Why Varicose Veins Form: The Leaking Vein Patterns Behind Them
Varicose veins form when the one-way valves in a leg vein fail and blood falls back down the leg under pressure. Which vein has failed matters more than how the surface looks. The great saphenous vein, the small saphenous vein, a side branch, a perforator or a pelvic vein each produce a different pattern, and each needs a different plan.
Two legs with the same bulging veins can hide very different problems underneath. One may have a single leaking valve at the groin; the other may be fed from the pelvis, or from a vein that was treated years ago and has found a new route. This guide explains the five places a leak can start, what each pattern looks like, how a scan tells them apart, and why the pattern decides the order of treatment. For the condition itself, its symptoms and the treatments available, see varicose veins. For one of the symptoms patients ask about most, see varicose veins and leg cramps.
The Five Places a Leak Can Start
Every leg has a deep system of veins inside the muscles and a superficial system just under the skin, joined at junctions and by small connecting veins. Reflux can begin in five places:
The great saphenous vein, running up the inner leg to the groin.
The small saphenous vein, running up the back of the calf to the knee crease.
A side branch (tributary), while the main trunks themselves stay healthy.
A perforator vein, one of the short veins that pass through the muscle to connect deep and superficial systems.
A pelvic vein, where the pressure comes from above the leg altogether.
Many legs have more than one source at once. That is why the visible veins are a poor guide on their own, and why a full map of the leg comes before any treatment plan.
The Great Saphenous Vein: The Commonest Source
The great saphenous vein is the longest vein in the body and the most common source of varicose veins. When the valve where it joins the deep system at the groin fails, blood falls back down the vein, stretching it and its branches. The result is usually varicose veins along the inner thigh, the inner knee and the inner calf.
Reflux may run the whole length of the vein or affect only one segment, with blood entering and leaving the trunk through branches along the way. The difference matters, because treatment closes the leaking segment, not necessarily the whole vein.
When the great saphenous vein is the source, NICE guidance recommends endothermal ablation as the first treatment, ahead of foam sclerotherapy and surgery. Heat from a catheter placed inside the vein, by endovenous laser ablation or radiofrequency, seals the leaking segment from within.
The Small Saphenous Vein: Behind the Calf
The small saphenous vein runs up the back of the calf and usually joins the deep system in the crease behind the knee. When its valves fail, the varicose veins appear on the back and outer side of the calf, and sometimes around the outer ankle.
Two features make this pattern different. The point where the vein joins the deep system varies more from person to person than at the groin, so the scan has to find it precisely. And in the lower calf the vein runs close to a small sensory nerve, which shapes how far down a closure procedure is taken.
When the Main Trunk Is Healthy: Side-Branch Reflux
Varicose veins do not always come from a failing trunk. A study of 860 legs in the European Journal of Vascular and Endovascular Surgery found reflux confined to side branches, with both saphenous trunks working normally, in about 1 in 10 legs. Most of those leaking branches belonged to the great saphenous system, fewer to the small saphenous system, and only a small minority to neither.
This pattern changes the plan entirely. There is no trunk to close, so treatment targets the branches themselves, by removal through tiny incisions or by foam sclerotherapy. Closing a healthy trunk would add risk and nothing else.
Side branches also explain a common picture at the skin. Spider veins and fine thread veins are often fed by a leaking branch just beneath them, which is why surface treatment works better once the feeder is dealt with. For the surface veins themselves, see spider vein treatments compared.
Perforator Veins: Leaks From the Deep System
Perforator veins are short connecting veins that pass through the muscle wall, normally carrying blood inward from the superficial veins to the deep ones. When their valves fail, the calf muscle pump can drive blood outward under high pressure into the skin and the veins beneath it.
Leaking perforators matter most in the lower leg, where they are closely linked with skin damage and ulcers around the ankle. In a leg with simple varicose veins, they are often a secondary finding that improves once the main source is treated. In a leg with skin changes, they are frequently treated in their own right.
Pelvic Veins: When the Source Is Above the Leg
Some varicose veins are fed from the pelvis. The ovarian or internal iliac veins fail, and blood finds its way into the leg through veins around the vulva, the upper inner thigh or the back of the thigh. The pattern is most common in women who have had children.
A study of women with recurrent varicose veins, published in the Journal of Vascular Surgery: Venous and Lymphatic Disorders, found pelvic venous reflux to be a major contributing cause in about a quarter of affected legs, rising to a third in women who had had children and had not had a hysterectomy. The same paper notes that leg varicose veins are linked with pelvic reflux in around 1 in 5 women who have had children.
A standard leg scan shows where reflux enters the leg but not the pelvic veins themselves. When the pattern points to the pelvis, further imaging follows, and the pelvic source is considered before the leg veins are treated, because treating the leg alone tends to fail.
Recurrence: Why Veins Come Back After Treatment
Varicose veins that return after earlier treatment are a pattern of their own. They have recognised causes, and each needs a different answer:
A missed or untreated source, such as a pelvic vein or a second trunk.
New vessel growth at the site of a previous junction operation, known as neovascularisation.
A remnant of the original vein left behind at the junction.
Leaking perforators that were not addressed.
Natural progression, with new veins failing over the years.
A study of 160 patients with recurrent varices after surgery, published in International Angiology, found that about half of recurrences at the groin came from a remaining stump of the great saphenous vein, and that leaking perforators were involved in 44 per cent of cases. Treating recurrence well starts with finding which of these causes is at work, because repeating the original operation rarely fixes it.
Mapping the Pattern: What the Scan Records
The pattern is found with a duplex ultrasound scan, performed standing, because veins empty when the leg is horizontal and reflux can disappear. The scan follows each vein from the groin and the knee crease down to the ankle, recording:
which junctions leak, and for how long blood flows backwards after the calf is squeezed;
whether reflux runs the whole length of a trunk or only a segment;
which side branches and perforators carry reflux, and where they join;
the width of each leaking vein, which affects how it can be treated;
whether the deep veins are open and working;
whether reflux enters the leg from the pelvis or from a previous treatment site.
Both legs are scanned, because they are often affected differently, and a leg without visible varicose veins can still carry reflux.
From Pattern to Plan
The pattern sets the order of treatment. A pelvic source, where present, is considered first. A leaking trunk comes next, closed by heat, by a non-thermal method, or occasionally by surgery. Side branches follow, removed or injected, and surface veins come last. Working from the source outward means each step removes pressure from the next, and fewer veins come back.
For what the long-term trials show about how each treatment performs, see what the long-term trials show. For recovery after each procedure, see recovery after varicose vein treatment.
Choosing a Surgeon for Varicose Veins in Dubai
What should you look for when the plan depends on reading the pattern correctly? Specialist vascular training rather than general surgery or aesthetic medicine. A surgeon who maps the veins personally, since the person who sees where the reflux starts should be the one who plans its treatment. The ability to treat every source, from a trunk to a pelvic feeder to a single branch, so the plan follows the anatomy rather than the one procedure on offer. And experience of recurrent veins, where the original map no longer applies.
Dr. Sohrabi completed full specialist vascular training in the United Kingdom's National Health Service, holds the FRCS in Vascular Surgery and a CCT, and completed an Advanced Endovascular Fellowship at Cleveland Clinic. He performs and interprets his own duplex scans, so the map, the plan and the treatment come from the same surgeon. He offers thermal and non-thermal closure, removal of branches through tiny incisions, foam sclerotherapy and open surgery. He previously served as Clinical Director of Vascular Surgery Services in North Wales, leading ten consultants across three hospitals serving more than 700,000 people, and has published 77 peer-reviewed papers with more than 1,183 citations.
His practice follows NICE guidance and international protocols.
Dr. Soroush Sohrabi is a UK-trained Consultant Vascular and Endovascular Surgeon (FRCS, CCT) practising in Dubai, with a Cleveland Clinic Advanced Endovascular Fellowship and 77 peer-reviewed publications.
Book a consultation to have your veins mapped and the source of the leak identified.
Frequently Asked Questions
Which vein usually causes varicose veins?
The great saphenous vein, which runs up the inner leg to the groin, is the most common source. The small saphenous vein at the back of the calf is the next most common. In some legs the main veins are healthy and the leak starts in a side branch, a perforator or a pelvic vein, which is why a scan is needed to find the true source.
Can varicose veins come from the pelvis?
Yes. In some women, failing ovarian or internal iliac veins send blood into the leg through veins around the vulva, the upper inner thigh or the back of the thigh. The pattern is most common after pregnancy. When the leg scan suggests it, the pelvic veins are imaged and the pelvic source is considered before the leg veins are treated.
Why do I have varicose veins if my main vein is normal?
Reflux can start in a side branch while the saphenous trunks work normally. A study of 860 legs found this pattern in about 1 in 10. In that case the branches are treated directly, by removal or foam injection, and the healthy trunk is left alone.
What is a perforator vein?
A perforator is a short vein that passes through the muscle to connect the superficial veins with the deep ones. Its valves normally let blood flow only inward. When they fail, the calf pump drives blood outward under pressure, which matters most in the lower leg and around skin changes or ulcers.
Why did my varicose veins come back after surgery?
The usual reasons are a source that was missed or not treated, new vessels growing where the original junction was tied, a remnant of the original vein, leaking perforators, or new veins failing over time. A scan identifies which of these applies, and the treatment is chosen to match it rather than repeating the first operation.
Do both legs need scanning if only one has varicose veins?
Usually, yes. The two legs are often affected differently, and a leg with no visible varicose veins can still carry reflux. Scanning both gives a complete picture and avoids a second assessment later.
Key Takeaways
Varicose veins form when valves fail in one of five places: the great saphenous vein, the small saphenous vein, a side branch, a perforator vein or a pelvic vein, and many legs have more than one source.
The great saphenous vein is the most common source of varicose veins, and NICE guidance recommends endothermal ablation as the first treatment when it is the cause.
A study of 860 legs in the European Journal of Vascular and Endovascular Surgery found reflux confined to side branches, with normal saphenous trunks, in about 1 in 10 legs.
A study in the Journal of Vascular Surgery: Venous and Lymphatic Disorders found pelvic venous reflux to be a major contributing cause in about a quarter of legs with recurrent varicose veins in women.
A study of 160 patients in International Angiology found that about half of groin recurrences after surgery came from a remaining stump of the great saphenous vein.
A standing duplex ultrasound scan of both legs maps which junctions, trunks, branches and perforators leak, and the pattern sets the order of treatment from the source outward.
About the Author
Dr. Soroush Sohrabi MD, PhD, FRCS, CCT (UK), PGCert, MCPhleb is a Consultant Vascular and Endovascular Surgeon practising in Dubai. He trained in the United Kingdom and holds a Fellowship of the Royal College of Surgeons (FRCS) in Vascular Surgery and a Certificate of Completion of Training (CCT). He has published 77 peer-reviewed papers with over 1,183 academic citations and is a member of the European Society for Vascular Surgery (ESVS) and the Vascular Society of Great Britain and Ireland (VSGBI). He is licensed by the UK General Medical Council (GMC No. 5207627) and the Dubai Health Authority (DHA No. 48905551).
Medically reviewed by Dr. Soroush Sohrabi MD, PhD, FRCS, CCT, Consultant Vascular and Endovascular Surgeon, October 2026.
References
National Institute for Health and Care Excellence. Varicose veins: diagnosis and management. NICE guideline CG168. https://www.nice.org.uk/guidance/cg168
Labropoulos N, Kang SS, Mansour MA, et al. Primary superficial vein reflux with competent saphenous trunk. European Journal of Vascular and Endovascular Surgery. 1999;18(3):201-206. https://doi.org/10.1053/ejvs.1998.0794
Whiteley AM, Taylor DC, Dos Santos SJ, Whiteley MS. Pelvic venous reflux is a major contributory cause of recurrent varicose veins in more than a quarter of women. Journal of Vascular Surgery: Venous and Lymphatic Disorders. 2014;2(4):411-415. https://doi.org/10.1016/j.jvsv.2014.05.005
Bissacco D, Castronovo EL, Romagnoli S, Domanin M. Recurrent varices after surgery: a clinical and color-Doppler ultrasound scan analysis. International Angiology. 2018;37(2):176-180. https://doi.org/10.23736/S0392-9590.18.03939-1
