Abstract
2036
Objectives: 1. What is Extramedullary Leukemia (EML) 2. Understanding the pathogenesis of EML in brief 3. Imaging atlas showing various sites of involvement 4. In short, management of EML 5. Briefly describe the prognosis in EML.
Introduction: What is EML? Extramedullary leukemia is the presence of leukemic cell aggregates in the form of solid tumor outside that of bone marrow (1). It is most commonly seen with acute myeloid leukemia and less commonly with other forms of leukemia like acute lymphoblastic leukemia (2). Extramedullary myeloid leukemia is also known as myeloid sarcoma or chloroma and is basically a solid tumor of myeloblasts (3). EML is more commonly seen in the setting of disease relapse and less commonly at the time of initial presentation. A variety of extramedullary sites and organs can be involved, and examples of such will be presented (4). There is no specific terminology for extramedullary acute lymphoblastic leukemia and it can be challenging to diagnose this, especially in absence of marrow involvement (2). Pathogenesis: Myeloid sarcoma - Hematopoietic stem cells are present in the embryonic aorta-gonad- mesonephros during development and eventually are predominantly found in the bone marrow and liver in adult life. The extramedullary sites can get activated due to multiple genetic and molecular etiologies resulting including chemokine receptor signaling pathways, leading to the formation of solid tumors (1, 5). Pathogenesis of extramedullary lymphoblastic leukemia is not very well elucidated, however, it also appears to depend on chemokine receptor signaling pathways, resulting in migration and growth of tumor outside the medullary cavity (6) Management: Once the diagnosis of the extramedullary disease is made, the systemic treatment used for acute myeloid leukemia is initiated. Bone marrow/stem cell transplant is also utilized (7). In the research setting, multiple targeted drugs and immunotherapy have been employed. Surgery and radiation therapy for symptomatic or compressive masses may be considered in some cases (8, 9). Chemotherapy is the mainstay of treatment in extramedullary lymphoblastic leukemia. Rituximab may be added and has shown to improve survival (2). Prognosis: The presence of extramedullary leukemia has a poor prognosis as compared to medullary involvement. A study has shown that a multitude of factors like age, sex, race, and sites of involvement can affect overall survival (10).
Conclusions: As an imaging physician, one should be familiar with extramedullary manifestations of leukemia. There are various organs that can be involved in extramedullary leukemia and knowledge of these is imperative while detecting extramedullary leukemia. High clinical suspicion together with imaging findings usually guides biopsy and leads to the initiation of treatment. As a functional modality, FDG PET/ CT is a useful imaging modality for detecting sites of extramedullary leukemia at baseline, in addition to monitoring response to therapy, and evaluating for recurrence.
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