NI-11 Clinical significance of intracystic diffusion hyperintensity lesions remaining after treatment of intracranial germ cell tumor

Background and purpose: About 30% of intracranial germ cell tumors are mixed germ cell tumors and teratomas are often found as those components. Intense chemoradiotherapy is performed according to the malignancy of the histopathology, but high-intensity lesion inside the cystic tumor on diffusion weighted imaging (DWI) sometimes remains after completion of the chemoradiotherapy. In this study, we examined the clinical significance of the DWI high-intensity lesion remaining in the cyst. METHODS: Five patients after initial chemoradiotherapy were resected residual tumor by craniotomy at our hospital from 2009 to 2019. Preoperative gadolinium-enhanced MRI defined the non-contrast-enhanced part of the tumor as intracystic, and DWI intensity was classified by its look as low-intensity, equal-intensity, and high-intensity compared to the cortex of the same slice. DWI signals in the solid area, cyst wall, and cyst were evaluated. Results: All cases were mature teratoma in histopathology, and no other tumor components were observed. On DWI, the cyst wall and solid part were visualized with low signal. High-intensity lesions and equal-intensity lesions in the cyst cavity were found in 3 and 1 cases, respectively. In these cases, pathological findings revealed a keratin-like substance in the cyst. Discussion: The intracystic high and equal intensity lesions on DWI removed after completion of chemoradiotherapy are considered to reflect the keratin-like component of mature teratoma. If DWI- high intensity and equal intensity lesions remain in the cyst of the tumor after the completion of chemoradiotherapy, tumor shrinkage cannot be expected even if the chemotherapy is strengthened. In such cases, we should consider to removing them by surgery. Conclusion: When DWI high and equal intensity lesions are found in the cysts of tumors remaining after chemoradiotherapy for intracranial germ tumors, it is possible that mature teratoma remains.