Case 2. A: Preoperative CT scan revealing a right frontal lobe lesion with intralesional hemorrhage, peritumoral edema, and a mass effect. B–D: Preoperative axial T2-weighted (B), T1-weighted (C), and contrast-enhanced (D) MRI scans showing a cystic-solid lesion with enhancement. E and F: Postoperative axial T1-weighted (E) and contrast-enhanced (F) MRI scans showing total resection. In this case, total resection was evaluated according to the following signs. 1) The main solid and cystic components had been completely removed. 2) The resected extent had been extended and included regions approximately 0.5–1.0 cm surrounding the contrasted lesions and the cyst wall. 3) The peritumoral edema zone had been removed, which was absent on the postoperative MRI scans. 4) The frontopolar cortex and the anteromedial cyst wall (arrows in E) adjacent to the falx had been totally removed. 5) The notable contrast enhancement along the surgical cavity wall was significantly more intense and thicker than that in the preoperative cyst wall, and the postoperative radiological features after contrast enhancement were more likely associated with postoperative changes (i.e., minor bleeding and hemostasis material) rather than residuals; additionally, on the postoperative T1-weighted image (E), the hyperintense signal along the surgical cavity wall suggested postoperative changes that were quite different from signals of the preoperative MRI. 6) Because of an absence of parenchyma, the contrast enhancement along the falx and the frontopolar dura (F) precluded the possibility of residual. 7) Finally, most importantly, resection of this lesion was performed along the boundary between tumor and normal parenchyma, followed by extended resection that guaranteed total resection.

Histopathological examination revealed the typical morphology of MEPL. A–D: Based on H & E staining, MEPL displayed multipotential cellular lineages including a full spectrum of glioneuronal differentiation, and showed the structure of the primitive neuroepithelium arranged in tubular, ribbon-like, and/or papillary rosette formations lined by mitotic, pseudostratified columnar cells that resemble embryonic neural tube. E: Cytokeratin was focally presented in the neural tube–like structures. F: The Ki-67 proliferation index was calculated approximately up to 50%. G and H: Diffuse membranous CD99 and CD56 expression in neoplastic cells. I: GFAP immunoreactivity was evident in abundant primitive cells close to neuroepithelial structures. J: Neoplastic cells were strongly diffusely positive for MAP-2. K: Strong nestin immunoreactivity was seen in the epithelial structures. L: Local synaptophysin immunoreactivity was expressed. Figure is available in color online only.

Kaplan-Meier analyses illustrating the PFS (n = 38) and OS (n = 58) of MEPL based on the literature and our cohort (A), and showing the significantly different PFS (B) and OS (C) in patients reported before 2007 or later. This confounding factor was taken into consideration when performing the multivariate analysis. Chi-square values were obtained by log-rank (Mantel-Cox) testing during the Kaplan-Meier curve analysis. EMPT = estimated median PFS time; EMST = estimated median survival time. Figure is available in color online only.

Kaplan-Meier survival curves illustrating the different PFS (A–D) and OS (E–H) in patients with risk factors. Patients younger than 6 years (A), who did not undergo GTR (B), or had no radiotherapy (C) had a significantly worse PFS. Although the different PFS in patients with or without chemotherapy was not significant, the survival curve showed a poor outcome trend and shortened survival time in patients who did not undergo chemotherapy (D). The OS was significantly worse in patients younger than 6 years (E), those who did not undergo GTR (F), and had no radiotherapy (G) or chemotherapy (H). Chi-square values were obtained by log-rank (Mantel-Cox) testing during the Kaplan-Meier curve analysis. Figure is available in color online only.