A review of the literature and safe planes of augmentation.
Injection of the temporal fossa with dermal fillers can successfully correct and contour many of the age related changes, which contribute to a ‘hollowed’ appearance. The current literature surrounding the anatomy of the temple is widely inconsistent, most notably in the context of the descriptions of the temporal fascia and related vasculature, which is challenging for the clinician to interpret. Historically, anatomical papers frequently used embalmed specimens and as such have been shown to be more inaccurate as formalin can cause matting of tissue, which can distort findings. Studies which incorporate unembalmed specimens have been proven to resemble anatomical structures with a higher degree of accuracy.
The temporalis muscle covers the expanse of the temporal fossa, originating from the coarse surface of the temporal bone and inserting on to the coronoid process and inferiorly on to the anterior border of the mandibular ramus.
The temporal crest indicates the superior boundary of the temple with the anterior border of the zygomatic arch indicating the inferior border. The temporalis muscle receives its nervous supply from the mandibular division of the trigeminal nerve.
There are inconsistent reports within the literature regarding the number and location of the fat compartments located within the temporal fossa. A small number of studies indicate the presence of a superficial temporal fat pad located between the superficial temporal fascia and superficial component of the deep temporal fascia, this may vary between male and female specimens in conjunction with the overall thickness of the soft tissues. The deep fat pad is more consistently described and can be located approximately between the temporalis muscle and the zygomatic and/or temporal bone. It is important to note that some individuals may possess only one of these fat pads, and others may have both. Topographically, it remains challenging for the clinician to identify the presence and precise location of fat pads within the temporal fossa.
The septal boundaries of the temporal fossa hold key significance for the clinician in terms of selecting an appropriate technique for product placement. The superficial temporal fascia and superficial component of the deep temporal fascia have fixed boney attachments, to the temporal crest and anterior border of the zygomatic arch, respectively. These attachments and fixed boundaries represent safe planes of product placement with minimal risk of product migration. The most superficial fascial plane consistently described within the literature is the superficial temporal fascia, which is located beneath the skin and subcutaneous layer. The superficial component of the deep temporal fascia is located in the next layer followed by the deep temporal fascia, which overlies the temporalis muscle. Several recent studies concur that the superficial temporal fascia and the superficial component of the deep temporal fascia adhere anteriorly to the zygomatic arch. These fascial boundaries and points of adherence suggest that dermal filler placement with a blunt cannula provides a safe approach as it is less likely to penetrate the fine fascia and allows the clinician a higher degree of control in maneuvering to the desired plane and to visualize the tip of the device with clarity. Augmentation of the temple to place product within the fascial planes using a needle approach does not afford the necessary level of accuracy in this region as it may pierce the fine fascia. A sharp needle may be preferable to bolus product supraperiosteally. A suggested safe approach is to place product between the superficial temporal fascia and the superficial component of the deep temporal fascia as there are no significant anatomical structures crossing between these planes as well as minimal risk of migration.
The superficial temporal artery bifurcates as a frontal and parietal branch along its course of the temporal fossa. It can reside in the subcutaneous layer or between the superficial temporal fascia and the subcutaneous layer and travel anterior to the facial nerve at the tragus of the ear, on it’s superior path. Whilst the risk of blindness is a rare and devastating complication, placement of dermal filler within the subcutaneous plane of the temporal fossa could result in vascular compromise, and as such, it is recommended that injection of dermal filler is placed deep to this plane. A robust cannula technique is justifiably a safer approach to navigate the fascial planes and reduce the risk of vascular injury in comparison to a sharp needle. Used appropriately, a blunt cannula may reduce the risk of embolization as it is less likely to penetrate structures.
The sentinel vein can be topographically located lateral to the orbital rim and is at risk of trauma during augmentation of temple. It may be approximately located by marking a line from the supraorbital notch to the base of the zygoma, with a second line passing superiorly from the mental foramen to the angle formed by the superior border of the zygoma and lateral orbital rim.
Injury to the sentinel vein may cause unsightly bruising, particularly with a needle approach.
The facial nerve crosses the zygomatic arch to reside within the subcutaneous layer as multiple rami , traversing across the temporal fossa to innervate orbicularis oculi and the frontalis muscle. This further reinforces the importance of avoiding the placement of product within the subcutaneous layer. The zygomaticotemporal nerve is evident at the margin of the zygomatic bone, passing through a foramen adjacent to the zygomaticofrontal suture, providing sensation to the temple. The location of this nerve further reinforces the importance of a cannula approach to reduce sensory injury.
An advanced anatomical knowledge is key to safely treat the temple with dermal fillers, to yield an exceptional cosmetic result and to minimize the risk of complications. The use of a blunt cannula is advocated as a safer approach to augment the temporal fossa.