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A 16-month-old boy presents to the emergency department referred by his general practitioner with a painless lump on his right leg gradually increasing in size over the last 3 weeks. There is no associated trauma, no similar swellings elsewhere, and no weight loss, night sweats, fever or ill health. Although not walking independently, he can bear weight on his legs, stand with support and cruise. His fine motor and sociocommunicative milestones are age-appropriate. Examination reveals a 1.5 cm hard, painless, spherical lesion with smooth surface, non-mobile and likely adherent to the underlying bone. Its location is over the mid-shaft of the right tibia. Systemic examination is normal.
He had an anteroposterior and lateral X-ray of the tibia and fibula showing a radio-opaque nodule overlying the right tibia anteriorly and separate from the underlying bone with no underlying bony abnormality (figures 1 and 2), and an ultrasound of the lesion showing the nodule to be hyperechoic with significant posterior acoustic shadowing with no colour Doppler flow or vascularity. The lesion appears within the muscle layer (figure 3).
Test your knowledge
What is the likely diagnosis?
Calcified haemangioma
Myositis ossificans
Periosteal chondroma
Soft tissue sarcoma
Post-traumatic periostitis
Pilomatrixoma
What is the further management?
Watchful clinical surveillance only
Watchful clinical surveillance and ultrasound/X-ray in a few months
MRI or CT scan of the lesion
Incisional biopsy
Excision biopsy
What is the overall prognosis of the lesion?
Answers can be found on page 2.
Answers to the questions on page 1
Question 1
B. Myositis ossificans
Figure 4 demonstrates the anatomical layers of the leg in longitudinal view.
Table 1 demonstrates the key features of each of the options with clinical correlation.1–3
Question 2
B. Watchful clinical surveillance and ultrasound/X-ray in a few months
Since the lesion is painless, with no functional limitation or red flags, it is appropriate to remain watchful without active interventions such as biopsy or excision. A follow-up ultrasound and X-ray in a few months can assess for any changes in the radiological appearance of the underlying bone and the lesion itself. While a CT or an MRI will help discern anatomy better,4 it must be weighed against the risk involved.
The benefits of a CT scan include good spatial resolution showing the position of the lesion either entirely within the deep muscle or the periosteum, but lacks contrast between soft tissue layers. It can also visualise any gross abnormalities in the adjacent bone, although the marrow is not well assessed. Risks include larger dose of radiation in a young child with radiosensitive tissue and compliance with the procedure.
MRI is useful in characterising the lesion, its origin (muscle, fascia, periosteum or cortex) and the adjacent soft tissues and in the assessment of bone marrow for any signal abnormalities, which could indicate malignancy. MRI would be the primary method of characterising a neoplasm such as osteosarcoma. The disadvantages of MRI include limited characterisation of the lesion due to uniformly low signal related to calcification within the lesion. Also, the need for a general anaesthetic to improve compliance with the procedure poses a significant health risk. If however there were serious concerns about an underlying malignancy, then MRI would be the most beneficial investigation.
Question 3
Myositis ossificans (non-hereditary)—a misnomer from a calcified haematoma—is characterised by a heterotopic ossification within the muscle, typically presenting as a painful, enlarging tender mass following an injury, commonly within the large muscles seen in young adults and rare in preschool children. Prognosis is good, with treatment usually being conservative, resulting in spontaneous progressive resorption of the ossified mass.5 Surgical resection is usually curative but reserved for symptomatic lesions.
Ethics statements
Patient consent for publication
Footnotes
Contributors Original artwork by PR.
Funding The authors have not declared a specific grant for this research from any funding agency in the public, commercial or not-for-profit sectors.
Competing interests None declared.
Provenance and peer review Not commissioned; externally peer reviewed.