Interfascial Dissection for Protection of the Nerve Branches to the Frontalis Muscles during Supraorbital Trans-Eyebrow Approach: An Anatomical Study and Technical Note

Abstract

Introduction Preservation of the temporal branches of the facial nerve during anterolateral craniotomies is important. Damaging it can inflict undesirable cosmetic defects to the patient. The supraorbital trans-eyebrow approach (SOTE) is a versatile keyhole craniotomy but still has a high rate of frontalis muscle (FM) palsy. Objective Anatomical study to implement the interfascial dissection during the SOTE to preserve the nerves to the FM. Methods Slight modification of the standard technique of the SOTE was performed in 6 cadaveric specimens (12 sides). Results Distal rami to the FM were exposed. The standard "u-shape" incision of the FM can cross over the nerves. Alternatively, an "l-shape" incision was performed until the superior temporal line (STL). An interfascial dissection was performed near to the STL and the interfascial fat pad was used as a protective layer for the nerves. Conclusion Various pathologies can be addressed with the SOTE. In the majority of the cases the cosmetic results are good, but FM palsy remains a drawback of this approach. The interfascial dissection may be used in an attempt to prevent frontalis rami palsy.

Keywords: frontalis muscle palsy; interfascial dissection; nerve protection; supraorbital trans-eyebrow approach.

Fig. 1

Supraorbital nerve branches and FR of temporal branches of the facial never exposure. (A) A 5 cm skin incision lateral to the supraorbital notch. (B) Supraorbital nerve and FR exposure. Note that the myofascial flap will begin with an “l-shape” cut with the horizontal cut starting in a mean distance of 31.3 mm superior and posterior the lateral cantus of the eye (green arrow). If the cut is performed through the STL (red dots) the FR may be injured. (C) Distal nerve terminations of FR with the FM. Fibers from the orbitalis muscles can be seen with different direction when compared with the FM. (D) Loose areolar tissue in the subgaleal space, where the FR runs. (E) “l-shape” myofascial flap being detached from the bone. The cut is carried on from medial to lateral passing through the STL and reaching the superficial layer of the temporal fascia. (F) Facial nerve exposure (different specimen), demonstrating nervous supply of the orbicularis and occipito-frontalis muscles by auricularis/posterior (I), frontalis/medial (II) and orbicularis/anterior (III) facial branches. Note the extent of connections between the respective branches. FM, frontalis muscle; FR, frontalis rami; STL, superior temporal line.

Fig. 2

Interfascial dissection steps from medial to lateral. (A) Myofascial flap reflected anteriorly along with the STF, exposing the deep layer of the temporal fascia. (B) Maximum retraction of the myofascial flap. Blue arrow showing the point where the cut of the STF along with the interfascial fat pad should be done to keep mobilizing the STF and fat pad anteriorly. (C) Cutting the STF along with the interfascial fat pad. (D) View showing layers lateral to the STL, specially the interfascial fat pad that will protect the FR. (E) Flap retraction after interfascial dissection. Note that further anterior retraction is achieved. (F) Temporal muscle detached from the STL exposing the keyhole region. STF, superficial layer of the temporal fascia; STL, superior temporal line.

Fig. 3

(A–E) Stepwise frontoorbital craniotomy. (A) Keyhole region exposed lateral to the STL and under the detached temporal muscle. (B) MacCarty keyhole exposing the periorbit and the frontal dura separated by the orbital roof. (C) Osteotomies from the MacCarty keyhole following a u-shape line until the orbital rim lateral to the supraorbital notch. (D) Zygomatic process of the frontal bone drilled. (E) Chisel being used to cut though the orbital roof—note the protection of the periorbit with a spatula. (F) Sutures being used to retract the periorbit to gain more inferior space. STL, superior temporal line.

Fig. 4

(A) Frontoorbital bone flap in one piece. (B) Dural opening. (C) Dissection of the suprachiasmatic cistern showing the right A1 segment of the anterior cerebral artery and the right recurrent artery of Heubner. The superior portion of the carotid cistern can be opened exposing the internal carotid bifurcation. ON and optic chiasm can be gently mobilized in other to further exposure. Dissecting the infrachiasmatic cistern, the superior hypophyseal artery and it branches comes in to view and care must be taken to avoid injury. Opening the seller diaphragm, the connection between the stalk and the pituitary gland can be seen. ON, optic nerves.