Norman Dott was an Edinburgh-born neurosurgeon who, in 1931, treated an aneurysm on the proximal part of a middle cerebral artery in a patient by wrapping the lesion with crushed muscle. I wish we had the operation notes to read as thats a pretty amazing thing to think of doing. He was also a pioneer in early cerebral angiography using first sodium iodide and X-rays and later radioactive thorium dioxide.
Across the pond, Walter Dandy, performed the first clipping of an intracranial aneurysm in 1937. Dandy also operated on acoustic neuromas as early as 1922 – thats of personal interest since I had surgery for mine in 1999.
Neither came from a medical background and both seemed to rush through medical school as if the whole subject was no harder than kindergarten. They were operating on brains before antibiotics, before blood banks and 20 years in advance of open heart surgery.
The use of operating microscopes in neurosurgery did not become commonplace until mid 1950s.
Two years ago I wrote a post on the arguments for and against screening for intracranial aneurysms in people with ADPKD. This was when both safety and efficacy of a procedure called 3D Time-of-Flight MRI angiography had been demonstrated and because it does not entail use of contrast it was being recommended as the gold standard for screening in asymptomatic people at risk.
You, like me, will be surprised to read that in a survey of French-speaking nephrologists only 22% of them knew about this method of investigation for intracranial aneurysms – that they were French is probably a red herring, it is just where the survey was undertaken. I suppose they will argue that they treat many varieties of kidney pathology and most renal patients don’t have an increased risk for intracranial aneurysms. Few of them recommended systematic screening and most would not repeat a negative angiogram, so I am probably glad I don’t live in France (that and the snails).
Across the Mediterranean, in Egypt we have a proactive group of nephrologists (Arabic speaking one presumes) who have recently undertaken a study to assess the utility of aneurysm screening in young PKD patients. Of 60 asymptomatic patients with ADPKD aged between 12 and 29 they found a prevalence of 5% intracranial aneurysms. The 3 that they detected were all small, less than 3mm diameter and all in the anterior cerebral circulation (most are in PKD). Only one of these young people had a positive family history of intracranial aneurysms. [You will recall that they are more likely where there is a family history].
Of course from a doctor’s point of view, knowing that your patient has an aneurysm is to be prepared, you can monitor it over time and intervene when it grows beyond a certain size; but for the patient it must be way more emotive than that – more like “oh ***t!” and a definite preference for sitting absolutely still doing nothing.
So you have an intracranial aneurysm – now what?
Reassure yourself with some facts:
- When they are less than 7mm diameter, then over 5 years only 1 in 10,000 will rupture.
- If it is in the anterior cerebral circulation (and most are in PKD) then it has less risk of rupturing than one in the posterior cerebral circulation.
- It usually takes 10 years of follow-up to notice a change in size, and they don’t tend to rupture when small, they grow first, so that is when you start thinking of surgery.
and if you smoke, then stop!
This isn’t all good stuff though, the flip side is pretty grim and some will need to have closer follow-up. Finnish and Japanese both show higher incidence of rupture. Rupture occurs in 6 -16 out of every 100,00 patients and carries a risk of death or disability between 25 and 50%.
Neurosurgery today would probably be unrecognisable to Dott and Dandy. One neurosurgeon will probably perform more than 200 operations each year, and the procedures such as endovascular coil or stent insertions can be done by radiologists. I am not sure of this all makes it a less scary or more scary place to be! But some of us will end up undergoing neurosurgical procedures, even though the main problem is in the kidneys.
When is surgery the answer?
- Aneurysms larger than 7mm diameter are probably indications for surgery.
- If the wall is irregular or has daughter sacs then this too is usually recommended for treatment.
- When the risk of surgery is lower than the risk of rupture
Surgery can entail clipping the neck of the aneurysm, filling it with minute platinum coils or stenting (keeping patent) the vessel with a small tube. Clipping the aneurysm carries slightly more risk than the alternative of coiling, but does not often need repeating. Increasingly used now is a combination of coiling the aneurysm and inserting a stent in the blood vessel itself to keep the flow going.
The coils are like very very small slinkies (those wire coils that make everyone laugh just by rolling downstairs), not much wider than a human hair. They are fed into the aneurysm through an extremely thin tube that has been inserted at the groin and threaded up into the cranium. The one long coil is then cut as it emerges into the bulging vessel and the smaller coils all squidge up obliterating the aneurysm completely. They are platinum and will not move in an MRI scanner nor set of alarms at the airport. sometimes this procedure has to be repeated if the coils settle and don’t quite fill the whole aneurysm.
Overall, the various surgical procedures carry a 2-3% risk of symptomatic complications – this is operator and centre-dependent.
There are some potential new tools in this field:
- ACE Inhibitors and angiotensin blockers may reduce the risk of rupture – this has been noted in some studies, without necessarily having an effect on blood pressure. Since most of us need antihypertensives then it makes sense to use one of these if possible.
- Doxycycline has shown promise in reducing the incidence of aneurysms in animal models of PKD. This needs a little background as for the most part doxycycline is used as an antibiotic or to prevent malaria. It is, however also an inhibitor of MMPs. MMPs are matrix-metallo-proteinases, or, more simply, they are enzymes that break down collagen and their presence indicates inflammation and repair processes. Developing intracranial aneurysms involve a great deal of remodelling of tissue – there is inflammation with a flood of macrophages and a whole army of cells trying to stopper the potential hole in the dam. But it is an area where too much of this can make things worse. Recently it has been demonstrated that PKD mice with intracranial aneurysms have higher levels of MMP1 than the PKD mice without aneurysms. A similar study in humans had similar promising results. So not only might MMP measurements be an indicator or increased risk but they might also lead to medications that can reduce this risk.
- Other drugs have potential: – TNF-alpha may inhibit formation of aneurysms, and inhibitors of mast cell degranulation are also being investigated.
- Flow diversion is a technique of using tubes within the blood vessel to direct the flow away from the aneurysm, and while it is not under stress from turbulent flow the blood vessel can gradually heal itself in a more healthy manner with proper endothelium that blocks off the neck of the old aneurysm. At the moment this procedure is only licensed for use in very large aneurysms, greater than 10mm and specifically at the bifurcation of the internal carotid artery.
Usually small aneurysms are not indications for surgery. One study specifically looking at PKD patients with small aneurysms did demonstrate 100% success in treating aneurysms less than 3mm. A few people had mild neurological side effects initially but all had resolved by 30 days. On the whole though, surgery is saved for people with large or multiple aneurysms, and possibly for those who live long distances from medical care in who rupture would likely be devastating.
The bottom line is that some 90% of PKD patients who have surgery for intracerebral aneurysms have good clinical outcomes.