Peculiarities of the third ventricle surgery in endoscopic frontal transcortical approach

Materials and methods. The results of treatment of 27 patients with tumors and colloid cysts to the third ventricle were analyzed. In all 27 patients endoscopic frontal transcortical approach was perfomed. In 24 cases of them extended anterior choroidal dessection was perfomed (transchoroidal and transforaminal approach); in 3 cases — transcortical transforaminal approach (without choroidal dissection). In all case there was fully endoscopic removal (100 %).


Ukrainian Neurosurgical Journal. 2019;25(1):12-17
Introduction Int e r m e diat e t r an s c all o s al o r t r an s c o r t i c al approaches are widely used to treat pathology of the ventricular system.Each of these approaches has advantages and certain features, which are still under discussion [1,2].
The incidence of hydrocephalus, tumor location in the posterior third ventricle compartment, tumor spreading to the pineal region, cerebral peduncles or cerebral aqueduct, IV ventricle are the subjects related to the choice of surgical approach [3][4][5].Depending on tumor location, its size and ventricular hydrocephalus, t r a n s c o r t i c a l t r a n s f o r a m i n a l o r t r a n s c o r t i c a l transchoroidal approach or their combination may be used [6][7][8].The combination of them -extended transforaminal approach (transforaminal approach with anterior choroidal dissection) makes it possible to reduce postoperative complications, with adequate visualization of the pathology and an acceptable angle of "attack" upon the posterior third ventricle tumor.
The normal size of the foramen of Monro is just about several millimeters and there are so many important structures nearby, therefore, the operation around this area is very difficult and challenging.
The third ventricle is a location difficult to get approach.The region is deep seated and surrounded by critical structures that are easily injured, leading to potentially disastrous outcomes.

Goals.
To analyze the results of surgical treatment of patients with the third ventricular pathology.
Objective.To improve the methods of choroidal dissection.To make enough space for surgery of the third ventricle by expanding the foramen of Monro.To reduce the risk of surgical treatment in the posterior third ventricle pathology.

Materials and methods
There were analyzed the results of treatment of 27 patients with tumors and colloid cysts to the III ventricle in the period of 2015-2018.Tumors of the anterior and posterior third ventricle compartments (including 3 colloid cysts of the third ventricle) were found in 6 patients; tumors in the posterior part of the III ventricle -in 21 patients.Histological distribution was as following: primary tumors of the III ventricle-pineocytoma in 2 patients.Invasive tumors: subependymoma -6; central neurocytoma -2; astrocytoma -9; glioblastoma -4; anaplastic oligoastrocytoma -1.Colloid cysts to the third ventricle were found in 3 patients.The average size of tumors in the third ventricle was about 3.0 cm (varying from 1.7 cm to 5.2 cm; 60 % of them were more than 3.2 cm).All patients underwent preoperative CT and MRI scanning of the brain, and CT scanning with contrast postoperatively (at the first day).In total 64 CT and 34 MRI scanning of the brain, as well as one angiography procedure were performed.
Surgery.The endoscopic frontal transcor tical approach was performed in all 27 patients: the extended trasforaminal approach (transforaminal approach with anterior choroidal dissection) -24 cases; transforaminal approach alone (without choroidal dissection) -in 3 cases.In all of them fully endoscopic removal (100 %) was achieved.

Results and discussion
Tumor located in the posterior third ventricle compartment is always a challenge.A variety of surgical approaches to the posterior third ventricle region exist.The choice of approach depends on the exact location of the lesion, the tumor consistency and size [12].The transchoroidal approach begins with the opening of the taenia fornicis and the superior membrane of the tela choroidea, and then dissecting the vascular layer medially to the internal cerebral vein [8].After the inferior membrane of the tela choroidea and the choroid plexus of the third ventricle have been opened in the midline, the cavity of the third ventricle can be completely seen.The extended transforaminal approach eliminates this risk [11].Then the posterior limit of the foramen of Monro has been expanded through the choroidal fissure, without sacrificing any neural or even vascular structures.Thus additional space needed for surgery gained.The only structure that restricts further expansion of the foramen is the anterior septal vein, which can be sacrificed if necessary.Besides choroidal dissection at the posterior edge of the foramen of Monro at the very beginning of the internal cerebral veins is not that risky when doing transchoroidal exposure as internal cerebral veins diverge of the foramen of Monro, thus giving some space to start dissection between internal cerebral veins (which open roof of third ventricle without any risk) [9].
The thalamostriate vein is the largest tributary of the internal cerebral vein and is located in the striothalamic sulcus between the caudate nucleus and the thalamus, beneath the stria terminalis in the body of the lateral ventricle [6].The thalamostriate vein curves medially around the anterior tubercle of the thalamus, where it merges to the internal cerebral vein at the posterior margin of the foramen of Monro.This characteristic U-shaped junction of the thalamostriate vein and internal cerebral vein adjacent to the posterior margin of the foramen of Monro is referred to as the venous angle.The injury of thalamostriate vein or the internal cerebral vein may cause serious consequences including hemiplegia, coma and even death [7].The damage to the anterior part of the floor of the third ventricle may cause water-salt metabolism disorder symptoms.Lateral to the foramen of Monro there is thalamus and the internal capsule, the injury to which may lead to coma or hemiplegia [10].
The pоint is that chоrоidal dissеctіоn is done at the middle and posterior compartment of the roof of the thіrd ventricle (the internal cerebral veins are closest).Risk is due to the not enough spаce to conduct this dіssection [13,14].Anterior choroidal dissection proceeded to posterior edge of the foramen of Monro would eliminate this risk as internal cerebral veins diverge of the foramen of Monro to the sides.Extended transforaminal approach provides the opportunity to make a sufficient angle of attack to the posterior part of the third ventricle.Conducting anterior chroidal dissection, we expand the foramen of Monro, which gives us the opportunity to obtain a better visualization angle of the tumors of the posterior part and the entirely third ventricle.This visualization is enough to see internal cerebral veins, pineal recess, cerebral aqueduct, posterior commissure.
Hydrocephalus is often concomitant with the third ventricle tumors.In such cases, the enlargement of the foramen of Monro was present in 14 patients.In our series hydrocephalus occurred in 19 cases.In 6 cases it was caused by obstruction at the level of foramen Monro, in 13 cases it was caused by aqueduct tumor.Latter took place if the tumor is located at the posterior third ventricle compartment.Not all of these 19 hydrocephalus patients experienced the foramen of Monro expanded.It took place only in 14 patients.The foramen of Monro was expanded in 14 cases: 6 of them due to tumor blocking and enlargement and in 8 patients the foramen of Monro expanded spontaneously due to hydrocephalus.
Extended trasforaminal approach (transforaminal approach with anterior choroidal dissection) was used in cases when the foramen of Monro was not changed in size (so we enlarged it, expanded it backwards).Also extended trasforaminal approach was performed in cases when the tumor was located in the posterior third ventricle compartment (in such way we are trying to gain right angle of attack for the tumor visualization); the third indication for the extended trasforaminal approach was the significant size of the third ventricle tumor (we used extended trasforaminal approach to gain better visualization of anterior and posterior third ventricle compartment).
Tumor location in the anterior or posterior third ventricle compartment (with unchanged foramen of Monro -Fig. 1) or when the tumor is sizeable, we performed extended anterior choroidal dissection (transchoroidal approach with anterior choroidal dissection) (Fig. 2).Radicality.Total removal was performed in 14 patients; subtotal removal -in 13.Radicality of tumor removal depends on tumor density.If the tumor was jelly-like, the removal was mostly total.In those cases when the tumor was tough, it was not always possible to perform radical removal (Fig. 3).Bleeding of the tumor did not signify; since as the tumor had been removed, the bleeding decreased spontaneously (Fig. 4).Another important factor in the volume of tumor removal was tumor adhesion to the surrounding structures (especially with internal cerebral veins).The spread of the tumor to the thalamus, the brain stem, and the aqueduct also reduces the radicality of the removal.
According to Karnofsky Performance Scale all patients had ≥ 70 points in the postoperative period.Four patients (14.8 %) experienced complications.Selective mutism occurred in 4 cases (complete regression of speech disorders in all patients from 5 to 20 days; two of these patients experienced hemiparesis (complete regression in 2 weeks).No cases of postoperative mortality.

Conclusions
1. Transcortical transforaminal approach can be used for the pathology, which is located in the anterior part of the third ventricle.