The polystyrene beads sign: a simple MRI marker for the preoperative diagnosis of papillary hypothalamic craniopharyngiomas.
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OBJECTIVE: Craniopharyngiomas are classified as adamantinomatous or papillary subtypes. Papillary craniopharyngiomas harbor BRAF V600E mutations and demonstrate high response rates to BRAF/MEK inhibition. Craniopharyngiomas involving the hypothalamus are common and carry high surgical morbidity, including endocrine, metabolic, and neurocognitive complications. Therefore, reliable preoperative identification of papillary hypothalamic tumors could support consideration of biopsy followed by targeted therapy, potentially avoiding high-risk surgery. DESIGN: This study is a single-center retrospective study. METHODS: We retrospectively analyzed 61 adult patients with hypothalamic craniopharyngiomas. We defined a novel MRI biomarker, the polystyrene beads sign, as an agglomerate of small, rounded, contrast-enhancing nodules on high-resolution T1-weighted post-contrast MRI. Six independent clinicians, blinded to histopathology, evaluated the presence of the sign. Diagnostic performance (sensitivity, specificity, accuracy) and intra- and interrater reliability were assessed. RESULTS: The polystyrene beads sign identified papillary tumors with 92% sensitivity, 98% specificity, and 96% overall diagnostic accuracy. Intrarater reliability across 2 separate readings was high, and interrater reliability among all 6 clinicians was excellent. After a brief calibration session, the sign was consistently recognizable and distinguishable from enhancement patterns observed in adamantinomatous tumors. CONCLUSIONS: The polystyrene beads sign is a simple and reproducible preoperative MRI marker that may help identify papillary hypothalamic craniopharyngiomas. These findings support further evaluation in multicenter studies before clinical implementation. Its recognition may contribute to imaging-based diagnostic strategies, including selection of patients for confirmatory biopsy, molecular testing, and subsequent targeted therapy in appropriate cases.