PMC5364906_01
Preoperative MRI; (A) Post-contrasted sagittal MRI showing the suprasellar hypothalamic tumor (red circle) measuring 29 mm and pineal region tumor (black arrows) measuring 9 mm in the maximum diameters. Fourth ventricular nodules (red arrows), indicating dissemination, are seen. (B) Post-contrasted axial MRI showing no hydrocephalus (red circle), notice the extremely narrow foramina of Monro and the slit-like third ventricle (yellow circle). (C) FLAIR-MRI axial view, showing edema of the fornix with subsequent narrowing of the foramina of Monro "

left = 2.02 mm, right = 1.35 mm in diameters

" (yellow circle). (D) Zoom in (400%) at the level of the extremely narrow foramina of Monro, the right route (white line) is narrower than the left one (red line).
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Additionally, enhanced nodules were noticed within the left lateral and fourth ventricles (Fig. 1A). Small ventricles (Frontal and occipital horn ratio (FOR) [19] > 0.37) was seen (Fig. 1B). Extremely narrow FM were suspected (Fig. 1C, D). As an enhanced nodule was located in the left lateral ventricle, and the left FM was relatively wider than the right one (Fig. 1D), the neuroendoscopic approach was performed via left precoronal burr hole.
Neuroendoscopic video-captured images; (A, B, C) A 2.5 mm fiberscope during careful endoscopic inspection. The major anatomical landmarks were identified: "the choroid plexus (CP) passing through an extremely narrow FM (M) to the third ventricle, and at its lower margin the point where the thalamostriate vein unites with the septal vein (Sv)". The whitish hypothalamic tumor (T) was visualized inside the 3rd ventricle. Notice the (image B) flushing-induced dilatation of the FM. (D) A 3.7 mm fiberscope was used to get tumor biopsies. (E-I) A 5.0 mm videoscope was introduced in order to gain accurate pertinent anatomical orientation and to obtain reliable biopsies. Before flushing the ventricle was like a gorge (E), however, during flushing the landmarks became gradually obvious (F). Just before passing through the FM to the third-ventricle: a closer position of the fiberscopes showing the efficacy of the flush technique (B and G). Notice the degree of FM dilatation and its' increased diameter (a space was created around the CP "red arrows"). Additionally, the high resolution images obtained by the 5.0 mm videoscope ruled-out any forniceal injury (I). CP: choroid plexus, M: 
foramen of Monro, Sv: Septal vein, T: tumor, *: tumor forceps.
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Tokyo, Japan) was advanced towards the lateral ventricle. The ventricle was like a gorge (Fig. 2E), careful dripping irrigation was performed to ensure patency of the ingress route, using the controllable endoscopic channel which was connected to a reservoir of the warm artificial CSF solution. Major landmarks (choroid plexus passing through an ENFM to the third ventricle, and at its lower margin the point where the thalamostriate vein unites with the septal vein) were identified (Fig. 2A). Although some landmarks of the third ventricle were not distinguishable, a whitish hypothalamic tumor was clearly visualized (Fig. 2C). The 2.5 mm fiberscope was exchanged with 3.7 mm fiberscope (Fig. 2D) (Karl Storz, Tuttlingen, Germany) and an initial biopsy was taken for frozen section, followed by 5.0 mm videoscope (Fig. 2E-I) (Olympus Corp., Tokyo, Japan) in order to gain accurate anatomical orientation and to obtain reliable biopsies.
Schematic drawing showing the flush technique, (A) A direct bolus of 10-ml warm artificial CSF solution was flushed gradually, via the endoscopic channel (red arrow). (B) A moment increase in the intra-third-ventricular pressure (brown arrows) and subsequent dilatation of the FM were achived. Simultaneously, the fiberscope (red arrow) was safely advanced to the third ventricle (yellow arrow). The third ventricular size became comparable.
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In this flush technique, a direct bolus of 10 ml warm artificial CSF solution was flushed over 4 seconds, via the endoscopic channel, to induce a moment increase in the intra-third-ventricular pressure (Fig. 3) and subsequent dilatation of the FM (Fig. 2B). This slow injection accomplished a safe gradual dilatation of the FM.  In synchronization with this real-time dilatation of the FM, the fiberscope was advanced to the third ventricle without traumatizing the fornix, choroid plexus or related veins ( Fig. 3).
Postoperative and follow-up neuroimaging; (A) CT on postoperative day 1 ruled out surgery-related complications. (B) Follow-up post-contrasted sagittal MRI 3 months postoperatively (effect of adjuvant therapy) disclosed marvelous improvement of the condition and almost disappearance of the intracranial lesions C: Follow-up FLAIR-MRI axial view 6 months postoperatively, showing resolution of the forniceal edema and normalization of the foramina of Monro (left = 4.98 mm, right = 4.25 mm in diameters).
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 No evidence of surgical complications (Fig. 4A).  MRI 3- and 6-month-postoperatively disclosed marvelous improvement of the condition and almost disappearance of the intracranial lesions (Fig. 4B). FLAIR-MRI showed resolution of the forniceal edema and normalization of the FM (Fig. 4C).
Immunohistochemical and histopathological studies; (A) (AFP x 10) and (B) (AFP x 20): Immunohistochemical staining for alpha -fetoprotein (AFP), tumor cells showed strong cytoplasmic staining. (C) (HE x 10) and (D) (HE x 20): Photomicrograph of histopathological sections with hematoxylin and eosin (HE) staining: small slit-like spaces lined by atypical tumor cells. Tumor cells were pleomorphic, had abundant eosinophilic or clear cytoplasm and marked nucleoli which were arranged in nest or reticular pattern. Papillary growth pattern and mitotic figures could be found.
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Histopathological studies revealed a yolk sac tumor (Fig. 5).