A new study of the anatomic features and the strategies of intraoperative dissection of the temporal region

Yang Yang, Jiangang Wang, Xingang Li

Dept. Neurosurgery, Qilu Hospital ,Shandong University, Jinan , Shandong , P.R. China

 

Abstract

Objectives To list the commonly used terms to describe the anatomy of the temporal region and have a detailed review of the anatomical features and have a new research for the intraoperative strategies in temporal region to optimize the dissection and minimize the possibility of potential injury to the frontotemporal branches of the facial nerve.

Materials and Methods 10 cadaveric heads (20 sides) stepwise dissection were performed with the aid of surgical microscope; Pterional craniotomy were performed in 20 cases and frontoorbitozygomatic craniotomy performed in 4 cases , dealing with the temporal region with certain techniques.

Results All the conventionally described structures in the temporal region can be clearly defined in the cadaver dissections. The discrepancy is that the deep temporal fascia are divided into superficial and deep layers all over the whole temporal regions in all the specimens, not confined only to where the intermediate fat pad sits. In fact, the two layers can easily be separated by blunt dissection beyond the fat pad in all the cadaveric specimens although they becomes astonishing thinner in some areas. The intermediate fat pad is found absent in two of our patients.

Conclusion The deep temporal fascia is consists of superficial and deep layers in the whole temporal regions, by no means confined merely to where the intermediate fat pad sits as is previously described.

The intermediate fat pad is an important and useful but not the indispensable landmark in clinical practices and the interfascial dissection can still be completed even if the fat pad is absent.

Key words: Temporal Region, Facial nerve, Pterional craniotomy.

Introduction

The course of the frontotemporal branch of the facial nerve passes through the temple and forehead, placing this nerve at risk of injury at the time of surgical dissection [1]. Preservation of the frontotemporal branch of the facial nerve using the interfascial temporalis flap for pterional and zygomatic craniotomies is a indispensable idea [1-7]. The descriptions in the literatures to designate the multiple layers that surface temporal region is apparently complex due to the variety of terms and the lack of uniformity in terminology.

The tissue layers in the temporal region are usually defined as the skin, subcutaneous fat, superficial temporal fascia (STF), loose avascular areolar plane - Superficial temporal fat pad (Fig.1); the deep temporal fascia (DTF), and temporal muscle [2, 3] (Fig.2), (Fig.3), (Fig.4). The study of the temporal region is better understood if we consider the soft tissues as a series of concentric layers covering the head [3, 4].

The STF represents the continuance of the superficial musculoaponeurotic system (SMAS) of the face and the galea aponeurotica system of the scalp (Fig.5) and is loosely adherent to the subdermal fat and intimately associated with the frontotemporal branch of the facial nerve and the superficial temporal vessels. It is also called the temporoparietal fascia [4].

According to Yasargil and Eduardo, the deep temporal fascia a single layer over the upper part of the muscle and divides in superficial and deep layers inferiorly. The former layer runs on the superficial aspect of the zygomatic arch and continues with the parotidomasseteric fascia; The latter layer courses deep to the zygomatic arch (Fig.6) and continues with the posteromasseteric fascia. A fat pad (Yasargil's fat pad) fills the space between the two layers of the DTF, above the zygomatic arch [1, 2].

The objective of the present study is to list all the terms used to describe the anatomy of the temporal region and have a detailed review of the anatomical features and the intraoperative strategies of the region . The study was complemented by 10 cadaveric heads (20 sides) as well as our clinical practices in 24 patients . The results support the conventional theories in most aspects except some discrepancy.

Materials and Methods

Cadaver dissection:

10 cadaveric heads (20 sides) previously embalmed in formalin were soaked in ethanol of 70o for 2 weeks and stepwise dissection were then performed with the aid of surgical microscope under the magnification of 3~15.

Surgical practices:

Among the 24 cases of the patients. Pterional craniotomy (Fig.7) were performed in 20 cases and frontoorbitozygomatic craniotomy performed in 4 cases. The region dissection was carried down to the DTF. Carry out the dissection between the gauzy STF and the shiny DTF down to the intermediate fat pad (Yasargil's fat pad) (Fig.8). The superficial layer of the DTF overlying the fat pad is then incised (Fig.9) and the elevated with the fat pad , leaving the deep layer of the DTF intact (Fig.10). The superficial layer of the DTF is elevated from the outer surface and the deep layer peeled off the inner surface of the zygomatic arc during frontoorbitozygomatic craniotomy.

Results

Cadaver dissection:

The skin, Subcutaneous, loose avascular areolar plane - Superficial temporal fat pad STF (temporoparietal fascia ), superficial layer of DTF, intermediate fat pad, deep layer of DTF, deep fat pad and temporalis muscle are clearly define in our dissection.

The DTF, we found, however, can be divided into superficial and deep layers all over the whole temporal regions, by no means confined only to where the intermediate fat pad (Yasargil's fat pad )sits (Fig.11). In fact the two layers can be easily separated by blunt dissection without difficulty and is discernible in the whole temporal region although they becomes astonishing thinner in some areas beyond the fat pad (Fig.12). Beneath the temporalis muscle, only a layer of "subperiosteum" rather than intact periosteum overlies the temporal bone is identified (Fig.13).

The frontotemporal branch of the facial nerve traveling roughly along a trajectory of connecting the point 5 mm below the base of the tragus to a point 1.5 cm above the lateral extremity of the eyebrow [1, 5] and was quite superficial as it crossed the zygomatic arch [3] (Fig.14). Three rami of the frontotemporal branch of the facial nerve coursing in different directions described by Yasargil et al. [2], were also observed and singled out (Fig.15).

Surgical practices:

The absence of apparent intermediate fat pad was found in 2 cases and the two layers of the DTF could still be separated during the dissection. No sign of injury to the frontotemporal branch of the facial nerve in all the 24 patients.

Discussions

Three fascial layers were identified in the temporal region [1]. These were the STF and the two layers of the DTF, which consist of a superficial and a deep layer.

The DTF is a thick layer of elastic fibers that overlies the temporalis muscle. It is generally thought that DTF the a single layer over the upper part of the muscle [1-7]. It is divided into superficial and deep layers inferiorly (near the zygomatic arch). The superficial layer of the DTF attaches to the outer surface of the zygomatic arch and continues with the parotidomassSeteric fascia. The deep layer of the DTF attaches to the deep inner surface of the zygomatic arch and continues with the posteromasseteric fascia [1, 2]. All these layers are clearly defined in all of the cadaver specimens.

Enveloped between the 2 layers of the DTF lies the intermediate temporal fat pad which fills the space between the two layers of the DTF, above the zygomatic arch. In contrast to the conventional descriptions, however, our anatomic study find, that the DTF are divided into two layers overlying the temporal muscles all over the whole temporal region, and are by no means confined only to where the s intermediate fat pad sits and we managed to separated the two layers of the DTF anywhere during cadaver dissection (Fig.11), (Fig.12). Such architectures are generally verified in our present study with some exception that apparent fat pad is absent in two patients in our clinical practices./P>

There is another deep fat pad present under the deep temporal layer. The latter fat pad is continuous with the buccal fat pad [2].

The frontotemporal branches of the facial nerve traveled in a constant plane along the under surface of the STF (temporoparietal fascia) [1-5], within the superficial fat pad and loose areolar avascular plane [5, 6], traveling roughly along a line of connecting the point 5 mm below the base of the tragus to a point 1.5 cm above the lateral extremity of the eyebrow [1, 5] and was quite superficial as it crossed the zygomatic arch [3] (Fig.14). Three rami of the frontotemporal branch of the facial nerve, with anterior (for the orbicularis oculi and corrugator supercilii muscles) and the middle (for the frontalis muscle) rami running in the subcutaneous tissue over the zygomatic arch, about 1 cm anterior to the superficial temporal artery and the posterior ramus for the anterior and superior auricular and tragus muscles, respectively [2], were also observed in our cadaver dissection (Fig.15).

We always elevate the flap from beneath the STF to spare frontotemporal branches of the facial nerve in operations.

In some rare cases , an occasional twig of the frontotemporal branch of the facial nerve that runs within the intermediate fat pad to distally penetrate the frontalis muscle [6]. Dissection within the intermediate fat pad or close to the deep layer of the DTF is more protective to the frontotemporal branch than just beneath to STF and the superficial fat pad or just beneath the superficial layer of DTF [4].

Bearing this idea in mind, we perform the interfascial dissection along the under surface of the fat pad rather than the superficial layer of the DTF, and then elevate the intermediate (Yasargil's) fat pad together with the superficial layer of the DTF, leaving the deep layer of the DTF intact (Fig.9), (Fig.10) to avoid damage to the potentially existing frontotemporal branch of the facial nerve in the intermediate fat pad. When crossing the zygomatic arch to communicate the temporal area to the midface, the dissection can be done in the subperiosteal plane or with extreme care in the subcutaneous tissue plane [4]. We never make the incision into the deep layer of the DTF in operations to spare the deep fat pad because of its continuity with the masticatory space. This fat allows smooth gliding between the muscles and is important in masticatory function, then, any scarring in this space may compromise the function [3].

In clinical practices as well as in cadaver dissection , we can find that beneath the temporalis muscle there is only a layer of "subperiosteum" overlies the temporal bone just as Yoko et al. [4] put it that the subgaleal fascia in the temporal region corresponds to the periosteum in the frontoparietal region, there is no true periosteum beneath the temporal muscle in the temporal fossa [4, 7] (Fig.13).

Conclusions

The deep temporal fascia is consists of superficial and deep layers in the whole temporal regions , by no means confined merely to where the intermediate fat pad sits as is previously described.

The intermediate fat pad is an important and useful but not the indispensable landmark in clinical practices and the interfascial dissection can still be completed even if the fat pad is absent.

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