Periosteal osteoblastoma: report of a case with a rare histopathologic presentation and review of the literature

Murine models of HRAS-mediated cutaneous skeletal hypophosphatemia syndrome suggest bone as the FGF23 excess source

Cutaneous skeletal hypophosphatemia syndrome (CSHS) is a mosaic RASopathy characterized by the association of dysplastic skeletal lesions, congenital skin nevi of epidermal and/or melanocytic origin, and FGF23-mediated hypophosphatemia. The primary physiological source of circulating FGF23 is bone cells. However, several reports have suggested skin lesions as the source of excess FGF23 in CSHS. Consequently, without convincing evidence of efficacy, many patients with CSHS have undergone painful removal of cutaneous lesions in an effort to normalize blood phosphate levels. This study aims to elucidate whether the source of FGF23 excess in CSHS is RAS mutation-bearing bone or skin lesions. Toward this end, we analyzed the expression and activity of Fgf23 in two mouse models expressing similar HRAS/Hras activating mutations in a mosaic-like fashion in either bone or epidermal tissue. We found that HRAS hyperactivity in bone, not skin, caused excess of bioactive intact FGF23, hypophosphatemia, and osteomalacia. Our findings support RAS-mutated dysplastic bone as the primary source of physiologically active FGF23 excess in patients with CSHS. This evidence informs the care of patients with CSHS, arguing against the practice of nevi removal to decrease circulating, physiologically active FGF23.

Benign Bone-Forming Tumors

Benign bone-forming tumors comprise osteomas, osteoid osteomas, and osteoblastomas. Osteomas affect a wide age range and are usually discovered incidentally. They occur predominantly in the craniofacial skeleton and are classically composed of compact bone. Osteoid osteomas and osteoblastomas are painful lesions occurring in young patients. They are morphologically similar and characterized by FOS gene rearrangement and c-FOS expression at a protein level. Osteoid osteomas are usually smaller than 2 cm in maximum dimension with limited growth potential; osteoblastomas are larger than 2 cm and may be locally aggressive. Histologically both are composed of anastomosing trabeculae of woven bone.

Giant periosteal aggressive epithelioid osteoblastoma: 21-year-old male presents case in the midshaft of his femur

We report a rare case of giant periosteal osteoblastoma in the femur of a 21-year-old male. The patient presented with a painful, firm, non-tender mass in his left thigh. The pain was worse at night and was temporarily relieved with NSAIDS. He had no fevers, night sweats, or weight loss. The patient underwent preoperative radiological studies including plain radiographs, MRI, bone scan, and CT scan. An open biopsy was subsequently performed that was consistent with an aggressive, epithelioid osteoblastoma. Pathology demonstrated a neoplasm characterized by cohesive sheets of epithelioid osteoblasts, mixed with areas of conventional osteoblastoma displaying prominent osteoblastic rimming of woven bone trabeculae in a fibrovascular stroma. The patient subsequently underwent resection, cryosurgery, fixation, and bone grafting with cortical strut allografts. At final follow-up, 32 months postoperatively, there was no evidence of local recurrence. The patient had resumed all his normal activities. He could run without pain and had no restrictions with activities. The goal of this case report is to aid professionals in the diagnosis and treatment of highly uncommon aggressive osteoblastomas.

Periosteal osteoblastoma: Multimodal imaging of a rare neoplasm

Osteoblastoma is a rare neoplasm, accounting for only 1% of the primary bone neoplasms. We report a case of periosteal osteoblastoma, a rare subtype of osteoblastoma. To the best of our knowledge, only 30 cases of periosteal osteoblastoma appear in the English literature. Our case is that of a 41-year-old male with vague intermittent knee pain over a two-year period. Diagnostic imaging revealed an aggressive-appearing lesion in the posterior distal femur, which was initially considered to be a surface osteosarcoma. Roentgenographic, CT, MRI, and bone scan features are presented.

A rare case of rib osteoblastoma: imaging features and review of literature

Osteoblastoma is a rare benign, but locally aggressive bone tumor with rare malignant transformation. It mostly affects the vertebral column and long bones. Radiographically, it is seen as an expansile, oval, sclerotic or lytic mass-like lesion with well-defined borders, although sometimes it may mimic a malignant tumor such as osteogenic sarcoma by its irregular borders. Herein, we report a case of osteoblastoma in a 22 year-old man with a long history of back and neck pain accompanied with neck stiffness. On the routine chest X-ray, the salient lesion appeared as an expansile, oval, sclerotic mass with well-defined borders and speckled calcification without any internal lucency and periosteal reaction, involving the posterolateral aspect of the first left thoracic rib, a rare anatomical site. Despite the unusual location, osteoblastoma should be considered in the differential diagnosis of a solitary rib lesion.