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Page 4 of 11 Cappabianca et al. Mini-invasive Surg 2020;4:83 I http://dx.doi.org/10.20517/2574-1225.2020.67

with administration of intraoperative indocyanine green videoangiography. In meningiomas surgery,
this intraoperative tool finds special application in parasagittal tumors [42,43] . Maximal safe resection
of parasagittal meningiomas is the goal of correct surgical treatment, and it is intimately related to
the venous anatomy both near and directly involved by the tumor. Intraoperative indocyanine green
videoangiography enables confirming sinus occlusion, removing the occluded portion of the sinus, and
identifying and respecting the venous collateral circle.

Finally, in selected cases and alternative to the microscope, meningiomas removal can be performed under
[44]
exoscope image guidance .

Endoscope-assisted surgery
With increasing experience in skull base surgery, the concept of minimally invasive keyhole approaches
flourished, intended not only as limited cranial opening but also as limited approach-associated surgical
[45]
morbidity, achieved with less traumatism over the brain . The supraorbital route and a series of its
modifications (the supraorbital eyebrow incision approach, the mini-supraorbital keyhole craniotomy, the
transciliary approach, and the lateral supraorbital approach) epitomized the reconciliation of both concepts,
benefiting from the tenets of minimal, efficacious access of keyhole approaches and those of maximal,
effective, atraumatic brain exposures from skull base [46-48] .

The central difficulty of transcranial microsurgical keyhole approaches is the loss of intraoperative light and
angle of view due to the limited craniotomy and the need of brain retraction. Continuous improvements
in surgical visualization tools’ technology led to modern endoscopy and neurosurgeons began using
the endoscope as an allied adjunct to the microscope, for the purpose of bringing light and controlling
manipulation in the depth of the operating field. Besides, the endoscope’s assistance provides extended
[49]
viewing angle and clear depiction of details in close-up view .
The combined microscopic–endoscopic technique has demonstrated utility in two aspects of meningiomas
skull base surgery: extension of the surgical field into additional intracranial compartments and
visualization and resection of residual tumor not adequately visualized by the microscope around
neurovascular corners. In particular, the endoscope allows the extension of posterior cranial approaches to
the middle fossa through the tentorial incisura, increasing the resectability of Meckel’s cave and petroclival
meningiomas that often show a multi-compartment location, involving cavernous sinus, prepontine space,
cerebellopontine angle, and lower clivus [50-52] . During removal of such meningiomas, the endoscope enables
tumor visualization at specific microscopic blind spots: the anterolateral surface of the brainstem, the
entrance of the trigeminal nerve into the porous of Meckel’s cave and of the VII-VIII cranial nerves into
the internal acoustic meatus, and the jugular tubercle with the dural exit of the lower cranial nerves (IX-
XI) [53,54] . Thermal injury to neurovascular structures with the tip of the endoscope should also be taken
[51]
into account . For the removal of anterior skull base meningiomas, the endoscope’s assistance finds its
main application when combined with the supraorbital approach [51,55,56] . The endoscopic visualization
discloses surgical corridors to reach the tumor that extends superior, lateral, and under the ipsilateral optic
nerve and internal carotid artery, as well as the diaphragm sellae, without the need of splitting the Sylvian
fissure. Endoscopic assistance increases the visualization of tumor parts within the olfactory groove that is
otherwise limited by the orbital roof under the flat angle of view, as provided by the microscope.

Controversies remain about appropriate case selection, particularly with respect to the extended endoscopic
endonasal approaches [57-61] : the supraorbital route can be preferred for meningiomas with significant
lateral extension, encroaching the supraclinoid internal carotid artery and its branches and/or extending
laterally to the optic nerves that are outside the visibility and maneuverability of the endoscopic endonasal
approach. Another criterion to choose the supraorbital approach is the preservation of olfaction that is