Michael Kerin Morgan

48.1 Introduction

• For the purpose of illustration, a right-sided common carotid (CCA) to middle cerebral artery (MCA) bypass with an interposition saphenous vein graft (IPSVG) is described (CCA-MCA IPSVG).

• Variations to this procedure include distal anastomosis to the internal carotid artery (ICA) and posterior cerebral artery (PCA) as well as proximal anastomosis to the external carotid artery. However, the principles of performing a CCA-ICA IPSVG can be readily applied to these variations with minor adaptation that is obvious to those once CCA-MCA IPSVG is understood. Therefore, for economy of space, the details of these variations are not included.

• Various surgical techniques, many of which are unknown to this author, can be applied to achieve the same end.

• The author owes his understanding of the technique of performing CCA-MCA IPSVG to Dr. Sundt, perhaps the greatest innovator and executor of brain revascularization surgery in history. There are minor variations that have been incorporated into the author’s description from that taught by Dr. Sundt. Those ideas that you find helpful are either Dr. Sundt’s or inspired by Dr. Sundt while those that you find are not helpful assume are my ideas.

• In addition to the usual preparations for major neurosurgery, aspirin commenced preoperatively is appropriate. This does create difficulty with oozing continually with the three wounds that are created during this surgery.

48.2 Indications

• The high flow bypass is rarely a choice for any specific condition. The choice of such bypass is almost always a fallback solution when no other options are available or likely to succeed.

• Replacement of major intracranial arteries. These include ICA, MCA and basilar arteries. This is most commonly due to either aneurysm treatment or resection of skull base lesions.

• In the case of aneurysm treatment, this may be combined with internal bypasses for the management of MCA aneurysms where simpler clipping procedures are deemed at high risk. CCA-MCA IPSVG to one M2 branch with rotation of the other M2 branch as an internal bypass to the bypassed M2 branch can render a bifurcation aneurysm treatable that is otherwise unclippable. For basilar artery aneurysms untreated except for trapping, CCA-PCA IPSVG to the bypass may protect the upper basilar and branch circulation.

• In an emergency, when the ICA or MCA has been inadvertently damaged during surgery and cannot be repaired.

• Augmentation of flow is rarely needed to be corrected by high flow bypass because of the danger of producing a catastrophic intracerebral hemorrhage into a region of hyperemia consequent on bypass. In such cases, low flow superficial temporal to M4 bypass is appropriate.

48.3 Patient Positioning

• Patient position

◦ Bypass to M2 or ICA: the patient is positioned supine.

– The three-point head fixation is applied with the 2 points ipsilateral to the side of cranial surgery immediately superior to the transverse sigmoid sinus and the single point placed into the superior temporal line on the frontal bone.

– It is to be positioned so that no component of the device is in a plane above the most superior part of the skull when in the final position for surgery.

– The table will be slightly broken with the back rotated upward 10-15° and, similarly, the lower-limbs will be rotated upward by a similar degree.

– The table should be elevated or lowered to achieve a level in which the surgeon has his or her arms bent 90° at the elbows and the wrists are straight at level of the operating site at the head (taking into account surgical instruments at the target distal anastomosis).

◦ Bypass to the second and third part of the posterior cerebral artery (PCA), under the temporal lobe.

– The three-point head fixation is applied with the 2 points ipsilateral to the side of cranial surgery immediately superior to the transverse sigmoid sinus, the two-pin straddling the torcular and the single point placed into frontal bone of the forehead.

– It is to be positioned so that no component of the device is in a plane above the most superior part of the skull when in the final position for surgery.

– The table should be positioned at a level as for the more common bypass to the MCA.

• Head position

◦ Bypass to the M2 or ICA.

– The head is rotated 15° on its axis from the vertical, to the opposite side to the target artery, flexed 15° to the opposite shoulder in the coronal plane, rotated 15° backward in the sagittal plane and the head is lifted upward in this set position flexing the C7 on T1 and extending the skull on the cervical spine.

– This minimal rotation facilitates easy dissection of the Sylvian fissure by ensuring that the temporal lobe can be easily supported during fissure dissection and not falling onto the temporal lobe that would result in the need for vigorous retraction.

– In this position, the skin of the neck should be smooth and not wrinkled and the anterior border of the sternocleidomastoid muscle to be slightly tense allowing the skin incision to expose the carotid artery to be easily performed.

◦ Bypass to the PCA, under the temporal lobe.

– The head is rotated 60° from the vertical, to the opposite side to the target artery and tilted 10° toward the floor.

– In this position, the neck should be similarly exposed to the above.

• Shoulder position

◦ Bypass to the M2 or ICA: there is no role for altering the shoulders in the supine position.

◦ For bypass to the PCA under the temporal lobe: a sandbag is placed under the shoulder to reduce any stretch on the brachial plexus but the shoulder should remain below the plane of the anterior border of the ipsilateral sternocleidomastoid muscle.

• Lower limb position

◦ Both lower limbs are placed in a position and draped in such a way as to allow access to the entire long saphenous vein (SV) from its position immediately anterior to the medial malleolus to the inguinal ligament.

◦ Mark the line of this vein prior to surgery (venous duplex ultrasound assists with this task) so that the skin incision can be made more rapidly when it comes time to harvesting vein.

◦ Both lower limbs should be slightly everted so that the line of the skin incision can be readily seen. The lower limbs should be in a position that the surgeon can harvest vein below the knee by manipulating the lower limb with slight flexion of the knee to increase the ankle eversion at the time that the SV is harvested.

• Anti-decubitus device

◦ The surgery may be prolonged, and the patient should be placed on a mat that protects pressure areas on the back.

◦ Furthermore, the use of a heating blanket over the abdomen and chest is appropriate to prevent a fall in core temperature, as much of the patient will be uncovered in a cold operating room.

◦ After the table is flexed into position with both the back and the lower limbs raised, the elbows and hands are placed and protected from pressure areas.

◦ When the scalp flap is complete, it is critical for this scalp flap to be retracted down low over the eye and placing this flap under tension. Therefore, care needs to be made in placing pads over the eyes for protection. If these are unduly thick, the subsequent retraction of the scalp flap over these pads may lead to excessive pressure on the eye causing blindness.

• Anatomic structure put at highest point in the surgical field

◦ For the more commonly performed bypass to the M2 or ICA, the highest point of the surgical field is the malar eminence. For the less commonly performed bypass to the PCA, under the temporal lobe, the highest point of the surgical field is the frontal process of the zygoma.

◦ For the lower limb, the medial tip of the great toe should be the highest point, slightly superior to the plane of the medial patella.

◦ Curvilinear incision behind the hairline of the patient except at the inferior margin. In the case where the patient has receding hair, the incision can be placed in one of the superior forehead creases until the lateral margin of the incision where it joins the usual incision line.

◦ It commences 2 cm across the midline with the knife blade penetrating to a depth through the dermis, epidermis, and just through the galea.

◦ The depth to the level immediately penetrating the galea (but not through the temporalis fascia) is held constant throughout the course of the scalp incision with vascular scalp clips applied for hemostasis.

◦ The inferior point is immediately anterior to ear at the level of the inferior margin of the zygomatic arch.

◦ Subsequent blunt dissection with Metzenbaum scissors is performed to create the tunnel to accommodate the future introduction of the tunneler (to deliver the SV) between the craniotomy incision and the cervical incision deep to all skin layers.

◦ The early establishment of this tunnel ensures sufficient time for deep and not reachable oozing within to spontaneously thrombose well before the intradural surgery to reduce the risk of run-in bleeding at the time of the anastomosis.

• Lower limb incision to expose the long saphenous vein

◦ The site from which the SV is harvested is determined by the best and healthiest straight 23 cm length, even caliber lumen with the least number of tributaries, as determined by venous duplex ultrasound. Therefore, the site will be either left or right lower limb above or below the knee. If possible, selection of below the knee source is preferable because of the smaller diameter.

◦ Starting point, course and ending point:

– The incision is immediately over the vein. This is a straight line from the medial ankle to a point heading for the medial mid knee joint until two-thirds up the lower leg and then curving slightly backward and up to a point just behind the medial knee joint and then toward a point immediately medial to the femoral pulse at the inguinal ligament.

– If commencing at the ankle, the easiest location to find the SV (as there is very little tissue between the skin and vein at this site and it can be palpated either in the standing position or the recumbent position after restricting venous flow from the ankle by compression), the place to commence the incision is immediately anterior to the medial malleolus.

– Incision ends where 23 cm of straight, even caliber lumen, with a minimum of tributaries can be harvested. It is unusual to find such a segment included in the vein that straddles the level of the knee.

48.4.1 Critical Structures

• In the segment of the vein in the vicinity of the ankle, the saphenous nerve is immediately adjacent.

• Care in preserving the nerve will reduce the chance for bothersome paresthesia of the nearby skin.

48.5 Soft Tissue Dissection

48.5.1 Cranial Exposure