Key-words: Brow craniotomy - meningiomas - minimally-invasive - skull base - supraorbital
Introduction
Meningiomas are the most common benign intracranial tumors. Meningiomas constitute
30% of all intracranial tumors, of which anterior skull base meningiomas amount to
8.8%.[[1 ]] The most common midline anterior skull base locations are tuberculum sellae (3.6%)
followed by olfactory groove (3.1%).[[2 ]] The traditional approaches to these lesions would require a large pterional/frontal
craniotomy or one of their variations. The disadvantage of these large exposures is
unnecessary exposure of the brain, which can advertently be injured during retraction
or instrument passes. A tailored approach for anterior skull base pathology using
supraorbital craniotomy (SOC-brow craniotomy) was first described by Krause in the
early 1900s and then popularized by Axel Perneczky in the 1990s. Since then, this
has gained confidence of the operating surgeons worldwide and SOC is being utilized
more frequently in surgeries of the anterior skull base.[[3 ]],[[4 ]] More recently, Mahmoud et al. have described variants of SOC in the approaches
to orbital tumors.[[5 ]] Selection of lesions for resection using SOC depends upon the relation and position
of the lesion in the anterior cranial fossa, which is determined using preoperative
imaging. The goal of this approach would be to have an adequate access to the skull
base and be able to excise the lesion, with minimal retraction of the brain. The counterargument
for this approach lies in the adequacy of the surgical exposure when compared with
conventional approaches to the anterior cranial fossa. The main limitation of this
approach is that it has a steep learning curve as compared to traditional approaches,
made especially difficult as it needs frequent adjustments of the operating table,
microscope, and microinstruments needing coaxial control through the narrow surgical
window.[[6 ]] In this article, we have attempted to describe the advantages, disadvantages, and
technical nuances in approaching large anterior skull base meningiomas using SOC.
Methods
This is a single institute study from a retrospective review of prospectively collected
data. Seven cases of large anterior skull base meningiomas were operated through SOC
at our institute over a 5-year period from 2013 to 2018. The patients were selected
for SOC after a preoperative imaging review by the institutional tumor board. In general,
we included meningiomas of the anterior skull base, of any size, except when they
had extensive involvement of the frontal or ethmoidal sinus, or have gross optic nerve
involvement. We also avoid in patients where there is radiological evidence of involvement
of the circle of Willis or one of the major branches. All patients underwent standard
positioning, same operative techniques in exposure, and closure of SOC to maintain
uniformity. Any adverse events or surgical complications were also noted. Patients
had immediate postoperative imaging with either contrast-enhanced computed tomography
or magnetic resonance imaging. All patients had regular follow-up examinations postoperatively.
Operative procedure
All procedures were performed under general endotracheal anesthesia. Preprocedural
imaging data were acquired with skin fiducials and registered on SonoWand navigation
system (SONOWAND, Trondheim, Norway).
Next, the patient was positioned supine with head fixed on a Sugita frame. Head was
elevated 10° and extended 15°–20° as it allowed the frontal lobe to fall back. Degree
of head rotation toward the opposite side was based on the location of the tumor [[Figure 1 ]]. We chose nondominant side approach for midline tumors and ipsilateral side for
laterally placed tumors. The incision was made within the eyebrow (ciliary incision)
extending from 0.5 cm lateral to the supraorbital notch to the lateral edge of the
brow. Initial incision was carried across the skin and dermis. A pericranial flap
was elevated, with the base directed inferiorly over the orbital rim to exteriorize
the frontal sinus if needed. Monopolar Bovie is generally avoided during exposure
of skin and subcutaneous tissue. The attachment of periorbita to the rim of the supraorbital
ridge is better left undisturbed to prevent postoperative periorbital edema. Blunt
dissection of a small portion of temporalis muscle and fascia at the superior temporal
line was performed, and a 5-mm burr hole (or just adequate to pass the foot plate
of the B1/2 craniotome) was made on the lateral aspect of the exposure below the temporalis
muscle for a better cosmetic result as shown in [[Figure 2 ]]. Frontalis branch of the facial nerve was avoided by staying subfacial and not
exposing beyond the first 10 mm of the temporalis muscle. A craniotome was then used
to make two cuts: the first cut was made from the burr hole just flush with the supraorbital
ridge and the second cut was made in the shape of an inverted “U” and connecting the
burr hole with the medial edge of the first cut. Navigation was used to mark this
border, and all effort was made to avoid exposing the frontal sinus. In case of inadvertent
exposure of the sinus, the mucosa was stripped off and gel foam-soaked povidone-iodine
was used to pack the sinus, which was later exteriorized using the harvested pericranium
and fibrin glue. Next, a 4-mm cutting burr was used to drill the bony irregularities
on the supraorbital ridge and the orbital roof to maximize the surgical exposure.
Figure 1: We can approach various targets in supraorbital craniotomy with the help of rotation
of head, patient positioning, maneuvering the microscope, and adjusting the Operating
Table. Lesions include olfactory groove (1), planum sphenoidale (2) and clinoidal
(3) Meningiomas
Figure 2: (a) Position of the patient with neck extended and rotation toward contralateral
side; (b) surgical drapes before surgery; (c) subcutaneous and muscle flap turned
upward; (d) illustrative picture of size of craniotomy; (e) bone flap elevated after
craniotomy; (f) dural exposure and visualization of frontal lobe; (g) water tight
dural closure after tumor excision; (h) replacement of bone flap with miniplates and
screws
Dura was opened in semilunar fashion with the base at orbital rim. Cerebrospinal fluid
(CSF) cisterns were opened to aid brain relaxation, and the arachnoid plane was dissected.
The tumor was devascularized and debulked in piecemeal fashion, using a combination
of ultrasonic aspirator and the bipolar coagulation, followed by dissection of the
tumor from the surrounding brain tissue. Intraoperative navigation guidance was used
for better anatomical orientation during surgery. Once the excision was achieved,
the operative cavity was thoroughly inspected for residue with angled endoscopes in
all cases. The dural attachment was thoroughly coagulated and hemostasis achieved.
In cases where preoperative imaging revealed extension in the optic canal, the falciform
ligament was cut and deroofing of the optic canal was carefully done using a 2-mm
Diamond drill. The dura was closed in a watertight manner, and the cranial flap was
fixed with miniplates and screws. Bone cement may be occasionally used to cover the
gap at the edges of craniotomy and the replaced bone flap for better cosmesis. Multilayered
meticulous closure of muscle and subcutaneous tissue was performed. The skin was closed
in subcuticular fashion using nonabsorbable ethylon (nylon), which was subsequently
removed on day 7–10. Absorbable sutures were avoided as there is a higher chance of
thickened scar at this location secondary to the occasional inflammation caused by
the absorbable suture material. The various steps are illustrated in [[Figure 2 ]]. Photographs were taken preoperatively and at different time points during the
follow-up to keep a record of cosmetic outcomes [[Figure 3 ]].
Figure 3: (A) Postoperative scars (a, c, e, and g) and nonoperative contralateral side (b,
d, f, and h) in patients who underwent left supraorbital brow craniotomy. (B) Nonoperative
side (a, c, and e) and postoperative scars (b, d, and f) in patients who underwent
right supraorbital brow craniotomy (sides intentionally swapped to preserve patient
privacy)
Results
We operated seven cases of large anterior skull base meningiomas (defined as maximum
diameter >3 cm).[[6 ]] Of seven meningiomas, four were located in the planum sphenoidale, two were in
the orbital roof at the fronto-orbital junction, and one was located at tuberculum
sellae. Headache was the most common presentation and was seen in 5/7 cases. One patient
presented with progressive mono-ocular loss of vision and another patient had right
hemiparesis. Simpson's Grade 2 excision was achieved in all cases. One patient had
postoperative CSF leak which was managed conservatively with a lumbar drainage. One
patient had transient frontal branch of facial nerve weakness, which recovered over
6 weeks. Tube shaft instruments and endoscope were useful adjuncts in all our cases.
Frontal sinus was inadvertently opened in one case, which was packed with gel foam
and exteriorized with harvested pericranial flap. Case illustrations from 2 cases
are shown in [[Figure 4 ]] and [[Figure 5 ]].
Figure 4: (a) T1-weighted sagittal section magnetic resonance imaging brain with isointense
lesion in the planum sphenoidale, white arrow indicates anterior cerebral artery being
pushed upward and posteriorly by the lesion. (b) T2-weighted coronal section magnetic
resonance imaging brain with heterointense lesion the planum sphenoidale. (c) T1-weighted
postcontrast axial section magnetic resonance imaging brain with contrast enhancing
lesion in the planum sphenoidale. (d) T1-weighted postcontrast sagittal section magnetic
resonance imaging brain postoperative image with complete excision of the lesion
Figure 5: (a) T1-weighted sagittal section magnetic resonance imaging brain with isointense
lesion in the right orbital roof; (b) T1-weighted coronal section magnetic resonance
imaging brain with contrast enhancing lesion in the right orbital roof; (c) T2-weighted
axial section magnetic resonance imaging brain FLAIR sequence with lesion in the right
frontal region demonstrating the severe perilesional edema; (d) T2-weighted sagittal
section magnetic resonance imaging brain with complete excision of the right frontal
lesion
Discussion
Initial efforts on surgical management of large anterior skull base meningiomas were
limited to partial frontal lobectomy followed by excision of the lesion or a subtemporal
bony decompression.[[7 ]] Dandy was the first to describe bifrontal craniotomy with transbasal approach though
it still necessitated resection of part of the frontal lobe to excise meningioma.
With the advent of microscopes, many surgeons continued bifrontal approach for anterior
skull base lesions without resecting normal frontal lobes. Unilateral approaches were
popularized by Yasargil et al. when the familiarity with pterional craniotomy and
trans-sylvian approach increased. These procedures were further modified into fronto-orbito-zygomatic
approach which provided more basal exposure, necessitating lesser brain retraction.
The ideal surgical approach should provide adequate exposure of tumor, the surrounding
structures, and the dural attachments. It should aid to minimize brain retraction
and avoid manipulation of vital neurovascular structures. A tailored supraorbital
approach can be used based on the location of meningioma in the anterior cranial fossa.
With adequate patient positioning, trajectory adjustment, and brain relaxation, most
of the large anterior skull base meningiomas can be excised. SOC has been used to
address various other pathologies such as craniopharyngiomas and aneurysms.[[8 ]],[[9 ]] It has also been sparingly used in the treatment of arteriovenous malformations,
gliomas, pituitary lesions, and cavernous sinus lesions.[[10 ]] Gazzeri et al. reported a series of 41 cases of meningioma of anterior skull base
treated with the SOC approach, of which complete excision of tumors was achieved in
84.5%.[[11 ]] In our series of seven cases of large meningiomas of anterior skull base [[Table 1 ]], Simpson's Grade 2 resection was achieved in all the cases. Resection of the meningioma
was made possible by the use of surgical adjuncts, such as the tube shaft microinstruments
and an endoscope. Tube shaft instruments have an extremely thin shaft design and thereby
provide an almost completely unobstructed view. These are ideal attributes for surgeries
performed in the coaxial plane where the regular microinstruments obstruct the surgical
field. Endoscopes help in visualizing the extent of tumor resection in depth and obscure
bleeding from a tumor in the surgical field. We do not consider large frontal sinus
as a contraindication for supraorbital brow craniotomy.
Table 1: Clinical symptomatology and radiological characteristics
A similar case series of 23 patients operated using the SOC was reported by Iacoangeli
et al. They suggested using conventional approaches if lateral extent of a tumor lies
beyond the anterior circulation vessels and optic nerve, in case of complete encasement
of carotid arteries, invasion of ethmoidal sinuses, and presence of severe bifrontal
edema.[[12 ]]
Complications encountered with this approach are usually in relation to craniotomy
such as cosmetic deformities in the frontotemporal area, and this can be overcome
by filling the defect around the bone flap with bone cement and fixing the bone flap
with miniplates and screws. Zumofen et al. performed a PubMed/Medline database search
for publications on supraorbital craniotomy performed for either aneurysm repair or
tumor resection; overall, 2783 patients with 3085 lesions were found in various case
series or case cohort-type studies. Approach-related complications included 3.3% CSF
collection or leak, 4.3% permanent, and 1.6% temporary supraorbital hypesthesia, 2.9%
permanent and 1% temporary facial nerve palsy, and 1% wound-healing disturbance or
infection.[[13 ]] The esthetic outcome was typically reported as highly acceptable. Opening of frontal
sinus can cause CSF leak which can be avoided with neuronavigation. Inadvertently
opened frontal sinus should be sealed with bone wax. Thermal injuries to the eyebrow
due to microscopic light on 100% intensity can be avoided by protecting the surrounding
area with constant irrigation and cushioning with wet gauze.[[9 ]] Our series had one patient with CSF leak which was managed conservatively with
3 days of lumbar drain and strict bed rest. Two patients had transient ptosis which
improved completely within duration of 2 weeks. Ptosis encountered in brow craniotomies
is more often due to a muscular cause and is transient.
Potential errors while performing a supraorbital brow craniotomy may arise due to
inadequate preoperative planning, inadequate positioning of the patient, and inadequate
placement of craniotomy. All these may result in the suboptimal outcomes. With neuronavigation
and a meticulous preoperative planning, these pitfalls can be avoided. Drilling the
inner edge of the craniotomy provides additional working angle when the lesions are
deep-seated. Damage to the neurovascular bundle in the surgical field is likely due
to lack of orientation. Dural tears while performing craniotomies and inappropriate
closure of the dural reflection can cause postoperative CSF leaks and should be avoided.
Watertight dural closure with nonabsorbable sutures and tissue glues help in preventing
CSF leaks. Other anticipated local tissue-related problems would be an improper replacement
of bone flap and improper wound closure techniques which would hamper the cosmetic
outcome of the patient.
Conclusion
Supraorbital keyhole approach should be a part of every neurosurgeons armamentarium
in the management of skull base lesions. As shown by our case series, large anterior
skull base meningiomas can be safely operated with SOC with good cosmetic outcomes.
The utilization of endoscope, navigation, tube shaft instruments, hemostatic agents,
and tissue sealants makes the surgery safer and more effective. With careful selection
of appropriate lesions and adequate experience, excellent outcomes can be achieved
with minimal complications and near natural cosmesis.
Declaration of patient consent
The authors certify that they have obtained all appropriate patient consent forms.
In the form the patient(s) has/have given his/her/their consent for his/her/their
images and other clinical information to be reported in the journal. The patients
understand that their names and initials will not be published and due efforts will
be made to conceal their identity, but anonymity cannot be guaranteed.
