Fig. 2

ETV failure threshold. Threshold to identify ETV failure during early postoperative follow-up = Failure is directly proportional to the ETV-FT (the higher the score, the higher the tendency to show ETV failure): The failure threshold is defined as two red signs or score “4.” (ETV) endoscopic third ventriculostomy, (¶) cine phase contrast (PC)-magnetic resonance image (MRI) cerebrospinal fluid (CSF) flowmetry for qualitative and quantitative assessment of CSF flow dynamics through the ETV stoma to assess its patency: Qualitatively by observing the pulsatile CSF flow at mid-sagittal image. Quantitatively by measuring the region of interest (ROI) at ETV stoma on 3D steady state free precession (SSFP) images sequence with thin cuts that allows flow quantification and better CSF assessment, (OFA) overall flow amplitude: the most effective variable to predict the response to surgery. NB: Early postoperative flow index (FI) >40% is significantly linked with successful ETV. FI= (stroke volume of prepontine cistern / stroke volume of interpeduncular cistern) ×100, (§) patent stoma with low/impaired flow might be due to the presence of another CSF diversion pathway (internal drainage due to reopening of the aqueduct again after removal of tumor or cyst), (↑ICP) high intracranial pressure, (SG) subgaleal, (CSF) cerebrospinal fluid, (POD) postoperative day, (LP) lumbar puncture , (#) during the initial adaptation-period on POD-3/5 or within 2 weeks after ETV, (SAS) subarachnoid space, (‡) Type I SG-CSF collection: transient/ soft without CSF leak (or CSF leak from the SAS) during the adaptation-period, (‡) Type II SG-CSF collection: permanent/ tense without CSF leak (or controllable low-flow/clear CSF leak) during the adaptation-period, (*) stoma closure with new arachnoid membrane/scar. Uncontrollable high-flow and/or colored CSF leak