Anatomy of the Fibrofatty Adhesion Related to the Frontozygomatic Process for Suprafascial Dissection of the Pterional Scalp Flap: A Cadaveric and Clinical Study

Abstract

Background

With the existence of the fibrofatty adhesion (FFA) in the temporal region in relation to the frontotemporal branch of the facial nerve, the suprafascial dissection technique for two-layer pterional scalp flap creation was developed for standard pterional craniotomy. However, the exact anatomy of the FFA has not been well described. We clarified the anatomy of the FFA in cadavers and clinical cases.

Materials and Methods

Fourteen sides of the cadaveric head were dissected, and the location of the FFA was measured. Twenty patients with cerebral aneurysm who underwent pterional craniotomy using the suprafascial dissection technique between December 2023 and January 2025 were retrospectively reviewed and evaluated for the location of the FFA.

Results

In the cadaveric study, the mean distances between the superoposterior border of the FFA and the junction of the frontozygomatic process (FZP) and zygomatic arch were 2.2, 2.1, and 2.5 cm at the posterior, superoposterior, and superior borders of the FFA, respectively. The superior edge of the FFA was located inferior to the junction of the FZP and the temporal line at 2 and 1.8 cm on average for the cadaveric and clinical study, respectively.

Conclusion

The FFA was located in a small area posterior to the FZP, superior to the zygomatic arch, and below the junction of the FZP and the temporal line. The existence and anatomy of the FFA confirmed the safety of suprafascial dissection for pterional craniotomy. When exposing the zygomatic arch is necessary, interfascial or subfascial dissection must be performed.

 

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Keywords

pterional craniotomy - pterional scalp flap - suprafascial dissection - frontotemporal branch of the facial nerve - facial nerve - fibrofatty adhesion

Introduction

To obtain better exposure of the pterion and sphenoid rim when performing pterional craniotomy, it is necessary to use the two-layer technique of pterional scalp flap creation.[1] Two popular techniques, the interfascial and subfascial dissection techniques, have been suggested for creating the scalp flap to protect the frontotemporal branch of the facial nerve (FTFN), which innervates the frontalis muscle.[1] [2] [3] [4] [5] [6] [7] [8] The superior part of the frontozygomatic process (FZP) is the key structure to be exposed when performing the pterional scalp flap with the two-layer technique.

Salas et al and Sriamornrattanakul et al reported that exposing the superior part of the FZP (without exposing the zygomatic bone or zygomatic arch) is required for pterional or bifrontal craniotomy, and interfascial dissection is not necessary to protect the FTFN during scalp flap reflection.[7] [9] Suprafascial (subgaleal) dissection[9] [10] [11] provides adequate exposure for classic pterional[12] [13] [14] or bifrontal craniotomy[7] with FTFN protection. The subgaleal–suprafascial dissection plane is limited by the fibrofatty adhesion (FFA) within which the FTFN courses.[7]

The FFA, which is the adhesion between the galea aponeurosis (temporoparietal fascia or superficial temporal fascia) and the superficial layer of the deep temporal fascia (SdTF), has been described in a few cadaveric studies, but its exact location is not well studied.[6] [7] [15] [16] In 1998, Salas et al studied the anatomy of the FTFN in 10 temporal regions of cadavers and found that the FFA was located above the anteroinferior one-third of the temporalis muscle (3 cm posterior to the FZP and 2.3 cm above the root of zygoma); however, the exact anatomical data of the FFA in each cadaver and its relationship to the lateral orbital rim were not described in detail.[7] Furthermore, we have not found any clinical study of the FFA in clinical patients.

In this study, we aimed to investigate the exact anatomy of FFA related to the FZP and the zygomatic arch in cadavers and clinical cases, ensure the safety of suprafascial dissection for pterional craniotomy, and confirm the necessity of interfascial or subfascial dissection to access the zygomatic arch from the pterional scalp flap.

 

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Materials and Methods

Cadaveric Study

Fourteen sides of the cadaveric head were dissected for pterional scalp flap creation in the suprafascial–subgaleal plane. The suprafascial dissection technique, as described in the previous literature,[9] was applied to all specimens. We identified the FFA by the fusion of the galea aponeurosis and SdTF, which caused the well-defined subgaleal plane to disappear ([Fig. 1]). The superior, posterior, and superoposterior borders of the FFA were marked with pins through the skin. The junction of the FZP and zygomatic arch (point A) was also identified. We measured the distances from point A to the three borders of the FFA. The junction of the FZP and the temporal line (point B) was also marked, and the distance from point B to the superior border of the FFA was measured ([Fig. 2]).

Fig. 1 The fibrofatty adhesion and its border (blue line and red arrows) were identified in the subgaleal plane on the left side.

Fig. 2 Measurements on the left pterional area of the cadaveric head. (A) After the pterional scalp flap was reflected anteriorly in the subgaleal plane, the fibrofatty adhesion (FFA) (yellow area), its border (red arrow), and the anterior edge of the temporal line (green arrow) were identified. (B) The junction of the frontozygomatic process and zygomatic arch (yellow pin, point A) and the border of the FFA (red pins) were marked on the skin surface. The green arrow identifies the junction of the frontozygomatic process and the temporal line (point B). (C) The distance from point B (green arrow) to the superior edge of the FFA (yellow area) was measured (a). (D) The horizontal (b), oblique (c), and vertical (d) lengths of the FFA (yellow area) were measured from point A (yellow pin). Point B (green arrow) was also identified. The posterior border of the frontozygomatic process and the superior border of the zygomatic arch were drawn as a dotted white line, and the temporal line was drawn as a dotted blue line in (B) and (D).

 

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Clinical Study

We included 20 patients with cerebral aneurysm who underwent pterional craniotomy using suprafascial dissection from December 2023 to January 2025. We have described the suprafascial dissection technique in our previous study.[9]

In the suprafascial–subgaleal plane, the superoposterior border of the FFA (yellow area in [Fig. 3]) and the junction of the temporal line and the FZP (point B; blue arrow in [Fig. 3]) were identified. To avoid FTFN injury, we stopped the dissection of the FFA when the subgaleal plane disappeared (which is the starting point of FFA); therefore, the anterior and inferior borders of the FFA could not be identified in clinical cases. In addition, the junction of the zygomatic arch and FZP (point A) could not be confirmed through the subgaleal plane in clinical cases. We measured the distance between the superior border of the FFA and point B ([Fig. 3C, D]). The temporal fascia and temporalis muscle were detached from the temporal line, temporal squama, and the superior part of the FZP in the inferolateral direction. Detachment of the temporal fascia from the FZP was limited posteriorly by the FFA, which should be preserved ([Fig. 3E]). The function of the ipsilateral frontalis muscle, which elevates the ipsilateral eyebrow, was evaluated at 1 to 6 months after the operation.

Fig. 3 Area and location of the fibrofatty adhesion (FFA) in a clinical case that underwent right suprafascial dissection. (A) Area of the FFA (yellow area) is drawn on three-dimensional computed tomography angiography. The junction of the temporal line and the frontozygomatic process (point B) is marked by the blue arrow. The distance from point B (blue arrow) to the superior edge of the FFA was demonstrated (a). (B) Suprafascial dissection was performed on the right side. (C) The FFA was marked in the yellow area. The junction of the temporal line and the frontozygomatic process were estimated by palpation (blue arrow, point B). (D) The distance from the superior border of the FFA to point B (blue arrow) was measured (a, dotted blue line). The temporal line and the frontozygomatic process were drawn as a dotted black line and a dotted red line, respectively. (E) The temporalis muscle and the temporal fascia were detached from the temporal line (black dotted line), the temporal squama, and the superior part of the frontozygomatic process (red dotted line) in the inferolateral direction (yellow arrow). The length of the detachment from the frontozygomatic process (a) was the same length as that measured in (D).

 

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Results

FFA was identified in the cadaveric heads of all specimens. From the junction of the FZP and zygomatic arch (point A), the superoposterior border of the FFA was measured as 2.2, 2.1, and 2.5 cm for the horizontal, oblique, and vertical dimensions, respectively, on average. The lengths in the horizontal, oblique, and vertical dimensions ranged from 1.1 to 3.0, 0.8 to 2.8, and 1.3 to 3.2 cm, respectively. The distance from the junction of the FZP and the temporal line (point B) to the superior edge of the FFA was 2.0 cm on average (range: 1.5–3.0 cm) ([Fig. 4A], [Table 1]).

Fig. 4 Results of this study. (A) The results of the cadaveric study are illustrated. Yellow area: fibrofatty adhesion (FFA); yellow pin: junction of the frontozygomatic process and zygomatic arch (point A); green arrow: junction of the temporal line and frontozygomatic process (point B); dotted white line: posterior border of the frontozygomatic process and superior border of the zygomatic arch; dotted blue line: temporal line. (B) The results of the clinical study and measurement method are depicted. Yellow area: FFA; blue arrow: junction of the temporal line and frontozygomatic process (point B); dotted black line: temporal line; dotted red line: frontozygomatic process; dotted blue line: distance from the superior border of the FFA to point B.

Table 1 Results of the cadaveric dissection

No.	FFA from point A			Distance from point B to superior edge of FFA (cm)
	Horizontal length (cm)	Oblique length (cm)	Vertical length (cm)
1	2	2.1	3	1.8
2	2.6	2.8	2.1	1.8
3	2.5	2	3	2.1
4	2.8	2.7	2.6	2.4
5	2	1.8	2.3	3.0
6	1.5	2	3	1.8
7	1.5	1.7	2.6	1.5
8	2.2	2.5	3	2.3
9	2.5	2.6	3.2	1.8
10	1.1	0.8	1.4	1.5
11	2.5	1.5	1.3	1.8
12	2.5	2.5	2.4	2.8
13	3	2.6	2.6	1.5
14	2.2	2.4	2.6	2.5
Average	2.2	2.1	2.5	2

Abbreviation: FFA, fibrofatty adhesion.

Note: Point A is the junction of the frontozygomatic process and zygomatic arch; point B is the junction of the frontozygomatic process and temporal line.

In the clinical study, we enrolled 20 patients who underwent pterional craniotomy using the suprafascial dissection technique. Most patients (60%) were 41 to 60 years old. The patients included 15 women and 5 men. Eleven operations (55%) were performed on the right side. After the pterional scalp flap was reflected in the subgaleal–suprafascial plane, the FFA was identified in all patients. The superior edge of the FFA was located inferior to point B in all patients, and the distance was 1.8 cm on average (range: 1.3–2.6 cm) ([Fig. 4B], [Table 2]). We were able to access the superior part of the FZP without invading the FFA, and standard pterional craniotomy could be performed without limitation. With this dissection technique, no postoperative permanent frontalis paralysis occurred in any patient at 1 to 6 months after operation ([Table 2]).

Table 2 Results of the clinical study

Data	Number of patients (N = 20)
Age (y)
< 40	3
41–60	12
> 60	5
Gender Female:male	15:5
Surgical side Right:left	11:9
FFA was identified	20
Distance between the superior border of FFA and point B
1.0–1.5 cm	5
1.5–2.0 cm	14
2.0–2.5 cm	0
> 2.5 cm	1
Mean distance (cm)	1.8
Postoperative permanent frontalis paralysis (3–6 mo) (%)	0 (0)

Abbreviation: FFA, fibrofatty adhesion.

Note: Point B is the junction of the frontozygomatic process and the temporal line.

 

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Discussion

Course of the FTFN from the Stylomastoid Foramen to the Zygomatic Arch

After the facial nerve exits the stylomastoid foramen, it crosses the ramus of the mandible 2.5 cm below the zygomatic arch and enters the parotid gland, where it branches into the temporal (frontotemporal, FTFN), zygomatic, buccal, marginal mandibular, and cervical branches. After the FTFN leaves the parotid gland, the most posterior branch of the FTFN runs anterosuperiorly to cross the zygomatic arch at 1 to 2.4 cm from the tragus and divides into three main rami: the auricularis (posterior) rami, frontalis (middle) rami (also known as the frontal branch), and orbicularis (anterior) rami. The frontal rami innervate the frontalis muscle, which elevates the ipsilateral eyebrow.[4] [6] [15] [16] [17] [18]

Kucukguven et al reported that the risks of FTFN injury on the zygomatic arch were 0, 5, and 90% if the skin incision started anterior to the most anterior point of the tragus at 0 to 10, 10 to 14, and 14 to 16 mm, respectively.[17] Therefore, to avoid FTFN injury, the skin incision above the zygomatic arch should start within 10 to 14 mm anterior to the most anterior point of the tragus ([Fig. 5A]). In their cadaveric study, Tayfur et al reported that the mean distance of the most posterior branches of FTFN to the lateral orbital rim was 2.4 cm.[18]

Fig. 5 (A) Anatomy of the fibrofatty adhesion (FFA) (blue area) relating to the frontotemporal branch of the facial nerve (FTFN) and the superficial temporal artery (STA). (B) Section plane of figure A (dashed white line) shows the fascial planes relating to the FFA and FTFN. fSTA, frontal branch of the STA; mSTA, main trunk of the STA; pSTA, parietal branch of the STA; SMAS, superficial musculoaponeurotic system.

 

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Anatomy of the FFA and Its Relationship to the FTFN

Just after the FTFN passes the zygomatic arch, it runs anterosuperiorly just underneath the galea aponeurotica (temporoparietal fascia) in the FFA. The FFA is the fibrous adhesion of the galea, suprafascial (subgaleal) fat pad, loose areolar tissue, and SdTF. Within the FFA, the loose areolar tissue plane between the galea and SdTF disappears ([Fig. 5B]).[7] [15] [19] Spiriev et al studied 16 sides of the cadaveric head and found the fusion between the galea and SdTF (which they called the “fibrofatty layer”) above the zygomatic arch and the FTFN running within this layer.[16] Shin et al studied 55 sides of the cadaveric head and found that the FTFN courses in the fibrofatty layer deep to the superficial temporal fascia (galea aponeurosis). The FTFN generally courses 1 to 2 cm anteriorly and inferiorly to the frontal branch of the superficial temporal artery (fSTA) in the temporal region ([Fig. 5A]). However, the FTFN ran just underneath the fSTA in 3.6% of their specimens. When the STA bifurcation is higher, the fSTA and FTFN move further apart, whereas when the STA bifurcation is lower, the course of the fSTA becomes closer to the FTFN.[15]

Salas et al reported the results of a cadaveric study (10 sides of cadaveric heads) in which they found that the FFA was located above the anteroinferior one-third of the temporalis muscle (3 cm posterior to the FZP and 2.3 cm above the root of the zygoma). They described the difficult separation of the galea and the SdTF and suggested that the separation of the adhesion results in a high risk of FTFN injury. They recommended avoiding elevation of the galea and skin from the SdTF in this area. Although they described the FFA, data from each cadaver were not available in their study.[7]

In our cadaveric study, we dissected a larger number of specimens and provided the data of each specimen in detail. The results of our study showed high variation in the anatomy of FFA in the cadaveric study and also demonstrated the FFA in clinical patients. To the best of our knowledge, only three studies have described the FFA on cadaveric dissection—Salas et al, Shin et al, and Spiriev et al—but the exact location of the adhesion was not well reported.[7] [15] [16] In addition, the FFA was identified in only one clinical study, but the relation to FZP was not detailed.[9]

 

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FFA and the Protection of FTFN

In the area superoposterior to the FFA, the plane between the galea and SdTF is easily separated by the existence of loose areolar tissue. However, when we encountered the FFA, this well-developed plane disappeared. Therefore, the FFA provided the anatomical limitation of the subgaleal dissection to the area in which the FTFN was located. Therefore, in the area superoposterior to the FFA, we easily performed the elevation of the galea and the loose areolar tissue from the SdTF as well as safely performed fSTA harvesting (usually located 1–2 cm posterior to the FTFN) with a low risk of FTFN injury. After exiting the FFA, the FTFN runs anterosuperiorly just underneath the galea aponeurosis to innervate the frontalis muscle.[6] [7] [19]

Salas et al reported that FFA protected the FTFN during subgaleal plane dissection. They suggested that when performing a scalp incision to expose the superior part of the FZP without zygomatic bone or zygomatic arch exposure, interfascial dissection is not necessary, and the subgaleal (suprafascial) dissection provides an adequate exposure for standard pterional craniotomy with FTFN protection.[7] Sriamornrattanakul et al reported that suprafascial dissection with preservation of FFA can protect the FTFN in all patients. In their study, they detected transient ipsilateral frontalis paralysis in 20.4% of the patients, which completely recovered within 6 months. They also detected obvious temporal hollowing in 18.2% of the suprafascial group without a muscle cuff, which was significantly less than in the interfascial group (72.7%). However, although the surgical technique for suprafascial dissection was described in detail, the anatomical data of the FFA were not evaluated.[9]

In our clinical study, we described the location of the FFA in relation to the bony surface, and the protection of the FTFN was ensured by postoperative preservation of frontalis function.

 

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Anatomy of the FFA and Clinical Applications and Drawbacks of Suprafascial Dissection

To perform suprafascial dissection for two-layer scalp flap creation without FTFN injury, it is necessary to identify the exact location of the FFA and its relationship to the FZP and FTFN. Using the FFA as the posterior limitation, the temporal fascia with the temporalis muscle can be detached inferolaterally from the FZP to expose the pterion at an average of 1.8 cm without the risk of FTFN injury ([Fig. 3E]). Therefore, when performing suprafascial dissection, the FFA is the posterior limitation of the temporal fascia detachment from the FZP. The FFA limited the exposure of the inferior part of the FZP and zygomatic arch, which is the drawback of this method and what makes it inferior to the interfascial and subfascial techniques. However, the lower rate of postoperative temporal hollowing is an important advantage of the suprafascial technique.[9] Because the temporal fascia dissection was performed deep to the SdTF, both interfascial and subfascial dissection were not limited by the FFA and were able to provide full exposure of the FZP and also the zygomatic arch without the risk of FTFN injury. Therefore, when orbitozygomatic osteotomy or increased exposure of the FZP is required, the interfascial or subfascial dissection technique should be selected to avoid violating the FFA and the risk of FTFN injury.

 

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Strength and Limitations

The limitations of our study included (1) the retrospective descriptive design, (2) the inclusion of a relatively small number of cadavers and patients, as well as the suboptimal quality of cadavers (not fresh or of the soft type), and (3) the lack of evaluation of details of the clinical improvement of frontalis paralysis and the degree of temporal hollowing.

To the best of our knowledge, this is the first study of the FFA in clinical patients.

 

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Conclusion

The FFA was located in a small area posterior to the FZP, superior to the zygomatic arch, and below the junction of the FZP and the temporal line. The existence and anatomy of the FFA confirmed the safety of suprafascial dissection for pterional craniotomy. When exposing the zygomatic arch is necessary, interfascial or subfascial dissection must be performed.

 

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Conflict of Interest

None declared.

Author's Contribution

P.Y., K.S., N.A., and T.P. contributed to the conception and design, acquisition of data, analysis and interpretation of data, and drafting the article. : K.S. and N.A. critically revised the article. K.S. reviewed submitted version of the article and supervised the study.

Ethical Approval

The study was approved by the Institutional Review Board of the Faculty of Medicine Vajira Hospital. COA no. was 210/2567.

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Publikationsverlauf

Artikel online veröffentlicht:
20. Mai 2025