Extramedullary Hematopoiesis Presenting as Pleural Thickening in a Patient With Choroidal Melanoma.

Extramedullary hematopoiesis (EMH), the generation of blood cells by organs other than the bone marrow, most often occurs in the spleen or liver. However, it has been known to uncommonly occur in other locations. EMH in these locations does not consistently manifest in the same way, making this a difficult diagnosis to make. We report the case of a 79-year-old male former smoker with a history of choroidal melanoma and polycythemia vera who presented with a chronic cough and weight loss of 30 pounds over the last year. A CT scan revealed a 15 mm right basilar pleural enhancement suspicious for malignancy on imaging. Upon biopsy, it was found that the pleural enhancement was EMH due to post-polycythemia vera myelofibrosis. EMH can be difficult to distinguish from metastasis, especially in atypical locations and in patients with a history of malignancy.