Aggressive evolution of an occipital bone ABC-like lesion with dural invasion and intradural extension: a case report

Background Aneurysmal bone cysts (ABCs) of the skull are rare, particularly those arising in the occipital bone. Intracranial extension or dural destruction is extremely uncommon. Here, we report an occipital ABC-like lesion that recurred 19 months after gross-total resection with dural defects, intradural extension, and molecular evidence supporting aggressive neoplastic evolution. Case Description A 37-year-old woman presented with 2 months of headache and 1 month of binocular diplopia. CT and MRI demonstrated a large expansile lytic lesion of the occipital bone with poorly defined interfaces with the posterior superior sagittal sinus, torcular region, and bilateral transverse sinuses. Preoperative embolization using 1000-µm polyvinyl alcohol particles reduced tumor vascularity. Gross-total resection was achieved, and histopathology was initially interpreted as consistent with ABC. Cranioplasty was performed 8 months later. Nineteen months after the initial surgery, the patient developed dizziness, vomiting, and gait instability. Imaging revealed recurrent lesions extending through dural defects into the intradural compartment, compressing the left cerebellar hemisphere and occipital lobe. Gross-total resection was again performed. The recurrent lesion was soft, hypervascular, and contained foci of calcification and chronic hemorrhage. Histopathology showed increased cellularity, mitotic activity, and solid growth. Targeted next-generation sequencing demonstrated amplification of multiple genes located at 12q12–q15, including MDM2, CDK4, DDIT3, and CLL1, supporting diagnostic revision to a borderline/low-grade malignant mesenchymal neoplasm. Conclusion This case highlights that skull-based lesions initially diagnosed as ABC may recur with significant dural destruction and intradural extension, and may demonstrate aggressive neoplastic evolution. Long-term imaging surveillance should be considered after resection of cranial ABC/ABC-like lesions to enable early detection of recurrence and biologic progression.