Key-words:
Aneurysms - extradural anterior clinoidectomy - paraclinoid
Introduction
The paraclinoid segment of the internal carotid artery (ICA) aneurysms has been named
the area from where it exits the cavernous sinus and enters the subarachnoid space
to the origin of the posterior communicating artery.[[1]],[[2]],[[3]],[[4]],[[5]] ICA aneurysms present with unique challenges in both diagnosis and microsurgical
management because of their unique anatomic location, and these types of aneurysms
have been associated with a high morbidity and mortality.[[3]],[[6]],[[7]] Before the development of skull base techniques, the approach for these aneurysms
was difficult because the anterior clinoid process (ACP) obstructed the surgical field
and restricted the surgeon's working space. The clipping of paraclinoid aneurysms,
while attempting to preserve the ophthalmic artery and maintain patency of the ICA,
is a technically difficult procedure.
Advances in skull base approaches, especially the extradural anterior clinoidectomy,[[8]],[[9]],[[10]] have greatly improved surgical outcomes for patients with paraclinoid aneurysms.
An alternative treatment of paraclinoid aneurysms is endovascular procedure.[[11]],[[12]],[[13]] Microsurgery continues to result in a larger percentage of total occlusions compared
to other methods, especially for large and giant aneurysms, because total obliteration
with endovascular treatment is not as likely as it is with surgery,[[14]],[[15]] and coiling procedures have been associated with a higher rate of recurrent aneurysms
compared with that of surgical treatment.[[16]],[[17]] Although the extradural anterior clinoidectomy was developed specifically to improve
outcomes for paraclinoid aneurysms, many authors still report high complication rates
resulting from this approach.[[2]],[[3]],[[6]],[[17]]
The purpose of this study was to review our recent experiences using extradural anterior
clinoidectomy to surgically clip paraclinoid segment aneurysms.
Materials and Methods
Cerebral aneurysm patients were reviewed between September 2014 and December 2016
at the Banbuntane Hotokukai Hospital, Fujita Health University, Nagoya, Japan. A retrospective
analysis of all patients with unruptured paraclinoid ICA aneurysm was performed. Patients'
demographic data, site of the aneurysm, operation notes, and postoperative morbidities
or mortalities were reviewed and recorded. Institutional ethical clearance and patients'
consent for publication were taken. According to our department protocol, all patients
diagnosed with unruptured paraclinoid ICA aneurysms who are candidates for treatment
are discussed with the neuro-intervention team of our department. If not considered
a good candidate for intervention, the patient will be offered surgery. We use reconstructed
computed tomography angiography routinely for surgical planning, and in case of any
ambiguity, request a digital subtraction angiography. In our hospital, all neurovascular
surgeries are performed with OPMI ® Pentero ® Microscope (Carl Zeiss, Oberkochen,
Germany) with infra-red 800 camera equipped with FLOW 800 software (Carl Zeiss, Oberkochen,
Germany). Upon exposure of aneurysm, we perform indocyanine green-videoangiography
to clarify the aneurysm and its relation to all the surrounding vessels. Furthermore,
to evaluate any perforating artery or other structures hidden behind the aneurysm,
we introduce a rigid endoscope (Machida, Japan) under microscopic guidance. With this
technique, we check for the estimated final location of the aneurysm clip tips to
be away from any critical structure.
Surgical approach
All 33 paraclinoid aneurysms were treated using an ipsilateral pterional approach
with an extradural, ACP removal. Head is always rotated by 30° to the contralateral
side with slight flexion of the neck to avoid neck vein obstruction from hyperflexion.
The level of the head should be higher than the heart to decrease intracranial pressure
during surgery. Skin incision is started from the preauricular, zygomatic root area
and extends to cover the frontotemporal area and ends at the midline of the frontal
area. The temporalis muscle and pericranium layer are dissected with subperiosteal
dissection until the zygomatic root is observed. The craniotomy is done with high-speed
cutting. The sphenoid ridge is flattened first to make a wide space for exposure.
A large rongeur is also used to remove the cortical bone, and then the temporal and
frontal dura are elevated from the inner table of the skull by a periosteal elevator
or Penfield elevator. The superior orbital fissure and optic nerve are seen at the
temporal and frontal sides, respectively. The meningo-orbital band or orbitotemporal
periosteal fold is exposed at the temporal side lateral to the ACP. The dural groove
is the landmark for the junction of the periorbital and temporal dura. From this point,
we start to cut with the blade [[Figure 1]]. The next step is peeling the dura propria to separate it from the temporal side
to expose the oculomotor nerve, trochlear nerve, and ophthalmic (V1) branch from the
lateral wall of the cavernous sinus. Unroofing of the optic canal is then performed.
Following this, removal of ACP using a micro rongeur is done in a piecemeal fashion.
The correlation between the direction of the aneurysm and the tip of ACP should be
considered because we can punctiliously avoid premature rupture of the aneurysm, especially
the medial direction of the aneurysmal dome. Removal of the cortical bone of the ACP
allows for improved exposure of the ICA (ophthalmic and clinoid parts), aneurysm,
optic nerve, and oculomotor nerve. The distal dural ring is observed and the optic
strut is seen in the area of the Dolenc or clinoidal triangle. The bone in this area
must be removed with micro-forceps. The dura is incised from the sylvian area for
exposure of the sylvian fissure and through the distal part of the ICA. The aim of
opening the dura in this step is inspection and confirmation of the location of the
aneurysmal sac before the tip of the ACP is removed. An “L-” shaped dural incision
was performed along the sylvian fissure and frontal base. The dural incision extended
anteriorly over the third cranial nerve and toward the opening of the oculomotor foramen.
The distal dural ring was completely or partially released to allow for mobilization
of the ICA segment in order to improve access to the aneurysm for clipping [[Figure 2]].
Figure 1: Cutting of meningo-orbital band during extradural anterior clinoidectomy
Figure 2: Cutting of distal dural ring for mobilization of internal carotid artery and better
exposure of the aneurysm
Results
Between September 2014 and December 2016, a total of 93 ICA aneurysms were found.
It comprised 37 IC-posterior communicating artery aneurysms (IC-PC), 12 IC-anterior
choroidal (IC-Acho), 10 IC top (IC top), 1 IC fusiform, and 33 paraclinoid aneurysms
[[Figure 3]].
Figure 3: Location of internal carotid aneurysms
A total of 33 cases of paraclinoid IC aneurysms were present. Females comprised the
majority with 32 cases and only one male in the study. The mean age was 54.8 years,
ranging from 35 to 74 years. The mean size of the paraclinoid aneurysm was 5.3 mm
(range: 3–12 mm). Paraclinoid aneurysms were classified as per the projection, based
on the classification of juxta dural ring aneurysms of ICA by Kyoshima et al. [[Figure 4]].[[18]] Based on it, 9 paraclinoid aneurysms were found projecting dorsally, 7 laterally,
and 17 medially. No patient had any other types of vascular malformation [[Figure 5]].
Figure 4: Kazuhiko Kyoshim etal's. classification of paraclinoid aneurysms
Figure 5: Demographics of paraclinoid aneurysms
Morbidity
An immediate complete occlusion rate of 100% was achieved in the present series. We
noted morbidity in the form of visual disturbances in 6.2% of our patients. One of
our patients developed permanent loss of vision. No mortality was seen in our series.
No cerebrospinal fluid leakage, unplanned ICA occlusion, and epidural hematoma was
seen postoperatively in our patients.
Illustrated case 1
A 68-year-old male with incidental large 12-mm paraclinoid aneurysm was operated by
pterional approach and removal of ACP. After cutting the meningo-orbital band, piecemeal
removal of ACP and optic strut were performed using a micro rongeur. Dura was divided
over distal dural ring to facilitate mobilization of ICA and better exposure of the
aneurysm [[Figure 6]]a, [[Figure 6]]b, [[Figure 6]]c. As the aneurysm was a large one, suction decompression method of clipping was
used.
Figure 6: (a and b) Three-dimensional reconstructed images with paraclinoid aneurysm. (c) Intraoperative
photograph showing exposure of the paraclinoid aneurysm after extradural anterior
clinoidectomy and cutting of distal dural ring
Discussion
Various names have been given to the paraclinoid aneurysms, namely, ventral ICA segment
[[19]] and the carotid-ophthalmic segment.[[6]],[[20]] These aneurysms are technically challenging because access to the neck of the aneurysm
usually requires ACP removal,[[3]],[[6]],[[2]] and their location provides a restricted working space.
Obliteration of the aneurysm with endovascular treatment has a lower success rate
for total occlusion.[[14]],[[15]],[[21]] Further, recurrences are more frequent after endovascular treatment, especially
in lesions that were incompletely occluded during the initial procedure.[[16]],[[17]] Microsurgery, therefore, remains the primary treatment for paraclinoid segment
ICA aneurysms, as it provides a higher long-term success rate,[[17]] although in some cases, combined surgical and endovascular approaches have been
a useful treatment strategy.[[1]],[[5]],[[22]]
In 1968, Drake et al.[[23]] reported that only 40% of patients (with 14 paraclinoid aneurysms) achieved good
outcomes (Glasgow Outcome Scale score of 4 or 5) following microsurgery, while 60%
of patients died. However, subsequent clinical series have shown substantial improvements
in outcome. In 1994, Batjer et al.[[2]] reported positive outcomes in 87% of cases from a surgical series of 89 paraclinoid
aneurysms, with only a 12% morbidity rate. In 2001, Hoh et al.[[17]] reported that combined surgical and endovascular treatment of paraclinoid aneurysms
resulted in good outcomes in 90% of the 145 surgically treated aneurysms. In 2004,
Beretta et al.[[24]] reported good outcomes in 81% of the study patients with a 13% morbidity rate.
Recently in 2008, Raco et al.[[25]] reported good outcomes in 81% of patients and a long-term morbidity rate of 20%.
The current study reports more favorable outcomes with 100% immediate occlusion rates
and 6.2% morbidity in terms of visual disturbances, although one patient developed
permanent visual loss.
Optic nerve injury is one of the most common complications after surgical treatment
of paraclinoid aneurysms. Caution must be exercised when the optic canal is unroofed.
The dura overlying the optic canal must not be disrupted. Moreover, the pial vessels
of the optic nerve must not be disrupted while the dura is incised. Retraction of
the optic nerve must be brief and minimal. Before incising the dura on the distal
dural ring and the floor of the optic canal, the ophthalmic artery must be identified
to avoid its inadvertent injury. Superior hypophyseal artery occlusion may be accounted
as a contributing factor in visual disturbances. The cranial nerve can be injured
during ACP removal or clip blade advancement or from excessive retraction or overzealous
sinus packing. We experienced transient visual disturbances, which was far lower than
other series [[3]],[[17]],[[26]],[[27]] and one case had permanent visual loss. While applying the clip, we were careful
to confirm whether the end of clip blade injured a cranial nerve. In order to prevent
injury while retracting the temporal lobe, the carotid-oculomotor membrane was opened
sharply.
Rizzo [[28]] found two etiologies of worsened vision, including a fulminant orbital syndrome
caused by the compromise of large draining veins of the orbit and a retrobulbar optic
neuropathy caused either by direct injury or damage to the small dura vessels of the
posterior optic nerve. Kumon [[29]] believed that the occurrence of visual disturbances resulted from injury to the
ipsilateral optic nerve caused by excessive retraction or by the heat produced by
the diamond drill. We did not prefer the use of drill to remove ACP and optic strut.
Micro rongeurs were used to remove the ACP piecemeal, which we believe to be a very
safe option. Recently, use of ultrasonic bone cutter has also been introduced. The
use of this device does not automatically protect the soft tissues and the angle of
the tip and the optic canal should be as close to perpendicular as possible.
Hemostasis is a cause of major concern when the outer layer of the lateral dural wall
of the cavernous sinus is peeled off to expose the inner layer of deepest inferolateral
surface of ACP. Bleeding from the cavernous sinus should be distinguished from bleeding
from the dural draining vein, as the former can be well controlled with gentle packing
with hemostatic agents (packing appears as “cones” made by the hemostatic agent, while
the latter requires bipolar coagulation). Overzealous sinus packing must be avoided
owing to potential compressive injuries to the cranial nerves.
Conclusion
The surgical treatment of aneurysms that arise from the paraclinoid segment of the
ICA has been a technical challenge for cerebrovascular surgeons. The authors have
tried to avoid several complications in extradural anterior clinoidectomy approach
to paraclinoid aneurysms using several tactics. Micro scissors were used parallel
to the ACP in order to avoid injuring the cranial nerves. The ACP was rongeured instead
of drilling in order to minimize any thermal injury to the optic nerve. Precise anatomical
knowledge combined with these microsurgical tactics is required to prevent and manage
potential complications to achieve good outcomes.
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.
