Extramedullary Hematopoiesis: Cytomorphologic, Histologic, and Radiologic Findings in Sixteen Cases

We report a case series of extramedullary hematopoiesis (EMH) diagnosed from the fine needle aspiration (FNA) procedure. Unanticipated EMH is a markedly rare diagnosis that typically presents as a solitary mass of undetermined significance. As such, knowledge of cytopathologic characteristics as well as clinical and radiologic correlates of EMH is paramount.

A total of 16 EMH cytopathologic cases were seen at the Johns Hopkins Hospital in the past 22 years.

Median age at diagnosis was 61 years and there was no gender bias (male-to-female ratio: 1:1). Presenting signs and symptoms varied widely, from incidental radiographic findings to hemiparesis. Likewise, presumptive clinical diagnoses in 11 of the 16 cases were benign and the other 5 were considered malignant prior to the diagnostic FNA. The most common anatomic site for EMH was the liver, followed by the presacral soft tissue and pleura. While most EMH nodules were singular, a few presented with as many as three radiographically distinct nodules. The average EMH nodule measured 2.8 cm; the EMH liver nodules were larger and measured 4.3 cm on average (p = 0.0043).

We share here the salient clinical and radiologic findings and the diagnostic cytopathologic features of EMH in an effort to familiarize the pathologist/cytotechnologist community with this fascinating albeit rare entity.