Endoscopic skull base surgery

Endoscopic Skull Base Surgery: The Manchester Group

Presenter: Raj Bhalla, Omar Pathmanaban.

We’re going to talk to you about skull base surgery, particularly endoscopic skull base surgery. We run a number of courses, meetings and conferences in Manchester, and this is our list of supporters -disclosure-.

The orbit and the sinonasal cavity -as you’ve heard from Simon’s presentation but also Ben and Suzanne’s- is very amenable to access, particularly medial orbit. Ben showed you that other parts of the orbit are very accessible with the endoscope, but with our combined approach, we feel that we’re much better able to address not only orbital pathology but also pathology further back at the orbital apex and into the optic canal and optic sheaths themselves.

‘Why we feel it’s beneficial and minimally invasive surgery?’ There is nasal morbidity and that nasal morbidity does take some management and some care postoperatively, but very positively; we’re avoiding access scars on the face, less in the way of brain retraction, subtle issues with memory and long-term function -if you look for them you’ll find them-. The endoscopic corridors can avoid crossing major neurovascular boundaries for tumours placed favourably, but also earlier control of tumour feeding vessels, to be able to devascularise tumours quite early in the operative process. ‘The downside?’ it takes longer to do, it’s a partnership; you’re working with three or four hands depending on where tumours are and how complex they are to get. Also, there can be issues with loss of olfaction and now that we’re doing more of this surgery, this is certainly much more on our radar. They’re managing CSF leaks, and the learning curve that does come with this is usually with reconstruction.

Just a coronal CT scan and showing paranasal sinuses, the ethmoid sinuses sitting between the two orbits, and that -as you’ve seen from Ben’s work- really is our corridor to the medial orbit but then further back in the sinuses. Looking at this patient’s left side, we’ve already seen the medial orbital wall exposed on earlier presentations with a large maxillary antrostomy, ethmoidectomy, sphenoidotomy, the middle turbinate, giving excellent access to the medial orbits. The anterior ethmoidal artery to control bleeding, but also further back at the orbital apex in the sphenoid sinus, a very positive and favourable access, and just removing a little bit more bone, as well as the lamina papyracea further back. This is just a uninarial approach, but exposing the optic sheath on a single side, giving access and decompression along the whole medial wall of that orbit and optic nerve. And then just extrapolating and taking that slightly further, a bilateral approach.

This is now binarial also two nostril approach, two surgeons with suction, endoscope, drill, other retracting type instruments but with a wide sphenoidotomy on the right and the wide sphenoidotomy on the left and the back part of the nasal septum removed, really can get very excellent access to both optic sheaths and the skull base in that region. This approach is very favourable for tumours -such as a transosseous transcranial tumour- rather than just a medial orbit and optic nerve sheath decompression. With this approach, we really can start to decompress the optic sheath and optic nerve more like 270 degrees rather than a traditional medial 180 degree decompression. By modifying techniques, working together, we’re able to take that surgery further.

Looking at endoscopic skull base surgery, the most established pathology really is pituitary, and that’s not to say that ‘the endoscope is always better than the microscope’, that those debates go on and on. The truth is there is no difference for a number of tumours, but the real benefit is for when you’ve got significant suprasellar extent and you can use angled optics. The other interesting thing is with regards to the orbit and how we’re now being able to manage things more aggressively, which we might have shied away from in the past.

This is sort of bucking the trend because by a large intracranial pathology which is benign, there has been a switch towards a much more conservative approach. But the endoscope has allowed us, because it is safe and effective from the medial trajectory, to actually be more aggressive with some of the lesions where it’s required. And that’s true not in this case, but certainly when you have a pituitary lesion extending into the cavernous sinus, where previously you certainly wouldn’t want to go into the cavernous sinus from the lateral side. We know that from surgery done in the 80s and 90s, where a lot of mobility was produced by damaging the nerves on that lateral side of the cavernous sinus, we can very safely go into the medial compartments of the cavernous sinus with an endoscope with good visualization and good control.

Slightly more controversial still than pituitary, which is well established as an endoscopic pathology, is meningiomas. There are many neurosurgeons who would still consider meningioma to be an intracranial disease, which should be treated only with transcranial approaches. There is more than one way to skin a cat, and I’m not going to preach that this is the only way to do it, but I think there are certain advantages for certain tumours when they’re selected appropriately.

In this case for instance, this is a suprasellar meningioma with some calcification within it, presented with visual failure and rapidly down to counting fingers only. The beautiful thing about approaching this via with an endoscope, if you’ve got the confidence of your team -that you are not going to have lots of problems fallout from CSF leaks and so, because you’ve got your partnership working well in terms of reconstruction-, is that actually you’re not having to cross any boundaries. You’re going directly onto the tumour, you’re able to bring the tumour away from the important structures rather than having to work around and blind-sighted by them.

This is just another one illustrating that often when the tumour is extending into the medial inferior optic canal. It’s really favourable to do this for an endoscopic approach, which actually is quite difficult to do from a transcranial approach, and runs a risk of damaging the nerve and its vascular supply when you do try to do it that way. This is a suprasellar meningioma being removed and you can see the optic nerve coming into view there and how distorted it is and it’s not surprising that the vision is being dramatically affected.

One of the nice things from this approach, is that you can often pick up an arachnoid membrane around it, and you’ll see vessels that you simply don’t see from the transcranial approach coming from the superior hypophyseal vessels, which come in a sort of arcade, a very fine network of vessels which are important for vision. You can see some of those vessels coming onto the nerve, which is easy to preserve when you come from this trajectory, as opposed to being working from the other side and looking round with a dissector and perhaps not seeing them when you’re dissecting. Certainly we’ve seen some really stunning visual outcomes from people with very badly effected vision, particularly when it’s done early with this approach. You can get good outcomes of the transcranial approach, but certainly in my hands, I’ve seen some spectacular results this way -which I haven’t seen to the same extent with open approaches-.

Craniopharyngioma is another interesting point and it brings up again this point about how the endoscope has bucked the trend of conservatism to some degree. There is a constant pendulum and concern, as lots of articles written on it over decades with craniopharyngioma, of having damage to the hypothalamus, which can cause absolutely horrific morbidity, therefore we have moved towards a more conservative management. The problem with that is, particularly in young people, that actually they do an accrued number of procedures over their lifetime, which each one of those procedures has its own morbidity. Perhaps, as we’re now starting to collect more data, we may not have done them as much of a favour as we thought we had, and in terms of hypothalamic outcomes, it’s yet to be proven that a safe maximal resection is worse than a more conservative approach. Although that would still be what most people would say.

To the endoscope, because it gives you a very clear view directly onto the structures -and allows you to pick up the pituitary stalk and the optic apparatus early- has allowed us to be a little bit more aggressive with these tumours safely, and then to pick up planes with the hypothalamus, which you again struggle to see clearly via most of the transcranial approaches. Here you can see the pituitary stalk, nicely demonstrated there coming off the top of the gland and therefore the pituitary stalk -actually, contrary to what people would say in terms of it being at more risk- is nicely visualised in this approach. There is however, an increased chance of getting endocrinopathy after this approach versus a transcranial approach. I think partly that is because you can see in those cases, when it’s arising out of the stalk, it’s difficult not to continue resecting the tumour out, not for when you don’t see it quite as clearly if you would be happier to have a substance. It’s something to keep in mind when doing that surgery.

For the retrochiasmatic craniopharyngiomas, this is passing underneath the chiasm, now you get a very nice view once you’ve taken them out, going up into the lateral ventricles, and down there to the basilar apex, picking up the CNIII nerves which are coming out down there. It is a spectacular view, which you’re not afforded by any other approach for this type of tumour, and I think particularly for the retrochiasmatic craniopharyngiomas, there isn’t a better approach than the endoscopic approach for these cases.

Clival chordomas and chondrosarcomas, these are one of the last bastions of aggressive cranial surgery because you need to be, because if you’re not, then it is a fatal disease, and you need to get maximal clearance of the brainstem in order to allow proton beam therapy. We work very closely in our multidisciplinary team with our proton radiotherapist Gill and she will tell us what is and what isn’t acceptable, and therefore we can define our risk boundaries at the time of surgery and how far we’re going to push it.

But the endoscope will allow us to get all the way down through the nose, the level of CII, the craniocervical junction without any difficulty in most cases, and all the way up to the posterior clinoids and beyond if we need to take this kind of tumour out. It really allows you a direct trajectory onto these tumours without needing to cross major neurovascular boundaries, and therefore potentially put them at risk. It also avoids the transoral approach in most cases and some of the morbidity that you can get from the oral pharyngeal problems, including CSF leaks which are greater than with the transnasal approaches. Although it needs to be combined sometimes in some cases. This is looking out all the way into the CP angle in an extra dural chordoma, that went all the way out and you can get all the way out to the IAM, you can even drill tumour out into the anterior porus if it’s there using angled instruments.

Ben alluded to the nasal septal flap in the earlier presentation, so that really is a workhorse of what we do. It allows Omar to do the sort of extended resections that he’s able to do, because we’re able to plug the skull base defects and avoid subsequent problems with CSF leakage and extended stays in hospital. This is looking in a right nasal passage and just using monopolar cautery to mark out the margins of a pedicled vascularised mucoperiosteum – mucoperichondrium flap, that then it allows us to elevate that flap in a subperichondrium plane. There we’ve got three layers: mucosa of the right nostril, perichondrium, and lining cartilage. Getting into this plane underneath the perichondrium, we can hinging that flap on the nasal septal artery -that’s a branch of the sphenopalatine artery, coming off the external carotid system-.

The nasal septal flap has revolutionised what we’ve been able to achieve, in terms of transnasal expanded endoscopic approaches. Then during surgery, that flap is stored either in the nasopharynx or in the maxillary sinus -just depending on where we’re working- to be used later to reconstruct those skull based defects. We use a multi-layer skull base closure, so autologous grafts are an option, but we’ve moved quite substantially towards allograft material. What you’re looking at here is allograft, human cadaveric fascia lata. It avoids the morbidity of a scar problems with muscle for up to a year after surgery. Certainly in the UK, it’s becoming much more acceptable to use allograft materials. There are some issues abroad certain in Europe and Scotland -I don’t think they’re allowed to use cadaveric materials-, but we found that it has made a big difference to our recovery. In this part, this is an intradural intracranial layer and then the nasal septal flap -that was stored in the nasopharynx- comes to sit on top of that for the final layer of reconstruction.

To summarise our three key points: endoscopic ventral skull base corridor can make many more skull base tumours accessible without crossing to the blind side of cranial nerves and vessels, as Omar alluded to. Brain retraction and nerve retraction, which are key, brain retraction certainly as a subtle sign -but again if you ask your patients and you assess brain function a year, five years after surgery, brain retraction is an issue-. There is quite a substantial learning curve for both of us, but also in the partnership for micro surgical technique in narrow spaces and working, so we’re not conflicting each other but working in sort of harmony, so we can achieve the designated outcomes.
Q & As section

Question 1
Can I ask about your comments about the limits of laterality away from the mid line when dealing with intracranial pathology via endoscopic route?

Answer
That’s an important question. When you’ve got a hammer everything looks like a nail, and I think that’s what we’re trying to avoid. It’s very tempting; once you’ve got over the learning curve to continue to push on the boundaries and we need to do that to some extent, but at the same time doing it sensibly and safely, making sure there isn’t a better way of doing it. If you take for instance the suprasellar meningioma, the classical teaching has been that it’s got to be purely mid line, very little tipping over the internal carotid artery and optic nerve. If it’s not encasing the vessel and nerve, it can be up to even 50% of the tumour mass sitting over the top and if it’s a soft one with suitable imaging characteristics on T2, it’s usually reasonable to do that. But I think the question you’ve always got to ask yourself ‘Is there a better way to do it?’ This sort of surgery has to be done in a setting where you have all available techniques, where it’s discussed with everybody to make sure that you are using the right approach and not just doing it because you can.

Question 2
How is having two consultants in one theatre all the time? Is that something that raises an eyebrow ever?

Answer
It’s a process of evolution, the managers at the outset go nuts if you say that you’re working together, they’re losing 50% productivity, and they just don’t like it. But when you have managed to set up a service and you work collaboratively, and becomes formalised, you’re actually looking at buddying up. It’s not just the two of us, but now with another team, so that we can work even longer and even further. You need to have someone with vision in that sort of management role, but there are plenty of examples now where that sort of collaborative working works. Now we’ve also got the benefit of our lateral skull base program, which has been established for many years, the joint collaborative approach working between neurosurgeons and ENT surgeons has existed. We’re just working much more collaboratively amongst the three teams involved with that part of the anatomy

Question 3
Would you work with orbital surgeons on some of those pathologies?

Answer
Yes, very much. For sphenoid wing meningiomas, we have a very established program in Manchester and Saj is very well involved with that and organised with Scott Rutherford, one of our other numerous surgeons. Along with our head and neck counterpart, it gives us the opportunity to deal with pathologies in a single centre with the best outcomes that we can possibly give to the patient. I can’t really emphasize enough, that the collaborative approach that we have in Manchester has worked so well for our patients.