SURGICAL ANATOMY AND TECHNIQUE

Microsurgical Anatomy of the Interfascial Vein.Its Significance in the Interfascial Dissection ofthe Pterional Approach

Alvaro Campero, MD, PhD∗

Pablo Ajler, MD, PhD‡

Martín Paíz, MD∗

Ramiro López Elizalde, MD§

∗Department of Neurological Surgery,Hospital Padilla, Tucumán, Argentina;‡Department of Neurological Surgery,Hospital Italiano, Buenos Aires, Argentina;§Department of Neurological Surgery,Hospital Valentin Gómez Farías Issste,Zapopan, México

Correspondence:Alvaro Campero, MD, PhD,Department of Neurological Surgery,Hospital Padilla Country Las Yungas,Yerba Buena CP 4107 Tucumán,Argentina.E-mail: alvarocampero@yahoo.com.ar

Received, July 7, 2016.Accepted, February 16, 2017.

Copyright C⃝ 2017 by theCongress of Neurological Surgeons

BACKGROUND: The pterional approach (PA), together with its variants, is still one of themost common methods used by surgeons to reach the anterior and middle cranial base.A highly important technical detail during a PA is the preservation of the frontotemporalbranch of the facial nerve, which can be achieved through an interfascial dissection.OBJECTIVE: To describe the anatomy of the interfascial vein (IFV), highlighting its recog-nition as a significant anatomic reference to perform an interfascial dissection (IFD).METHODS: Eight adult cadaveric heads, fixed with formaldehyde and injected withcolored silicone, were studied. In 6 heads, an IFD was performed, simulating a PA. In the2 remaining heads, the IFV was dissected. In addition, an IFD was performed in 10 patients,studying the IFV anatomy.RESULTS: In the 6 cadaveric heads in which the PA with an IFD was performed, and in the10 patients who underwent a PA with an IFD, the IFV was found. If the interfascial space isdivided into thirds, in all cases, the IFVwas locatedwithin themiddle thirdof the interfascialfat pad. On the 2 cadaveric heads in which the IFV was anatomically dissected, the IFV wasalso located within the middle third of the interfascial space.CONCLUSION: Recognizing the IFV in the interfascial space is of great help as an anatomiclandmark to confirm that one is actually between both layers of the superficial temporalfascia.

KEYWORDS: Pterional approach, Interfascial dissection, Facial nerve, Interfascial vein

Operative Neurosurgery 0:1–5, 2017 DOI: 10.1093/ons/opx047

T he pterional approach (PA), described byYasargil more than 30 yr ago,1-3 togetherwith its variants,4 is still one of the most

common methods used by surgeons to reachthe circle of Willis, the supra- and parasellarregions, the anterior and middle cranial fossae,the mesial temporal lobe, and the insular lobe.A highly important technical detail during a PAis the preservation of the frontotemporal branch(FTB) of the facial nerve, which can be achievedthrough an interfascial dissection (IFD).3 Thereare 3 fat pads in the anterior temporal region: (1)the subgaleal fat pad (between the galea and theexternal layer of the superficial temporal fascia;the FTB courses within this plane); (2) the inter-fascial fat pad (between the external and internal

ABBREVIATIONS: FTB, frontotemporal branch;IFD, interfascial dissection; IFV, interfascial vein;PA, pterional approach

layers of the superficial temporal fascia); and(3) the subfascial fat pad (between the internallayer of the superficial temporal fascia and thetemporalis muscle itself ).5-7 It is important tohighlight that the interfascial fat pad is notpresent on all the external surface of the tempo-ralis muscle, but only on its anterior fourth,from approximately 4 cm behind the orbitalrim.6 It is at that level that the IFD should bestarted.

Even though IFD was described many yearsago, it still involves a certain degree of difficultyto perform, and it continues to be discussed inpublications.5,6,8-11 A potential problem duringIFD is the confusion of the subgaleal fat padwith the interfascial fat pad, thus bringingthe dissection to the plane where the facialnerve branches are located.5,6,8 The interfascialvein (IFV) is always located in the inter-fascial space; thus, its recognition is a goodanatomic landmark to perform a correct IFD.

OPERATIVE NEUROSURGERY VOLUME 0 | NUMBER 0 | 2017 | 1

CAMPERO ET AL

The aim of the present study is to describe the anatomy of theIFV, highlighting its recognition as a highly significant anatomicreference to perform an IFD.

METHODSEight adult cadaveric heads, fixed with formaldehyde and injected

with colored silicone, were studied (a total of 16 sides). In 6 heads (12approaches), an IFD was performed, simulating a PA. In the 2 remainingheads (4 sides), the IFV was dissected until its junction with the super-ficial temporal vein. In addition, in 10 patients who had undergone aPA, an IFD was performed to study the IFV anatomy. Five patientswere operated for anterior circulation aneurysms, 2 for tuberculum sellaemeningiomas, 1 for macroadenoma, 1 for craniopharyngioma, and 1 forcavernoma of the mesial temporal region.

In all dissections, we divided the interfascial space (from the superiortemporal line until the zygomatic arch) into thirds, studying in whichsector the IFV was located (Figures 1C and 2A).

RESULTS

In the 6 cadaveric heads (12 sides) in which the PA with anIFD was performed, and in the 10 patients who underwent aPA with an IFD, the IFV was found within the interfascial fatpad (between the external and internal layers of the superficialtemporal fascia; Figures 2-4). The interfascial space is located inthe anterior fourth of the outer surface of the temporal muscleand distributed from the superior temporal line to the zygomaticarch. Regarding its location, if the interfascial space is dividedinto thirds (from the superior temporal line superiorly to thezygomatic arch inferiorly), in all cases the IFV was found in themiddle third (Figures 1C and 2A). Also, it was observed that theIFV is oblique in its course within the interfascial space, goingdorsally and caudally. Of the 10 patients operated on with a PA,no palsy of the FTB was observed in the postoperative follow-up.

On the 2 cadaveric heads (4 sides), in which the IFV wasanatomically dissected, the same oblique course was observed,coursing through the interfascial space until reaching the super-ficial temporal vein, just ventral and cranial to the tragus(Figure 1). Also in these cases, the IFV was located in the middlethird of the interfascial space. Measurements showed that theangle of the IFV was located 4.3 mm from the superior temporalline and 2.5 mm from the zygomatic arch (Figure 3E).

DISCUSSION

The PA and its variants (transzygomatic and orbitozygomaticapproaches) have been designed in order to reach a wide varietyof vascular and tumor lesions located in the anterior and middlecranial fossae.4 Because these pathways reach the skull via itsanterolateral sector, it is essential to dissect and liberate the tempo-ralis muscle. From an anatomic point of view, the most superiorand posterior branch of the facial nerve in this sector is the FTB,which courses toward the frontalis muscle in order to raise the

2 | VOLUME 0 | NUMBER 0 | 2017 www.operativeneurosurgery-online.com

INTERFASCIAL VEIN, ITS SIGNIFICANCE IN THE INTERFACIAL DISSECTION

FIGURE 1. Step-by-step anatomic dissection of the IFV. A, Subgalealdissection: it can be observed that the IFV is in a deeper plane to the externallayer of the superficial temporal fascia. B, The external layer of the super-ficial temporal fascia has been removed; the interfascial fat pad and the IFVare observed. C, The superficial temporal fascia has been removed behind theinterfascial space, and it is observed that the IFV is a branch of the superficialtemporal vein. We can also observe that the IFV is located in the middle thirdof the interfascial space. IF, interfascial; IFV, interfascial vein; Sup., super-ficial; STF, superficial temporal fascia; Temp., temporal; V., vein.

FIGURE 2. The first steps of the PA. A, The interfascial space (from thesuperior temporal line to the zygomatic arch) has been divided into thirds,and the IFV is observed to be located in the middle third. B, The IFV has beencut simulating a surgery in order to expose the orbital rim. IF, interfascial; IFV,interfascial vein; STF, superficial temporal fascia.

eyebrow. This branch courses within the subgaleal space approx-imately 2 to 3 cm behind the orbital rim. Therefore, for itsanatomic and functional preservation, it is necessary to performthe dissection deeply in relation to the subgaleal plane. A purelysubgaleal dissection may produce palsy of the frontalis muscle inapproximately 30% of cases.3 Thus, there are 3 ways to preserve

FIGURE3. Step-by-step PA.A, Incision.B, Subgaleal dissection. The superiortemporal artery has been exposed. C, IFD. The IFV has been exposed. D,The IFV has been cut, exposing the orbital rim. E, Enlarged vision of theIFD. Distance A: between the IFV angle (star) and the superior temporal line.Distance B: between the IFV angle (star) and the zygomatic arch. A., artery; IF,interfascial; IFV, interfascial vein; Sup., superficial; STF, superficial temporalfascia; Temp., temporal.

the FTB: (1) myocutaneous flap,7 (2) subfascial dissection,7 and(3) IFD.5,6,8-11 The myocutaneous flap consists of mobilizationof the soft parts of the approach (skin, subcutaneous tissue, andtemporalis muscle with its fascias) in only 1 plane; this techniquevirtually eliminates risk of FTB nerve injury, but at the expense ofexposure, as the bulge produced by the temporalis muscle usuallyblocks visualization through the sphenoid rim.3 The subfascialtechnique involves making the dissection deeply into both layersof the superficial temporal fascia, between the internal layer of thesuperficial temporal fascia and the temporalis muscle itself. Thistechnique is also good to eliminate the risk of FTB injury, but the

OPERATIVE NEUROSURGERY VOLUME 0 | NUMBER 0 | 2017 | 3

CAMPERO ET AL

FIGURE 4. A, B, and C, 3 examples of interfascial dissections in patientswho underwent a PA. IF, interfascial; IFV, interfascial vein; STF, superficialtemporal fascia. At the beginning of the cases we exposed the IFV in all theinterfascial spaceC, but then we learned to expose just 1 cm of vein and thencoagulate and cut A and B.

subperiosteal exposure of the zygomatic arch and the orbital rimis more difficult than the IFD.

The IFD consists of incising the external layer of the super-ficial temporal fascia together with the interfascial fat pad, andof bringing both elements rostrally; thus, dissection is performedin a deeper plane, where the FTB is located, preventing its

damage. In order to carry out this technique, it is necessary torecognize, coagulate, and cut the IFV. The IFV, first describedby Yasargil in 198412, runs through the interfascial space,then descends through the subgaleal space, draining into thesuperficial temporal vein just superior and ventral to thetragus.

The authors consider that recognizing the IFV in the inter-fascial fat space may serve as a helpful anatomic landmark for thesurgeon to confirm that the IFD is being correctly performed. Inthe case of the subfascial dissection, the IFV also should be coagu-lated and incised, but posterior to the interfascial fat pad, in thesubfascial space.

CONCLUSION

Recognizing the IFV in the interfascial space is of great help toconfirm that one is actually in the fat pad located between bothlayers of the superficial temporal fascia. It is necessary to coagulateand cut the IFV in order to rostrally mobilize the soft part of theapproach toward the orbital rim.

DisclosureThe authors have no personal, financial, or institutional interest in any of the

drugs, materials, or devices described in this article.

REFERENCES1. Yasargil MG. General operative techniques. In: Yasargil MG, ed. Microneuro-

surgery. Vol. 1. Stuttgart: Georg Thieme Verlag; 1984:208-271.2. Yasargil MG, Teddy PJ, Roth P. Selective amygdalo-hippocampectomy.Operative

anatomy and surgical technique. In: Symon L, ed.Advances and Technical Standardsin Neurosurgery. Vol. 12. Wien: Springer-Verlag; 1985:93-123.

3. Yasargil MG, Reichman MV, Kubik S. Preservation of the frontotemporal branchof the facial nerve using the interfascial temporalis flap for pterional craniotomy.Technical article. J Neurosurg. 1987;67(3):463-466.

4. Campero A, Ajler P, Goldschmidt E, Rica C, Martins C, Rhoton A. Three-step antero-lateral approaches to the skull base. J Clin Neurosci. 2014;21(10):1803-1807.

5. Ammirati M, Spallone A, Ma J, Cheatham M, Becker D. An anatomicosurgicalstudy of the temporal branch of the facial nerve. Neurosurgery. 1993;33(6):1038-1044.

6. Poblete T, Jiang X, Komune N, Matsushima K, Rhoton AL Jr. Preservationof the nerves to the frontalis muscle during pterional craniotomy. J Neurosurg.2015;122(6):1274-1282.

7. Coscarella E, Vishteh AG, Spetzler RF, Seoane E, Zabramski JM. Subfascialand submuscular methods of temporal muscle dissection and their relationship tothe frontal branch of the facial nerve. Technical note. J Neurosurg. 2000;92(5):877-880.

8. Ammirati M, Spallone A, Ma J, Cheatham M, Becker D. Preservation of thetemporal branch of the facial nerve in pterional-transzygomatic craniotomy. ActaNeurochir (Wien). 1994;128(1-4):163-165.

9. Salas E, Ziyal IM, Bejjani GK, Sekhar LN. Anatomy of the frontotemporalbranch of the facial nerve and indications for interfascial dissection. Neurosurgery.1998;43(3):563-569.

10. Krayenbühl N, Isolan GR, Hafez A, Yasargil MG. The relationship ofthe fronto-temporal branches of the facial nerve to the fascias of the temporalregion: a literature review applied to practical anatomical dissection.Neurosurg Rev.2007;30(1):8-15.

11. Spiriev T, Ebner FH, Hirt B, et al. Fronto-temporal branch of facial nerve withinthe interfascial fat pad: is the interfascial dissection really safe? Acta Neurochir.2016;158(3):527-532.

12. Yasargil MG. General operative techniques. In: Yasargil MG , ed. Microneuro-surgery. Vol. 1. Stuttgart: Georg Thieme Verlag; 1984:218.

4 | VOLUME 0 | NUMBER 0 | 2017 www.operativeneurosurgery-online.com

INTERFASCIAL VEIN, ITS SIGNIFICANCE IN THE INTERFACIAL DISSECTION

COMMENT

T he authors elegantly describe and illustrate a basic but very importantlandmark for the safe execution of the interfascial dissection of the

temporalis muscle. The most common mistake leading to injury of thefrontal branch of the facial nerve is misidentification of the correct layer.If an excessively deep dissection is readily identified when the fibers of thetemporalis muscle are exposed, an excessively superficial dissection can

easily go unrecognized. The subgaleal fat pad is always present and canbe quite prominent in certain individuals to the point of being confusedwith the interfascial fat pad. Identification of the interfascial vein remainsthe most reliable landmark to identify the correct layer and allow theinterfascial dissection to proceed safely.

Siviero AgazziTampa, Florida

OPERATIVE NEUROSURGERY VOLUME 0 | NUMBER 0 | 2017 | 5