Extramedullary Hematopoiesis in the Appendix Associated With Myelodysplastic Syndrome: A Case Report.

Extramedullary hematopoiesis (EMH) is characterized by the presence of hematopoietic tissue outside the bone marrow, more commonly in the liver and the spleen. However, there are very few reports of nonhepatosplenic extramedullary hematopoiesis (NHS-EMH). Among the NHS-EMHs, NHS-EMH in the appendix is extremely uncommon. We hereby present a case of appendiceal NHS-EMH and discuss it with a literature review. The patient was a gentleman in his 70s who had been treated for follicular lymphoma seven years ago. He gradually developed leukopenia and six months ago was diagnosed with myelodysplastic syndrome (MDS). Four days prior to admission, he developed abdominal pain that was localized to the right lower quadrant and was accompanied by fever and loss of appetite. Abdominal CT revealed a thickening of the appendiceal wall and increased fat density around it. A diagnosis of acute appendicitis was made, and he was treated conservatively. However, his condition did not improve, and a laparoscopic appendectomy was performed. Diffuse proliferation of hematopoietic cells in the submucosal layer of the appendix was observed on histopathological examination. This confirmed the diagnosis of NHS-EMH. The postoperative course was uneventful; however, the patient's MDS progressed to acute leukemia in the next four months, and he died 14 months after surgery. Appendiceal NHS-EMH is an extremely rare condition associated with clinical features that are similar to those of acute appendicitis, making preoperative diagnosis challenging. Temporary symptom control could be achieved with an appendectomy.