Anaplastic cutaneous lymphoma mimicking an infection.

We present a case of a 17-year-old boy who presented with a skin lesion with extension to the soft tissues of the left thigh. On ultrasound, a homogeneous and hypoechoic expansile formation in the subcutaneous tissue was found, measuring 6.5 × 5 × 3.5 cm, with scarce vascularization. Computed tomography showed a low attenuating neoformation with surrounding edema. An inflammatory disorder was the first diagnosis, but the absence of improvement with antibiotics led us to perform magnetic resonance imaging that showed a high signal lesion on T2-weighted imaging and low intensity signal on T1-weighted imaging and surrounding contrast uptake. Positron emission tomography and computed tomography showed uptake of 18F-fluorodeoxyglucose by the lesion. The final diagnosis was anaplastic cutaneous lymphoma.