Primary intraosseous anastomosing hemangioma of the sacrum: illustrative case.

backgroundAnastomosing hemangioma (AH) is a rare benign vascular neoplasm recognized as a distinct entity in the 2020 WHO classification of soft tissue and bone tumors. Although primarily described in soft tissue and visceral organs, intraosseous AH is exceedingly rare and, to the authors' knowledge, primary sacral involvement has not been previously reported. OBSERVATIONS: A 79-year-old woman presented with progressive sacral pain. MRI revealed a large, T2-hyperintense, heterogeneously enhancing sacral mass (60.2 × 48.5 × 39.8 mm) with osteolytic changes and focal cortical thinning, initially suspected to represent a malignant tumor. PET/CT demonstrated fluorodeoxyglucose uptake (maximum standardized uptake value 3.8). Preoperative transarterial embolization was performed to mitigate hemorrhagic risk. Gross-total resection under microscopic visualization with spinopelvic reconstruction was achieved. Histopathological examination revealed anastomosing capillary-sized vascular channels lined by flat to hobnail endothelial cells, with immunoreactivity for CD31 and CD34, confirming the diagnosis of AH. LESSONS: Sacral intraosseous AH may closely mimic aggressive neoplasms including chordoma, giant cell tumor, and metastasis, posing a significant diagnostic challenge. Accurate diagnosis requires histopathological confirmation. Preoperative embolization may facilitate safe resection by reducing intraoperative bleeding in hypervascular sacral tumors. https://thejns.org/doi/10.3171/CASE26302.