Transsylvian Transclinoidal and Transcavernous Approach for Basilar Bifurcation Aneurysms

Patient Selection

14.1.1 Indications for Surgery and Alternatives

Options for treatment of basilar apex region aneurysms include surgical clipping or endovascular treatment with coils. The preference for endovascular treatment tends to be even greater for basilar apex aneurysms because of the historically higher surgical morbidity with posterior circulation aneurysms compared with anterior circulation aneurysms, the establishment of Guglielmi detachable coils as an accepted modality for treating aneurysms in general, and the diminishing number of neurosurgeons with experience in the treatment of complex and posterior circulation aneurysms.

On the other hand, endovascular therapy has a high chance of failure in large aneurysms with wide necks. It also fails more commonly in aneurysms with a hemodynamic configuration, such as those at the basilar bifurcation region. The recanalization rate after endovascular therapy in general ranges between 20 and 30%, and it may be even higher with basilar apex aneurysms. In addition, the chance of future bleeding after coiling of basilar aneurysms is as high as 1 to 2% per year in some series.

The decision to treat basilar apex aneurysms endovascularly or with open surgery should take these features into consideration, as well as the aneurysm neck width, size, presence of intraluminal thrombus, location in relation to the posterior clinoids, and direction of projection of the aneurysm. The author has made extensive use of the transcavernous transclinoidal approach, which provides a much wider exposure at the depth of the surgical field and has helped achieve a more perfect clipping of the aneurysm, decreased the chance of recanalization, and improved the durability of treatment. This approach is indicated for basilar aneurysms that are large or giant and have a posteriorly projecting aneurysm dome ( ▶ Fig. 14.1), low bifurcation, wide dysmorphic base, and dolichoectasia ( ▶ Fig. 14.2). It is not indicated for small aneurysms that have small necks and project anteriorly above the level of the posterior clinoids ( ▶ Fig. 14.3).

Fig. 14.1 Anteroposterior and lateral views of a large, wide-based, complex, posteriorly projecting basilar apex aneurysm.

Fig. 14.2 Computed tomography angiography of a wide-based, dysmorphic, basilar apex aneurysm.

Fig. 14.3 Computed tomography angiography of a small basilar apex aneurysm located above the posterior clinoid process not needing the transcavernous approach.

14.1.2 Contraindications for Surgery

Patients with large basilar apex aneurysms who have a life expectancy of less than 5 years are considered only for endovascular therapy. Otherwise, patients are offered endovascular and microsurgical clipping and are informed of the risks and benefits of each to help them make their own decision.

14.1.3 Timing of Surgery

Although there are no strict rules and the decision is usually individualized, we use some guidelines based on the Yasargil subarachnoid hemorrhage (SAH) grading system ( ▶ Table 14.1). Patients who are grades 1 to 3 with associated hydrocephalus are operated on as soon as they present. Patients who are in grade 4 or worse are usually managed conservatively until their condition improves, after which treatment is initiated.

**Table 14.1** Yasargil subarachnoid hemorrhage grading system
Grade	Condition	Deficit, cranial neuropathy, or A or B hemisyndrome
0 (unruptured)	Asymptomatic	A	No
0 (unruptured)	Symptomatic	B	Yes
1 (SAH)	No deficits	A	No
1 (SAH)	Minimal deficits such as cranial neuropathy	B	Yes
2 (SAH)	Headache and meningismus	A	No
2 (SAH)	Minimal deficits	B	Yes
3 (SAH)	Lethargic, confused, combative	A	No
3 (SAH)	With hemisyndrome	B	Yes
4 (SAH)	Semicomatose, respond to pain but not voice
5 (SAH)	Comatose, no reaction, failing vital signs
Abbreviation: SAH, subarachnoid hemorrhage.

14.2 Preoperative Preparation

An arterial line is inserted in patients with SAH upon admission to the intensive care unit. Blood pressure is controlled in awake patients with a β-blocker such as atenolol (25 mg orally) or a clonidine patch (0.1–0.2 mg) or both. This will usually adequately control the blood pressure without the need for intravenous agents. In patients who have significant ventriculomegaly, an external ventricular drain may be inserted and kept at 15 cm above the level of the external auditory meatus. This is usually done in patients who are grade 3 or 4 with evidence of ventriculomegaly because it can results in significant clinical improvement, leading the author to recommend immediate surgery. Perioperative antibiotics, hydrocortisone, and an anticonvulsant such as phenytoin are administered and continued postoperatively.

In addition to catheter angiography, a computed tomography angiography (CTA) is obtained in most patients as a baseline with which to compare postoperative CTA. We often obtain a magnetic resonance imaging scan with perfusion and diffusion images in patients who are grade 3 or worse. This detects ischemic changes before surgery and may be an indication to delay surgery. One etiology is SAH within the week or so before the current presentation, leading to vasospasm and ischemia.

We monitor somatosensory evoked potential and brainstem evoked responses during surgery. Changes in evoked potentials are an indication to remove temporary clips, if placed, and the clipping process should be adjusted accordingly.

14.3 Operative Procedure

14.3.1 Skin Incision and Craniotomy

Under general endotracheal anesthesia, the patient is placed in a supine position and the head is turned, usually to the left side. Preparation is made for a frontotemporal craniotomy with pretemporal extension. The hair is shaved along a strip where the incision will be made ( ▶ Fig. 14.4). After scrubbing and draping the wound in a sterile fashion, the skin incision is made, and hemostasis is established with scalp clips.

Fig. 14.4 The head position and the marking of the skin incision. The arrow connects the beginning and the end of the incision, which illustrates how the base of the flap will reach the junction of the frontal zygoma to the orbital rim (red ball).

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