The occurrence of extramedullary hematopoiesis in the pleura is rare and is usually asymptomatic. It is generally diagnosed on postmortem examination. Herein we describe a 61-year-old woman with agnogenic myeloid metaplasia who sought medical assessment because of progressive dyspnea. Thoracentesis yielded sanguineous fluid with 10% myeloblasts. A 99mTc bone marrow scan demonstrated increased tracer activity throughout both lungs, an outcome consistent with extramedullary hematopoiesis. Fine-needle aspiration and video-assisted thoracoscopy were considered but deferred because of the potential risk of profuse bleeding. Treatment with low-dose external beam irradiation to the left posterior pleura was successful. To date, no hemothorax has recurred.

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