Diagnostic and Treatment Strategies for Adult Non-Ossifying Fibromas: A Case Report and Literature Review.

BACKGROUND Non-ossifying fibroma (NOF) is the most common benign bone tumor in children, but presents diagnostic and therapeutic dilemmas in adults when lesions are large or radiographically atypical. Unlike pediatric cases that typically regress spontaneously, NOF in skeletally mature patients can persist, expand, and mimic aggressive neoplasms (eg, giant cell tumor of bone or aneurysmal bone cyst), leading to diagnostic difficulties. This case highlights challenges in differentiating NOF from malignant or aggressive bone tumors in adults and outlines evidence-based surgical decision-making for large, cortically-compromised lesions. CASE REPORT We report the case of a 28-year-old man with neurofibromatosis type 1 (NF1) who presented with a painless proximal tibial mass initially misdiagnosed as a giant cell tumor or aneurysmal bone cyst on imaging. The lesion measured 55×34 mm with cortical breach, exceeding 50% of the bone diameter, posing significant pathological fracture risk. Core-needle biopsy confirmed NOF. Given the patient's skeletal maturity (no potential for spontaneous regression), lesion size (>33 mm), and cortical disruption, we performed extended curettage, polymethylmethacrylate (PMMA) bone cement augmentation, and prophylactic plate fixation to enable immediate mechanical stability and early weight-bearing. Two-month follow-up confirmed union without recurrence. CONCLUSIONS This case illustrates 3 critical clinical lessons: (1) NOF in adults requires heightened suspicion for aggressive bone tumors due to atypical imaging features and absence of expected involution; (2) Biopsy is mandatory for radiologically indeterminate lesions to avoid misdiagnosis and overtreatment; and (3) Surgical indication in adult NOF should be based on lesion size (>33 mm), cortical integrity, and fracture risk rather than symptoms alone. Prophylactic stabilization with bone cement provides immediate mechanical strength in mature bone.