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The supraorbital craniotomy is a lateral skull base approach suitable to access the parasellar, parachiasmatic and intrasylvian space. This approach attempts to minimize brain retraction, an important consideration for surgeons attempting to reach deep lesions, especially underneath the dominant hemisphere. When combined with removal of the orbital roof, intraorbital tumors become readily accessible via this approach.
When combined with an eyebrow incision, the supraorbital craniotomy is a minimally invasive keyhole approach. This concept of a keyhole approach has gained special popularity. Several authors have described various modifications of the conventional frontal and frontotemporal approaches, creating some confusion. Variations of the subfrontal route can be referred to as supraorbital, eyebrow supraorbital, frontolateral, supraciliary frontolateral keyhole, lateral supraorbital, and several other combinations.
When compared with the standard pterional lateral subfrontal exposure, the more anterior trajectory of the supraorbital subfrontal corridor affords a longer operative working distance, but potentially requires less brain manipulation and retraction. The use of dynamic retraction through the strategic use of suction apparatus and dissectors bestows the supraorbital subfrontal route flexible working angles for managing complex lesions, including anterior circulation aneurysms and large anterior skull base tumors.
We often underestimate the function of the basal frontal lobes during subfrontal operations. The orbitofrontal and mediobasal cortices are often misleadingly considered ‘silent’ and ‘noneloquent.’ However, their functions are apparent to the patients’ families and coworkers, especially when the patient is high functioning. Subfrontal injury frequently leads to disinhibition caused by damaging the orbitofrontal region, which is involved in cognitive processing and decision-making (see Wikipedia).
Mediobasal injury leads to anterograde and retrograde amnesia. These deficits are not apparent to the treating neurosurgeon, but readily detectable on a neuropsychological examination.
Extraneous frontal lobe injuries can be avoided with proper planning of the operative approach and patient positioning to use gravity retraction, enhanced bony removal, brain relaxation, wide arachnoid dissection and most importantly, strategic use of dynamic retraction and handling of the normal brain during manipulation of the pathology.
Indications for the Approach
A supraorbital craniotomy is used for large (<5cm) anterior skull base tumors such as olfactory groove, planum sphenoidale, and tuberculum sella meningiomas, as well as vascular lesions such as anteriorly and inferiorly pointing anterior communicating artery (A-Comm) and common ophthalmic aneurysms. Parasellar tumors such as craniopharyngiomas are also ideal candidates for this approach. However, more posteriorly situated lesions with significant cranial extensions are not suitable for this approach due to the limited vertical reach of this corridor.
Appropriately selected small lesions within the mid to medial anterior Sylvian fissure (such as small middle cerebral artery aneurysms) and the interpeduncular space (small tumors) are also reasonable contenders for this approach. The long working distance to these targets restricts the working angles needed to manipulate large tumors or complex aneurysms.
This is a slightly increased risk of cosmetic concerns associated with the eye-brow incision. Patients with sparse eye-brows should consider traditional pterional routes. Moreover, tumors along the sphenoid wing and extending into the middle fossa are best approached through the traditional corridors.
Preoperative tumor embolization may help minimize blood loss; however, I hardly ever use this method for meningiomas because the craniotomy allows tumor devascularization along the anterior skull base. Preoperative scans should be reviewed to assess the lateral extent of the frontal sinus and the potential to avoid its entry. If this sinus is entered, the mucosa must be removed and the cavity packed with muscle and bone wax. A pericranial flap harvested during the exposure can be preserved and used to cover the frontal sinus opening.
The basal cisterns may be difficult to reach early in the surgery without significant retraction of a tense frontal lobe. Therefore, a lumbar drain may be used for patients who have associated lesional edema and expected increased intracranial tension.
The patient is placed on the operating table in a supine position. The degree of head turn is determined by the characteristics of the lesion. Since this approach is mainly used for midline lesions, I frequently turn the patient’s head only 20 degrees.
The pins are placed directly across from each other along the superior temporal line, with the single pin directly above the pinna. The double-pin arm may be rotated to prevent its interference with the bicoronal incision. The patient should be well secured to the table in case the need arises to ‘airplane’ the table in one direction or another.
There are two alternative incision styles for a supraorbital craniotomy: bicoronal and eyebrow incision.
The supraorbital rim must be exposed to gain the appropriate exposure. The pericranium is elevated separately, reflected anteriorly, and kept moist. Fishhook retractors are crucial for maximizing bony exposure for an eyebrow scalp flap. The skin in this region is mobile and can allow for a sizable craniotomy.
A single burr hole is made under the temporalis muscle at the keyhole to expose the frontal dura. The location of this burr hole will determine how easily the craniotomy can be created flush with the orbital roof. A true McCarty keyhole burr hole will expose the frontal dura, and the orbit and can be used to complete a modified orbitozygomatic osteotomy, if necessary.
A dissector can be used to “feel” the roof of the orbit through the keyhole to guide the inferior cut of the craniotomy parallel to the roof. The “tallest” craniotomy should be made through the eyebrow incision. The height of the craniotomy is often the most limiting aspect of the supraorbital eyebrow incision during the intradural work. Navigation may be used to avoid violation of the frontal sinus with the craniotomy. However, bone removal and exposure should not be compromised at the expense of leaving the sinus intact.
The dura is opened in a U-shaped fashion based on the orbital rim. When the dura is secured with sutures, the frontal lobes will be mobilized away from the cranial base using appropriate methods of brain relaxation such as a lumbar drain and opening of the optico-carotid cisterns. The anterior sylvian fissure is split and optico-carotid arachnoid membranes are released.
A subgaleal drain is not implanted and the scalp is closed in the standard fashion. The skin edges are carefully approximated and not strangulated using absorbable sutures. The eyebrow incision must be carefully closed to ensure acceptable cosmetic results.
Orbital Rim Osteotomy or Fronto-Orbital Craniotomy
The patient is observed in the intensive care unit for 1-2 days and then transferred to the wards. The lumbar drain can be used for 1-2 days after surgery to help divert cerebrospinal fluid (CSF) pressures if there is a concern for CSF leakage through the frontal sinus.
It is not uncommon for patients to suffer temporary frontalis palsy after surgery related to retraction of this nerve, but this weakness generally resolves in 4-6 weeks. Numbness in the distribution of the supraorbital nerve is undesirable, and should be avoided during the early steps of the operation by minimizing traction on the nerve.
Pearls and Pitfalls
- The patient’s head must be tilted back to take full advantage of gravity retraction during a supraorbital craniotomy.
- Removal of the supraorbital rim can significantly expand access to the anterior cranial base. This osteotomy will improve the inferior-to-superior operative trajectory.
- An eyebrow incision allows exposure of a variety of lesions in a minimally invasive way. The exposure should be not only minimally invasive, but also minimally disruptive.
- The inferior edge of the craniotomy should be flush with the roof of the orbit.
Contributor: Marcus A. Acioly, MD, PhD
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