Risk Areas Markings for Prevention of Damage to the Branches of the Facial Nerve

For deep-plane dissection the risk area is situated anteriorly to the parotis up to the area of incorporation of the branches into the fibro-fatty tissue of the SMAS. As the frontal ramus is the most endangered branch I always mark its pathway from 1.5 cm in front of the tragus to the 0.8 cm2 area around the midpoint between the lateral canthus and the facial helix implantation. I do not perform a deep dissection in-between these markings, or closer than 0.5 cm when dissecting from above [22].

The sub-SMAS dissection of the mobile anterior face is performed at the lateral third of the forehead, the two thirds of the brow and infrabrow segment from the periosteum or temporal fascia, at the lateral canthal and maxillo-malar regions to the nasolabial fold and lateral lip corner. This is safe whenever the tip of the curved scissors is sliding in close contact to the temporal fascia or periosteum (Fig. 41.3).

The main ligaments of the upper two thirds of the anterior face are transected: the malar ligament, described in 1987 by Bossé and Papillon [4], the orbicular ligament of fibres which join the dermis and periosteum along the inferior border of the orbicularis muscle [23], which probably is similar to the malar septum [37]; and also the "orbital ligament" which, at the crista frontalis lateralis, joins the fascia temporo-parietalis with the temporal fascia [18, 19, 29]. At this level I described that a few veins and an artery trespass the temporal muscle and fascia and anastomose with the superficial vessels of the anterior branch of the superficial temporal artery, which run on the surface of the temporo-parietalis fascia. The main vein was denominated in 1991 "the sentinel vessel" by de la Plaza and Arroyo [38].

The lateral two thirds of the preseptal and orbital orbicularis muscle are undermined, however, without dissection of the zygomatic muscles. Contrary to the opinion of Ramirez and Santamarina [39], no damage occurs to the ramus of the upper zygomatic branch to the lower orbicularis muscle, as it is located more superficially, incorporated in the fibro-fatty tissue of the SMAS, while the zygomatic muscles are located on a deeper level (Fig. 41.4).

Facial Nerve Damage Pictures
  1. 41.3. Left: The pathway of the frontal ramus, which crosses an area of 0.8 cm2 at the centre between the lateral canthus and the facial implantation of the radix helicis. Right: Dissection corresponding to the cadaver in Fig. 41.2; the SMAS has been turned forward to show the dissected frontal ramus and subdivisions from the SMAS deep fibro-fatty tissue. The tip of blunt scissors, inserted in close contact with the temporalis fascia, is located beneath the area of the frontal ramus and its first
  2. 41.3. Left: The pathway of the frontal ramus, which crosses an area of 0.8 cm2 at the centre between the lateral canthus and the facial implantation of the radix helicis. Right: Dissection corresponding to the cadaver in Fig. 41.2; the SMAS has been turned forward to show the dissected frontal ramus and subdivisions from the SMAS deep fibro-fatty tissue. The tip of blunt scissors, inserted in close contact with the temporalis fascia, is located beneath the area of the frontal ramus and its first divisions, dissected from the fibro-fatty tissue of the SMAS. The deep dissection is safe anterior to the marking, and also from above at 0.5 cm from the pathway of the frontal branch between both branches. Any deep dissection along the pathway and below may endanger the temporal division of the facial nerve when leaving the protection of the parotis to ascend into the SMAS tissue in which it proceeds to the respective muscles
  1. 41.4. Dissection of the temporal division of the facial nerve (in blue) performed with Alfonso Rodríguez Baeza (University of Barcelona). 1 The terminal frontal branch. 2 Two branches to the upper orbicularis muscle. 3 The upper zygomatic branch running within the deep fibro-fatty tissue of the SMAS towards the inferior orbicularis muscle is located in a superficial plane compared with the deeper plane of the zygomatic muscle. 4 The lower zygomatic branch running deep to the zygomatic muscle. (9). 5 Anastomotic buccal branch joining the hom
  2. 41.4. Dissection of the temporal division of the facial nerve (in blue) performed with Alfonso Rodríguez Baeza (University of Barcelona). 1 The terminal frontal branch. 2 Two branches to the upper orbicularis muscle. 3 The upper zygomatic branch running within the deep fibro-fatty tissue of the SMAS towards the inferior orbicularis muscle is located in a superficial plane compared with the deeper plane of the zygomatic muscle. 4 The lower zygomatic branch running deep to the zygomatic muscle. (9). 5 Anastomotic buccal branch joining the hom onymous branches. 6 The inferior division of the facial nerve crossing the masseter muscle. (8) beneath its fascia. The lower part of the parotis (7) has been removed (dots indicate the cutting surface of the border) to show a buccal branch and the masseter. In green the midpoint between the lateral canthus and the facial helix implantation. The interrupted line shows the lateral limit of dissection of the mobile anterior segment of the face and also the limit of the deep downward posterior dissection

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