The American Society of Dermatopathology

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Interactive Case Study - October 2021

An enlarging right arm mass in a 7-month-old male

Anna Agaronov, OMS-III; Narciss Mobini, MD

Question 1:

A 7-month-old male presented with a right arm mass that had been growing for the past 4 months. Clinical differential diagnoses included lipoma, hemangioma, or rhabdomyosarcoma and the imaging studies including MRI, ultrasound, and doppler flows suggested the lesion to be either a hemangioma or rhabdomyosarcoma. A biopsy of the lesion revealed the following histopathologic changes:

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Which of the following is the best diagnosis?