Fig. 1

ETV difficulty scale. Serious intraoperative findings that haunts neurosurgeons and can be encountered during ETV journey and could predict achievability/difficulty. Difficultly is directly proportional to the ETV-DS (the higher the score, the higher the alarming sign = tendency to face a challenging operation/ complications, require special surgical pearls and predict ETV failure): (ETV) endoscopic third ventriculostomy, (III-VT) third ventricle, (§) including post-hemorrhagic deposits and/or postinfectious debris, (ENFM) extreme narrow foramen of Monro, (mFM) membrane masking the foramen of Monro, (AnLS) aneurysm-like structure, (*) achievable: can be opened surgically, (Aq.Slv) aqueduct of Sylvius, (#) ETV seems impossible “in our hands” as we could not reach the III-VT floor, therefore, we ensure reasonable CSF flow via debulking of the posterior part of the tumor that covers the Aq.Slv., (SAS/BC) subarachnoid space/ basal cisterns, (DS) dorsum sellae, (¶) measured with the maximal diameter of Fogarty arterial embolectomy catheters (FAEC) (code 12A0805F/120805F) size 5F (inflated balloon diameter of 11 mm), (LM-DL) Liliequist membrane diencephalic layer, (DEBA) dolicoectatic basilar artery, (LM-ML) Liliequist membrane mesencephalic layer, (CN) cranial nerve, (ǂ) oculomotor (III) and/or abducent (VI) nerves in the basal cisterns, (CSF) cerebrospinal fluid, (‡) initial sampling before irrigation/lavage and at the end of the procedure if iatrogenic hemorrhagic insult occurred