Extramedullary hematopoiesis mimicking acute appendicitis: a rare complication of idiopathic myelofibrosis.

Extramedullary hematopoiesis (EMH) is rarely found in the gastrointestinal tract. To our knowledge, EMH involving the appendix was not described. We report a case with a previous history of idiopathic myelofibrosis, which presented with clinical findings of acute appendicitis that necessitate appendectomy after the relief of his anemia. Microscopic examination and immunohistochemistry revealed foci of EMH throughout the mucosa and the submucosa. In the latter, small clusters of hematopoietic cells were also detected in a few dilated vascular structures. The histopathological features of acute appendicitis were not observed. Our case supports that EMH might develop in organs that are not involved in hematopoiesis. Although in gastrointestinal system, obstruction and bleeding are the most common symptomatic manifestations, this case emphasizes that EMH might also present clinically as acute appendicitis. The absence of histopathological features of acute appendicitis raises the possibility that local production of some mediators from hematopoietic precursor cells might contribute to this clinical presentation.