Extramedullary Hematopoiesis on the Aortic Valve

A 74-year-old woman was a nonsmoker who had asymptomatic mild aortic stenosis. On close follow-up observation, she was noted to have increased intensity of her murmur. She had noticed new-onset exertional chest discomfort but appeared otherwise to be healthy. She had no hematologic abnormalities and had not been exposed to exogenous myeloid growth factors. Further evaluation revealed a heavily calcified trileaflet aortic valve, with a peak gradient of 47 mmHg and a calculated valve area of 0.68 cm². The patient subsequently chose to undergo aortic valve replacement.

On examination, the explanted heart valve showed nodular fibrosis and myxoid degeneration. Microscopy revealed extensive metaplastic bone formation in association with extramedullary hematopoiesis characterized by appropriate populations of megakaryocytes, erythroid cells, and myeloid cells (Figs. 1 and 2).

Fig. 1 Photomicrograph of aortic valve shows metaplastic lamellar bone formation (arrow) and scattered extramedullary hematopoietic cellular elements (arrowhead) with fat cells (round clear voids) (H & E, orig. ×4).

Fig. 2 Photomicrograph of aortic valve shows extramedullary hematopoiesis characterized by populations of megakaryocytes, erythroid cells, myeloid cells, and fat cells (H & E, orig. ×12).

Comment

Around one tenth of all calcified aortic valves have heterotopic ossification; however, they rarely harbor myeloid elements.¹ The mechanism of such nonhepatosplenic extramedullary hemopoiesis in the absence of hematologic disorder is poorly understood. Of interest is the possibility that hematopoiesis contributed to the severity of this patient's valvular stenosis.