Middle Cerebral Artery – Internal Maxillary Artery Bypass

49 Middle Cerebral Artery – Internal Maxillary Artery Bypass

Ahmed Maamoun Ashour, Katie Huynh, Joanna Kemp, Brian Kang, Nathan Cherian, Savannah Scott, Sneha Koduru, and Saleem I. Abdulrauf

49.1 Introduction

Traditional high-flow bypass procedures involve the main trunk of the external carotid, the internal carotid artery, or the common carotid artery as the inflow for the bypass. The main limitations of the aforementioned sites are the requirement for a longer graft and the need for cervical neck incision.

In this chapter, we describe our technique of using the internal maxillary artery (IMAX) as the main inflow to the bypass. This is now commonly referred to as the “Abdulrauf Bypass.” This allows for a shorter graft in addition to avoiding cervical exploration and anastomosis.

49.2 Indications

• Flow preservation to maintain cerebral blood flow (CBF) in patients undergoing acute vessel sacrifice, (i.e., aneurysm trapping or artery encased by tumor).

• Some aneurysms are not amenable to direct microsurgical clipping or endovascular coiling due to extreme size, location, calcification, atherosclerosis, dissection, or the incorporation of perforators or major arteries.

• Flow augmentation to increase CBF in patients with chronic compromised CBF (chronic cerebral ischemia, Moya-Moya).

49.2.1 Patient Positioning (Fig. 49.1)

• Position: The patient is positioned supine with the head fixed in a Mayfield head holder.

• Head: The head is rotated 30° to the contralateral side. The neck is slightly extended with the vertex aimed toward the floor. It is positioned above the level of the heart.

• The malar eminence is the highest point in the operative field. This position allows the frontal lobe to fall away from the orbital roof and the temporal lobe from the middle fossa floor, without retraction.

49.3 Skin Incision

• Pterional shaped incision

◦ Starting point: The starting point corresponds to the inferior margin of the root of the zygoma, 1 cm anterior to the tragus.

◦ The posterior limb (parietal branch) of the superficial temporal artery (STA) should be spared in case the STA is needed for a microvascular bypass.

◦ Course: The incision runs, encircling posteriorly just above the external auditory meatus, and then curved anteriorly and medially toward the midline just behind the hairline.

Fig. 49.1 Patient positioning. The patient is positioned supine with the head fixed in a Mayfield head holder. Head is rotated 30° to the contralateral side, neck is slightly extended with the vertex pointing down.

Fig. 49.2 Right side. Scalp flap is elevated from the underlying temporal fascia. Care is utilized to preserve the fat pad, which contains the frontotemporal branch of the facial nerve and the pericranium. Temporal muscle is underneath the temporal fascia. Right-pointing arrow marks the superior temporal line. Up-pointing arrow marks the C-shaped incision for interfascial dissection of the superficial and deep temporal fascia.
Abbreviations: FP = fat pad; P = pericranium; TM = temporal muscle.

Fig. 49.3 Right side. Interfascial dissection is performed to separate the superficial and deep temporal fascia at the C-shaped incision pointed out by the black arrow to elevate the fat pad.
Abbreviations: FP = fat pad; P = pericranium; TM = temporal muscle.

49.3.1 Critical Structures

• Superficial temporal artery.

49.4 Soft Tissue Dissection

• Fascia level

◦ The skin flap is separated from the underlying temporal fascia anteriorly until the superficial temporal fat pad is encountered. Care is exercised to preserve the underlying pericranium in the event it needs to be harvested in patients with large frontal sinus (Fig. 49.2).

◦ A C-shaped incision is made on the temporal fascia 2 cm posterior to the zygomatic process of the frontal bone and extended from the keyhole anteriorly to the root of the zygoma inferiorly (Fig. 49.2).

◦ Interfascial dissection is performed with a scalpel to separate the superficial and deep temporal fascia. This preserves the frontotemporal branches of the facial nerve (Fig. 49.3).

◦ Blunt dissection is then used to elevate the superficial fascia and fat pad together from the deep temporal fascia until the lateral orbital rim and superior zygomatic arch are exposed (Fig. 49.4). The pericranium is harvested at this time (if indicated) (see Chapter 17).

• Muscle

◦ The divided temporal muscle is completely elevated with the periosteal elevator before being retracted laterally and inferiorly. This provides bony exposure of the frontotemporal region (Figs. 49.5, 49.6).

• Bone exposure

◦ The frontotemporal region, superior zygomatic arch, superior and lateral orbital rim should now be completely exposed.

Fig. 49.4 Right side. Interfascial dissection is completed, the superficial fascia and fat pad are elevated from the deep temporal fascia beneath. Curved black line is the site of previous C-incision.
Abbreviations: FP = fat pad; P = pericranium; TMF = temporal muscle fascia.

Fig. 49.5 Right side. In patients with thick temporal muscle, which could limit the bony window underneath, the muscle can be split a little more anterior to reduce the muscle bulk. A cuff of fascia is left on the bone to help anchor and reattach the temporal muscle during closure. The harvested pericranium is safely tucked under a moist Telfa.
Abbreviations: FB = frontal bone; FP = fat pad; P = pericranium; TM = temporal muscle.

◦ The periorbit is dissected from the superior orbital rim from medial to lateral, then from the lateral orbital rim from caudal to cranial. Dissection should be performed carefully to avoid damage to the lacrimal apparatus (Fig. 49.7).

◦ If the supraorbital nerve and vessels are in a foramen instead of a notch, they can be freed from the foramen with a small osteotome on either side of these structures to avoid injury (see Chapter 6).