Fibrous and Fibro-Osseous Lesions of Bone

Degradation-Resistant Hypoxia Inducible Factor-2α in Murine Osteocytes Promotes a High Bone Mass Phenotype

Molecular oxygen levels vary during development and disease. Adaptations to decreased oxygen bioavailability (hypoxia) are mediated by hypoxia-inducible factor (HIF) transcription factors. HIFs are composed of an oxygen-dependent α subunit (HIF-α), of which there are two transcriptionally active isoforms (HIF-1α and HIF-2α), and a constitutively expressed β subunit (HIFβ). Under normoxic conditions, HIF-α is hydroxylated via prolyl hydroxylase domain (PHD) proteins and targeted for degradation via Von Hippel-Lindau (VHL). Under hypoxic conditions, hydroxylation via PHD is inhibited, allowing for HIF-α stabilization and induction of target transcriptional changes. Our previous studies showed that Vhl deletion in osteocytes (Dmp1-cre; Vhl f/f ) resulted in HIF-α stabilization and generation of a high bone mass (HBM) phenotype. The skeletal impact of HIF-1α accumulation has been well characterized; however, the unique skeletal impacts of HIF-2α remain understudied. Because osteocytes orchestrate skeletal development and homeostasis, we investigated the role of osteocytic HIF-α isoforms in driving HBM phenotypes via osteocyte-specific loss-of-function and gain-of-function HIF-1α and HIF-2α mutations in C57BL/6 female mice. Deletion of Hif1a or Hif2a in osteocytes showed no effect on skeletal microarchitecture. Constitutively stable, degradation-resistant HIF-2α (HIF-2α cDR), but not HIF-1α cDR, generated dramatic increases in bone mass, enhanced osteoclast activity, and expansion of metaphyseal marrow stromal tissue at the expense of hematopoietic tissue. Our studies reveal a novel influence of osteocytic HIF-2α in driving HBM phenotypes that can potentially be harnessed pharmacologically to improve bone mass and reduce fracture risk. © 2023 The Authors. JBMR Plus published by Wiley Periodicals LLC on behalf of American Society for Bone and Mineral Research.

Polyostotic Fibrous Dysplasia: A Case Report of Rarity

A skeletal condition known as fibrous dysplasia (FD) is characterized by the replacement of healthy bone with fibrous bone tissue. One bone (monostotic) or several bones could be involved (polyostotic). Any bone in the body might become affected by FD. The skull and face bones are the most typical locations. It is connected to a GNAS1 gene mutation (20q13.2). It begins during childhood and could continue far into adolescence and adulthood. In this case study, a 22-year-old woman was identified as having polyostotic FD based on her clinical, radiological, and histological characteristics.

FDG PET/CT and Bone Scintigraphy in Desmoplastic Fibroma of the Bone

ABSTRACT

Desmoplastic fibroma is a very rare benign bone tumor with local aggressiveness. We describe imaging findings in 2 cases with desmoplastic fibroma of the bone. One case had a desmoplastic fibroma in the right distal femur, showing bone destruction with sclerotic margins and inhomogeneous FDG uptake. The other case had a desmoplastic fibroma in the left ninth rib, showing progressive peripheral enhancement and increased 99m Tc-MDP uptake.

Endoscopic Endonasal Trans-Agger Nasi Approach for Resection of Ossifying Fibroma Involving the Anterior Skull Base: Surgical Anatomy and Technical Note

OBJECTIVE

A variety of approaches for resection of the ossifying fibromas in sinonasal cavities have been described. However, for those involving the anterior skull base, endoscopic surgery remains challenging because of limitations in identification of tumor boundaries from the anterior skull base and proper control of the tumor-feeding vessel. This study aimed to describe a technique for resection of ossifying fibromas involving the anterior skull base through an endoscopic endonasal trans-agger nasi approach, based on anatomic studies and surgeries.

METHODS

Two human cadaveric heads were prepared for study of the anatomic relationship between agger nasi and anterior skull base. Two clinical cases were used to illustrate the technique and feasibility of the approach.

RESULTS

The agger nasi was located anterior and inferior to the frontal ostium and the anterior skull base. The frontal ostium and anterior skull base could be visualized and accessed under the 0-degree endoscope by removing the agger nasi. Application of the endoscopic endonasal trans-agger nasi approach in the two patients resulted in complete resection of the tumors with no surgical complications.

CONCLUSIONS

An endoscopic endonasal trans-agger nasi approach provides a direct access to the anterior skull base. It would be feasible, effective, and safe for selected cases of ossifying fibroma involving anterior skull base.