Hybrid Anterior Clinoidectomy in the Clipping of Paraclinoid Aneurysms: Technique, Utility and Case Illustration
Keywords: Anterior clinoidectomy hybrid, microsurgical clipping, neck control, paraclinoid aneurysm
The paraclinoid segment of the internal carotid artery represents a critical and challenging area. Meticulous surgical exposure of this area is indispensable in certain vascular and neoplastic pathologies of the parasellar area.[1–3] Removal of the anterior clinoid process and deroofing of the optic nerve allow several key advantages in such surgeries by enabling optic nerve mobilization, increasing exposure towards the skull base and exposure of the clinoidal segment of the internal carotid artery (ICA)., It is standard teaching and practice that these steps are carried out intradurally in aneurysm surgery while a purely extradural technique is preferred in tumor surgeries. In this article, we present the surgical technique of a combined extra- and intra-dural clinoidectomy through a video presentation. This hybrid technique has several advantages and may be an extremely useful technique in certain situations.
To demonstrate the surgical technique and clinical utility of combined extra- and intra-dural clinoidectomy in the clipping of dorsal wall paraclinoid ICA aneurysms.
A 51-year-old lady who presented with sudden onset severe holocranial headache seven days prior to admission was admitted under our care. Upon examination, she was conscious and oriented without any neurological signs apart from mild nuchal rigidity.
On the computed tomography (CT) scan, she had a Fischer grade 3 subarachnoid hemorrhage in the right Sylvian fissure. On CT angiogram, she had a broad-based anterolaterally directed aneurysm arising from the dorsal wall of the right ICA. The interior wall of the fundus and the neck of the aneurysm closely abutted the optic strut without any discernible segment of ICA between the aneurysm and the anterior clinoid process [Figure 1].
Due to the possible adherence of the aneurysm dome with the optic strut and a lack of proximal ICA control in the intracranial segment, we planned to carry out an anterior clinoidectomy followed by aneurysm clipping, after having a neck control of the ICA. In this hybrid technique, we planned to disconnect 2 of the 3 connections of the anterior clinoid process (ACP) extradurally (lateral root attached to the lesser wing of the sphenoid and superomedial root connected to the planum sphenoidale, the latter also forming the roof of the bony optic canal) while the optic strut was drilled intradurally along with the removal of the entire ACP, keeping the aneurysm under vision [Figure 2].
The patient was operated under general anesthesia. We positioned the patient supine with the head rotated around 15°–20° to align our viewing trajectory along the sphenoid ridge and eventually the ACP. The head was slightly extended, after having elevated the torso of the patient and leg elevation to ensure optimal venous drainage from the periphery towards the heart. A standard frontotemporal incision was made along the hairline and a pterional craniotomy was created, with a slightly larger frontal exposure than usual. The lower edge of the craniotomy was drilled flush with the anterior skull base to have a better basal view. The sphenoid ridge was drilled until the superior orbital fissure and the frontotemporal dural fold was exposed. However, this dural fold was not opened as we neither intended a complete exposure of the ACP at this point nor wanted to have unnecessary exposure of the cavernous sinus.
A limited orbitotomy was performed on the medial side horizontal part of the superior orbital fissure (SOF) and this bony window was utilized to deroof the optic nerve extradurally (180 degrees) and in the process, remove the anterior root of the ACP. Then the intradural work started with the opening of the Sylvian fissure, visualization of the aneurysms and distal ICA. As though preoperatively, proximal ICA was not seen, being inside the carotid collar. Dura over the optic strut (bone lateral to the optic nerve) and ACP was coagulated and opened. The optic strut was drilled while keeping the ICA with the aneurysm and the optic nerve under direct vision. Afterwards, the ACP was removed. This exposed the clinoidal segment of the ICA, complete exposure of the aneurysm, 3rd cranial nerve and the posterior communicating artery. The aneurysm neck was clipped using a right-angled clip parallel to the ICA. Intraoperative indocyanine green video angiography was used to confirm aneurysm occlusion, parent artery and ICA branches/perforators. After ensuring complete hemostasis, closure ensued. [Figure 3] shows the operative steps.
The patient had an uneventful recovery after surgery. She had transient ptosis which recovered in two weeks' time. At the three-month follow-up, the patient was independent and functional. Postoperative CT showed the extent of bony work and the clip in situ [Figure 4].
Video link: https://youtu.be/5djDhIutmm4
Video timeline with audio transcript
00:11–00:43 - History of the patient with image findings
This was a 51-year-old female who presented with a history of headaches of sudden severe nature seven days prior to admission. Apart from mild nuchal signs, she was neurologically intact at the time of presentation. On cranial CT scan, she had a fisher grade 3 subarachnoid hemorrhage involving the right Sylvian fissure and the adjoining suprasellar cistern. There was a wide-necked aneurysm that was arising from the internal carotid artery (ICA), dorsal wall. It was a sessile aneurysm and it was closely abutting the optic strut.
00:44–1:21 - Surgical strategy
It is apparent from these reconstructed images that adequate exposure of the aneurysm during surgery would necessitate removal of the anterior clinoid process (ACP) and deroofing of the optic nerve. Therefore, we planned the following:
01:26–02:45 – Anatomy of paraclinoid region
The paraclinoid area is an extremely complex area and its anatomy is extremely important for successful surgery in this location. The ACP is attached to the skull base bone through three attachments. It is attached to the lesser wing of the sphenoid. It is attached to the planum sphenoidale which is also called the roof of the optic foramen, and lastly, and most importantly, it is attached to the body of the sphenoid bone by a structure called the optic strut. The optic strut is a structure that lies between the optic nerve and the superior orbital fissure, and this structure is important because just posterior to it lies the ICA. It therefore represents the most critically important of the three attachments of the ACP.
02:10–02:46 - What is a hybrid clinoidectomy?
Normally anterior clinoidectomy is either performed purely extradurally or intradurally, depending on the pathology that we are dealing with. The standard teaching is that, in aneurysm surgery, anterior clinoidectomy is done intradurally whereas is in tumor surgeries, one can do this job entirely extradurally.
Now, what is essentially done in hybrid clinoidectomy is that the detachment with the lesser wing of the sphenoid and the planum sphenoidale. i.e., the anterior root is done extradurally whereas the most critical part, i.e., the optic strut and removal of the entire ACP, after detaching the roots are done intradurally.
02:47–04:27 - Extradural exposure
In this video, the right pterional approach is taken in this patient. The patient was positioned supine with the head elevated above the torso, and the head was fixed on four pins. After a frontotemporal skin incision and elevation of the bone flap, we started, we started by lowering at the lateral edge of the craniotomy, and the SOF was defined after reaching the meningo-orbital band. Thereafter, a limited orbitotomy was performed so that we could have both the epidural as well as the view from the orbital side. Using this plane, bone was removed in piecemeal in order to reach the optic nerve foramen. And while drilling in this area, we encountered one air cell in the area of the planum sphenoidale. It was located above and medial to the optic nerve foramen. Using this opening, the optic nerve was deroofed and with incremental drilling using diamond burr, the optic nerve was deroofed. This process has to be done very carefully because the optic nerve doesn't respond well to the manipulations. By progressive thinning of the bone and with the help of a dissector, the optic nerve was decompressed 180°. After this was done, this was the area of the optic strut. The optic strut was inclined obliquely and it was partially drilled from outside. This opened up the air cell which was packed with betadine soaked gel foam. Thereafter, the dura was opened.
04:27–05:13 - Sylvian fissure dissection with partial aneurysm exposure
The Sylvian fissure was split laterally. The fissure had thick blood clots inside, as was seen on the preoperative imaging. This clot was cleared. As we approached the proximal part of the fissure more clot was encountered. Therefore, we started on the side of the optic nerve. The area of the clot was further explored, and using gentle maneuvers, this clot was removed to expose the ICA, initially the distal segment and then the ICA bifurcation. Using a retrograde technique, we zeroed in on the aneurysm. The aneurysm had a clot over it.
05:14–06:57- Intradural bone drilling
As you can see, it was difficult to see the proximal part of the neck. Therefore, for better exposure, the dura over the ACP and the falciform ligament was coagulated and sharply divided, and the dura was reflected on the aneurysm to act as a protective cover. As we know, the dura extends over the optic nerve as the falciform ligament; therefore this falciform ligament was divided and this maneuver released the optic nerve completely and the area of the optic strut was drilled, in an incremental fashion. As you will realize, the optic strut is very obliquely placed and it goes almost beneath the optic nerve. This orientation is very important because this process can be difficult if one doesn't appreciate this anatomy. As you can see, visualization of the optic strut required the further opening of the optic nerve sheath, and once this was done, the residual part of the optic strut was visualized well and this was drilled. After drilling of the optic strut, the dissector was used to break the remaining cortical attachment. Once there is detachment, the clinoid process starts moving. And it was then removed by manipulating it away from the aneurysm. This exposes the clinoidal cone. This lengthened the ICA and the optic nerve became further free.
06:58–08:07 - Complete exposure of the aneurysm
This allowed us to extend the aneurysm dissection proximally. On the posterior side, the aneurysm was stuck to the interclinoid ligament from where it was freed by using sharp dissection using scissors. This is the area of the carotico oculomotor triangle. This is the proximal ICA, C5 segment. Its exposure was facilitated by the removal of the ACP. The neck of the aneurysm was defined using sharp dissection here, and on the posterior aspect, further sharp dissection was used to expose the aneurysm from all around. This is the remnant of the distal dural ring. On further dissection, we could clearly see that the oculomotor nerve was located in this area. Just close to it was the Posterior communicating artery (p-comm) P-comartery arising from just below the aneurysm. By careful dissection, this area was further cleared.
08:08–08:32 – Pre-clipping ICG
At this point, we did an intraoperative Indocyanine green (ICG) angiography. It showed the distal vessels very well and the filling of the proximal ICA, but the aneurysm did not show much filling; perhaps it was partially thrombosed. On Glow 800 mode, the vessels were seen green and the P-com was seen more clearly here in between the fibrous strands.
08:33–09:14 - Clipping of aneurysm
A right-angled clip was applied parallel to the ICA across the neck and the proximal ICA was defined. The ICG angiogram showed patency of the vessels beneath the aneurysm proximal as well as distal to it and patency of the P-com artery. Glow 800 mode showed this more clearly as the green dye shows the structures more clearly in the background of fibrous strands. Hemostasis was obtained. Dural and skin closure was ensured.
09:15–09:28 - Post status – postoperatively
Postoperatively the patient recovered with mild 3rd nerve paresis on the right side. However, she recovered completely after three months follow-up and she is doing absolutely fine. The postoperative scan shows the extent of bone removal that was done and the clip in situ.
09:29–10:05 - Conclusion
A hybrid clinoidectomy is the third option as far as anterior clinoidectomy is concerned.
And this is particularly useful because the critical part, i.e., the optic strut is drilled under direct vision.
And one can thus minimize the intradural part of the drilling and its drawback. It could be particularly useful in dorsal wall aneurysms and aneurysm which is stuck to the clinoid process or the optic strut, and in certain rare anomalies like the middle clinoid process, the proximal origin of the ophthalmic artery wherein the drilling is better performed under direct vision.
Pearls and pitfalls
Challenges in the clipping of paraclinoid aneurysms include the need to minimize optic nerve handling by allowing its immobilization, expose the aneurysm widely and, if possible, gain a proximal length of ICA intracranially by opening the clinoidal/cavernous segment.,,,,, The last part allows for determination of the true extent of the aneurysm (e.g., transitional aneurysms straddle the distal dural ring, DDR), and application of temporary clip on the clinoidal ICA which is not only anatomically preferable but also avoids a separate neck incision for carotid control in experienced hands. Thus, the value of anterior clinoidectomy and optic nerve deroofing are indispensable in these cases., This technique, however, is not easy to master, given the anatomical location of the ACP, its complicated dural reflections, and the pneumatization in and around it.[6–8] In particular, drilling the optic strut is the most challenging part of this process. There are mainly two techniques of achieving ACP removal: extradural and intradural techniques. In traditional neurosurgery teaching, extradural clinoidectomy is recommended for tumors while intradural clinoidectomy is recommended for paraclinoid aneurysms., It is important to note that the preference of an approach is not evidence-based.
Lawton et al. recently published their technique called anterior clinoidectomy using a two-step hybrid (ACTH) technique. They proposed drawing two lines, called lines A and B, between the beginning of the superior orbital fissure and the optic foramen. Both these lines are assessed extradurally. They propose drilling between lines A and B, which as shown in the cadaveric specimen by them, detaches the lesser sphenoid wing (LSW) and planum sphenoidale (PS) connections, deroofing the optic nerve and leaving only the OS and the body of the ACP. The remaining part of the OS and ACP are drilled intradurally.
The advantages of the hybrid technique can be summarized as follows:
A hybrid clinoidectomy may be a useful technique in paraclinoid aneurysms, particularly those which are stuck to the optic strut or the anterior clinoid process. The same technique may be useful in large clinoidal meningiomas where the tumor mass does not allow for a complete extradural exposure. In this way, one can utilize the advantages of both the techniques of clinoidectomy, and hence maximize their potential in complex cases.
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Conflicts of interest
There are no conflicts of interest.
[Figure 1], [Figure 2], [Figure 3], [Figure 4]