Utility and limitations of 18F-fluciclovine PET for biopsy targeting in a nonenhancing diffuse glioma with a gliomatosis cerebri-like growth pattern: illustrative case.
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BACKGROUND: Contrast-enhanced MRI reflects blood-brain barrier (BBB) disruption rather than tumor biological activity, whereas 18F-fluciclovine (18F-FACBC) PET reflects amino acid metabolism independent of BBB integrity. The authors compared regional 18F-FACBC uptake with histopathological and molecular findings in a diffuse astrocytoma, IDH-wildtype, not elsewhere classified, with a gliomatosis cerebri (GC)-like infiltrative growth pattern. OBSERVATIONS: A woman in her 50s presented with headache. MRI revealed a nonenhancing, diffusely infiltrating right parietal white matter lesion. 18F-FACBC PET showed focal uptake that guided stereotactic biopsy. Six weeks later, progression caused left uncal herniation requiring emergency decompression, during which PET-negative left temporal tissue was resected. The PET-positive region showed a high Ki-67 index, high-level PDGFRA amplification, and CDKN2A/B homozygous deletion, with a methylation profile matching pediatric-type diffuse high-grade glioma, RTK1 subclass. The PET-negative region was predominantly gliotic, with only low-level PDGFRA amplification. Thus, uptake marked a more proliferative, molecularly altered component. However, both the fatal mass effect and out-of-field recurrence following chemoradiotherapy occurred in regions without corresponding uptake. LESSONS: 18F-FACBC PET identified an aggressive, high-risk tumor component, supporting its use for biopsy targeting in nonenhancing gliomas. However, because life-threatening progression occurred without corresponding uptake, 18F-FACBC uptake reflects proliferative burden rather than the full infiltrative extent. https://thejns.org/doi/10.3171/CASE26761.