Variable Aβ tracer uptake in hyperostosis frontalis interna: implications for brain Aβ PET/CT interpretation

Hyperostosis frontalis interna (HFI) is a relatively common incidental finding on head computed tomography (CT). We report two patients with HFI identified on amyloid-beta (Aβ) positron emission tomography (PET)/CT who demonstrated distinct patterns of tracer uptake within the affected calvarium.

Both patients underwent ¹⁸F-florbetaben PET/CT imaging to assess eligibility for Aβ-targeting therapy.

Patient 1 was an 85-year-old woman with amnestic mild cognitive impairment whose ¹⁸F-florbetaben PET/CT scan revealed a Centiloid value of 59 and marked tracer uptake within the calvarium affected by HFI. Patient 2 was a 76-year-old woman with a Centiloid value of 82 who exhibited HFI on CT but no ¹⁸F-florbetaben uptake within the HFI region.

Off-target tracer retention within the calvarium may represent a source of visual and quantitative misinterpretation in Aβ and tau PET scans in patients with HFI, particularly older women. Careful visual inspection and adjustment of automated quantification masks are essential to avoid inaccurate Centiloid and standardized uptake value ratio measurements.