Contributed by Milon Amin, MD and Sara Monaco, MD
An 86-year-old woman presented to an outpatient orthopedic clinic with lower back pain, exacerbated by sitting. She also noted the presence of a 'bump' in her lower back that was slowly growing over the past two years.
Physical examination revealed a firm, palpable area in the sacrococcygeal region. The skin overlying this mass was intact, with some erythema and bluish discoloration. A computed tomography scan showed a 10 x 9 x 8 cm soft tissue mass in the sacrococcygeal region.
A fine needle aspiration (FNA) of this mass was performed by the pathologist.
After reviewing the Romanowsky-type stained slides (Images 1, 2, 3 and 4), the clinician asks for an immediate impression.