The Course of the Main Trunk and Parietal Branch of the Superficial Temporal Artery for a Pterional Scalp Flap with Superficial Temporal Artery Preservation: Cadaveric and Clinical Study

Abstract

Background

The pterional incision is usually performed near the course of the superficial temporal artery (STA), which carries a risk of injury to a branch or even the main trunk of the STA (mSTA). In this study, we assessed the usual course of the mSTA and its parietal branch of the STA (pSTA) and evaluated the efficacy of a modified pterional scalp incision for the preservation of all STA branches.

Materials and Methods

Sixteen sides of cadaveric heads were dissected to study the location and paths of the mSTA and pSTA in the vicinity of the ear cartilage and the oculomeatal (OM) line. We also performed a clinical study of 31 patients who underwent pterional craniotomy using the modified pterional scalp incision. Postoperative STA preservation was retrospectively evaluated.

Results

The mean distances between the mSTA and the anterior edge of the ear cartilage were 0.5 and 0.6 mm. The mean angle of the pSTA axis was 88.3 degrees (range 75–95 degrees) from the OM line. Among the patients treated using the modified pterional scalp incision, the mSTA, the pSTA, and the frontal branch of the STA (fSTA) were preserved within the scalp flap in 93.5, 96.7, and 88.9%, respectively.

Conclusion

The mSTA was found to pass very close to the ear cartilage, while the axis of pSTA coursed approximately perpendicular to the OM line. To preserve all branches of the STA, the pterional skin incision should begin just anterior to the ear cartilage and then curve slightly to the posterior above the pinna.

Keywords

main trunk of STA - parietal branch of STA preservation - pterional craniotomy - pterional scalp flap - pterional scalp incision - superficial temporal artery preservation

Introduction

The pterional (frontotemporosphenoidal) craniotomy is the most frequently used form of craniotomy in neurosurgery, especially in the treatment of aneurysms. However, a curvilinear skin incision for a pterional (frontotemporal) scalp flap is necessary before a pterional craniotomy is performed. For a standard pterional skin incision ([Fig. 1]), the recommended starting point is 1 to 1.5 cm in front of the tragus, with the crossing point of the hairline and the ipsilateral midpupillary line as the endpoint. The incision is usually superimposed over the course of the superficial temporal artery (STA). As a consequence, the STA may be transected during incision and dissection of the scalp.[1] [2] [3]

Fig. 1 The image shows a standard pterional skin incision (white line), a minipterional incision (black line), and a modified pterional incision (dashed white line). The dotted black line and the green area are the superior temporal line and a standard pterional skull flap, respectively. The dotted red lines represent the fSTA and pSTA. The yellow line is the superior border of the zygomatic arch and frontozygomatic process. The dotted yellow line demonstrates the inferior border of the zygomatic arch. The red line (the distal Sylvian fissure) is the lateral canthus to Chater's point. fSTA, frontal branch of the superficial temporal artery; pSTA, parietal branch of the superficial temporal artery.

The STA is a terminal branch of the external carotid artery and a main feeder of the scalp. It usually divides into two branches to supply the frontotemporal area.[4] [5] The preservation of the STA could prevent postoperative complications caused by insufficient blood supply to the scalp and also allow the use of this preserved artery in possible future extracranial–intracranial bypass surgery. The STA passes vertically in front of the tragus. Therefore, it is especially vulnerable to injury during the creation of a pterional scalp flap.[3] [4] However, the exact location of the STA and STA preservation techniques for standard pterional craniotomies have not been well described in the previous literature, and research into STA preservation is sparse.[3]

Although the technique for minipterional craniotomies ([Fig. 1]) with STA preservation has been well developed, an important limitation of this minimally invasive technique is the limited operative field, which provides inadequate access to lesions, especially in aneurysm surgery.[6] Standard pterional craniotomies are still required for adequate exposure, and the STA should be preserved for future extracranial–intracranial bypass surgery, especially in patients with complex intracranial pathologies.

For a large pterional craniotomy with a standard pterional skull flap, Katsuno et al recommend a modified pterional scalp incision ([Fig. 1]) that begins just anterior to the tragus and extends slightly more to the posterior than a standard pterional skin incision.[7] With this incision, the main trunk of the STA (mSTA), the frontal branch of the STA (fSTA), and the parietal branch of the STA (pSTA) are preserved within the scalp flap. We have used this newly designed scalp incision to preserve the STA during standard pterional craniotomy.

This study aims to clarify the usual course of STA in cadavers, especially the mSTA and pSTA, and to evaluate the STA preservation rate achieved in clinical cases using the new scalp incision.

Materials and Methods

To study the STA location and course, 16 sides of adult cadaveric heads were dissected, and the mSTA, fSTA, and pSTA were identified. This was achieved by reflecting the skin through the subcutaneous plane. All branches of the STA were preserved and left in place in the cadaveric head, adhering to the galea aponeurosis ([Fig. 2A]). The zygomatic root was also identified for the superior and inferior borders. The axis of the pSTA was drawn from the point where it crossed the temporal line (if the pSTA bifurcates, the posterior branch was used for study) to the point where the STA crossed the superior border of the zygomatic arch. The oculomeatal (OM) line was drawn from the lateral canthus to the external auditory meatus (EAM). The angle between the OM line and the axis of the pSTA was measured ([Fig. 2A]). At the levels of the inferior and superior borders of the zygomatic root, the distances between the STA and the anterior edge of the ear cartilage were measured. The distance from the STA bifurcation to the superior border of the zygomatic arch was measured ([Fig. 2B]).

Fig. 2 The left side of a cadaveric head dissected to study the path of the superficial temporal artery (STA). (A) The mSTA and the fSTA and pSTA were dissected. The axes of the pSTA (dashed yellow line), the temporal line (yellow line), and the OM line (dashed white line) were drawn. The red dashed line represents the superior border of the zygomatic arch. The angle (X, yellow area) between the OM line and the axis of the pSTA was measured. (B) The inferior (dashed white line) and superior (solid white line) borders of the zygomatic root were drawn. The distance between the STA bifurcation and the zygomatic arch (a) was measured. The distances from the STA and the anterior edge of the ear cartilage were measured at the level of the inferior (b) and superior borders (c) of the zygomatic root. fSTA, frontal branch of the superficial temporal artery; mSTA, main trunk of the superficial temporal artery; OM, oculomeatal; pSTA, parietal branch of the superficial temporal artery; STA, superficial temporal artery.

To assess the efficacy of the modified pterional scalp incision, patients with cerebral aneurysms who had undergone pterional craniotomy at our institution between January 2022 and November 2022 were enrolled. The inclusion criteria were the patients who (1) had received the modified pterional scalp incision[7] ([Figs. 1] and [3]) and (2) had undergone both preoperative and postoperative computed tomography angiography (CTA). The exclusion criteria were previous zygomatic arch osteotomy and harvesting of the STA. The existence of an ipsilateral STA (mSTA, pSTA, and fSTA), as detected on the preoperative and postoperative CTA, was determined in each patient. On the postoperative CTA, we evaluated and analyzed the preservation of the STA branches within the scalp flap.

Fig. 3 The findings of our cadaveric study of the location and path of the superficial temporal artery. The blue dashed line and yellow dashed line represent the oculomeatal line and the axis of the pSTA, respectively. The black area represents the region covered by hair. The modified pterional scalp incision is shown as a white dotted line. fSTA, frontal branch of the superficial temporal artery; FZP, frontozygomatic process; mSTA, main trunk of the superficial temporal artery; pSTA, parietal branch of the superficial temporal artery; TL, temporal line; ZA, zygomatic arch.

Operative Technique for the Modified Pterional Scalp Incision

The skin incision was made just anterior to the ear cartilage of the tragus at the level of the superior border of the zygomatic root. It was then extended slightly more posteriorly than the traditional pterional skin incision. When it was just inferior to the temporal line, the curve incision was extended anteriorly to the ipsilateral hairline ([Fig. 3]).[7]

Results

The mSTA and fSTA were detected in all cadaveric heads, but the pSTA was detected in 15/16 (93.75%) of the head sides. The mean distances from the STA to the anterior edge of the ear cartilage were 0.5 and 0.6 cm at the levels of the inferior and superior borders of the zygomatic root, respectively. The mean angle between the OM line and the pSTA axis was 88.8 degrees (range 75–95 degrees). Below the temporal line, no STA was found posterior to the pSTA axis. The mean distance from the STA bifurcation to the zygomatic arch was 3 cm (range 1.5–4.5 cm) ([Table 1], [Fig. 3]).

Table 1 The results of cadaveric head dissection for the determination of the location of the STA

No.	Distance from STA to ear cartilage		Angle between pSTA axis and OM line (deg)	Distance from STA bifurcation to zygomatic arch (cm)
	At upper border of zygomatic root (cm)	At lower border of zygomatic root (cm)
1	0.6	0.6	75	4.5
2	0.7	1	85	3
3	0.3	0.5	90	3
4	0.4	0.4	95	2.5
5	0.9	1	90	3.5
6	0.6	0.6	92	1.5
7	0.5	0.6	90	3
8	0.4	0.5	93	2.2
9	0.3	0.3	85	3.5
10	0.4	0.4	82	4.5
11	0.3	0.3	80	4
12[a]	0.6	0.8	−	−
13	0.6	0.8	87	3.4
14	0.6	0.7	95	2.7
15	0.4	0.5	98	2.2
16	1.2	0.9	95	2
Average	0.5	0.6	88.8	3

Abbreviations: -, no parietal branch of superficial temporal artery; mSTA, main trunk of superficial temporal artery; OM line, oculomeatal line; pSTA, parietal branch of superficial temporal artery; STA, superficial temporal artery.

^a No parietal branch was found.

There were 31 patients included in our clinical study, with an average age of 56.4 years. Of these, 10 (32.2%) were male. The pterional craniotomy was performed on the left side in 14 (45.2%) of the patients. The most common aneurysm site was the anterior communicating artery (41.9%). In the preoperative CTA, the mSTA, fSTA, and pSTA were detected in 100% (31/31), 96.8% (30/31), and 87.1% (27/31) of the patients, respectively. In the postoperative CTA, the mSTA, fSTA, and pSTA were detected in 93.5, 93.5, and 77.4%, respectively ([Table 2]). The STA preservation rates were 93.5% (29/31), 96.7% (29/30), and 88.9% (24/27) for the mSTA, fSTA, and pSTA, respectively. In the patients with three STA branches (n = 26), all three branches were preserved in 84.6% (22) ([Table 3]). No ear cartilage injury was detected in any of the patients.

Table 2 The results of preoperative and postoperative CTA in patients who underwent pterional craniotomy

No.	Gender/age (y)	Side	Location of aneurysm	Preoperative CTA			Postoperative CTA
				mSTA	fSTA	pSTA	mSTA	fSTA	pSTA
1	27/F	L	OphA	Y	Y	Y	Y	Y	Y
2	43/F	L	AcoA	Y	Y	Y	Y	Y	Y
3	61/M	L	AcoA	Y	Y	Y	Y	Y	Y
4	57/M	R	PcoA	Y	Y	Y	Y	Y	Y
5	73/F	R	AcoA	Y	Y	Y	Y	Y	Y
6	79/F	L	AcoA	Y	Y	Y	N	N	N
7	30/F	R	AcoA	Y	Y	Y	Y	Y	Y
8	69/F	L	MCA-b	Y	Y	N	Y	Y	N
9	64/F	R	BT	Y	Y	Y	Y	Y	Y
10	56/M	L	AcoA	Y	Y	N	Y	Y	N
11	36/F	R	AcoA	Y	Y	Y	Y	Y	Y
12	70/M	R	IC-term	Y	Y	Y	Y	Y	N
13	55/F	R	MCA-b	Y	Y	Y	Y	Y	N
14	58/F	L	True-PcoA	Y	Y	Y	Y	Y	Y
15	56/M	L	MCA-b	Y	Y	N	Y	Y	N
16	72/F	R	AcoA	Y	Y	Y	Y	Y	Y
17	67/F	L	MCA-b	Y	Y	Y	Y	Y	Y
18	61/F	R	PcoA	Y	Y	Y	N	Y	Y
19	61/F	R	AcoA	Y	N	Y	Y	N	Y
20	85/F	L	PcoA	Y	Y	Y	Y	Y	Y
21	39/M	R	AcoA	Y	Y	Y	Y	Y	Y
22	39/M	R	AcoA	Y	Y	Y	Y	Y	Y
23	57/M	L	AcoA	Y	Y	Y	Y	Y	Y
24	69/F	L	PcoA	Y	Y	N	Y	Y	N
25	62/F	L	PcoA	Y	Y	Y	Y	Y	Y
26	54/M	R	C2	Y	Y	Y	Y	Y	Y
27	56/F	R	PcoA	Y	Y	Y	Y	Y	Y
28	57/F	L	AcoA	Y	Y	Y	Y	Y	Y
29	49/F	R	MCA-b	Y	Y	Y	Y	Y	Y
30	58/M	R	P1-P2	Y	Y	Y	Y	Y	Y
31	29/F	R	C2	Y	Y	Y	Y	Y	Y
				100%	96.8%	87.1%	93.5%	93.5%	77.4%

Abbreviations: AcoA, anterior communicating artery aneurysm; BT, basilar tip aneurysm; C2, ophthalmic segment of internal carotid artery aneurysm; CTA, computed tomography angiography; F, female; fSTA, frontal branch of superficial temporal artery; IC-term, terminal internal carotid artery aneurysm; L, left; M, male; mSTA, main trunk of superficial temporal artery; MCA-b, middle cerebral artery bifurcation aneurysm; OphA, Ophthalmic artery aneurysm; P1-P2, P1-P2 segment of posterior cerebral artery aneurysm; PcoA, posterior communicating artery aneurysm; pSTA, parietal branch of superficial temporal artery; R, right; true-PcoA, true posterior communicating artery aneurysm.

Table 3 The STA preservation rates of patients who underwent pterional craniotomy with a modified pterional scalp incision

	mSTA	fSTA	pSTA	All STA
Preoperative existence	31	30	27	26
Postoperative existence	29	29	24	22
Preservation	93.5%	96.7%	88.9%	84.6%

Abbreviations: fSTA, frontal branch of superficial temporal artery; mSTA, main trunk of superficial temporal artery; pSTA, parietal branch of superficial temporal artery; STA, superficial temporal artery.

Illustrative Cases

Illustrative Case 1 (Patient No. 2)

A 43-year-old woman was diagnosed with a ruptured aneurysm in the anterior communicating artery. A left pterional craniotomy with a transsylvian approach was performed. All three branches of the STA were detected on the patient's preoperative CTA ([Fig. 4A]). The modified skin incision for STA preservation was used ([Fig. 4B]). The patient's postoperative CTA revealed successful preservation of all branches of the STA ([Fig. 4C]).

Fig. 4 Patient no. 2. A 43-year-old woman underwent a left pterional craniotomy for a ruptured aneurysm in the anterior communicating artery. (A) Preoperative CTA identified the mSTA (white arrow), pSTA (blue arrow), and fSTA (green arrow). (B) Scalp incision (dashed line) for pterional scalp flap. (C) The postoperative CTA showed the skin incision line (staples) and the successful preservation of the mSTA (white arrow), pSTA (blue arrow), and fSTA (green arrow). The lower figures are magnified details of the black boxes in the upper figures. CTA, computed tomography angiography; fSTA, frontal branch of the superficial temporal artery; mSTA, main trunk of the superficial temporal artery; pSTA, parietal branch of the superficial temporal artery.

Illustrative Case 2 (Patient No. 12)

A 70-year-old man was diagnosed with a ruptured aneurysm of the right terminal internal carotid artery. A right pterional craniotomy with a transsylvian approach was performed. All three branches of the STA were detected on preoperative CTA ([Fig. 5A]). The modified skin incision for STA preservation was used. The patient's postoperative CTA revealed successful preservation of the mSTA and fSTA ([Fig. 5B, C]).

Fig. 5 Patient no. 12. A 70-year-old man underwent a right pterional craniotomy for a ruptured aneurysm of the right terminal internal carotid artery. (A) Preoperative CTA identified the mSTA (yellow arrow), fSTA (blue arrow), and pSTA (red arrow). (B) The postoperative CTA showed the skin incision line (staples) and successful preservation of the mSTA (yellow arrow) and fSTA (blue arrow). The pSTA was not detected postoperatively. CTA, computed tomography angiography; fSTA, frontal branch of the superficial temporal artery; mSTA, main trunk of the superficial temporal artery; pSTA, parietal branch of the superficial temporal artery.

Discussion

Previous Anatomical Studies of STA Location

Several anatomical studies of STA location have utilized both cadaveric dissection and patient imaging scans. Previous research has suggested various landmarks for STA localization. Chen et al studied the course of the STA in 26 Chinese adult cadavers. They found mean STA locations of 1.14 cm anterior to the bony external auditory canal, 1.22 cm anterior to the superior attachment of the pinna to the head, and 1.35 cm anterior to a point 2 cm above the pinna attachment. In 86.5% of their sample, the bifurcation of the STA occurred above the zygomatic arch.[8] Koziej et al studied 419 STAs using head CTA imaging. They detected the fSTA and pSTA branches in 98.1 and 90.7% of the patients, respectively. The STA bifurcation was located above the zygomatic arch in 75.6%, below the arch in 14.7%, and on the zygomatic arch in 9.7%. The mean distance from the center of the zygomatic arch to the STA bifurcation was 16.8 mm. The mean distance between the STA and the EAM was 8.9 mm (range 5.6 − 13.1 mm). The mean angle between the fSTA and pSTA was 67.5 ± 24.9 degrees (range 5.0 − 161.3 degrees), and the mean angle between the fSTA and the zygomatic arch was 43.2 ± 12.2 degrees (range 6.5 − 110.8 degrees). The angle between the fSTA and pSTA was greater in high-branching arteries.[9]

Tubbs et al studied the anatomy of the STA in relation to deeper brain structures in 26 sides of cadaveric heads. They found STA bifurcation to be located, on average, 3 cm superior to the tragus. Many deeper brain structures can be used to identify the STA branches, but the course of these branches should first be determined by palpation or Doppler.[10]

Pinar and Govsa studied the anatomy of the STA in 27 sides of cadavers and found that the diameter of the fSTA was greater than that of the pSTA in 55.5%. In 74.07%, the STA bifurcation was located above the zygomatic arch. The frontal branch was found to be slightly more persistent than the parietal branch (100 and 96.3%), and the mSTA was located, on average, 16.68 mm anterior to the tragus (at its tip) on the OM line.[4]

Tayfur et al studied 33 cadaveric heads and reported that the STA bifurcation was located above the zygomatic arch in 62%. The mean distance between the STA bifurcation and the superior border of the zygomatic arch was 2.3 cm.[11]

Kim et al studied the anatomy of the STA using the three-dimensional (3D)-CTA images of 35 patients. Three landmarks (the posterior margin of the mandible condyle, the superior margin of the zygomatic arch, and the keyhole) were identified as reference points for the localization of the STA bifurcation. They found that 82.6% of STA bifurcations were located above the zygomatic arch at a mean distance of 21.7 mm. The majority (98.6%) of STAs were composed of frontal and parietal branches. Only 1.4% had only a frontal branch. The mean location of the STA bifurcation was 9.5 ± 5.3 mm anterior to the posterior margin of the mandible condyle, 21.7 ± 15.8 mm superior to the superior margin of the zygomatic arch, and 53.2 ± 5.9 mm posterior to the keyhole. Due to the high standard deviations of the STA bifurcation, they suggested that 3D-CTA is most useful for preoperative localization.[12]

Jean–Philippe et al reported the anatomy of the STA in 57 patients who underwent head and neck CTA. They found that the STA was located, on average, 15.55 mm in front of the tragus (at the tip) on the eye-tragus line. The STA bifurcation was located above the zygomatic arch in 61.54% of their sample and was nearly above the eye-tragus line in 99.04%. The distance between the STA bifurcation and the zygomatic arch ranged from 0 to 47 mm with a mean value of 12.31 mm. The angle between the mSTA and the OM line ranged from 75 to 140 degrees with a mean of 109 degrees. The mean angle between the pSTA axis and the OM line was 92.93 degrees (range 46–132 degrees).[13]

Koziej et al performed a meta-analysis of STA morphology research. They found that the STA is bilaterally present in nearly 100% of humans. The STA bifurcation is located above and on the zygomatic arch in 79.1 and 11.1%, respectively. The frontal and parietal branches of the STA are present in 97.6 and 96.4%, respectively. The fSTA has a significantly larger diameter than the pSTA, suggesting that the fSTA is the main branch. There was no bifurcation of the STA in 3.1%.[14]

In the present study, all STA bifurcations were located above the zygomatic arch, and the mean distance from the STA bifurcation to the zygomatic arch was 3 cm (range 1.5 − 4.5 cm). The frontal and parietal branches of the STA were present in 96.8 and 87.1%, respectively. These results are comparable to those of the previous studies described earlier. The angles of the mSTA and pSTA in relation to the OM line were separately evaluated by Jean–Philippe et al.[13] However, our method included the mSTA (above the zygomatic arch) and the pSTA (from the STA bifurcation to the superior temporal line) in the pSTA axis (mean 88.3 degrees). No STAs were found posterior to the pSTA axis.

Relation of mSTA to the Ear

The mean distance between the tragus tip and the mSTA was found to be 16.68 mm by Pinar and Govsa[4] and 15.55 mm by Jean–Philippe et al.[13] Because of both age differences and individual differences in the size of the tragus, its tip may not be a good reference point with which to locate the mSTA.

Other studies have proposed the EAM as an mSTA reference point. Koziej et al reported an average distance of 8.9 mm (range 5.6–13.1 mm) between the STA and EAM.[9] However, the EAM can be difficult to palpate while performing the skin incision for a pterional scalp flap as it is overlaid by the cartilage of the tragus.

We used the anterior edge of the ear cartilage as the reference point for mSTA localization. The ear cartilage of the tragus is easily palpated while performing a skin incision anterior to the tragus. The mean distance between the mSTA and the most anterior edge of the ear cartilage was 0.5 and 0.6 cm at the levels of the inferior and superior borders of the zygomatic root, respectively. This indicates that the mSTA is located very close to the ear cartilage, with the inferior part of the mSTA closer to the ear cartilage than the superior part. This morphology means that extension of the incision to the lower border of the zygomatic root, as in zygomatic arch osteotomy, increases the risk of STA damage. To avoid STA injury, the modified pterional scalp incision should be used. This is performed just anterior to the ear cartilage ([Figs. 1] and [3]).[7]

Estimation of pSTA Location

The location of the pSTA is difficult to estimate due to variations in the STA bifurcation. There have been few studies concerned with the localization of the pSTA.

Jean–Philippe et al separately measured the precise angles of the mSTA and pSTA in relation to the OM line. The angle between the mSTA and the OM line ranged from 75 to 140 degrees, with a mean of 109 degrees. The pSTA angle in relation to the OM line ranged from 46 to 132 degrees, with a mean of 92.93 degrees. Their estimation of the course of the pSTA depended on both the angle of the mSTA (with a relatively wide range) and the location of STA bifurcation, which is variable (range 0–47 mm; mean 12.31 mm). Therefore, the exact course of the pSTA remains difficult to estimate in clinical practice.[13]

With our method, the course of the pSTA can be approximated using the pSTA axis (a straight line from the point where the pSTA crosses the temporal line to the point where the STA crosses the superior border of the zygomatic arch), which includes the mSTA, the STA bifurcation, and the pSTA. Although the tortuosity of the artery was detected, no STA was found posterior to the pSTA axis; therefore, the incision posterior to this line should not injure any STA branches. Moreover, the pSTA axis (88.3 degrees [range 75–95 degrees]), which is approximately perpendicular to the OM line, is easy to use in routine pterional flap creation.

Pterional Scalp Flaps with STA Preservation

The advantages of pterional scalp flaps with STA preservation are (1) the vascularized flap prevents wound healing problems, (2) wound infection is less likely to occur, and (3) the STA is still available for future bypass surgery in patients with complex cerebrovascular or skull-based lesions.[3]

For a standard pterional skin incision, Menovsky et al recommend that the skin incision start ∼1 cm anterior to the tragus. In their study using this approach, the STA was successfully preserved in 44%.[3] Therefore, several techniques for STA preservation during pterional scalp incision have been proposed. Kim et al suggest that the preservation of the mSTA is critically important. They propose that, for the preservation of the mSTA, the skin incision should be posterior to the mSTA rather than anterior at the tragus level.[12] Kuruoglu et al estimated the location of both STA branches using preoperative 3D CTA. To preserve both branches, they suggested that the inferior ending of the skin incision should begin above the STA bifurcation ([Fig. 1], black line).[5] However, the STA bifurcation is usually located 20 to 21 mm above the superior border of the zygomatic arch.[6] [12] Therefore, this incision limited the scalp flap and restricted skull flap creation and inferior temporal extension. Also, the preoperative CTA used in their study was not the image routinely used for tumor resection. Ahn et al performed minipterional craniotomies using STA-sparing scalp flaps ([Fig. 1], black line) in 117 patients. The skin incision was made just above the STA bifurcation (similar to the former study), curvilinear to the medial hairline. The height of the STA bifurcation above the zygomatic arch was measured on preoperative CTA, and the main trunk and frontal and parietal branches of the STA were localized using micro-Doppler. The mean height of the STA bifurcation was 20.5 from the superior border of the zygomatic arch. STA preservation was successful in all of the patients, but this minimally invasive approach is limited by a narrow surgical field, which limits instrument use, provides inadequate access to lesions, and makes it difficult to control bleeding during aneurysm surgery.[6]

Katsuno et al have proposed a modified pterional scalp incision in which the incision begins just anterior to the tragus and is extended slightly more posteriorly than a standard pterional skin incision ([Fig. 1] and [3]).[7] With this technique, the skin incision is approximately posterior to the mSTA and pSTA axis, and a standard or large pterional craniotomy can be placed, with preservation of all STA branches within the scalp flap. When an STA graft is needed, the STA can be harvested from inside the scalp flap without the need to extend the scalp incision. Our clinical study followed this recommendation and proved the efficacy of STA preservation using this method. Using this scalp incision, our STA preservation rates were 93.5, 96.7, and 88.9% for the mSTA, fSTA, and pSTA, respectively.

We utilized the anatomical findings of this study to ensure the preservation of all STA branches during a standard pterional craniotomy. Before designing the skin incision, we first drew the imaginary line of the mean pSTA axis (88.3 degrees) approximately perpendicular to the OM line, at the point where the STA crosses the upper border of the zygomatic arch (just anterior to the cartilage of the tragus). We then began the incision just anterior to the ear cartilage, above the upper border of the zygomatic arch. The incision was curved just posterior to the mean pSTA axis and then curved anterior to the hairline. In some patients, the exact location of the pSTA axis can be confirmed by palpation. The risk of STA injury is highest in the preauricular area; therefore, the scalp incision should be performed precisely and carefully in this area. The disadvantages of this incision include its length, as it is longer than the standard pterional incision; the risk of injury to the ear cartilage; and difficulties with skin closure in the preauricular area.

Ear Cartilage Injury

Due to the proximity of the mSTA to the ear cartilage, the skin incision should be made just anterior to the ear cartilage to avoid mSTA injury. Mischkowski et al studied the postoperative complications in 52 patients after ear cartilage harvesting as graft material for reconstructive surgery. In 23 (36%) of the patients, the cartilage was harvested from the tragus. For tragus grafts, the postoperative complication rate was not high (hematoma formation requiring drainage in 3.3% and a clicking sensation in the scar area in 3.2%).[15] To avoid these postoperative complications, incisions in the preauricular area should be made meticulously.

Limitations

The limitations of this study include its retrospective descriptive design, the relatively small number of cadaveric heads and clinical cases, and the lack of digital subtraction angiographic studies to evaluate the preservation of the STA.

To the best of our knowledge, this is the first cadaveric study of STA location to use the anterior edge of the ear cartilage as the reference point and the first clinical study to evaluate the STA preservation efficacy of the modified pterional incision.

Conclusion

The mSTA is located very close to the ear cartilage and the axis of the pSTA courses approximately perpendicular to the OM line. To preserve all branches of the STA, the pterional skin incision should be started just anterior to the ear cartilage, for mSTA preservation, and slightly curve to the posterior above the pinna, to cover the pSTA.

Conflict of Interest

None declared.

Authors' Contributions

N.S., K.S., and T.P. were actively involved in the conception and design of the study, as well as in the acquisition, analysis, and interpretation of data. They collaboratively contributed to drafting the manuscript. Additionally, K.S. undertook the critical revision of the article, reviewed the submitted version, and provided overall supervision throughout the study.

Ethical Approval

The study was approved by the Institutional Review Board of the Faculty of Medicine Vajira Hospital. COA no. was 084/2567.

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Publication History

Article published online:
20 May 2025