Rare aneurysmal bone cysts: multifocal, extraosseous, and surface variants.

Multifocal, extraosseous, and surface aneurysmal bone cysts are rare variants of the primary lesions. The clinicopathological features are similar, and the optimal treatment is surgical. Although local recurrences may occur, the prognosis is excellent. This review article introduces the readers to a rare diagnosis which they may have been previously unfamiliar with, presents the clinicopathological and imaging features of these rare aneurysmal bone cyst variants, and discusses their diagnosis and treatment. The clinicians who treat patients with aneurysmal bone cysts should be familiar with these uncommon entities and their differential diagnosis.