Objective:To investigate the imaging features and clinicopathological characteristics of eosinophilic granuloma of bone（EGB）in pediatric patients.Methods:A retrospective analysis was performed on the imaging and clinicopathological data of 55 pediatric patients diagnosed with EGB at Shengjing Hospital of China Medical University，from January 1st，2018 to October 1st，2024.Data collected included gender，age，location，imaging findings，frozen sections diagnosis，immunohistochemical（IHC）staining，and paraffin sections diagnosis.Results:A total of 55 patients（31 males，24 females；median age 5 years）were included.Lesions were predominantly located in the skull（19 cases），limb and trunk bones（18 cases），vertebrae（12 cases），mandible（3 cases），ilium（1 case），pubis（1 case）and ischium（1 case）.Based on imaging findings，EGB was considered the likely diagnosis in 32 of 55 cases（58.18%）.The radiological manifestations were primarily featured by lytic destruction，periosteal reaction，and soft tissue masses，with or without surrounding soft tissue swelling.Lytic bone destruction had statistical significance for the accurate diagnosis of EGB（ χ2=6.352， P<0.05）.Intraoperative frozen section analysis was performed in 32 cases，with 26（26/32，81.25%）yielding a diagnosis of "consider EGB" and 6 cases（6/32，18.75%）diagnosed as "consider inflammatory lesion ".IHC was crucial for definitive diagnosis.Among 55 cases，the IHC staining for CD1α，S-100，Langerin，and CD68 were performed on 52 paraffin samples.The expression of CD1α and Langerin were positive in all tested samples（52/52，100%）.S-100 expression was positive in 50 samples（50/52，96.15%），and CD68 expression was positive in 49 samples（49/52，94.23%）. Conclusion:The imaging features of EGB are complex and diverse，often confused with infectious lesions such as tuberculosis and osteomyelitis，or neoplastic lesions like osteosarcoma，and the diagnosis rate is less than 60%. Intraoperative frozen section analysis demonstrated a high diagnostic accuracy exceeding 80%.For pediatric patients diagnosed with EGB intraoperatively，lesion curettage and local injection of glucocorticoid were performed. Furthermore，bone grafting was added when necessary.This approach achieved curative outcomes with minimal recurrence rates. Definitive diagnosis requires combined morphological evaluation and the positive expression of immunohistochemical markers（CD1α，S-100，Langerin，and CD68）.

Objective This study aims to understand the characteristics of the time sequence of ICR mouse first mandibular molar tooth germ development through dynamic observation.Methods Tooth germ of Embryos (E11.5,E12.5,E13.5,E14.5,E15.5,E16.5,E17.5 and E18.5) and postnatal (PN1,PN2) mice were obtained.The heads (E11.5-E15.5) and mandibles (E16.5-PN2) of mice were dissected,fixed and embedded for serial sections and HE staining.All the results were assessed under light microscopy.Results The tooth germ underwent various development stages including the bud,cap and bell stages.Mouse odontogenesis was initiated at E11.5.Proliferation of oral epithelium formed the bud stage at E13.5.Then the cap stage was observed at E14.5-E15.5 and the bell stage was appeared beginning from E16.5.The pre-dentin was observed at PN1,as well as the dentin at PN2.Conclusions Establishing the regular development pattern of the first mandibular molar of ICR mice will provide a reliable basis for the future use in the specific tooth germ developmental research.