Department of Neurology, Faculty of Medicine and University Hospital Cologne, University of Cologne, Germany.
Institute of Neuroscience and Medicine (INM-3/-4), Reseach Center Juelich, Juelich, Germany.
Neuro Oncol. 2019 Oct 9;21(10):1331-1338. doi: 10.1093/neuonc/noz083.
O-(2-[18F]-fluoroethyl)-L-tyrosine (FET) PET has a sensitivity of more than 90% to detect gliomas. In the remaining small fraction of gliomas without increased tracer uptake, some tumors even show photopenic defects whose clinical significance is unclear.
Glioma patients with a negative FET PET scan prior to neuropathological confirmation were identified retrospectively. Gliomas were rated visually as (i) having indifferent FET uptake or (ii) photopenic, if FET uptake was below background activity. FET uptake in the area of signal hyperintensity on the T2/fluid attenuated inversion recovery-weighted MRI was evaluated by mean standardized uptake value (SUV) and mean tumor-to-brain ratio (TBR). The progression-free survival (PFS) of photopenic gliomas was compared with that of gliomas with indifferent FET uptake.
Of 100 FET-negative gliomas, 40 cases with photopenic defects were identified. Fifteen of these 40 cases (38%) had World Health Organization (WHO) grades III and IV gliomas. FET uptake in photopenic gliomas was significantly decreased compared with both the healthy-appearing brain tissue (SUV, 0.89 ± 0.26 vs 1.08 ± 0.23; P < 0.001) and gliomas with indifferent FET uptake (TBR, 0.82 ± 0.09 vs 0.96 ± 0.13; P < 0.001). Irrespective of the applied treatment, isocitrate dehydrogenase (IDH)-mutated WHO grade II diffuse astrocytoma patients with indifferent FET uptake (n = 25) had a significantly longer PFS than patients with IDH-mutated diffuse astrocytomas (WHO grade II) with photopenic defects (n = 11) (51 vs 24 mo; P = 0.027). The multivariate survival analysis indicated that photopenic defects predict an unfavorable PFS (P = 0.009).
Photopenic gliomas in negative FET PET scans should be managed more actively, as they seem to have a higher risk of harboring a higher-grade glioma and an unfavorable outcome.
O-(2-[18F]-氟乙基)-L-酪氨酸（FET）PET 对检测神经胶质瘤的灵敏度超过 90%。在剩余的无摄取增加的小部分神经胶质瘤中，一些肿瘤甚至显示出光密度缺陷，其临床意义尚不清楚。
回顾性确定了经神经病理证实前 FET PET 扫描阴性的神经胶质瘤患者。通过视觉将神经胶质瘤评定为（i）摄取无差异，或（ii）光密度降低，如果 FET 摄取低于背景活性。通过平均标准化摄取值（SUV）和平均肿瘤与脑比值（TBR）评估 T2/液体衰减反转恢复加权 MRI 上信号高信号区域的 FET 摄取。比较光密度降低的神经胶质瘤的无进展生存期（PFS）与摄取无差异的神经胶质瘤的 PFS。
在 100 例 FET 阴性神经胶质瘤中，确定了 40 例存在光密度缺陷的病例。其中 15 例（38%）为世界卫生组织（WHO）分级 III 和 IV 级神经胶质瘤。与正常外观的脑组织（SUV，0.89 ± 0.26 比 1.08 ± 0.23；P < 0.001）和摄取无差异的神经胶质瘤（TBR，0.82 ± 0.09 比 0.96 ± 0.13；P < 0.001）相比，光密度降低的神经胶质瘤的 FET 摄取明显降低。无论应用何种治疗方法，摄取无差异的 IDH 突变型 WHO 级 II 级弥漫性星形细胞瘤患者（n = 25）的 PFS 明显长于 IDH 突变型弥漫性星形细胞瘤（WHO 级 II）伴有光密度缺陷的患者（n = 11）（51 比 24 个月；P = 0.027）。多变量生存分析表明，光密度缺陷预测预后不良的 PFS（P = 0.009）。
在 FET PET 扫描阴性的病例中，光密度降低的神经胶质瘤应更积极地治疗，因为它们似乎有更高的风险存在高级别神经胶质瘤和预后不良。
