Surgical Techniques in Moyamoya Vasculopathy. Peter Vajkoczy

Chapter 23. PAA-MCA Bypass

Menno R. Germans and Luca Regli


Sometimes the superficial temporal artery is not available as a donor vessel for extracranial-intracranial (ECIC) bypass surgery. Also, in case of refractory moyamoya disease with an ECIC bypass in situ, there is need for an additional artery that can be used as a donor vessel. The posterior auricular artery (PAA) is a potential donor, if its diameter is large enough. The PAA runs behind the ear and in about half of cases it runs until the temporoparietal region where it can be used as an alternative donor artery for ECIC bypass surgery. The artery runs vertically along the posterior part of a standard craniotomy around the Sylvian point. It can easily be identified on a lateral DSA, where it branches off the ECA and runs behind the external auditory meatus. Note that the DSA needs to be displayed sufficiently caudal to identify the origin of the PAA. The awareness among cerebrovascular surgeons about the presence of a PAA and knowledge about its anatomy may be valuable.

Keywords: cerebral revascularization, extracranial-intracranial arterial bypass, posterior auricular artery, middle cerebral artery

23.1 History and Initial Description

The posterior auricular artery (PAA) has been used for decades in reconstructive, and ear, nose, and throat surgery, because of its arterial supply to myocutaneous and myofascial flaps.1,2 It lasted until some years ago, before this artery was used by neurosurgeons for extracranial- intracranial (ECIC) bypass surgery.3-5

The PAA supplies a small area behind the ear and the auricle itself. It is usually present as three to five small branches which anastomose with the superficial temporal artery (STA), but sometimes it is suitable as a donor artery for ECIC bypass surgery. In the majority, the PAA branches off the external carotid artery (ECA) just superior to the occipital artery, but in 10 to 15% cases it arises from the occipital artery after an occipitoauricular trunk (see Fig. 23.1). It continues between the mastoid tip and auricle, and in 33 to 50% cases, it is large enough to extend to the temporoparietal region.6 In these cases, it runs almost vertically toward the vertex until a mean distance of 7.5 cm from the mastoid tip. Its course at approximately 1.2 cm posterior to the external auditory meatus is ideal for a bypass, because it is located at the posterior margin of a standard craniotomy around the Sylvian point. In 1.2 to 5.7% of cases, the PAA diameter is large enough to function as a donor artery.3,6

23.2 Indications

Sometimes the STA is not available as donor vessel for bypass surgery due to hypoplasia of the artery, sacrifice of the artery at previous craniotomy, damage of the artery during dissection, or if it has already been used for a bypass. In such cases, the PAA can be used as an alternative donor artery, if its diameter is large enough. Moreover, in case of refractory moyamoya disease with a standard ECIC bypass in situ, or in case of the need for a double-barrel bypass, the PAA can be used as an additional revascularization technique.4 Cerebrovascular surgeons must be aware about a PAA when assessing the preoperative angiography of the ECA. When performing a craniotomy for moyamoya disease, knowledge about PAA anatomy may be valuable for planning proper incision and not damaging the PAA.

23.3 Key Principles

The PAA is easily identified on a lateral digital subtraction angiography (DSA), where it branches off the ECA and runs behind the EAC (see Fig. 23.2). In about half the cases, it extends until the temporoparietal region. The diameter must be large enough (> 1 mm) to be used as a donor artery. Its almost vertical course along the temporoparietal region locates the artery at the posterior margin of the standard craniotomy around the Sylvian point. Because only the posterior part of the temporal muscle must be dissected to mobilize to PAA for an ECIC bypass, it causes less injury to the muscle.

23.4 SWOT Analysis

23.4.1 Strengths

 Procedure comparable to that of STA-MCA bypass, proven to be a successful alternative.3-5

 Less injury to temporal muscle.

 Can be used with standard craniotomy around Sylvian point; rescue procedure in case of injury to STA.

23.4.2 Weakness

 Low availability of PAA of appropriate size (1.2-5.7%).

23.4.3 Opportunity

 To get more acquainted with the presence of an appropriately sized PAA in both neurosurgeons and neuroradiologists minds.

23.4.4 Threat

 The use of indirect bypass procedures in (refractory) moyamoya disease offers an alternative to direct bypass procedures such as PAA-MCA.

23.5 Contraindications

When the artery is too small (< 1 mm diameter) or not extending to the temporoparietal region, it cannot be used for a bypass. Due to the location of the artery, it is usually too short to revascularize the anterior cerebral artery territory. When a flow of more than 35 mL/min is anticipated, the PAA might not be patent enough to meet this flow rate.

23.6 Special Considerations

The preoperative DSA of the ECA needs to be displayed sufficiently caudal to identify the origin of the PAA. In addition, radiologists or neurosurgeons reporting the results of the DSA should be aware of the possible presence of a PAA that could be used as a donor artery.

23.7 Pitfalls, Risk Assessment, and Complications

The risks for a bypass using the PAA as a donor artery are comparable to that of the STA, and patients can be informed as such.

Although several case reports have described the successful use of the PAA, the long-term patency of this artery is unknown. Nevertheless, the indications, technique, and flow dynamics of the PAA at ECIC bypass surgery are comparable with that of the STA. Therefore, the longterm patency is judged to be comparable with that of an STA-MCA bypass.

23.8 Special Instructions, Position, and Anesthesia

Positioning and anesthesiological regimen are comparable to bypass surgery using the STA. It might make it easier to tape the auricle anteriorly to expose the PAA on its complete trajectory. Care should be taken that the auricle is not hypoperfused with this maneuver, because this can lead to ischemia of the auricle.

23.9 Patient Position with Skin Incision and Key Surgical Steps

The patient is positioned with a small roll under the ipsilateral shoulder with the head turned to the contralateral side and fixated in the headholder. The trajectory of the PAA and the craniotomy site are then exposed with taping the auricle anteriorly if necessary. The PAA is identified by doppler and/or digital palpation, and a straight incision directly over the artery is planned. As an alternative, one can use the cranial navigation software to draw the location of the PAA as well as the craniotomy. Depending on the area that needs reperfusion and in case of a more posterior location of the PAA, the incision can be made more curvilinear with extension toward anterior to expose the craniotomy site (see Fig. 23.3). For a double-barrel bypass with both the PAA and STA as donor arteries, a horseshoe or question mark incision can be made, taking care not to interrupt the PAA.

The PAA needs to be exposed and dissected from surrounding tissue at least from the level of the external acustic meatus (EAM) because the artery has to be transposed forward to reach the Sylvian point (see Fig. 23.4).

For artery dissection, craniotomy around the Sylvian point, and bypass technique, please refer to Chapter 9.

23.10 Difficulties Encountered

 When a straight incision over the PAA is used, the craniotomy might be located too posteriorly to expose the Sylvian point.

 Preoperative planning is mandatory to prevent this error, and intraoperative navigation to plan the craniotomy site for localization of the optimal recipient vessel can be considered. Otherwise, a curvilinear incision can be used.

 The PAA only reaches until the posterior border of the craniotomy. Exposure of the artery from at least the level of the EAM makes it easier to transpose it forward.

23.11 Bailout, Rescue, and Salvage Maneuvers

The usage of alternative donor vessels, such as the STA or the occipital artery or interposition grafts.

23.12 Tips, Pearls, and Lessons Learned

 When the DSA is not showing the origin of the PAA, it might be mistaken for a parietal branch of the STA. In such cases, the incision might be planned too much anterior and the donor artery will not be found.

• Knowledge about the presence of a potential suitable PAA and its relation to the auricle and craniotomy makes preoperative planning easier and safer.


[1] Choung PH. The auriculomastoid fasciocutaneous island flap: a new flap for orofacial reconstruction. J Oral Maxillofac Surg. 1996; 54(5): 559-567, discussion 568

[2] Gibb AG, Tan KK, Sim RS. The Singapore swing. J Laryngol Otol. 1997; 111(6):527-530

[3] Germans MR, Regli L. Posterior auricular artery as an alternative donor vessel for extracranial-intracranial bypass surgery. Acta Neuro- chir (Wien). 2014; 156(11):2095-2101, discussion 2101

[4] Horiuchi T, Kusano Y, Asanuma M, Hongo K. Posterior auricular artery-middle cerebral artery bypass for additional surgery of moyamoya disease. Acta Neurochir (Wien). 2012; 154(3):455- 456

[5] Tokugawa J, Nakao Y, Kudo K, et al. Posterior auricular artery-middle cerebral artery bypass: a rare superficial temporal artery variant with well-developed posterior auricular artery-case report. Neurol Med Chir(Tokyo).2014; 54(10):841-844

[6] Tokugawa J, Cho N, Suzuki H, et al. Novel classification of the posterior auricular artery based on angiographical appearance. PLoS One. 2015; 10(6):e0128723

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