Fluid-filled lesion on a child's leg

A white male, aged 5 years, presents to the dermatology clinic for diagnosis and management of a lesion on his thigh. His mother reports the lesion began 5 months ago as a small plaque, with subsequent enlargement and development of fluid-filled lesions at the skin surface.

The lesions are asymptomatic but bleed with minor trauma. The boy has no other ...