Basilar tip aneurysms account for 5% - 8% of all intracranial aneurysms and 50% of vertebro-basilar system aneurysms are located in the basilar apex   . They carry a higher risk of rupture than aneurysms in other locations and constitute a major surgical challenge, due mainly to difficulties controlling proximal feeding arteries or complex anatomy of the basilar bifurcation and their depth within an extremely narrow surgical field    . General principles governing surgical treatment of intracranial aneurysms namely proximal and distal control of feeding arteries, microdissection, meticulous saving of thalamoperforating arteries and minimal injury to complex nerve structures are difficult to achieve in the setting of posterior circulation aneurysms  . But endovascular treatment of these aneurysms with complex techniques, such as double balloon remodelling, Y-stent-assisted coil embolization and Waffle-cone stenting is safe; but the extent medical literature is crowded with evidence of studies showing such techniques to be associated with relatively low complete occlusion rates and high recurrences and retreatment rates   . Despite an ever-growing number of endovascular procedures being performed, giant or wide-necked aneurysms and those which involve the posterior cerebral artery at its neck generally are not occluded with endovascular techniques but are rather clipped  . In Ivory Coast, any endovascular technique is not yet available. Approaches to basilar bifurcation aneurysms in most series are the subtemporal, pterional, “half-and-half” and frontotemporal routes  -  . It is widely reported that each of these approaches have advantages and disadvantages and; they are nonetheless associated with some degree of morbidity and mortality      . We sought to report this case of a basilar apex aneurysm successfully occluded with non-ferromagnetic SUGITA clips and to share our experience of clipping these lesions through the frontotemporal approach. In the following, we will detail our clinical case and technical nuances of our surgical approach, as well as present our clinical experience with it.
2. Case Report
Mrs. OG, a 60-year-old right-handed patient presented to our Neurosurgical Unit in February 2nd 2013 after a sudden onset of altered consciousness. Her husband recalled Mrs. OG complaining of severe headaches which were associated with easy and projected vomiting before collapsing on the bed. She has not had any episode of fever nor convulsions prior to her admission. The patient has a 4-year history of a poorly treated high blood pressure and, sustained a left capsular-thalamic ischemic stroke 2 years before admission. The husband denied alcohol or tobacco use and pill medication. She is nonetheless diabetic and has reached menopause with no hormonal replacement treatment.
We examined Mrs. OG on arrival and found a patient with an altered consciousness, a Glasgow coma scale of 12; pupils were equal, normal size and reactive to light. The neck was stiff with positive Kerning and Brundzinski signs, a right hemiparesis (probably a sequelae of a previous stroke) with hyperactive reflexes and a Babinski sign on the right.
Brain NECT scan 24 h post ictus showed a subarachnoid haemorrhage around the basal cisterns, maximal in interpeduncular and prepontine cisterns (Figure 1(a) and Figure 1(b)). According to the WFNS and Fisher grading systems, the patient was grade IV on both scales.
Brain CT angiography revealed a basilar tip aneurysm (Figure 2(a) and Figure 2(b)) which presented with a height of 3.8 mm and a lateral diameter of 5.2 mm, and was oriented backward and 15 mm above the level of the dorsum sellae, on the right of the interpeduncular cistern.
Surgical clipping of the aneurysm was indicated but to multiple technical barriers, surgery was delayed and the patient underwent surgery after the critical vasospasm period.
Thirty days later, a thorough neurological examination revealed motor aphasia, right hemiparesis and a Glasgow coma scale of 13.
Brain NECT scan (Figure 3) showed persistent hydrocephalus and a lacunar ischemia in the left internal capsule consistent with the right hemiparesis.
Surgical clipping and third ventriculostomy was indicated and the patient underwent surgery on March 10th 2013.
Figure 1. Brain NECT scan axial view (a) and sagittal view (b) showing subarachnoid haemorrhage around the basal cisterns, maximal in interpeduncular and prepontine cisterns.
Figure 2. Brain CT angiography sagittal view (a) and coronal view (b) showing a basilar tip aneurysm oriented above the level of the dorsum sellae.
Figure 3. Brain NECT Scan axial view showing secondary hydrocephalus.
The patient was placed in the supine position with the head turned slightly 35˚ to the left. A frontotemporal arch-shaped skin incision centered to the pterion was fashioned. It began immediately in front of the tragus and coursed slightly posterior, behind the hairline and superior to the highest point of the external ear; then curved medially and anteriorly to finish just behind the hairline in the frontal area. After retracting the skin flap anteriorly, careful interfascial dissection of the temporalis muscle was carried out to protect the frontal branch of the facial nerve. The temporalis muscle was retracted inferiorly, frontotemporal craniotomy was performed. After removing the bone flap, and beginning at the frontal limit of the craniotomy, an S-shaped dural incision was carried to the level of the impression of the lesser sphenoid wing. After opening the dura, we punctured the frontal horn of the right lateral ventricle to drain 15 ml of CSF which relaxed the brain cortex. Then the sylvian fissure and basal cisterns were widely dissected (Figure 4). Further drainage of the chiasmatic cistern allowed maximal brain relaxing. Outer and inner layers of middle fossa dura were separated by blunt dissection and, such blunt dissection was continued medially until exposure of the anterior clinoid process. Then the anterior clinoid process, and the optic strut were removed, exposing the supraclinoid segment of the internal carotid artery until its bifurcation. Dura was incised medially toward the optic sheath and the distal dural ring was divided laterally, anteriorly, and posteriorly, making it possible to mobilize the internal carotid artery. Retracting the intradural segment of the ICA medially, prevented excision of the posterior communicating artery. We proceeded to the identification of the right anterior choroid and posterior communicating arteries, and the latest appeared small. Further dissection exposed the right oculomotor nerve and its vascular relationships as it courses between the posterior cerebral artery and the anterior and superior cerebellar artery. As we followed the right P2 and P1 segments of the posterior cerebral artery, the neck of the aneurysm was identified. After dissecting the neck, a right non-ferromagnetic SUGITA clip was inserted. To assure total exclusion of the aneurysm, a second clip was inserted just below the first clip (Figure 5(a) and Figure 5(b)); and that goal was achieved.
The second phase of the operation consisted in performing the third ventriculostomy through an opening of the lamina terminalis.
We completed our surgery by abundant rinsing with saline until satisfactory clearing of the working space. The dura was closed and suspended as was the bone flap. The skin was closed and two drains (one extradural and another subgaleal) were left in place.
The patient developed a hospital acquired pneumonia after surgery and was successfully treated with antibiotics. Following the antibiotics course, her clinical status improved significantly and was discharged 21 days after surgery with outpatient appointments for further follow-up. She was reviewed 3 and 6 months
Figure 4. Surgical exposure of the lateral fissure. The supraclinoid portion of the ICA bifurcates laterally at the optic chiasma into the anterior cerebral artery (A1) and middle cerebral artery (M1). ON optic nerve, FL frontal lobe, TL temporal lobe, III 3rd cranial nerve and PCoA posterior communicating artery.
Figure 5. (a) (b): Clipping the basilar tip aneurysm neck.
later and did not yield any clinical sign of relapse and since, she has been asymptomatic.
Endovascular therapy has largely replaced microsurgical clipping for the treatment of basilar tip aneurysms since the dawn of the International Subarachnoid Aneurysm Trial, which associated in its findings with higher morbidity and mortality to surgical clipping of basilar bifurcation aneurysms  . In most modern centres, the majority of basilar apex aneurysms are treated via endovascular means, albeit with the expectation of relatively low complete occlusion rates and a higher percentage of recurrences and retreatment  . Microsurgery is still appropriate for aneurysms with complex neck morphologies and in young patients desiring a more durable treatment  .
In most series, approaches to basilar bifurcation aneurysms are via the subtemporal, pterional, “half-and-half” and frontotemporal routes      . It is widely reported that each of these approaches have advantages and disadvantages and; they are nonetheless associated with some degree of morbidity and mortality      . Anatomical complexity of these lesions has led to the variations of these conventional techniques as attempts to overcome obvious limitations during surgery   -  . Unfortunately, such variations have not provided adequate solutions to problems presented by limited working space at the depths of some basal cisterns.
Depending on the orientation of the basilar apex aneurysm, many authors usually associate the orbitozygomatic osteotomy with high basilar bifurcation aneurysms and the transcavernous-transsellar approach with low-lying lesions     . Our patient’s lesion was 15 mm above the level of the dorsum sellae, which is a high basilar tip aneurysm; and would have benefitted from a pterional approach with orbitozygomatic osteotomy. This approach is anatomically damaging however, and we held the view that the frontotemporal perspective would be less invasive or just well suited for the lesion; and we were confident that our choice would be vindicated by the outcome, which turned out to be the case. We performed a frontotemporal approach combined with an anterior clinoidectomy. Medial retraction of the ICA was helpful indeed, in a sense that routine resection of the posterior communicating artery, presented in most series, was not necessary in our case   . In addition to the main lesion, the patient developed hydrocephalus and given the peculiar surgical trajectory of our approach; performing a third ventriculostomy became straightforward. It is the authors’ personal experience that wider dissection of the sylvian fissure provided a sufficient access to the aneurysm neck and the interpeduncular fossa. The satisfactory view of the interpeduncular fossa through this trans-sylvian perspective, reduces subsequent traction on the temporal lobe and manipulation of the III cranial nerve  . The subsequent anterior clinoidectomy widened the working space, allowing sufficient mobilization of the internal carotid artery. Such action is helpful in successfully clipping aneurysms as high as that of our patient  .
Yasargil is known to have initiated the frontotemporal approach as a standard approach for skull base surgery. The frontotemporal approach when combined with an anterior clinoidectomy is particularly useful for treating most basilar artery bifurcation aneurysms located between the clivus and a line 1 cm above the posterior clinoid processes.
Drake and Peerless devised this approach as a mean of treating posterior circulation aneurysms associated with anterior circulation ones and; the surgeon may choose the ideal trajectory and change the angle of view, depending on the peculiarities of each specific case    . However, changing the angle of view does not always provide additional space at the deep limits of the exposure   .
Opponents of the frontotemporal perspective have however, associated it with an approach with a reduced working space where the angle of view is narrow and oblique, especially for lesions hidden by posterior clinoid processes or the dorsum sellae and upper clivus   . In the era of more advanced endovascular techniques, the bar for surgical expertise has been raised by selecting out groups of patients that have more difficult aneurysms  . More dramatic skull base approaches have been described to deal with such aneurysms, including anterior petrosectomy and the transcavernous approach      . These may be considered basal extensions of subtemporal and pterional approaches, respectively. But anterior petrosectomy provides a narrow working space and can cause serious damage to important neurovascular structures in the vicinity of the petrous bone. Dolenc described the transcavernous approach as a means of increasing the working space around the interpenducular and prepontine cisterns and provide a wider exposure of the deep anatomy  . This approach involves removing the anterior clinoid process, incising the distal and proximal dural rings, opening the cavernous sinus, and drilling the dorsum sellae and clivus to varying extents.
Sano described the temporopolar approach, also known as the half-and-half approach which provides a wider exposure of the interpeduncular fossa and sufficient proximal and distal control of the basilar and the posterior cerebral arteries respectively    . In a series reported by Sekhar et al., the authors used this perspective and performed an anterior petrosectomy to reduce bone constraints and achieved sufficient mobilization of the internal carotid artery  .
Despite an ever-growing number of endovascular techniques, surgical clipping of basilar tip aneurysms remain the treatment of choice for giant or complex aneurysms and basilar artery bifurcation aneurysms of the youth. However complex and challenging the lateral sulcus approach may be, it is the authors’ view that this approach is a valuable alternative to more traditional routes to basilar tip aneurysms. The frontotemporal approach when combined with anterior clinoidectomy is particularly useful for treating most basilar artery bifurcation aneurysms.
There is no conflict of interest from any of the authors.
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