A 12-year-old girl is brought to dermatology by her mother for evaluation of a lesion on her arm. It’s been there for two years without causing symptoms—but lately it has grown, as has the mother’s concern.
The child is otherwise healthy. The mother reports that the child has neither a personal nor a family history of seizures.
EXAMINATION
A solitary, firm, subcutaneous nodule measuring 2 cm is located on the lateral aspect of the child’s left triceps. It is bluish pink, nontender, and firm on palpation. No other overlying skin changes are seen.
Lateral digital traction toward the center of the lesion produces no dimpling, while lateral traction toward its periphery accentuates the lesion’s central raised portion. The lesion is moderately mobile. No lymph nodes are felt on palpation of nodal sites in the area, and no other such lesions are found elsewhere on the child’s skin.
What is the diagnosis?