Indications
Ruptured Aneurysm
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All ruptured paraclinoid aneurysms with subarachnoid hemorrhage as the presentation need to be treated. Multiple and bilateral aneurysms are more common among this group of aneurysms. In case of multiple aneurysms with subarachnoid hemorrhage, if the paraclinoid aneurysm is present ipsilateral to the ruptured aneurysm, occasionally it can be clipped at the same sitting.
Symptomatic Unruptured Aneurysm
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Generally, large or giant aneurysms are symptomatic from mass effect. Because of close proximity to anterior optic pathways, these aneurysms may cause visual disturbances as presenting symptoms. These cases need to be treated to prevent further visual loss or for improvement of vision.
Asymptomatic Unruptured Aneurysm
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The yearly risk of subarachnoid hemorrhage from an unruptured intracranial aneurysm is estimated to be around 1% for lesions 7 to 10 mm in diameter.
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For small incidental aneurysms less than 5 mm, conservative management is recommended.
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Patients younger than 60 years old with aneurysms larger than 5 mm should be offered treatment unless there is a significant contraindication.
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Large, incidental aneurysms greater than 10 mm should be treated in all healthy patients younger than 70 years.
Contraindications
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Aneurysms that are large or giant, have calcified walls, are complex, or have ill-defined necks are difficult to clip and may require carotid occlusion and a bypass as a definitive treatment.
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Other relative contraindications for definitive surgical clipping are patient factors such as advanced age and serious comorbidities.
Planning and positioning
Preoperative Radiologic Evaluation
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Preoperative radiologic evaluation includes cerebral angiography to assess the size and shape of the aneurysm.
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In the case of thrombosed aneurysms, magnetic resonance imaging (MRI) is indicated to assess the true size of the aneurysm.
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MRI not only shows the relationship of the aneurysm with adjacent structures, but also shows calcification of the wall of the aneurysm.
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MRI source images may be useful in studying not only the neck and dome, but also the surrounding structures.
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Preoperative computed tomography (CT) angiography with three-dimensional reconstruction of the cranial base shows the relationship of the aneurysm to the bony anatomy. This information might help in cranial base drilling.
Figure 23-1:
Three-dimensional reconstruction of the aneurysm in complex cases is useful to study the morphology of the aneurysm.
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Thin CT sections through the region of the clinoid process may show calcification in the aneurysm wall and any erosion of the clinoid process.
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CT scans with 0.5-mm thickness with reconstructions through the clinoid process area are helpful in assessing the pneumatization of the anterior clinoid process (ACP). Preoperative evaluation for pneumatization of the ACP may help to avoid cerebrospinal fluid rhinorrhea.
Balloon Test Occlusion
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Aneurysms that are difficult to clip may require carotid occlusion as a bailout option or treatment alternative. In such cases, balloon test occlusion (BTO) is needed to assess the collateral circulation.
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Complete angiography with and without compression of the involved carotid artery to assess the collateral circulation is required when BTO is planned.
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Monitoring of cerebral perfusion with single photon emission computed tomography (SPECT) or xenon CT is also advised. If the patient tolerates the test clinically and without any perfusion defects on SPECT, permanent occlusion of the internal carotid artery (ICA) and trapping of the aneurysm can be performed safely. Patients who do not tolerate BTO either clinically or radiologically may require a bypass graft.
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According to the protocol developed by Sekhar et al, patients who tolerate BTO with cerebral blood flow greater than 35 mL/100 g/min need no revascularization. Patients who tolerate BTO with cerebral blood flow 15 to 35 mL/100 g/min have a moderate risk and typically require revascularization. Patients who develop neurologic deficits during BTO are at high risk and may require a revascularization.
Positioning
Procedure
Proximal Control
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Traditionally, proximal control is achieved by exposing and clamping the carotid artery in the neck, before craniotomy. The aneurysm may be trapped by a temporary clip on the ICA proximal to the posterior communicating artery.
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Dolenc has advocated proximal control of the subclinoid ICA by a combined epidural and subdural approach.
Figure 23-3:
Batjer and Sampson in 1990 described retrograde suction decompression of giant paraclinoid aneurysms. A vascular clamp is placed across the cervical ICA, and a temporary clip is placed across the supraclinoid ICA immediately proximal to the posterior communicating artery. After temporary trapping, a No. 18 angiocatheter is inserted into the cervical ICA. An extension set and stopcock are connected, and a 7F surgical suction tube is inserted into the stopcock port. Through controlled digital manipulation of the suction, the collateral flow into the trapped arterial segment via the ophthalmic artery and cavernous branches can be removed.
Figure 23-4:
Endovascular retrograde suction decompression is achieved by placing a double lumen balloon catheter in the ICA by the transfemoral route. After balloon inflation and placement of a temporary clip distal to the aneurysm, the trapped segment and the aneurysm can be deflated.
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In large and more proximal aneurysms, we routinely establish proximal control by exposing the ICA in the neck before craniotomy.
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We have occasionally used retrograde suction decompression in selected cases.
Skin Incision and Craniotomy
