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Azab et al. Mini-invasive Surg 2020;4:88 I http://dx.doi.org/10.20517/2574-1225.2020.75 Page 7 of 11

posterior wall of the frontal bone, the more contralateral head rotation is required. Neuronavigation is very
important for planning the procedure and should be used in all cases.

Under general anesthesia with the patient in the supine position, the head is secured in a MAYFIELD skull
clamp® and rotated 25°-30° to the left for a right-sided approach. The head is then extended 10°-15° to allow
a gravitational fall of the frontal lobe away from the skull base. This helps decreasing the brain retraction
required to develop the operative corridor. Slight contralateral lateral flexion is then undertaken to help
provide easier instrument maneuverability during the procedure.

Skin incision
The skin incision lies within the eyebrow and starts just lateral to the supraorbital notch - to avoid injury to
the supraorbital nerve and consequent postoperative forehead numbness- and ends at the lateral end of the
eyebrow over the zygomatic process. In some cases, the incision may be extended laterally a further 5-10 mm
in a skin crease without significant cosmetic sequelae.

At the superior temporal line, the temporalis fascia is incised using the monopolar coagulation for about 2 cm
and the frontalis fascia is then cut from the temporal line in a semicircular fashion over the frontal bone
with its base at the orbital rim. The temporalis muscle is subsequently dissected off the bone and retracted
posteriorly for 1-2 cm.

Craniotomy
A single burr hole is made using a sharp pit attached to the high-speed drill in the temporal fossa lateral to
the superior temporal line. The burr hole position is chosen at a point that is slightly higher than the classic
MacCarty’s burr hole. A frontal direction of drilling prevents entering the orbit. A craniotome is then used
to perform a 2-3.5 cm × 2-2.5 cm bone flap. Care should be taken to avoid opening the frontal air sinus
at the medial border of the craniotomy. Small bony extensions of the frontal skull base should be drilled
off extradurally and the inner edge of the craniotomy is to be beveled to increase the space available for
instrument maneuverability and to gain unobstructed view in the depth of the field.

Dural opening and intradural steps
The dural flap is fashioned with its base at the orbital roof. Under microscopic or endoscopic control, the
subfrontal corridor is developed. The ipsilateral optic nerve and supraclinoid carotid artery are identified,
and the arachnoid membranes of the optico-carotid and carotid-occulomotor cisterns are opened to allow
CSF egress. CSF release is essential to achieve adequate brain relaxation that opens the surgical corridor.
The rigid 4-mm endoscope is held by an assistant or fixed by a holder during an endoscope-controlled
procedure. An irrigation sheath is very helpful to clear the smudged lens. Surgery then proceeds using
the standard microsurgical techniques. It should be noted that tuberculum sellae meningiomas grow in a
subchiasmatic location displacing the optic chiasm backwards and the optic nerves laterally and superiorly
creating a prechiasmatic working space and facilitating the resection of these tumors via a supraorbital
[47]
eyebrow approach . In far anterior olfactory groove meningiomas, visualization of the attachment point
of the tumor in the midline depression of the olfactory groove may not be possible with the operating
[35]
microscope. This can be overcome with an angled endoscope and angled instruments . Wound closure is
then undertaken in the usual manner.

Approach selection for anterior skull base meningiomas: endoscope-assisted supraorbital
keyhole versus endoscopic endonasal surgery
[48]
Advances in endoscopic technology and the subsequent development of the expanded endoscopic
endonasal approach [6,49] created significant controversy regarding whether an endonasal or a keyhole
supraorbital approach provides the best results [6,10,50] . On the one hand, the advantages of endoscopic