Clinicopathological characteristics of extramedullary acute megakaryoblastic leukemia (AMKL): report of a case with initial mastoid presentation and review of literature to compare extramedullary AMKL and non-AMKL cases.

Extramedullary acute megakaryoblastic leukemia (AMKL) is a rare neoplasm with a varied clinical presentation. AMKL with initial mastoid presentation has never been reported. The extreme rarity of mastoid AMKL, together with the tendency of extramedullary AMKL to mimic other small blue cell tumors, can create a diagnostic challenge. We report a case of AMKL that initially presented as a mastoid lesion and provide a comprehensive review and analysis that compares the characteristics of extramedullary AMKL and nonmegakaryoblastic acute myeloid leukemia (AML) in reported pediatric cases over the past 30 years. We found that patients with extramedullary AMKL were not only younger than patients without megakaryocytic differentiation but were also limited to those ≤ 2 years of age. In addition, girls predominated in both AMKL and AML MLL(+) groups compared with other types of AML (P  =  0.0366 and P  =  0.0082). Furthermore, we found that extramedullary AMKL was more likely to involve bone than AML MLL(+) (P < 0.0001) or other types of AML (P  =  0.0002). These findings suggest that extramedullary AMKL should be considered in the differential diagnosis of SBCT in children, especially in patients with mastoid or other bony lesions, those ≤ 2 years of age, and female patients.