Microsurgery for Ruptured Aneurysms
Pearls
The patient’s head should be elevated above heart level, with systolic blood pressure around 100 mm Hg. The head position, incision, and bone flap should be tailored according to the location and orientation of the aneurysm.
A slack brain is achieved by high-quality modern neuroanesthesia and the release of cerebrospinal fluid (CSF) from the basal cisterns, the lamina terminalis, and ventricular drainage.
Continuous hemostasis is maintained throughout the procedure under a mouth-piece-controlled operating microscope with high magnification.
Sufficient proximal control for safety, frequent use of temporary clips to soften the aneurysm, meticulous dissection of the aneurysm, use of the shortest possible clip (usually 1.5 times the neck width) to prevent branch occlusions and kinking of the parent artery, intraoperative confirmation of aneurysm occlusion, and branch patency with indocyanine green (ICG) angiography and micro-Doppler are hallmarks of a successful surgery.
Immediate postoperative computed tomography (CT), computed tomography angiography (CTA), or digital subtraction angiography (DSA) are performed for quality control. Young patients, especially those with multiple aneurysms or with a family history of intracranial aneurysms, should be followed to exclude possible de novo aneurysms in the long run.
♦ Epidemiology and Natural History
The worldwide overall incidence of aneurysmal subarachnoid hemorrhage (SAH) is approximately 6 to 10 per 100,000 person-years, but in some countries, such as Finland and Japan, is as high as 16 to 20 per 100,000 person-years.1 SAH caused by intracranial aneurysm rupture has a 50% overall mortality, and one third of the survivors suffer from significant neurologic deficits.2
Risk factors for aneurysmal SAH are smoking, hypertension, excessive use of alcohol, and family history.3 , 4 Unruptured aneurysms are estimated to have an approximately 1% rupture rate per year.5 Risk factors for aneurysm rupture include female gender; smoking; older age; high blood pressure; large aneurysm size; aneurysm location, especially posterior circulation location; country of origin; and history of subarachnoid hemorrhage.4
After the International Subarachnoid Aneurysm Trial (ISAT)6 , 7 study, there has been a strong increase in the use of the endovascular techniques that have been overshadowing the most recent developments of microvascular neurosurgery. As endovascular techniques remain expensive, and not all of the aneurysms can be treated using them, there is still a place for high-quality microsurgery. Our philosophy when treating both anterior and posterior circulation aneurysms using microneurosurgery is to apply microsurgical techniques that are “simple, fast, and preserve normal anatomy.”8 , 9
We review here the microneurosurgical experience of the senior author (J.H.) at two of the five Finnish neurosurgical units, the Kuopio and Helsinki University Hospitals, which have treated more than 10,000 intracranial aneurysms since the beginning of the microneurosurgical era in Finland in the mid-1970s. At present, in our institutions approximately 350 ruptured aneurysms are treated each year, most of them using state-of-the-art microneurosurgery.10
♦ Indications
All patients of southern and eastern Finland come to Helsinki and Kuopio, which are two of the five neurosurgical units of Finland with a catchment area of nearly 3 million people. These two units cannot select their patients, in contrast to many metropolitan hospitals, which show a strong patient selection in their reports. Admitting all patients, including those with a poor grade and elderly patients with aneurysmal SAH for treatment from a defined catchment area, means that we face a management mortality of 20 to 35%, even when our surgeons have extensive experience and use the most sophisticated treatment methods. Depending on the selection of patients, treatment mortality can be between 1% and 25%, or even higher. These figures are highly influenced by the preoperative patient condition, the practitioners’ treatment skills, and the length of the follow-up.
Location of the aneurysms | % |
Middle cerebral artery | 38 |
Anterior communicating artery | 26 |
Internal carotid artery | 23 |
Pericallosal artery | 6 |
Vertebrobasilar arteries | 7 |
♦ Selection of Patients for Active Treatment
Our policy is to treat all SAH patients in the acute phase as soon as possible, usually during the first 24 hours after the aneurysm rupture. Nearly half (45%) of all patients are operated on within 24 hours. Distribution of intracranial aneurysms in the Finnish population according to their site of origin is represented in Table 21.1 .
Patients with expansive hematomas, in our population most often due to ruptured middle cerebral artery (MCA) aneurysm,11 are operated on immediately. We operate even on patients with fixed, dilated pupils if the patient is young and the pupil dilatation has been present for only a very short time. Microsurgical clipping is preferred in these patients, as it allows also the removal of the hematoma and application of the extraventricular drain (EVD). The EVD can be placed either through the lamina terminalis during the surgery or through an additional cortical puncture. We prefer the former method.12 Especially patients with poor grade should have no treatment delays, and are treated during the first day. Multivariate analysis shows that among patients with ruptured aneurysms, the major determinants of outcome are preoperative grade, intracerebral hematoma (ICH) or intraventricular hematoma (IVH) on initial computed tomography (CT) scan, and preoperative hydrocephalus13 ( Table 21.2 ). In addition, perioperative aneurysmal rupture, occlusion of major vessels, postoperative hematoma, and perforator injury are also related to unfavorable outcome.
♦ Preoperative Treatment
Before the ruptured aneurysm has been secured, systolic arterial blood pressure must be controlled, and blood pressures above 160 mm Hg should be treated with labetalol. At the same time, a systolic pressure that is too low will not provide sufficient perfusion pressure and should be prevented as well. In patients with an intracranial space-occupying hematoma, a higher blood pressure can be allowed to secure adequate cerebral perfusion pressure. The transmural pressure of the aneurysm sac is one of the determinants of the risk of rebleeding, and as it cannot be measured individually, the accepted blood pressure remains to be determined individually. In all SAH patients arterial blood pressure is measured invasively. In conscious patients, spontaneous breathing is usually adequate, but in patients with a Glasgow Coma Scale (GCS) score of 8 or less, an artificial airway and controlled ventilation are indicated. Adequate anesthesia is required before intubation to prevent rebleeding, because laryngoscopy and intubation induce a stress response with an increase in blood pressure. Sedation using propofol should be considered in patients under controlled ventilation.
Tranexamic acid (1 g IV every 6 hours up to 3 days) is administered to prevent rebleeding until clipping. Nimodipine (PO or IV) is given to all patients with ruptured aneurysms to prevent vasospasm. A more detailed description of our anesthesiologic principles in treatment of SAH patients are described elsewhere.14
♦ Neuroradiologic Investigations
Since the late 1970s, CT has been the primary diagnostic tool for detecting SAH and for determining the presence of an ICH or hydrocephalus. Digital subtraction angiography (DSA) has been replaced by CT angiography (CTA) at our department since the year 2000 as the primary imaging method for detecting intracranial aneurysms.14 CTA is fast and noninvasive, and it gives information about bony landmarks and provides accurate diagnosis of aneurysms larger than 2 mm. Furthermore, three-dimensional (3D) CTA images provide a surgical view of the aneurysms15 ( Fig. 21.1 ). Postoperatively, all patients undergo CT and CTA16 ( Fig. 21.2 ). CTA is used during the follow-up to determine the presence of aneurysm remnants or regrowth ( Fig. 21.3 ). DSA is reserved for complex, giant, or previously coiled aneurysms, and it can be used also intraoperatively during the surgery.
♦ Surgical Techniques
Anterior Circulation Aneurysms
Surgical Approaches
We operate on nearly all aneurysms of the anterior circulation, except those of the pericallosal artery, using the lateral supraorbital (LSO) approach. The LSO approach has been used by the senior author (J.H.) for more than 25 years in treatment of both vascular18 – 24 and neoplastic lesions of the anterior cranial fossa.17 , 18 This approach is a less invasive modification of the pterional approach. It is located more frontally, with the bone flap of approximately 3 × 4 cm in diameter ( Figs. 21.4 and 21.5 ). We do not use the orbitozygomatic approach or any of its different modifications mainly because in our experience the removal of the orbital roof causes swelling of the orbital contents and thereby takes much (or all) of the extra space achieved.
The LSO approach has been described in detail else where.19 Briefly, the head is fixed to the Sugita frame and (1) elevated clearly above the cardiac level; (2) rotated 15 to 30 degrees toward the opposite side according to the position of the aneurysm; (3) extended or slight flexed depending on the height of the aneurysm from the skull base; and (4) tilted laterally to make the proximal part of the sylvian fissure nearly vertical. We adjust the position of the fixed head and body during the operation as needed. After mini mal shaving and injection of a local anesthetic combined with Adrenaline for vasoconstriction, a 7- to 9-cm-long, curved skin incision is placed just behind the hairline. A one-layer skin-muscle flap is retracted frontally with spring hooks, and the superior orbital rim and the anterior zygomatic arch are exposed. The extent of the craniotomy depends on the surgeon’s experience and preference. It may be tailored according to the location and the size of the aneurysm. Usually, a small LSO craniotomy is all that is necessary, but for giant aneurysms a slightly larger bone flap is planned. A single bur hole is placed just under the temporal line in the bone, that is, the superior insertion of the temporal muscle. A bone flap of 3 × 4 cm is detached mostly by a side-cutting drill, and the basal part is partially drilled to remove most of the sphenoid wing ( Fig. 21.5 ). The dura is incised curvilinearly with the base in the frontobasal direction, and dural edges are elevated using multiple stitches, extended over craniotomy dressings. From this point on, all surgery is performed under the operating microscope, including the skin closure. The LSO approach is simple and fast with little removal of the skull base; the whole approach takes only 10 to 15 minutes. Our record in performing this LSO craniotomy from skin to skin in an unruptured MCA aneurysm is 25 minutes, with uneventful recovery of the patient. A fast operation is naturally not the major goal in itself, but it allows more operations to be performed in a single operating room during a single day, thereby being more cost-effective, and potentially the risk of the infection is lower. Our experience is that clean surgery is fast, and it results in a good outcome for the patient.
The LSO approach, like any other approach for ruptured aneurysms, requires a slack and relaxed brain, achieved by modern neuroanesthesia20 to minimize brain retraction.18 For paraclinoid aneurysms or those of the posterior communicating artery (PCoA) close to the anterior clinoid, an intradural clinoidectomy with ultrasonic bone curette (Sonopet Omni, Model UST-2001 Ultrasonic Surgical System, Synergetics, Inc., Miwatec Co., Kawasaki, Japan) is performed to have the proximal control of the aneurysm. The anterior clinoid is not removed routinely, but the decision is made only after the initial inspection of the anatomic relation between the aneurysm and the parent artery.
Distal anterior cerebral artery (DACA) aneurysms or pericallosal aneurysms differ from other anterior circulation aneurysms in the sense that they require a different approach, namely the interhemispheric approach.21 – 25 This can be done with the patient either lying supine with the head in neutral position and elevated approximately 20 degrees above the heart level, or placed in the lateral park bench position with the head elevated and tilted upward. We prefer the supine position. For most DACA aneurysms the skin incision is curvilinear over the midline behind the coronal suture. A single bur hole is placed on the midline, and a paramedian bone flap is placed slightly over the midline to facilitate retraction of the falx medially. The size of the bone flap, usually 3 to 4 cm in diameter, depends both on the surgeon’s experience and on the presence of an ICH. A flap too small may not provide sufficient room for working between the bridging veins. The dura is opened under the microscope as a C-shaped flap with its base at the midline. Nowadays, we recommend the use of a neuronavigator to help intraoperative localization of the aneurysm inside the interhemispheric fissure, which does not have a good anatomic landmark.
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