19 Individualized Extracranial-Intracranial Revascularization in the Treatment of Late-Stage Moyamoya Disease
Abstract
Late stage moyamoya disease is defined as the one at stage 5 to 6 of Suzuki’s grading system, despite of spontaneous collaterals from branches of external carotid artery, cerebral revascularization is still necessary in most patients. But the diversity and complexity of collateral paths make it difficult to preserve the already-formed collaterals, which is the principle of this kind of surgical procedure. Individualized revascularization seems to be an effective solution. Here we will introduce a set of strategies, including individualized designation of skin flap, temporal muscle flap, bone flap, dura matter flap, and target revascularization. The set of strategies is proved to be safe and effective in our single institution case series.
19.1 History and Initial Description
Late-stage moyamoya disease (MMD) is defined as the one at stage 5 to 6 of Suzuki’s grading system and is characterized by spontaneous collaterals from branches of external carotid artery. In a series of 336 patients affected by late-stage MMD treated in the Department of Neurosurgery of Huashan hospital from 2005 to 2015, spontaneous collaterals are fully developed in only 3 cases (1% of the entire series) without any symptoms or cerebral hemodynamic impairment who need no surgical treatment (Fig. 19‑1). About 333 patients of late-stage MMD were operated for cerebral ischemia or intracranial hemorrhage, or both, with impaired hemodynamics which could be detected by CT perfusion (CTP) or single-photon emission computed tomography (SPECT) routinely.
19.2 Indications
The indication of individualized extracranial-intracranial (EC-IC) revascularization in late-stage MMD is carefully analyzed. Microsurgical treatment of the patients is planned with attention to any preexisted spontaneous collaterals, ischemic symptoms, and hemorrhagic history.
19.3 Key Principles
The key principle of the surgery is to use all the three layered external carotid artery (ECA) branches including superficial temporal artery (STA), posterior auricular artery (PAA) or occipital artery (OA) that are feeding the scalp, deep temporal artery (DTA) feeding the temporal muscle, and middle meningeal artery (MMA) feeding the dura, meanwhile preserving the already-formed collaterals.
19.4 SWOT Analysis
19.4.1 Strength
Combined direct and indirect approach allows the full use of all the branches coming from the ECA, while preserving preexisted spontaneous collaterals.
19.4.2 Weaknesses
Due to poorer MCA vessel networks of late-stage MMD, the recipient artery may not distribute blood flow as efficiently as in early stage MMD with heathier MCA vessel network.
The mean blood flow in bypass is reduced compared with those bypass flow performed in patients with early stage of MMD.
There can be a competition between the bypass flow and the original flow in MCA network that may cause blood flow congestion and edema of the cortex, which have consequently higher occurrence of postoperative transient neurological deficit.
19.4.3 Opportunities
Carefully designed revascularization, based on a comprehensive understanding of clinical symptoms, spontaneous collaterals, hemodynamic characters, and recipient artery networks, could replace the blood flow to most suffering ischemic area of the brain cortex.
Late stage of MMD already has some spontaneous stomas from ECA branches with a better potential to form new stomas by encephalo-duro-myo-synangiosis (EDMS), the indirect part of the surgery.
19.4.4 Threats
Due to the barrier of ventricles, although the ischemic condition of deep structure such as thalamus and basal ganglion could be improved, the blood flow via the moyamoya vessels is still needed in most cases.
The occurrence of rehemorrhage cannot be totally obliterated.
19.5 Contraindications
The contraindications to perform this technique are when the ECA already developed full collateral blood flow.
19.6 Special Considerations
Neurosurgeons should analyze the spontaneous collaterals in the preoperative digital subtraction angiography (DSA) very carefully (Fig. 19‑2). Main collateral paths in the abovementioned group of 336 cases are listed in Table 19‑1 .
MMA is the most common source of spontaneous collaterals. It enters the floor of the middle cranial fossa through the foramen spinosum, passes laterally on to the temporal bone, and curves anteriorly over the great wing of sphenoid. Thereafter, it divides into anterior and posterior branch. MMA can provide important collateral flow through dura mater. Normally, it is the anterior (frontal) branch that provides collateral blood flow to anterior cerebral artery (ACA) territory through falx. MMA could be originated from ophthalmic artery in anatomic variated cases. MMA is vulnerable to the routine pterional craniotomy because hyperplasia MMA may be located deep in the cranial sulcus, increasing the risk of damage, causing post-procedural ischemic stroke.
Scalp arteries, such as STA, OA, and sometimes PAA, are rare sources of spontaneous collaterals, but in patients with any kind of craniotomy history like cerebral hematoma evacuation or external ventricular drainage, the proportion is greatly increased. In this situation, individualized designation of scalp flap is of great importance.
Heparin saline irrigation is recommended only during anastomosis; we do not recommend a general heparinization.
19.7 Pitfalls, Risk Assessment, and Complications
In some cases, direct bypass may not be feasible due to the small size of recipient artery.
Sometimes the dimeter ratio of donor–recipient artery is larger than 2.5 times, the operator may quit direct bypass because of the high possibility of postoperative hemorrhage.
The recipient MCA network is very poor on DSA and MR angiography (MRA). There is poor blood flow in some branches of MCA that looks pale and poorly filled under microscope. It is also a contradiction for direct bypass.
The EC-IC revascularization holds the potential risk of postoperative transient neurological deficits, seizure, and postoperative hemorrhage.
19.8 Special Instructions, Position, and Anesthesia
Supine position was used as a routine for STA–MCA or PAA-MCA bypass. Park-bench position was used for OA–PCA bypass. The use of head clamp should be avoided to protect contralateral STA. Blood pressure was maintained within the patient’s baseline range throughout the surgical procedural. Hyperventilation was avoided in order to prevent vasoconstriction. During the perioperative period, blood volume was expanded using crystalloid, normally 1.25 to 1.4 times maintenance through postoperative day 2.
19.9 Patient Position with Skin Incision and Key Surgical Steps
19.9.1 Skin Incision
The main concern of individualized designation of skin incision is to recognize the preexisted spontaneous anastomosis; meanwhile, the bone flap should cover the ischemic area. Selected ECA angiogram is routinely performed before surgery; MRA or CT angiography (CTA) could not provide all the necessary details of spontaneous collaterals.
In our routine procedure, an extended pterional skin incision is adopted to make full use of DTA of temporal muscle and of STA branches located in the scalp flap. The incision is extended by 1.0 to 1.5 cm above the superior temporal line. Individualized adjustments would be made in the following situations (Fig. 19‑3):
Spontaneous collaterals from STA branch are carefully identified in the angiography. The area of ischemic cortex is defined by CT perfusion or SPECT. Scalp incision should be adjusted forward or backward so as to avoid injury of scalp artery with preexisted spontaneous collaterals and to cover the ischemic cortex.
When routine pterional craniotomy cannot cover ischemic region, the procedure can be planned differently. For example, in patients with ischemic bilateral ACA territory, bilateral frontal lobe should be covered in the way that a coronal incision is adopted (Fig. 19‑1; Fig. 19‑8). When the ischemic area is located in the occipital lobe, horseshoe-shape scalp incision covering the temporal-parietal-occipital lobe is adopted.
Fig. 19.3 Individualized skin incision and surgical plan. (a) Routine skin incision in our case series, middle meningeal artery (MMA, body surface projection) and superficial temporal artery (STA) parietal branch (p-STA) is localized. (b) Double-window craniotomy is planned to protect MMA with spontaneous collaterals. (c) Individualized bone flaps in accordance with MMA course. (d) Forwarded skin incision to protect p-STA with spontaneous collaterals. (e) Back-warded incision to cover ischemic occipital lobe. (f) Posterior auricular artery (PAA) was used because there is no parietal branch of STA in this case. (g) Bone flap was made between MMA branches (red arrows) with collaterals, p-STA was used as donor artery. (h) Partly bone flap posterior to MMA to protect collaterals, using p-STA as donor artery. (i) Coronal incision in a patient with bilateral anterior cerebral artery (ACA) region ischemia. Blue triangle, posterior STA branch; red triangle, anterior STA branch; green arrow, MMA trunk; red arrow, MMA branches; red star, superior temporal line; green star, occipital artery; yellow star, posterior auricular artery.
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