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Black Toenail: Is It a Bruise, Fungus, or Something More Serious?
You glance down after a long run or a rough day at work and notice it. One toenail has turned dark purple or black.
Medically Reviewed by
Dr. Paul Hanna, DO, RPVI
Board Certified Vascular Surgeon
One swollen leg is easy to blame on a long flight, a hard workout, or a day on your feet. When the swelling keeps showing up in the same leg, and it is the left one, a less familiar cause may be worth discussing with a doctor. May-Thurner syndrome is one of them.
It is a quiet condition. Many people who have it never know, while others first learn about it after a blood clot. In this blog post, we explain what May-Thurner syndrome is, why it tends to affect the left leg, what the symptoms look like, how doctors confirm it, and how treatment is usually approached.
May-Thurner syndrome is a condition where a vein in the pelvis gets squeezed. Cleveland Clinic explains that the right iliac artery, which carries blood to the right leg, presses on the left iliac vein, which carries blood from the left leg back toward the heart. The result is that blood may have a harder time moving up and out of the leg.
You may also see it called iliac vein compression syndrome or Cockett syndrome. The names describe the same basic problem. Some sources write it without the hyphen as May Thurner syndrome, so if you have seen it spelled that way, it is the same condition.
The answer comes down to anatomy. In the pelvis, the right iliac artery crosses over the left iliac vein, and the vein sits just above the spine. The same clinic compares the effect to stepping on a garden hose. Most of the time this crossing causes no trouble, but in some people the squeeze is tight enough to slow blood flow.
Over time, the constant pulse of the artery against the vein wall may irritate it. A peer-reviewed review indexed on PubMed Central describes how this repeated pressure can lead to fibrous changes in the vein, which may narrow it further. That is one reason the problem tends to stay on one side.
Compression of the iliac vein is more common than many people realize. As noted earlier, about 1 in 5 people have some degree of iliac vein compression. Most of them never have symptoms or a formal diagnosis, because the compression alone does not always cause problems.
That detail is important for anyone worried after reading about this condition. Having a pinched vein on a scan is not the same as having a disease that needs treatment. Doctors look at the full picture, including your symptoms, your history, and your imaging, before deciding whether the compression is the likely cause of a problem.
The same clinic also notes that May-Thurner syndrome is slightly more common in women and in adults between 20 and 50. That review reports an average age around 42 among people who are diagnosed, although men can be affected too.
Certain life situations may raise the chance that a squeezed vein turns into a clot. A case report in Annals of Vascular Diseases points to long periods of immobility and pregnancy as times when symptoms may appear in younger women. Other clot risk factors, like surgery, hormone therapy, or a family history of clotting, may also play a part.
May-Thurner syndrome symptoms depend on how tight the squeeze is. The Society for Vascular Surgery explains that mild compression may cause no symptoms at all, moderate compression may bring chronic left leg pain, heaviness, swelling, varicose veins, or skin changes, and severe compression may lead to a clot.
That same clinic lists similar signs on the left side, including a heavy feeling, pain, swelling, skin discoloration, and varicose veins, along with open sores in some people. If one leg often feels tired or heavy, our article on why legs feel heavy can help you sort through common causes.
The most serious complication is deep vein thrombosis, or DVT. A clot in the iliac vein can cause sudden swelling of the whole leg, along with pain, warmth, or a change in skin color. These symptoms need prompt medical attention, and they should not be written off as a sore muscle.
If you want a full list of warning signs, our guide to DVT symptoms in the leg walks through them. You can also read about DVT causes and care on our deep vein thrombosis page. Do not wait if swelling appears suddenly, especially if it comes with pain or redness.
Yes, a clot in a leg vein can break loose and travel to the lungs, which is called a pulmonary embolism. This is an emergency. The same clinic advises calling 911 for new or worsening signs, including sudden chest pain that gets worse when you breathe in, shortness of breath, a racing heartbeat, or coughing up blood.
We cover the topic in more depth in our article on how a blood clot travels from the leg to the lungs. The key point here is simple. If you have leg swelling and you also feel chest pain or trouble breathing, treat it as an emergency and do not wait for an appointment.
Because the compression can last for years, some people develop changes that build slowly. The same review notes that chronic cases can bring pigmentation changes, varicose veins, ongoing leg pain, and recurring skin ulcers. These signs may appear even without a known clot.
Slow changes like these are easy to ignore because they come on gradually. If you have darkened skin near the ankle, a wound that is slow to heal, or veins that look larger over time, ask about it. Our pages on vein disease and venous leg ulcers explain how vein problems can show up in the skin.
Diagnosis starts with your history and a physical exam. Your doctor will ask about which leg is affected, how long it has lasted, and whether you have had clots, pregnancies, or long periods of bed rest. The exam looks for swelling, skin changes, and visible veins.
Then imaging comes in. As noted earlier, the society says the condition is usually found with a pelvic CT scan or MRI, and that a venogram or intravascular ultrasound is sometimes needed. Our overview of vascular imaging explains how ultrasound, CT, MRI, and angiography compare.
Because so many people have some compression, a scan that shows a squeezed vein does not settle the question. The review also states that there are no standardized criteria for diagnosis and that compression alone is not enough. Doctors weigh imaging together with symptoms.
The same review also notes that ultrasound has limits, because the iliac veins sit deep in the pelvis and can be hard to see. A normal ultrasound does not rule out the condition. That is why a vascular specialist may suggest a different test when symptoms point toward the pelvis.
Not every swollen leg is May-Thurner syndrome. Leg swelling can come from heart, kidney, or liver problems, from medicines, from an injury, or from other vein conditions. Heavy legs and swollen ankles on both sides often point somewhere else than a one-sided clot.
When only one leg is larger, doctors look harder at the veins. Our article on one leg being bigger than the other explains what that sign can mean, and our piece on arterial versus venous disease shows how vein problems differ from artery problems. A vascular surgeon can help sort out which applies to you.
Not everyone does. The same society says people with no symptoms usually do not need treatment, people with mild symptoms may only need compression stockings, and people with severe symptoms may need a procedure. Many people live with the condition for years without problems.
If you have mild swelling, your doctor may suggest compression stockings, movement breaks, and regular follow-up. Our guide to compression stockings explains when they help and when they may not be enough. Never start or stop a medical treatment on your own, because the right plan depends on your exam and imaging.
If a clot is found, treatment aims to stop it from growing and to lower the risk of new ones. The clinic mentioned earlier says providers may use blood-thinning medicine, and in some cases clot-dissolving medicine delivered through a catheter. Doctors may also discuss a filter that catches clots before they reach the lungs.
Blood thinners help with the clot, but they do not change the squeeze on the vein. The same case report points out that anticoagulation alone does not treat the underlying compression, which is why some patients are later evaluated for a procedure. Our IVC filter guide explains when filters are used and why they are often removed later.
When symptoms are significant, a stent is the option people hear about most. The society calls placement of a left iliac vein stent the most common procedure, done through small punctures with wires and catheters. The vein is opened with a balloon, and a small mesh tube is placed to help keep it open.
That clinic also lists bypass surgery and surgery to move the artery as other options for selected cases. A May-Thurner syndrome stent is not right for everyone, and no one can promise a result. Our page on angiogram, angioplasty, and stenting explains how these procedures work in general.
Doctors are still learning which patients benefit most. That report notes that recent studies have suggested endovascular treatment as a front-line option, especially after a clot. It is a single case report, so it describes one patient, not a guarantee for others.
That review adds a note of caution. It says stent patency over the long term is a concern in the literature, and that more studies are needed to find the best approach. In plain terms, the decision to place a stent should be made carefully, with a specialist who explains the benefits and the unknowns.
Recovery looks different for each person. After an endovascular procedure, patients are usually given instructions about activity, medicines, and follow-up imaging, and the details depend on their health and the procedure performed. Your care team sets the plan, and it can change if your symptoms change.
Follow-up matters because the condition can come back or lead to new problems. Keep your appointments, take prescribed medicine as directed, and report any new swelling, pain, or skin changes. Our team uses a patient’s history and imaging to tailor follow-up, and we explain the reasons behind each step.
You cannot prevent May-Thurner syndrome, because experts do not know exactly why the compression happens. You can support circulation, though. The same clinic’s advice includes avoiding long stretches of sitting, drinking plenty of water, exercising regularly, not smoking, and managing conditions like diabetes and high blood pressure.
On long drives or flights, stand up and walk when you can, and flex your ankles. If a doctor has recommended compression socks, wear them as directed. These habits do not replace medical care, but they can be part of a sensible routine, especially if you already have vein problems.
Make an appointment if one leg is often swollen, heavy, or painful, if you have new varicose veins on one side, or if skin changes or ulcers appear near the ankle. Seek emergency care right away for sudden leg swelling with pain, or for chest pain and trouble breathing.
A vascular surgeon looks at both veins and arteries, so the evaluation can cover the whole picture. If you want to know more about the specialty, read our guide to seeing a vascular surgeon in Miami. You can also explore our full range of care on our vascular surgery page.
Our team starts with a careful history and exam, then uses imaging to look at the veins and decide what is most likely behind your symptoms. We explain the findings in plain language, so you can ask questions and weigh your options.
If you have a swollen left leg, a history of clots, or questions about this condition, call us at 833-735-3668 or reach out through our contact page. Bring a list of your medicines, any past imaging results, and notes on when your symptoms started.
This article is for general education and does not replace medical advice, diagnosis, or treatment. Leg swelling and clots can be serious, and only a medical evaluation can confirm the cause. If you have sudden swelling, chest pain, trouble breathing, or you cough up blood, call 911 right away.
It is a condition where the right iliac artery presses on the left iliac vein in the pelvis, which can make it harder for blood to flow out of the left leg. Many people have no symptoms, but some develop swelling, pain, or blood clots.
The anatomy explains it. The right iliac artery crosses over the left iliac vein, and the vein sits against the spine, so it can get squeezed in between. That is why the left leg is the most common side, though other forms have been described.
Symptoms can include left leg swelling, pain, heaviness, skin color changes, varicose veins, and sometimes ulcers near the ankle. Some people have none. A sudden, severe swelling of the leg may signal a clot and needs urgent medical care.
Doctors combine your history and exam with imaging, such as a pelvic CT scan or MRI, and sometimes a venogram or intravascular ultrasound. Because compression is common, imaging is read alongside your symptoms before a diagnosis is made.
No. People without symptoms usually do not need treatment, and mild symptoms may be managed with compression stockings. A stent is considered mainly for more significant symptoms or after a clot. Your vascular surgeon can explain whether it fits your situation.
It can raise the risk of a leg clot, and a leg clot can travel to the lungs. If you have chest pain, shortness of breath, a racing heartbeat, or you cough up blood, call 911 right away. These are signs of an emergency.
It depends on the person. Many people live for years without problems, while others develop clots or long-term vein changes. The condition is worth taking seriously because of the clot risk, but a diagnosis does not mean something dangerous is happening right now.
May-Thurner Syndrome, Cleveland Clinic
A Guide for Patients: May Thurner Syndrome, Society for Vascular Surgery
Endovascular Management of May-Thurner Syndrome, Annals of Vascular Diseases
Iliac vein compression syndrome: Clinical, imaging and pathologic findings, PubMed Central
Dr. Paul Hanna is a board-certified vascular surgeon with specialized fellowship training in complex vascular interventions and minimally invasive endovascular techniques. He serves as Director of Vascular Surgery and General Surgery at South Florida Multispecialty Medical Group, with over a decade of experience treating vascular conditions affecting the limbs, aorta, and peripheral arterial system.
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