patient to be recorded with this diagnosis.
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