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

## TL;DR

A patient with a history of cancer and blood disorder had pleural thickening caused by blood cell production outside the bone marrow, which was initially mistaken for cancer spread.

## Contribution

This case highlights the diagnostic challenge of extramedullary hematopoiesis mimicking malignancy in atypical locations.

## Key findings

- Pleural enhancement was diagnosed as extramedullary hematopoiesis, not cancer metastasis.
- The condition was linked to post-polycythemia vera myelofibrosis.
- EMH can present as pleural thickening, complicating cancer follow-up.

## Abstract

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.