Fig. 1.

Aneurysmal bone cyst classification according to morphology. Reproduced with permission from Capanna et al. [23]. Type I: centrally located lesions that are well contained with no outline or slightly expanded outline. Type II: very expansile tumors with cortical thinning involving the entire bone segment. Type III: eccentric metaphyseal lesions that typically involve only one cortex. Type IV: subperiosteal lesions growing away from the bone. Type V: periosteal lesions expanding peripherally to ultimately penetrate the underlying cortex