Neurologist Help - Medical Contraindication to Diving?

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CPT OZZY

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Location
Ft Bragg
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50 - 99
This post is a bit long, but I want to include all the relevant information:

I'm thinking about OW Certification for my son and His girlfreind, But my son does have a congenital condition that causes me concern.

He is missing 3 of 4 peripheral communicating arteries (P-coms) which help to feed his visual cortex. We discovered this via MRI because his vision would occasionally (a couple of times a year) "grey out" if he stood up too fast.... similar to the lightheadedness one feels occasionally if you stand up too fast (orthostatic hypotension), but instead of dizziness he only experiences diminished vision for 30 seconds or so.

I'm an RN, so I have a bit more access to medical opinions than the average person, but my community hospital has no Neurologist on staff at this time. When this was first discovered a couple of years ago I showed the MRI and radiologist report to a couple of Neurologist aquantainces, and there opinion was that since There is no aneurism, it's just an essentially benign, albeit medically interesting, congenital abnormality (apparently many of us are born missing one P-com, and rarely two, but they didn't know of anyone missing 3 of 4 with essentially unnaffected vision).

My son, was very active in Martial Arts/Taekwondo (2nd degree Black belt, Former US Junior National Champion with several international competative medals), and he HAS scuba-dived before.....we both did a resort dive when he was 11.
He is now in college, and I'm thinking of Certification for him and his girlfreind as a Xmas present (so I don't want to spill the beans to them just yet-which having a Diving specific exam would entail)

I got the application and medical waiver from my LDS and discussed this with the LDS owner / OW instructor. He has no other medical conditions. He didn't feel that it would prevent certification or diving, as long as his Buddy is aware of the condition. He mentioned that Visually impaired persons do get certified, and he has certified handicapped divers.

I cannot think of a reason that an orthostatic / hypotensive event would happen underwater but what advice do you have?

I would appreciate any input from instructors and Especially Physicians

Thanks
 
Orthostatic hypotension can happen after longer immersions. We have seen this several times following 24+ hour cave dives. In fact, there is a study going at the US Navy Experimental Diving Unit now looking at fatigue and orthostatic intolerance following long 8+ hour immersions. So I would have him consider this as he progresses to longer and longer dives.

I can only think of one case report of hypotension following breath holding on ascent (intrathoracic pressure increase), yet one more reason not to skip breathe:
Radermacher, P; Muth, CM; Santak, B; Wenzel, J. A case of breath holding and ascent-induced circulatory hypotension. Undersea Hyperb Med. 1993 Jun;20(2):159-61. RRR ID: 2141

I am not sure what additional inflammatory response there might be to the eye with the limited perfusion adding in decompression stress and would like to hear an opinion from an Opthamologist if one is available?

Other than these possibilities, I see no plausible reason to worry. But hey, I'm not a doc... just a lab rat. :D
 
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I'm quite sure there's no literature to tell us what to do here . . . The intersection of the sets of people who are known to have this anatomy, and people who dive, has got to be extremely tiny!

Looking at it from a theoretical standpoint, I can come up with two potential concerns: One is that high ppO2s are vasoconstrictive, which might argue against deep diving or Nitrox. (But I would imagine he would notice symptoms, and be able to move up in the water column if his vision began to seem impaired.) The other is that volume depletion predisposes to orthostatic events, so the diuresis that comes with immersion might make him more likely to have symptoms on EXIT from the water. That would be manageable with diligent hydration, I would think.

Hopefully, our neurosurgeon friend, shakeybrainsurgeon, will weigh in here.
 
I agree with TS&M's considerations.

Because of what I can (not 100% reliably) recall about PComA branching, in the long term what concerns me more than optic disturbances is the possibility of involvement of thalamic structures. Nothing was mentioned of such a history during a very active lifestyle to date, but this may change as he ages -- IIRC, it's been reported that the caliber of PComA naturally declines with age, although not so of its branches.

I'd like to believe that as long as he and his partners react quickly and safely to warning symptoms (i.e. visual disturbances, lightheadedness), then recreational diving is still manageable and ok for the present. Greater prep and planning, including intervention and evacuation contingencies, would be wise.
 
I agree with TS&M's considerations.

Because of what I can (not 100% reliably) recall about PComA branching, in the long term what concerns me more than optic disturbances is the possibility of involvement of thalamic structures. Nothing was mentioned of such a history during a very active lifestyle to date, but this may change as he ages -- IIRC, it's been reported that the caliber of PComA naturally declines with age, although not so of its branches.

How would Thalamic involment manifest itself clinically?

I really appreciate the input from all so-far
 
I don't understand his anatomy. The circle of Willis has only 2 Pcomms, a right and a left, not 4. The Pcomms connect the anterior circulation (carotid) with the posterior circulation (vertebral) and many people lack one, or both, pcomms without symptoms. I suspect he is missing the pcomms plus something else, like a P1 segment of the posterior cerebral, but then he would likely have only a transient field cut, not blindness.

Are both vertebrals open? If so, and both PCA are OK, he shouldn't need pcomms at a young age.

Without detailed knowledge of his anatomy, it is impossible to assess his risk. Did he have an MRA or MRI? Have the arteries of his neck AND aortic arch been looked at too? Could he be at risk for subclavian steal? Given his symptoms, a high quality MRA of the brain and CT angio of the arch and neck (or MRA) should be done. Can you post the impression on the radiographic report of his brain study? These symptoms may be harmless, but they may not be, particularly as he ages and his arteries become diseased. Note: he better not be a smoker. That would be bad. :shakehead:
 
How would Thalamic involment manifest itself clinically?

I really appreciate the input from all so-far

I was only reflecting on the PComA's having variable branches (IIRC, "thalamoperforating arteries") which are a supply for the posterior hypothalamus, mamillary bodies, subthalamus, and optic tract and chiasm. The former are associated with or related to basic functions such as breathing and pulse rate, arousal (consciousness), and emotions such as fear, anger. The latter optic structures likely relate to shakeybrainsurgeon's "field cut"; a.k.a. "hemianopsia".

As a personal aside, the "circle of Willis" mentioned by shakeybrainsurgeon was a profound epiphany for me long ago. It is a nearly fail-safe artery circuit; a natural "ring topology" in network-speak. Here was a clear and compact example of the body's many adaptations for redundancy, alternatives, and compensation for survival. There's always another resource; another way to carry on.
 
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Technically, an acetazolamide challenge SPECT might hold vital and possibly decisive information on the reactivity of his PCAs.
 
I don't understand his anatomy. The circle of Willis has only 2 Pcomms, a right and a left, not 4. The Pcomms connect the anterior circulation (carotid) with the posterior circulation (vertebral) and many people lack one, or both, pcomms without symptoms. I suspect he is missing the pcomms plus something else, like a P1 segment of the posterior cerebral, but then he would likely have only a transient field cut, not blindness.
I don't have a copy of his MRI/Radiologist report here at home, I will try to get hold of one Monday. Now that you mentioned it I do remember the segment(P1??) being mentioned, perhaps I misremembered - perhaps he is missing 3 of 4 p? segments from the P-Com...would that make more sense? What really stuck in my head was that he was missing "3 of 4 _____, and that was unusual"

This diagnosis came literally days before I deployed (I'm Active duty Military). The civilian Neurologist/neurosurgeon we were referred to wanted to do a diagnostic angiogram (which he said had a 5-10% chance of causing a stroke) and an experimental procedure using an autograft from his scalp to re-supply the underserved area. Both of these procedures sounded way too risky - my son did not want to do them, and I was leaving that week. While I was deployed I showed the radiologist report to a colleague and later to a visiting civilian neurologist and both said that it appeared to be essentially a benign but interesting physiologic variance

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Are both vertebrals open? If so, and both PCA are OK, he shouldn't need pcomms at a young age.
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I believe so, again I'll try to get the radiologist report ASAP

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Without detailed knowledge of his anatomy, it is impossible to assess his risk. Did he have an MRA or MRI? Have the arteries of his neck AND aortic arch been looked at too? Could he be at risk for subclavian steal? Given his symptoms, a high quality MRA of the brain and CT angio of the arch and neck (or MRA) should be done. Can you post the impression on the radiographic report of his brain study? These symptoms may be harmless, but they may not be, particularly as he ages and his arteries become diseased.
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I will try to get the radiologist report to you ASAP

[/QUOTE]Note: he better not be a smoker. That would be bad. :shakehead:[/QUOTE]

Unfortunately he is. I found out he was smoking a few months ago. the goood news is that his girlfreind is also bugging him to quit (and she's the one that REALLY wants to get scuba certified) - I'm going to show him your (above) comments as further ammunition to get him to quit.

I REALLY appreciate your help with this. More to follow

Eric
 
The autograft you speak of is the act of diverting a scalp artery into the brain and hooking it up to an intracranial artery. This was typically done to hook the superficial temporal artery (the big thumping artery in front of your ear) to the middle cerebral artery (the main branch of the carotid in the head). This STA-MCA bypass was intended to prevent strokes in patients with hardened carotids in the neck, but has been largely abandoned due to a 1985 report that found it was, essentially, usless or even worse than useless. (I wrote an article about this sad chapter in brain surgery for Discover magazine about ten years ago...it was sad because the operation was done for 20 years on hundreds of thousands of patients worldwide before someone actually did a large study of the results. The operation was fun and very lucrative and surgeons were not anxious to find out it didn't actually do anything. It is still used on very rare occasions, but the indications for such bypasses are very few.)

In this case, the artery bypass would be from the occipital to the posterior cerebral, about which even less is known. The bypass only has a chance of working if the flow rate in the brain artery is far below normal, otherwise no blood will be shunted and the bypass will clot off. In this case, without a functional blood flow test (like a xenon study), we don't even know if the vascular anomaly here is actually compromising blood flow at all.

In people with STA-MCA bypasses, I should note, scuba would be impossible. These patients were not allowed to wear hats postoperatively, for fear of compressing the scalp artery bypass, let alone a scuba mask strap.
 

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