[Clinicopathological analysis of intraosseous hibernoma]

Objective: To investigate the clinical, radiological and histological features of intraosseous hibernoma. Methods: Two cases of intraosseous hibernoma diagnosed in the Department of Pathology, the Sixth People's Hospital Affiliated to Shanghai Jiaotong University School of Medicine from 2020 to 2023 were analyzed. Related literature was also reviewed. Results: One case was a 44-year-old female with abnormal signals in the proximal right femur revealed by MRI, who underwent curettage of the lesion. The other case was a 41-year-old female with an occupying lesion in the second sacral vertebrae revealed by CT and MRI, who underwent CT-guided biopsy. Microscopically, both tumors were composed of large polygonal cells, with finely vacuolated cytoplasm and distinct cell membranes and variably admixed mature adipose cells or hematopoietic components within the stroma. Nuclei were small, centrally or paracentrally situated and displayed prominent scalloping. Nuclear atypia was absent. A relatively clear tumor boundary could be observed in one case. Immunohistochemical staining showed that tumor cells were positive for S-100 protein, while negative for keratin, CD68, H3F3A, and Brachyury. Conclusions: Intraosseous hibernoma is extremely rare and tends to affect middle-aged and elderly patients. It most frequently occurs in the spine and pelvis. It needs to be differentiated from metastatic cancer, Erdheim-Chester disease, intraosseous lipoma with necrosis, and benign notochordal cell tumor. Increasing awareness of it helps to avoid missed diagnoses or excessive treatment due to misdiagnosis.