Distal transsylvian keyhole approach for unruptured anterior circulation small aneurysms
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To reduce complications associated with conventional pterional craniotomy, a transsylvian keyhole approach for unruptured small anterior circulation aneurysms is proposed.
A 7-cm linear scalp incision is made along the hairline, beginning at the zygoma, followed by minimal temporal muscle dissection. Two burr holes are drilled out at McCarty’s point and the temporal bone, and a 3-cm equilateral triangle bone flap is made, whose apex is located above the sylvian point. After the sphenoid ridge is drilled off, aneurysms are exposed and clipped with conventional microsurgical instruments.
This approach permits access to aneurysms via the transsylvian corridor with a smaller area of potential injury of superficial structures.
KeywordsKeyhole approach Transsylvian approach Cerebral aneurysm Clipping
In line with recent advances in endovascular surgery, the need for less invasive direct aneurysm surgery has been increasing. Some types of keyhole approaches have been developed as alternatives to the conventional pterional craniotomy. However, most reported approaches are via supraorbital or subfrontal routes [1, 3, 7] and have drawbacks including a narrow surgical corridor, need for special microsurgical instruments, and damage to the superior orbital nerve . In this study, the surgical techniques and important factors that enable usual pterional conventional microsurgical manipulations for anterior-circulation aneurysms via a keyhole approach are described.
Relevant surgical anatomy
It is important to understand of the running of a facial nerve for its preservation in this approach. At the axial level of the upper edge of the zygomatic arch, the mean distance between the anterior border of the tragus and the most posterior branch of the facial nerve is 15.3 mm (range, 11.0–22.9 mm; SD, 3.5 mm) . The branches of the facial nerve that innervates the orbicularis and frontalis muscle are located in the surface of superficial layers of deep temporal fascia and cross at a mean distance of 40.4 mm (range, 35.2–45.6 mm; SD, 3.3 mm) above the lateral canthus of the eye . The most posterior temporal branch to the frontalis muscle that intersected the superior temporal line is located a mean distance of 34.9 mm (range, 29.1–40.6 mm; SD, 4.4 mm) posterosuperior to the lateral canthus of the eye .
Description of the technique
Because of minimal preparation and dissection of bones and muscles, iatrogenic surgical trauma, cranial deformities, and temporal muscle atrophy are significantly decreased postoperatively (Fig. 6).
We use a perforator to shape the two burr holes in this approach as well as conventional pterional craniotomy, because it is a familiar and routine procedure for us. However, to minimize the further bone lost and avoid the use of calcium phosphates, the use of a drill instead of a perforator is recommended.
Conversely, this technique is contraindicated for patients with ruptured aneurysms, complex aneurysms including large or partially thrombosed aneurysms, and those requiring removal of the anterior clinoid process or bypass.
This approach provides the same clear anatomic exposure as the conventional pterional approach, and it provides a familiar view to neurosurgeons. The sylvian fissure is seen in the center of the surgical window. The approaches from the sylvian fissure to the carotid cisterns, suprachiasmatic cistern, and interhemispheric cistern are the same as with the conventional pterional approach, and the viewing angle along with the microscopic lighting is also equal to wide craniotomy.
The surgical procedure is carried out with conventional microsurgical, bayonet-shaped short instruments, without specialized skills. No particular instruments and devices—for example, a neuroendoscope to compensate for the limitation of the visualization—are needed.
More severe brain traction is not needed in this approach. As in the conventional pterional approach, wide opening of the fissure and cisterns requires less brain traction in dissection of the aneurysm.
However, the small size of the bone flap allows a more limited angle of clip applier insertion.
How to avoid complications
The key point to overcoming the problem of the limited angle of clip applier insertion is complete dissection of the aneurysm complex from surrounding structures, which makes the aneurysms ‘movable’ to permit changing their direction to that most suitable for neck clipping.
Specific perioperative considerations
Certainly, this approach cannot be applied to all patients with aneurysms. With careful evaluation of each patient for the possibility of proximal control, direction of the aneurysm, and application of the aneurysm clip, this approach should constitute an effective craniotomy technique.
Specific information to give to the patient about surgery and potential risks
This approach has a smaller area than the conventional pterional approach, but results in a pleasing cosmetic outcome while minimizing the likelihood of procedure-related morbidity.
Compliance with ethical standards
The authors report no conflict of interest concerning the materials or methods used in this study or the findings specified in this paper.
The patients have consented to submission of this “How I Do It” to the journal.
The video illustrates the necessary procedures to the pterional keyhole approach for unruptured aneurysmal clipping, showing a left MCA aneurysm as an example. (WMV 114835 kb)
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