Minimally Invasive Approaches: A Comparison Between Eyebrow Supraorbital Endoscopic Approach and Eyelid Transorbital Endoscopic Approach to Anterior and Middle Cranial Fossae

Background: In the last decades, minimally invasive surgery has gained wide popularity. The increasing application has evolved together with the advances in technology.

The purpose of this study was to compare two anterior minimally invasive approaches, namely supraorbital endoscopic approach (SEA) and transorbital endoscopic approach (TEA), with the aim of reporting the benefits and limitations of each, based on stepwise bony work.

Methods: With the aid of image guidance, ten colored silicone-injected human cadáver head specimens (20 sides) were dissected in a stepwise fashion through a SEA or TEA. For each approach, two subsequent steps of bone drilling were analyzed. Step I was the initial craniotomy: SEA was a supraorbital 2.5 × 1.5 cm craniotomy; TEA was a lateral/posterior orbital wall craniectomy. STEP II maximized the area of exposure of each approach: SEA required lesser sphenoid wing drilling and TEA was supplemented with removal of the orbital roof.

Fixed target points along the ipsilateral anterior and middle cranial fossae were identified, and distance of each from the midpoint of the craniotomy was calculated. Moreover, each target point was classified according to their visibility/possibility to operate by two authors independently. An intraclass correlation coefficient was measured for interobserver agreement.

At the end of each step, a scan was performed to measure the resection volume. The 3D Slicer 4.10.2 program was used to calculate the volume.

Results: For either step I approaches step I SEA and TEA volume of craniotomy were 2.95 ± 0.83 cm³ and 1.82 ± 0.83 cm³, it was not possible to reach both fossae simultaneously. SEA had excellent exposure of ipsilateral anterior cranial fossa (14.7 ± 1.7 cm²), with limited to no exposure of the middle cranial fossa; TEA provided good exposure of the middle cranial fossa (10.6 ± 12.6 cm²).with no exposure of the anterior cranial fossa.

After more extensive drilling step II SEA and TEA volume of craniotomy were 0.55 ± 0.23 cm³ and 1.49 ± 1.33 cm³, respectively, access to both fossae through each approach was augmented (mean SEA and TEA areas of exposure, 17.5 ± 1.8 cm² and 18.1 ± 2.7 cm², respectively).

However, exposure of the anterior cranial fossa through a step II TEA was inferior compared with step I SEA (7.4 and 14.7 cm², respectively), and the difference was statistically significant (p < 0.001).

On the contrary, exposure of middle cranial fossa through a step I TEA was significantly wider (p < 0.001) than step II SEA (10.6 and 2.8 cm², respectively).

Conclusions: SEA and TEA are valid approaches in selected patients. Their areas of exposure have minimal overlap in their “limited” (i.e., step I) initial exposure. However, wider exposure can be achieved through drilling of deeper bony structures, with minimal increase in risk of complication. SEA is superior for anterior fossa exposure and TEA for middle fossa.

Clinical results are necessary to draw more meaningful results.