Our current neuro orbital surgical approaches

Our current neuro-orbital surgical approaches
Presenter: Neil Kitchen

Good afternoon, I’m Neil Kitchen, neurosurgeon at the National Hospital Queen Square and I was given title ‘current neuro-orbital surgical approaches’.

I am going to address this issue talking about my experience and input into inner 3rd sphenoid wing and orbital apex meningiomata, where the visual pathways are affected or at risk. Further, I will address intradural microscopic surgery and its role in this condition.

When you think about sphenoid wing or orbital apex meningioma, there are three key aspects which interplay. One is – oncology, ‘what is the tumour doing?’, secondly ‘what’s the vision like?’, and thirdly ‘how does a proptosis affect the patient?’ For the tumour itself, our philosophy is to recommend a neurosurgical excision and/or radiotherapy. If the tumour is progressive, if failing vision predominates, we recommend either an extended trans-sphenoidal endoscopic decompression at the optic canal or neurosurgical decompression followed by via craniotomy. And if proptosis is the main issue, we generally favour orbital decompression by our colleagues at Moorfields.

My current philosophy is that I have largely given up massive single stop resections of hyperostotic bone instead for a more tailored minimally invasive approach agreed within the MDT setting. Why? Well, I think surgery is mostly non curative in this situation and has risk. It often doesn’t help proptosis significantly and the nature of the bony disease is very indolent indeed. The largely benign nature of the tumour, meningiomata are generally speaking benign pathologies, and I often say to trainees that more patients die from the treatment of meningiomata than they do of meningiomata themselves.

These are a couple cases where we our approach was conservative. This is a patient who had purely hyperostosis giving her mild exophthalmos that was dated 2012. This is 2019 vision intact, proptosis the same. This other patient has rather more diffuse disease at the orbital apex: with normal vision but with problems with tearing, requiring minor operations on the nasolacrimal duct. She was also 80 and had a rather extensive convexity meningioma, this was just one end of a very large disease process. This is example where we have recommended a simple canal decompression from below. Again, diffuse disease: you can see on the right side the optic nerve is being compressed within the canal. This patient has combined interosseous and intradural disease, which had progressed with oedema and presented with seizures. Post intracranial surgery and endoscopic decompression of the optic canal and radiotherapy.

‘Where does neurosurgery have a role here?’ Well, one in the pterional approach and two, occasionally a supra-orbital craniotomy and I am going to talk about both these. The pterional craniotomy is an extremely flexible neurosurgical approach to the anterior and middle cranial fossae. It’s an oblique approach, it’s used in a variety of intracranial intradural pathologies, from aneurysms, to AVMs, gliomas and including the almost infinite variety of sphenoid wing meningiomata which we encounter.

Here are a few cases that illustrate the point. This patient presented with a seizure; she had normal vision and this large inner 3rd sphenoid wing meningioma adjacent to the optic apparatus and above the optic canal, without compression of the optic nerve. This other patient again has normal vision and presents with headaches. We used a standard pterional approach to this tumour, resected it we left a small portion of the tumour adjacent to the optic nerve and internal carotid artery as you can see on this picture which was then treated with stereotactic radiosurgery; these are the dots from the radiotherapy machine we were using.

This patient doesn’t have normal vision: she has right-sided visual failure, there’s no compression of the optic nerve within the canal, but had intracranial issues with this soft meningioma on the right side. You can’t see the optic nerve at this point, you can just see it now bottom right of the tumour and again more clearly stretching over the top and behind this tumour.

When it is a straightforward matter to resect via the trans-sylvian approach, we perform the pterional approach. We look at the head of a patient at operation. We do a curvilinear incision in front of the ear and across the forehead, hopefully behind the hairline. We expose the bone by scraping away temporalis and that brings us directly down onto the pterion, which is the junction of the four sutures: the squamous temporal bone, the frontal, parietal, and sphenoid bones. It is necessary to drill burr holes, the way we perform it is just an example of the many ways it can be done: one temporary, one frontally and one actually on the sphenoid wing itself; and then join up the burr holes with the standard craniotomy, both temporally and frontally. Better access is gained by drilling off the skull base, particularly the sphenoid wing down to and beyond the orbital meningeal artery, to reflect the dura more and allow you to drill more bone away. The incision is generally a C-shaped incision.

During the trans-sylvian approach, you encounter first the veins which you need to dissect away carefully and split the fissure. Whether they are outer third or inner third sphenoid wing tumours, is you need visualise the tumour first of all. Only later on indeed right at the end of the operation, quite often you see the optic nerve and internal carotid artery, then you have to dissect the tumour off these, and particularly if they’re being engulfed by the tumour – and that can be technically challenging. The bottom picture shows another issue: the middle cerebral vessels can also be wrapped up within the tumour, but quite often within a cleft of the tumour rather than directly being engulfed by them. This has to be detected off very carefully. But that’s with where the bone is normal, the pterional bone work gets much more difficult with any hyperostosis, which is extremely common in orbital apex meningiomata, it makes it a lot more difficult.

In the following case, on the surgical video we observe a right-sided tumour, a small clinoidal one beyond the right optic nerve. The white structure is the left optic nerve and now I’m trying to dissect tumour in front of the nerve, you can see the carotid artery to the right of my instrument. Now I’m dividing the lacunar ligament over the optic foramen and dividing the dura with a sharp blade. You can see bone there, and then using the high-speed drill to carefully drill over and decompress the optic foramen from above. When the bone is thin enough, a one millimetre Kerrison punch is used to decompress the optic nerve at the canal entrance.

Regarding the orbito-zygomatic (O-Z) approach, essentially it’s the same craniotomy but with osteotomies in the zygomatic arch and into the orbit itself. It’s basically an extended pterional approach, quite popular in North America, but not particularly in the UK where we largely gone back to the simple pterional approach. The pterional approach allows you to drill away the skull base internally from within rather than doing these extended approaches. The O-Z approach is useful it when approach started very deep midline intra-dural structures and became popular and during operations on the midbrain or on the basilar artery, but not so well used now and again it’s much more difficult in the case of hyperostosis for obvious reasons.

This is a case for which we probably would use an O-Z approach, where the bone is not thickened and where there is extensive soft tumour both intracranial, extracranial and intra-orbitally. In contrast, this other case wouldn’t be a great candidate because that huge amount of bone there makes it extremely difficult to do in my experience.

A word about the hyperostosis. Katherine mentioned it earlier; sometimes there meningioma adjacent to pure hyperostosis with no tumour within it. On the left hand picture you actually see meningioma within the trabecular bone. Although a substantial proportion of orbital apex hyperostosis related to meningiomata will have meningioma within it, I don’t that occurs in all of cases.

Briefly, supraorbital craniotomy is a simple orthogonal approach to the upper orbit. You need to be aware of the frontal air sinus: we use a bi-coronal skin incision, reflect the periosteum (so we can repair the sinus if necessary), and then drill away or remove the very thin orbital roof to gain access to the upper orbit. This case is a young man who had a biopsy of this tumour, which was shown to be a Grade III Haemangiopericytoma, or a rather malignant variant of a meningioma. He went on to have en bloc resection here. That’s the early post-operative picture, before having radiotherapy. Five years later he’s disease-free, except that two months ago he came back to the clinic saying he had a lump in his scar. The bright object observed on the MRI has been removed. It was a metastatic tumour from the original orbital tumour.

My three key points are: you need to define the place of neurosurgery within the MDT plan of every individual patient. And working with colleagues in a team is invaluable in these complex cases. From the neurosurgeon involved in this practice, you just got to master the pterional approach. The two common indications for this approach in this situation are intra-dural tumour debulking and intra-dural decompression of the optic nerve.

Q & As section

Question 1
What’s been your main complication in your work with sphenoid wing meningiomata?

Answer
What we worry about is not the nerves actually, it’s the vessels. Thankfully I haven’t avulsed the internal carotid artery at the skull base, but I have damaged and perforated a vessel, leading to a complete stroke. I see this man every every six months in the clinic and in fact his residual disease is progressing but he refuses to have surgery, quite naturally. If that happens it’s a disaster because that was a very large tumour but he’s going to have his stroke now for the next 20 years.

Question 2
Can I just ask you and the other neurosurgeon just to clarify in my own head: Do you talk about an intra-dural approach to decompress the optic nerve? In my experience with colleagues it is largely an extradural approach with a clinoidectomy.

Answer
In the other neurosurgeon’s case, the tumour was intra-dural. It’s only really relevant when the tumour is compressing intra-durally at the optic canal.

Question 3
What about when you leave the hyperostotic bone in. Does that have any implications for the therapy pathway?

Answer
I think Gillian may have a view on that. I think mostly it is included in the radiotherapy field. There has been about half a dozen papers on meningioma related hyperostosis starting with the Al-Mefty paper in 1999, the range of hyperostosis found is quite wide. I mean meningiomata within the hyperostosis is quite wide ranging about 20% to about 70%. Or only my experience tells me that the intraosseous disease tends to be very indolent.

Question 4
How many of these late post-radiotherapy meningiomata do you see? Do you think that they’re more aggressive than anyone who hasn’t had previous radiotherapy?

Answer
In our ‘late-effects’ clinic, we see intracranial meningiomata for patients who’ve had radiotherapy for childhood leukaemias or whatever. They tend to be multiple but not always. All the ones we’ve removed have been grade I meningiomata, and some of them we treat bizarrely with radiotherapy as well. Last week, we had a case who had a single very small intra-dural meningioma. Of course there are patients who survived a terrible illness during their childhood and they’re precious to their parents and family. In the same week we were also referred a patient who had presented with de novo glioblastoma who had had radiotherapy as a child. So one case is completely curative, and then next case is essentially terminal. It can appear anywhere along the radiotherapy track.