Endoscopic Transfrontal Sinus Translamina Terminalis Approach to the Third Ventricle

Background: The endoscopic transventricular approach is a valid alternative for treatment of lesions in the third ventricle. Also, the translamina terminalis microscopic corridor has been used as a transcranial anterior route to treat anterior third ventricular tumors. The major limitation of these approaches is posterior extension of the tumor.

Objective: We aim to identify a safe endoscopic interhemispheric trans-lamina terminalis corridor through the frontal sinus to provide more posterior exposure of the third ventricle.

Methods: Fourteen adult cadaveric specimens to analyze the exact extension of a safe corridor through the lamina terminalis were used. Anatomic dissections were performed in colored latex–injected heads. Interhemispheric dissection of the arachnoid membranes was completed under microscopic view. An endoscope and endoscopic instruments were inserted from the point of entry via the frontal sinus to the lamina terminalis (LT). Four parameters were measured: the transverse and vertical diameters of the third ventricle at the level of the lamina terminalis, orientation of the scope between the superior or inferior borders of the frontal sinus and the lamina terminalis, and the distance between the keyhole and the lamina terminalis as well as the posterior commissure of the third ventricle.

Results: Drilling of the ipsilateral frontal sinus area was performed to create a 2.5 × 2.5 cm transfrontal sinus keyhole in 7 cadaveric specimens compared with a 2.5 × 2.5 cm subfrontal keyhole just lateral to the superior sagittal sinus and sparing the frontal sinus in 7 cadaveric specimens. In both conditions, we expose the interhemispheric fissure. Splitting this fissure and using a 2 cm diameter, 5 cm length port exposed the optic chiasm and lamina terminalis. Completion of an opening of the lamina terminalis opened a 4.5 mm (transverse length) × 10 mm (vertical length) corridor, providing direct access to the third ventricle. The frontal sinus provided a more favorable angle to reach the posterior part of the third ventricle ([Fig. 1]) compared with the subfrontal craniotomy ([Fig. 2]). The median distance between the site of the frontal sinusotomy or the subfrontal craniotomy and the lamina terminalis was 55 mm; however, the median distance to the posterior commissure of the third ventricle was 90 mm, easily reached with conventional instruments used in microscopic or endoscopic surgeries. The opening of the lamina terminalis was performed below the arteries of the anterior cerebral circulation. The endoscopic transfrontal sinus translaminar terminalis approach is thereby accomplished by drilling the ipsifrontal sinus and widening the opening to 2.5 × 2.5 cm, providing an ideal angle for visualization of the posterior third ventricle, even in the absence of hydrocephalus.

Conclusion: The endoscopic transfrontal sinus translaminar terminalis approach to the third ventricle provides a unique and direct surgical corridor to the posterior part of the third ventricle, minimizing brain retraction and corpus callosum manipulation. This approach can be performed purely endoscopically, although surgical maneuverability is still limited due to the narrow surgical corridor.