Pathology: aneurysmal bone cyst

Aneurysmal bone cyst

  • Cystic spaces filled with blood separated by fibrous septa

  • Septa contain fibroblasts with fascicular pattern; monomorphic ovoid nuclei; inconspicuous mitotic activity

  • Intervening stroma contains osteoclast-type giant cells, woven bone rimmed by osteoblasts, and so-called "blue bone"

  • RNA-seq: KLF3::USP6 gene fusion

Aneurysmal bone cyst

  • Cystic spaces filled with blood separated by broad fibrous septa

  • Septa contain fibroblasts with fascicular pattern; monomorphic ovoid nuclei with prominent nucleoli; inconspicuous mitotic activity

  • Intervening stroma contains osteoclast-type giant cells, woven bone rimmed by osteoblasts, and extravasated erythrocytes with occasional siderophages

  • RNA-seq: TAF7::USP6 gene fusion*

* To date unreported in the literature

Aneurysmal bone cyst

  • Focal cyst lining

  • Fibrous septa containing fibroblasts with fascicular pattern; monomorphic ovoid nuclei; inconspicuous mitotic activity

  • Stroma contains osteoclast-type giant cells, woven bone rimmed by osteoblasts, and so-called "blue bone"