Zebras, not horses: popliteal artery entrapment syndrome

mega mushroom
Adding a vascular surgeon to a hospital is like eating one of these. It turns Mario into Mega Mario. Vascular surgeons turn community hospitals into tertiary care centers.

Recalling the medical school adage, “when you hear hoofbeats, it’s probably horses, not zebras,” it is critical to think about rarities down on the differential list whenever you come across a patient. Vascular diseases suffer from inadvertent obscurantism arising from its absence from medical school curricula such that common disorders like mesenteric ischemia and critical limb threatening ischemia are frequently missed by even experienced medical practitioners. Vascular zebras are even harder to pin down because many experienced vascular specialists practice for years before they encounter, for example, adventitial cystic disease or dysphagia lusoria with a Kommerell’s diverticulum. Even so, real patients have these disorders, and we are all subject to inexperience bias -the feeling that something does not exist until you see it. You may completely miss something staring at you in the face or worse, deny its existence.

The patient is a middle aged man in his 50’s who aside from mild hypertension had no real risk factors. One day, at work, his right leg stopped working. He developed a severe calf cramp and the forefoot was numb and cool. He went to his local hospital and the doctors there appreciated the lack of pulses in the right leg and got a CTA, of which I only had the report which found a right popliteal artery occlusion.

The next morning, as he had signals and was not having rest pain, his doctors discharged the patient on clopidogrel and scheduled for angiography and stenting, per patient. As his debilitating claudication did not go away over the weekend, he came to our emergency room. While he had no rest pain, he did have minimal walking distance before his calf muscles seized up. On exam, his right foot was cool and cyanotic, with intact motor function and sensation. There was a weak monophasic posterior tibial artery signal. Bedside point of care photoplethysmography showed dampened waveforms (below).

Look at the blue line. The waveforms are dampened in the ischemic foot.

Because he did not bring his CT, I repeated the study. I have written extensively on the need to be able to share CTA studies without barriers. After his study, I brought it up on 3D reconstruction software.


It clearly showed a Type II Popliteal Artery Entrapment affecting both legs (CTA images in series above). Stenting it would have failed.  I spoke with the patient about operating the next day. The plan was popliteal artery exploration and thromboendartectomy with myotomy of the congenitally errant medial head of the gastrocnemius muscle. The patient was agreeable and I took him to the operating room for a myotomy and popliteal thrombendarterectomy in the prone position. The medial head of the gastrocnemius muscle went over the  popliteal artery and inserted laterally onto the femur.

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Endofibrosis, cut medial head of gastrocnemius muscle to right of distal clsmp

The artery was opened and while there was fresh clot, the artery showed signs of chronic injury as evidence by endofibrosis which pealed off. Pathology showed to be fibrotic in nature.

04-SP-19-4119 Trichorme stain showing fibrous tissue as green
Trichrome stain showing chronic endofibrosis

The artery was repaired with a pericardial patch and flow restored to the tibials, not all of which were completely patent.

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The patient was discharged after about a week and will be scheduling repair of his contralateral popliteal artery entrapment.

The vascular surgeon has a vital role in a hospital’s medical ecosystem. One time, I heard hospital administrator say that with the advance of endovascular technologies, the vascular surgeon would become an expensive, redundant luxury easily replaced by the overlapping skillset of radiologists, cardiologists, general surgeons, trauma surgeons, cardiac surgeons, nephrologists, neurosurgeons, neurologists, podiatrists, infectious disease, and wound care specialists. When I identify these zebras, these rare diagnoses, I am neither replacing all those aforementioned specialties, nor having special insight unavailable to the uninitiated. I am keeping my eyes open. In a non-smoking, active, otherwise healthy and employed middle aged man with no cardiac history, it is very strange to have isolated popliteal occlusion with otherwise pristine arteries throughout the rest of the CT scan. That is a statistical outlier. People who occlude blood vessels in this fashion usually have more comorbidities, usually are older, and usually have more atherosclerotic disease burden. While not quite like the teenager who presented last year with the same diagnosis (after a month of misdiagnosis and delayed treatment), the cleanliness of the arteries elsewhere in the body was disturbing to me. This puts me on a zebra hunt and not the usual horse roundup.

A hospital needs vascular surgeons in the way that America need the US Marine Corps. Every decade, there is some congressional movement to see how the USMC, which has fighter jets, tanks, planes, aircraft carriers, helicopters, and riflemen, can be phased out because it seems to duplicate the services of the Navy, Air Force, and Army, and every generation a conflict proves these arguments wrong. Individuals who know things broadly and deeply, who can do many things across specialty lines, work from head to toe, and whose specialty is to customize solutions to complex problems is the special quality that is the difference between tertiary hospitals and quaternary hospitals. While these qualities are goals within Vascular Surgery, it is a generalizable goal for anyone working in healthcare. My favorite professor in medical school was Dr. Harold Neu, chair of infectious diseases at P&S. He knew everything and was interested in everything and took every moment in the hospital to increase his knowledge a little more. That’s how and why I diagnosed a case of schistosomiasis earlier this year -the upper abdominal pain was not from a coincidental aortic aneurysm, but the fellow did swim in the Nile.

I texted Dr. Sean Lyden, my former boss and partner at the Cleveland Clinic main campus, if there was any situation where an asymptomatic popliteal entrapment who had gone over 50 years of life without complications could just be watched -it was a question from the patient actually. Dr. Lyden treats popliteal entrapment weekly and maintains a clinic specializing in popliteal artery entrapment (link). One of advantages of working in vascular is that the community is small and highly accessible, and I have a group of living textbooks on speed dial (that term pegs me as antique). There is an active social network of vascular specialists and the SVS maintains SVS Connect (link) for posting and discussing difficult questions. Despite the horrible hour that he received the text (“What’s the matter? Are you in trouble?” he asked) because of the time differences between Abu Dhabi and Cleveland, he answered, “no.” Sorry, Sean, for texting you at 4 in the morning.

When you look for four leaf clovers, and you have never seen one in your life, the moment you find one must be transformative. I have never found one, but I keep my eyes open, lest I trod on one.


The Pain Operations

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Absolute Neutral Position is suprisingly universal

A body floating in space, a fetus in the womb, a dad lounging in his favorite chair, share the feature of weightlessness and represent the absolute neutral position (figure above) of the human which is the position of a relaxed supine quadruped -a dead mouse. Anything else is a stress position, including standing. Repeating motions outside of this relaxed pose or holding those positions away from this absolute neutral for long periods of time is a nidus for injury and pain. That is why most land animals sleep flat on the ground.

The Pain Operations

Operations to relieve pain are often the most gratifying to both patient and surgeon to perform successfully. This circumstance applies to the commonly performed procedures such as spine surgery, endometrial ablations, and varicose vein resections. When the pain is due to a rare set of circumstances, things are not so easy. Typically for rarer pain syndromes, two things need to coincide for the successful operation to happen. First is the patient must suffer while more common and potentially life threatening diseases are ruled out and even treated if these are found. This may take months or years. The second necessary condition is finding a physician who has seen the particular pain syndrome before and understand how to test for it and treat it. That meant the majority of people never get treated, or are shunted into the circle of shame as malingering, drug seeking, and mentally unstable. The opioid epidemic creates double jeopardy for these patients -they can become addicts as their pain is never successfully diagnosed and treated and they get labeled as drug seeking.

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A random list of conditions that cause pain that should be on the mind after the usual things are ruled out. Also, vasculitis, autoimmune disorders, and foreign body reactions

All pain syndromes that can be successfully treated share common features that give you a degree of surety about the diagnosis, but at the end, there is a leap of faith on the part of both patient and practitioner because many of these operations have a failure rate ranging from 5-20 percent. First, the symptoms must be associated with sensory nerves, somatic or visceral. Second, there is a physical mechanism for that nerve to be inflamed from compression, swelling, or irritation that can be accounted for through history, physical examination, and imaging studies. Third, though not a constant, a major nerve trunk will be associated with a blood vessel, typically and artery, that is also affected by compression. Fourth, when swollen veins are the cause of pain, it has to be recognized that at an end stage the organ that the veins drain can also be affected.

The Pain Must Have a Testable Anatomic Basis

The somatic sensory nerves in the periphery are well mapped out and known since even classical times. The described pain should be consistent with a nerve. The best and easiest example is a neuroma that forms in an amputation stump. It triggers pain in its former distribution. It is palpable as a nodular mass. It is visible under ultrasound or cross sectional imaging. And it is easy to turn off temporarily with an injection of lidocaine, either under palpation or image guidance. If you can turn off the nerve and relieve the pain, it is likely that ablating or relieving the nerve of irritation will also relieve the pain. Such is the case in median arcuate ligament syndrome (figure below).Screen Shot 2019-03-03 at 5.34.02 PM.png The celiac plexus is caught under the median arcuate ligament and compressed. It causes a neuropathy that is felt in its visceral sensory distribution and the brain interprets these signals in the typical ways irritation of the stomach is interpreted -as pain, burning, nausea, sensations of bloating, and general malaise. These nerves can be turned off with a celiac plexus block and the effects tested by giving the patient a sandwich. When it works, the patient will say they will have had relief for the first time in years and operation to relieve the ligament compression and ablate the nerve can proceed. Same for many of the diseases listed.

Tight Spaces Impinging Nerves, Arteries, and Veins

Many of the tight spaces involving the nerves have accompanying arteries that are compressed. This results in injury to the artery in the form of intimal hyperplasia, post stenotic dilatation, aneurysm formation, and thromboembolism. Shared tight spaces that cause problems for nerves and arteries have the common features of fixed ligaments, adjacent bones and muscles, inflammation, and motion. These include the thoracic outlet, antecubital fossa, cubital canal, diaphragmatic hiatus at median arcuate ligament, inguinal ligament, popliteal fossa, carpal tunnel, obturator canal, mediastinum, retroperitoneum -basically anywhere nerve, compression, and motion occur. In some instances of median arcuate ligament syndrome, postures and breathing trigger the pain. Holding a child in an arm may trigger pain in neurogenic thoracic outlet. Or sitting while wearing tight jeans may trigger a burning pain in meralgia paresthetica. It is not uncommon to find damaged arteries in median arcuate ligament syndrome, thoracic outlet syndrome, and popliteal entrapment or thrombosed veins in nutcracker syndrome, May-Thurner Syndrome, and Paget-von Schroetter Syndrome. Because nerves are typically difficult to visualize, their compression may only be inferred by testing for compression in their adjacent arteries.

Dilated Veins and Swollen Organs and Visceral Pain

Venous hypertension is most commonly conceived of as varicose and spider veins of the legs and offer a model of pain when applied to other pain caused by venous dissension. The visceral sensory fibers veins and arteries trigger a very intense pain that localizes to the trigger. I have often witnessed this when I manipulate a blood vessel during local anesthesia cases. Visceral pain from swelling has a dull achiness that is localizable to my spider veins after a long day standing like a bruise (below).my spider vein The swelling from varicoceles which I have also had feel nothing less than feeling the aftereffects of getting a kick in the balls -not the immediate sharp pain but imagine about 5 minutes after with the mild nausea, abdominal discomfort and desire not to move too much, and even a little flank pain. Imagine this occurring low in the pelvis with ovarian vein varices in pelvic congestion syndrome. This kind of swollen gonad pain afflicts many women whose pain is so frequently dismissed by male physicians because they have no context -well imagine getting kicked in the balls hard, wait about 5 minutes and that moment stretch it out to whenever you stand for a long period of time (below).

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Actual Slide From Midwest Vascular Surgery Traveling Fellowship talk 2017, Chicago, IL, USA


When a limb is swollen from a thrombosis, the veins hurt and is similar to a bone pain from a fracture or a pulled muscle -that is how the brain processes the pain, but when the muscles and skin get tight from edema, the pain is sharp and dire. This is the same kind for pain from a distended left kidney from nutcracker syndrome or a spleen from a splenic vein thrombosis. These conditions can be modeled and predicted based on history and correct differential and confirmed with proper imaging -always.


Build a theory of the pain based on a testable proposition and set of nerves

That is the final message. These pain syndrome require some imagination and empathy to map and model. Predictive tests then can be performed on physical examination, functional testing, or imaging. Often, the adjacent artery is the only thing that can be reliably visualized and tested, knowing that it is the nerve that is compressed. Turning off the offending nerve with a block and relieving the pain is the most powerful argument for operating. It is building the argument for an operation that requires these objective data, but at the end, it does require some experience and faith. You have to believe in your patient and the science and when they coincide, you have to act.