Modified Retromastoid Approach and Clipping of “High-Riding“ VA-PICA Junction Aneurysm: An Operative Video
Correspondence Address: Source of Support: None, Conflict of Interest: None DOI: 10.4103/0028-3886.325361
Source of Support: None, Conflict of Interest: None
Keywords: Approach, clipping, far lateral, outcome, surgery, vertebral-posterior inferior cerebellar artery junctionKey message: Not all VA-PICA junction aneurysms can be dealt with using the same surgical strategy. Preoperative radiology must be thoroughly studied to recognize the rare high-riding VA-PICA junction aneurysms. Such aneurysms are best approached through a modified or an extended retromastoid approach.
Aneurysms at the vertebral artery-posterior inferior cerebellar artery (VA-PICA) comprise 2% of all aneurysms while constituting 9% of posterior circulation aneurysms., Located in front of the pontomedullary junction, these are surgically challenging. Despite a downward trend for microsurgery, some of these aneurysms are still considered the most suitable surgical candidates. The usual surgical approach to these aneurysms is through a far lateral approach (FLA).,,, Their clipping involves working through narrow corridors between the lower cranial nerves. Rarely, the VA-PICA junction may be high-riding and harbor an aneurysm. Zhao et al. defined them to be those located more than 23 mm from the foramen magnum in the vertical dimension. FLA in such cases may create oblique and awkward working angles through which proper clip application may be difficult, thus resulting in sub-optimal surgical outcomes. We demonstrate a simpler modified retromastoid approach (MRMA) with a trajectory through the glossopharyno-cochlear triangle (GCT) for tackling such aneurysms.
High-riding VA-PICA junction aneurysms are rare and unique and require different surgical considerations. We demonstrate the technique of successful microsurgical clipping of one such aneurysm in this video.
A 50-year-old lady presented with a history of sudden severe headache 10 days prior to admission. After initial treatment elsewhere, she was referred to us for further treatment. On examination, she was conscious, oriented, and neurologically intact. There was no neck rigidity.
On review of the neuroimaging, a hyperdensity suggesting blood was noted at the level of the left internal auditory meatus (IAM) involving the middle cerebellar peduncle. A computed tomographic angiography revealed a large (fundus: 18 mm) superiorly projecting broad-based (neck size: 6 mm) saccular aneurysm arising from the left VA-PICA junction. The left V4 segment was elongated, tortuous forming a dome-like curve before diving down toward basilar artery formation. The aneurysm arose from this dome and the PICA took off just lateral to the neck of the aneurysm. An intraarterial angiogram confirmed this finding.
We planned a retromastoid craniotomy with extension of the lateral bony drilling to expose nearly the half of sigmoid sinus and removal of the foramen magnum rim till the retro-condylar fossa. For this approach (i.e. modified retromastoid approach or MRMA), we used a lateral position while the head was fixed on pins. The right arm was supported with a sling after padding the axilla. Trunk was kept elevated above the heart level.
Video link: https://youtu.be/AWR268y-ag0
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Video timeline with audio transcript
0.01–0.12: In this video, we demonstrate the surgical technique of clipping a high-riding VA-PICA junction aneurysm through a modified retromastoid approach through the GCT.
0.12–0.16: Requisite consent was obtained.
0.16–0.28: This was a 50-year-old lady with a history of sudden onset of holocranial headache 10 days prior to admission. She was treated in a private hospital and was referred to us. On examination, she was conscious, oriented, and without any deficit.
0.30–0.52: On imaging, she had a bleed in the level of the middle cerebellar peduncle on the left side. On angiogram, the left VA was abnormally tortuous and tented; at the level of the tent, there was a broad-based aneurysm directed superiorly. This aneurysm was reaching the level of the IAM and located 27 mm above the level of the foramen magnum rim. The PICA was arising from its neck.
0.52–01.10: The conventional FLA here would have given us an inferior to superior oblique trajectory; thus, we decided to go for a modified retromastoid approach to have a horizontal exposure and a horizontal angle of attack. This would lead us to the aneurysm through the 7th/8th cranial nerve and the glossopharyngeal nerve.
1.11–1.27: Thus, we took the patient for a retromastoid approach and took the lateral position and fixed the head on pins. A lazy S incision was marked behind the pinna and after exposure of the muscle subperiosteally, a lateral suboccipital craniotomy was performed and the rim of the foramen magnum (FM) was removed.
1.28–1.54: Further lateral removal of the bone was performed using a drill. The drilling was performed carefully to avoid injuring the sigmoid sinus. Bony bleeding was controlled with the help of bone wax and particular attention was paid to drilling the edge of the FM. This step is very important because it allows a proper reflection of the dura.
1.54–2.24: The dura was opened in a limited fashion caudally to drain CSF from the lateral cerebellomedullary cistern. And after draining the CSF, the brain became lax as one can see the dural pulsation. Hitch sutures were taken to reflect the dural edges, and the duratomy was completed in a c-shaped fashion and the dura was reflected laterally with the help of a suture.
2.24–04:00: Thereafter, we dissected from below; the arachnoid over the lateral cerebellomedullary cistern was opened and the caudal PICA was exposed. With further cranial dissection, the lateral surface of the medulla came into our view as well as the V4 segment of the VA that was draped by the LCNs. We can see the accessory nerve coming down. The dissection was performed proximally and the glossopharyngeal nerve was exposed. The flocculus here was obstructing the view of the aneurysm above the glossopharyngeal nerve. This was the fundus of the aneurysm. To have an unretracted view, we did arachnoid dissection superiorly and exposed the 8th cranial nerve. The flocculus was resected to have an unhindered view of the aneurysm. This aneurysm was a broad-based aneurysm, arising from the dome-shaped tent of the VA and the PICA was arising very close to the neck. This PICA was dissected free of the fundus and this aneurysm was seen very well through this triangle between the glossopharyngeal nerve and the 8th nerve, the so-called glossopharyngo-cochlear triangle.
04:00–05:13: We realized at this point that the and it was tense. Thus, we created space for the application of a temporary clip. The proximal VA was cleared from LCN and a temporary clip was applied. As you can see, despite the application of the temporary clip, the aneurysm did not lose its turgor and it was still very tense. Careful dissection was performed on either side of the neck with particular attention to the surface that was adherent to the brainstem. After separation, we attempted to apply a straight clip across the neck, slightly away from the origin of the PICA; it showed that the VA was having an abnormal tent-shaped structure here and was diving deep and below to meet the contralateral side. An intraoperative ICG angiogram here showed a poor flow through the PICA and the aneurysm was still filling.
05:14–06:15: Therefore, we decided to isolate this segment of VA by applying distal and proximal temporary clips. This permanent clip was removed. We decided that this aneurysm was going to require a tandem clipping for an effective control. So, a straight clip was applied distally on the fundus; after that, another straight clip was applied proximal to this, preserving the VA and the origin of the PICA. Once these clips were applied, the temporary clips were removed—first the distal one and then the proximal one. At this point, we did another intraoperative ICG angiogram. This angiogram showed a very nice flow through the PICA, complete obliteration of the aneurysm, and patency of the VA.
06:15–06:34: The handled segment of the VA was covered with papaverine-soaked gelfoam and cranial nerves were protected. Gelfoam was placed distally as well. After ensuring hemostasis by application of surgical over the removed flocculus, the wound was closed and the craniotomy flap was placed back.
06:35–06:55: The patient was extubated the next morning without any neurological deficits. She had mild ataxia, which resolved in 2 days. She was completely asymptomatic at 4 months follow-up, and she was doing well at 4 months follow-up. The postoperative CT shows the angle of attack we obtained by removing the extra bone lateral to the craniotomy exposure and the aneurysm was totally clipped.
06:55–07:20: In conclusion, a careful study of preoperative imaging is very important to detect high-riding VA-PICA based on certain criteria such as elongation of VA, the vertical height from the FM rim, and relationship with IAM. As we have shown, these aneurysms are best clipped through a modified retromastoid approach because FLA will give an oblique trajectory and we can use the GCT.
07:20–07:24: These are my references. Thank you for listening.
The patient was extubated on the table after surgery. She regained full consciousness and there were no neurological deficits, including the LCNs. She had transient ataxia for 2 days, which improved completely. She is doing well at 4 months follow-up.
VA-PICA junction aneurysms in the setting of a normal PICA origin generally lie anterior to the brainstem. Therefore, one of the classic skull-based approaches needs to be employed to reach the target while avoiding brain retraction., FLA is generally sufficient in situations where the VBJ is normally positioned. The corridor between the LCNs, labeled as vago-accessory triangle (VAT), is most often utilized., A prominent jugular bulb needs to be ruled out on preoperative imaging as it can hinder dissection and clip application through this approach.
In the setting of a high VBJ or a high-riding VA-PICA junction due to tortuosity of the V4 segment of VA like in our case, FLA provides an inferior to superior viewing angle, potentially creating a blind area distal to the aneurysm when the VA is diving down and deep.
A retromastoid approach is generally employed for cerebellopontine angle tumors. It often requires retraction of the cerebellum and view of the ventral brainstem is inadequate despite cerebellar retraction. For adequate visualization of the ventral brainstem, more aggressive lateral bone removal has been recommended (the so-called extended RMA)., This allows reflection of the sigmoid sinus anteriorly, providing a direct lateral view with better working angles and a reduction in the working distance. In our case, the approach was intermediate, hence the name “modified.” Here, we drilled the FM rim until the retrocondylar fossa, much more laterally than in a conventional retro sigmoid approach, similar to a far lateral exposure. In addition, we drilled the lateral end of the mastoid bone, exposing nearly half of the sigmoid sinus. The very idea was to have a ventral view of the brainstem. We did not perform a more aggressive lateral exposure as we thought it was not necessary and feared the resultant CSF leak-related complications.
That said, it is paramount to open the lateral cerebellomedullary cistern to allow SCF egress that eventually makes the cerebellum very lax. If needed, a ventricular tap through Frazier's point will also help in allowing the cerebellum to relax. The best way to reach the aneurysm is an antegrade tracing of the V4 segment of VA and a retrograde delineation of the PICA, and an aneurysm is usually revealed by triangulating these two arteries. The lower cranial nerves must be carefully dissected and safeguarded using Teflon or gelfoam pledgets. It is imperative to handle the cochlear nerve gently. Moreover, in large to giant aneurysms, tandem clipping is a more effective strategy as the distally applied clip allows one more clip to be applied proximally rather easily than a single direct clip across the neck. The latter has a tendency for the clip to slip back onto the parent artery due to aneurysm turgor.
The PICA is one of the most complex and variable arteries in the posterior circulation. In about 85%–90% of cases, it arises from the V4 segment of the vertebral artery anywhere between 8.6 mm above the FM to within 15 mm of the vertebrobasilar junction. In about 15% of the cases, PICA may arise extradurally from the V3 segment. Therefore, angiographic study is necessary to evaluate not only the course but also the origin of this artery.
VA-PICA aneurysms may arise at the origin of PICA (called pre-PICA) or distally (post-PICA). Pre-PICA aneurysms are located either in front or anterolateral to the brainstem (pontomedullary junction), while post-PICA aneurysms are located either on the lateral aspect of the brainstem or posterior to it. Therefore, the location of the aneurysm determines the surgical approach. Generally, FLA is preferred in aneurysms located anterior or anterolateral to the brainstem while more lateral aneurysms can be dealt with using a retromastoid approach., Those aneurysms that arise from the distal PICA can be safely clipped using a midline suboccipital approach. In pre-PICA aneurysms, the aneurysm and the parent artery are often covered by the rootlets of the lower cranial nerves. Therefore, one has to work through the various corridors between these nerves, through the different triangles. The vagal-accessory triangle (VAT) is most commonly utilized within which there are three triangles, namely suprahypoglossal, infrahypoglossal, and hypoglossal triangles, to work through., Needless to say, careful handling of these nerves is as important as securing the aneurysm.
A high-riding VA-PICA junction aneurysm is a special surgical scenario. Such a situation arises when the VA harboring the aneurysm has an elongated and curvy course before diving down to join its fellow from the opposite side forming the VBJ., The VA-PICA junction in this situation is usually located at the peak of the VA curve, possibly from an altered hemodynamic shear stress; an aneurysm here typically projects at the level of the IAM. Recently, Zhao et al. described these aneurysms and defined two diagnostic criteria for their recognition, namely the vertical height of the aneurysm fundus from FM rim ≥23 mm and a vertical height from the dural entry of the VA to the neck of the aneurysm ≥30 mm. So, how is this high-riding VA surgically relevant? First, a FLA to the usual VA-PICA junction aneurysm will expose the pontomedullary junction mainly. This means that we will have to look up from an inferior to superior direction. Second, as the VA beyond the aneurysm is diving deep to form the VBJ, the distal end of the clip may not secure the aneurysm completely or that step may not be under a direct vision. Therefore, surgical difficulty, sub-optimal viewing and working angles, and potential catastrophes are more likely with FLA. By contrast, a retromastoid craniotomy with a more lateral bony exposure provides a direct lateral view of the aneurysm in a horizontal plane. Moreover, at this height, one may utilize a more capacious glossopharyngeal-cochlear triangle (GCT) for both proximal control and aneurysm clipping. In addition, the MRMA is simpler and more comfortable for neurosurgeons.
A careful study of preoperative radiology is essential to recognize a high-riding VA-PICA aneurysm. The VA must be inspected for an abnormal curve and elongation of the V4 segment, vertical height from the FM rim, and relationship with IAM. If present, a high-riding VA-PICA junction aneurysm is best clipped using a simpler modified retrosigmoid approach through the GCT.
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