Anatomical layers of temporal region. (1) Skin; (2) subcutaneous tissue; (3) temporoparietal fascia (superficial temporal vessel); (4) lose areolar tissue; (5) temporalis muscle fascia (middle temporal artery); (6) temporalis muscle (deep temporal artery); (7) bone with pericranium
4.1.1 Neurovascular Anatomy
The superficial temporal region is supplied by the superficial temporal vascular system that originates from the superficial temporal artery.
The superficial temporal artery (STA) represents, together with the internal maxillary artery, a terminal branch of the external carotid artery. The latter runs deep in the parotid gland where it ascends and just behind the neck of the mandible divides into its two terminal arteries.
While the internal maxillary artery runs forward directed to the infratemporal fossa, the STA (which measures a diameter of about 1.90 mm at its origin) rises about 5 mm in front of the tragus, ascends upward lying posteriorly to the ramus of the mandible and reaching the temporoparietal fascia. In the second superficial tract of its course, the artery is accompanied by the corresponding vein and the auriculotemporal nerve. It runs up toward the temporal region, crossing the posterior third of the zygomatic arch and going beyond it for about 4 cm, where it divides into its two terminal branches: the frontal (anterior) and the parietal (posterior). These two arteries have similar size, with the frontal branch that seems to be less variable than the parietal [3]. The superficial temporal artery supplies the skin and the muscles of the same side of the face and scalp, the parotid gland, and the temporomandibolar joint.
The frontal branch has a winding course toward the frontal region proceeding in an anterosuperior direction; it is usually slightly larger than the parietal one (1.2 and 1.1 mm, respectively) [4], and it anastomoses with the corresponding branches of the opposite side and with branches from the ophthalmic artery. Conversely, the parietal artery curves upward and backward, toward the vertex, until it anastomoses with the contralateral one and with the posterior auricular and the occipital arteries.
Before ending in these terminal vessels, the superficial temporal artery gives several collateral branches: the transverse facial artery, the zygomatico-orbital artery, the middle temporal artery, and anterior auricular arteries. The first one originates deep into the parotid gland, just below the zygomatic process of the temporal bone, and it runs forward horizontally lying over the masseter; once emerged from the gland, it is accompanied by branches of the facial nerve. It supplies the parotid gland and its duct, the masseter muscle, and the skin.
The zygomatico-orbital artery branches superiorly and runs horizontally along the superior border of the zygomatic arch, between the two layers of the temporal fascia, reaching the lateral orbital angle. It anastomoses with branches from the ophthalmic artery.
The middle temporal artery originates just above the zygomatic process and supplies the temporalis fascia anastomosing with branches from deep temporal arteries, which originate from the internal maxillary artery. These different vascularized networks [5], which supply separately the superficial temporoparietal fascia and the temporalis fascia, represent a crucial anatomic feature which makes this flap ideal when requiring a highly vascularized tissue in the surgical bed.
The last arteries, the auricular branches, arise posteriorly and bring blood flow to the lateral surface of the auricle and to the external acoustic meatus.
A widespread venous network across the scalp forms, at the level of zygomatic arch, the superficial temporal vein, which runs down close to the artery. It may be single or duplicate.
In most cases, it runs superficially to the artery, though in 20–30% of the cases the vessel diverges from the artery and runs up to 3 cm posteriorly [6, 7].
It is remarkable how the venous drainage of the region seems to consist in the superficial temporal vein and the posterior auricular venous network [8]. However, this anatomical pattern seems to be purely descriptive, and actually variations in temporal venous drainage have been described in literature. Indeed, authors have reported how the superficial temporal vein does not appear to be always the dominant vessel and is not constant. Sometimes, the posterior auricular vein represents the main drainage of the region. Particularly, they described three different patterns of venous vascularization: type 1 consists in a dominant superficial temporal vein, type 2 with a posterior auricular vein predominant, and finally type 3 with both the venous vessel equally represented. In author’s opinion [8], it’s advisable to assess these different anatomical conditions preoperatively with angiography, in order to avoid complications during the microsurgical phase of the free flap technique: a slight venous vessel will not be suitable for an appropriate vascular microanastomosis and would not be able to guarantee the venous drainage of the flap [8] efficaciously.
There are several nervous branches lying in the temporoparietal region that the surgeon may encounter during the dissection. The auriculotemporal nerve is a sensory branch from the trigeminal nerve, runs within the superficial temporoparietal fascia close to the vascular pedicle, and gives sensitivity to the skin of the region dividing into its superficial temporal twigs.
Another important nervous structure of the region is the temporal branch of the facial nerve. The temporal ramus of the facial nerve is the first of the five terminal branches arising from the main trunk of the nerve, deep within the parotid parenchyma. The temporal nerve runs upward and leaves the parotid gland by its superomedial surface. It crosses the zygomatic arch in the middle, where it assumes a more superficial course [9], and lying in a superficial subcutaneous layer supplies the facial muscles [3]. The temporal ramus has an oblique direction, following a virtual line (Pitanguy line) which goes from 0.5 cm below the tragus to 1.5 cm above the lateral extremity of the eyebrow; it is at risk of injury during the anterior dissection of the flap.
4.2 Flap Harvesting
4.2.1 Preoperative Management
Many factors could influence the feasibility of reconstruction using TPFF. First of all, it’s mandatory to exclude preoperatively all those factors that could have compromised the vascular pattern of the temporal region, that is to say, history of previous radiation to the region, previous local surgery, external carotid embolization or ligature, and autoimmune arteritis (e.g., giant cell arteritis). All these anamnestic risk factors represent a contraindication to the use of this flap.
For these reasons, when projecting the surgical plan, it’s fundamental to assess preoperatively the entity of the blood flow through the vascular pedicle using a Doppler ultrasonography. Therefore, this precaution allows to exclude any anatomical variants of the superficial temporal vessels and to ensure the vascular supply of the TPFF.
In literature, some authors have proposed how a preoperative angiography could be useful to evaluate the exact pattern of venous drainage of temporal region, thus avoiding the use of TPFF as a free flap when the superficial temporal vein seems not to be the dominant vessel [8].
A good recommendation, although not indispensable, is to shave accurately the hair of the temporal region preoperatively. Shaving could be limited just to the incisional area.
It is advisable to identify and drawn preoperatively the course of the vascular network of the region. The course of the arterious vessel will be easily identified through a meticulous palpation of the region or by the use of Doppler ultrasonography. For what concern the course of the venous vessel, in our experience, a useful tip is to apply a firm pressure at the level of the vascular pedicle in the pretragal region in order to cause a blockage to the venous drainage. This will consequently bring to a swelling of the venous vessel immediately appreciable beneath the skin, making the course of the vein clearly evident.
In conclusion, these few and easily reproducible suggestions may be sufficient for an accurate preoperative evaluation and will make the dissection easier.
4.3 Surgical Steps
4.3.1 Step 1: Surgical Incision
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