Eyebrow Keyhole Approach in Aneurysm Surgery
The concept of keyhole neurosurgery is not only to perform small incision and reduce the craniotomy size for the sake of a small opening as we called “keyhole,” but it is rather to make “minimum craniotomy” required to access deep intracranial lesions at the end of the route. Standard craniotomy forms a “funnel-shaped surgical corridor” to reach deeper area of the brain. In contrast, keyhole mini craniotomy forms a “reverse funnel-shaped surgical corridor” that provides adequate working space through a small incision and bone window to reach the target. The concept of this approach is that the deep area of the brain can be accessed through smaller craniotomy since the superficial optical field is widened if the size of craniotomy is bigger (Fig. 2.1).
2.1 Basic Consept
Intracranial aneurysm surgery using eyebrow keyhole approach has been reported by Van Lindert and Perneczky in 1998, and since then, this approach has been accepted as minimally invasive approach for aneurysm clipping surgery in addition to the existing standard approach.
2.2 Preoperative Planning
The planning and execution of the approach play a critical role in performing this keyhole surgery. The smaller the craniotomy, the greater the need for precise planning and self-made completion of the approach because the corridor of surgical dissection cannot be changed during the procedure.
2.3 Step of the Approach
2.3.1 Positioning and Preparation
The surgeon must plan and perform the proper positioning of the patient by himself. Self-made preparation and positioning are essential for creating keyhole craniotomies. After the patient is anesthetized, the patient head is positioned in supine with head holder, and the head is higher up approximately 15° to facilitate venous drainage. A slightly chin-up position is preferable to support the frontal lobe that will slightly fall down according to the gravity force. The degree of head rotation should be determined by preoperative 3D simulation, but generally the head is rotated between 15° and 45° toward the contralateral side, determined by the location and dome projection of aneurysm. The placement of lumbar drain or extraventricular drainage also allows for brain relaxation specially in ruptured aneurysm case with brain edema.
2.3.2 Skin Cut
The skin is cut according to the preoperative planning and anatomical orientation. The skin is cut at lateral two-thirds of the eyebrow, from supraorbital notch to the lateral part, sometimes extending few millimeters to the temporal line. To achieve a good cosmetic appearance, the incision should follow the orbital rim, in the hair line. It is advisable not to overuse bipolar coagulation to avoid damaging hair follicles and surrounding tissues. After skin incision, skin flap is dissected subcutaneously to obtain optimal exposure to surrounding muscles. We could clearly identify the frontal, orbicularis oculi and temporal muscles. After dividing the muscular layers gently, we have to identify pericranium at supraorbital edge, and it is cut perpendicularly following superior temporal line to get good bone exposure.
2.3.3 Mini Craniotomy and Dural Incision
2.3.4 Intradural Dissection
2.3.5 Closure and Bone Flap Replacement
2.4 Complications and How to Avoid
Temporary or permanent supraorbital hypesthesia. In eyebrow keyhole craniotomy, the surgical field is very narrow, and medially the surgical field is limited by supraorbital notch that contains supraorbital nerve. Perioperative anatomical landmark should be prepared precisely to avoid damaging these structures. Certainly, keeping a distance of the craniotomy site at least 5–10 mm lateral to the orbital notch can reduce the risk of supraorbital nerve injury. Sometimes stretching the nerve during surgery is unavoidable, but preserving the nerve continuity will provide good chance to have functional recovery after surgery.
Frontal deformity. The frontobasal burr hole needs to be placed behind the temporal line after retracting the temporal muscle laterally. The burr hole site will be covered with the muscle to prevent deformity in this area. Proper repositioning of the bone flap is also an important step to prevent frontal deformity for a better cosmetic result. Bone flap should be fixed frontally and medially without any bony distance; make sure the mini plate tightly fixed the bone in proper position.
Suboptimal cosmetic result. Skin incision should be made within the eyebrow and follow the orbital rim. Retraction of the skin flap should be in gentle manner to prevent soft tissue necrosis, and it is better to minimize the use of bipolar cauterization during skin and soft tissue procedures. The skin is closed with interrupted suture to have an optimal skin tension with good approximation.
Infection. If the frontal sinus opened during procedure, careful repair is mandatory. The periosteum or fascia flap, bone wax, or abdominal fat tissue can be used to repair the injured sinus. Make sure the dura is closed watertightly with interrupted suture; if still dehiscence occurred, a small muscle patch should be used for this purpose.
This approach is contraindicated in patient with massive brain swelling after subarachnoid hemorrhage.
This approach could not be a standard for all of aneurysm surgery; the indication should be strict and rely on the surgeon’s experience.
The keyhole craniotomy may limit the microsurgery working angles, so it is mandatory to use a high magnification microscope and specific keyhole microsurgery instruments.
It is preferred not to use this approach for patient with large frontal sinus, because the greater risk of infection may occur.
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