Presentation
Pain and palpable protruding mass under the skin on the anterior surface of the lower one-third of the left thigh.
Patient Data
On the x-ray, there is evidence of a bony protrusion located at the metaphysis on the anteromedial side of the distal femur. The lesion is pedunculated, pushing the corresponding soft tissue outward. The cortex of the lesion is continuous with the cortex of the healthy bone, and the medullary cavity is continuous with that of the healthy bone. There is no calcification and no periosteal reaction.
The MRI confirms the findings described on the x-ray, adding further details such as the absence of a soft tissue mass, with a visible cartilage cap measuring approximately 4 mm, showing high signal intensity on STIR and PDFS sequences. The lesion is solitary, and no signs suspicious of malignant transformation are noted.
Case Discussion
The findings on x-ray and MRI are typical for osteochondroma, a common benign bone tumor, often asymptomatic, solitary, and with a low rate of malignant transformation. When multiple and symmetrical, these lesions may be associated with hereditary multiple exostoses syndrome. Typical lesions are usually found in long bones, at the metaphyseal region, and can be pedunculated, sessile, or cauliflower-shaped, with ring-and-arc calcifications, a cartilage cap, and continuity between the cortex and medullary cavity of the lesion with the healthy bone. These can occur at any age, with no malignant features such as periosteal reaction, soft tissue mass formation, or cortical destruction.
Some features of malignant transformation that should be noted are as follows:
G: growth after skeletal maturity
L: lucency (new)
A: additional scintigraphic activity
D: destruction (cortical)
P: pain after puberty
a: and
S: soft tissue mass
T: thickened cartilage cap >1.5 cm
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