Low-Flow Combined Vascular Malformation with Limb Overgrowth
- KLIPPEL-TRÉNAUNAY(-WEBER) SYNDROME is a sporadic, congenital, low-flow combined capillary-lymphatic-venous malformation (CLVM) with limb overgrowth. In the ISSVA classification it sits under 'combined' vascular malformations; Klippel-Trénaunay syndrome is defined as CLVM + limb overgrowth. The classic triad is a capillary malformation (port-wine stain), atypical varicosities or venous malformation and limb overgrowth (usually one lower limb). In the Mayo series of 252 patients, capillary malformation was present in 98%, varicosities/venous malformation in 72% and hypertrophy in 67%; the full triad in 63%.
- The cause is a somatic MOSAIC activating mutation of PIK3CA in the malformed tissue (Luks: 19 of 21 KTS patients were somatic mosaic; five mutations accounted for ~80% of cases, and many specimens contained fewer than 10% mutant cells) - so it is not inherited, does not run in families, and belongs to the PIK3CA-related overgrowth spectrum (PROS) together with CLOVES and related disorders.
- The lateral marginal vein of Servelle - a persistent embryonic lateral leg vein - is characteristic, reported in fewer than 20% of patients, and matters because it drives venous hypertension and potentially lethal thromboembolism. Before any varicosity is ablated or stripped, the deep venous system must be confirmed on imaging, because it may be absent or hypoplastic.
- COMPLICATIONS include localised intravascular coagulopathy (LIC) - raised D-dimer, phleboliths, episodic pain, and in severe LIC a falling fibrinogen with bleeding risk; venous thromboembolism (DVT and pulmonary embolism, especially peri-procedural); bleeding from varicosities or visceral involvement (rectal bleeding, haematuria); cellulitis; and orthopaedic sequelae - limb-length discrepancy, macrodactyly, angular deformity, scoliosis and gait disturbance.
- ORTHOPAEDIC workload is real: of 410 Mayo KTS patients, 64% required orthopaedic evaluation; of those, 84% had limb-length discrepancy, and half underwent surgery, most commonly (62%) for limb-length discrepancy. The clearest surgical indication is a projected limb-length discrepancy exceeding ~2 cm at skeletal maturity, treated with epiphysiodesis in the growing child.
- MANAGEMENT is conservative first: graded compression garments are the hallmark, with surveillance. Symptomatic venous elements are treated by sclerotherapy, endovenous thermal ablation or surgery (including ablation of a significant lateral marginal vein to reduce thromboembolic risk); sirolimus (mTOR inhibitor) has phase-II evidence in complicated vascular anomalies, and alpelisib (PI3K inhibitor) is licensed for PROS from age two years. Peri-procedural thromboprophylaxis is essential.
- “KTW = low-flow combined CLVM + limb overgrowth; NOT an AVM, NOT inherited (somatic mosaic PIK3CA, PROS).
- “Triad: port-wine stain (98%), atypical/lateral varicosities (72%), limb overgrowth (67%); full triad 63% (Mayo 252).
- “Lateral marginal vein of Servelle (<20%) - venous hypertension + thromboembolism; confirm the deep system before any venous intervention.
- “LIC: raised D-dimer + phleboliths + pain; severe LIC = low fibrinogen = bleeding risk; LMWH treats the pain.
- “Orthopaedics: 84% of referred patients have LLD; epiphysiodesis when projected discrepancy exceeds ~2 cm.
- “Parkes-Weber = high-flow AVM (bruit, thrill, warmth, high-output failure) - the critical distinction.
Overview, Terminology & Epidemiology
Klippel-Trénaunay syndrome (often written Klippel-Trénaunay-Weber, acknowledging Weber's later descriptions of limb hypertrophy with vascular malformation) is a congenital, sporadic, low-flow combined vascular malformation with limb overgrowth. The defining lesion is a combined capillary-lymphatic-venous malformation (CLVM). Under the International Society for the Study of Vascular Anomalies (ISSVA) classification, Klippel-Trénaunay syndrome is the eponym for CLVM with limb overgrowth: a 'combined' vascular malformation, not a vascular tumour and not an arteriovenous malformation (Wassef 2015).
How rare. It is sporadic and uncommon. A frequently quoted estimate, from the recent case-report literature, is an incidence of about 1 in 100,000. There is no sex or ancestral predilection and no familial recurrence, consistent with a post-zygotic mosaic mechanism.
The eponym problem. Much of the older literature mixed Klippel-Trénaunay syndrome with other overgrowth and high-flow conditions, so modern series use strict criteria: low-flow CLVM plus overgrowth. Some authors argue that patients should be classified by their phenotype, meaning the malformation components and the tissue overgrown, rather than by the eponym at all (Brandigi 2018). For the clinician, the safe habit is to state the malformation type and the ISSVA category, then add the eponym.
The history. Klippel and Trénaunay described the 'naevus variqueux ostéo-hypertrophique' in 1900. Parkes Weber reported limb hypertrophy with vascular malformation in 1907 and described the high-flow arteriovenous variant in 1918, which is the reason the two eponyms must not be fused. These papers predate MEDLINE and carry no PMID; they are listed under References.
Genetics & Pathophysiology: PIK3CA Mosaicism
The mutation. Klippel-Trénaunay syndrome is caused by somatic (post-zygotic) activating mutations of PIK3CA, the catalytic subunit of phosphoinositide 3-kinase, within the malformed tissue. The mutation activates the PI3K/AKT/mTOR growth and angiogenesis pathway in a mosaic patch, producing a segmental lesion: a combined capillary-lymphatic-venous malformation with overgrowth of the affected limb. Because the mutation is mosaic, the condition is sporadic, not inherited (Luks 2015; Mirzaa, GeneReviews).
Finding the mutation. In the Luks series (2015), 19 of 21 patients with Klippel-Trénaunay syndrome (90%) were somatic mosaic for PIK3CA mutations. Across isolated lymphatic malformations and the PIK3CA-overgrowth disorders, five specific PIK3CA mutations accounted for about 80% of cases, and many affected-tissue specimens contained fewer than 10% mutant cells. That is why blood testing is often negative, and detection requires sampling of affected tissue with deep-sequencing techniques able to find low-level mosaicism.
The overgrowth spectrum. Klippel-Trénaunay syndrome sits within the PIK3CA-related overgrowth spectrum (PROS) alongside CLOVES syndrome, fibroadipose vascular anomaly and megalencephaly-capillary malformation. The shared biology has therapeutic consequences: the pathway can be targeted with the PI3K inhibitor alpelisib or, downstream, the mTOR inhibitor sirolimus, both covered under medical therapy.
Clinical Presentation: The Triad and Its Variants
- Frequency
- 246/252 (98%)
- Notes
- Usually on the affected limb; may be geographic
- Frequency
- 182/252 (72%)
- Notes
- Characteristically a LATERAL embryonic vein (lateral marginal vein of Servelle); may be present from childhood
- Frequency
- 170/252 (67%)
- Notes
- Present at birth or emerging in early childhood; progressive through growth
- Frequency
- 159/252 (63%)
- Notes
- 37% had two of the three features - absence of one element does not exclude the diagnosis
- Frequency
- 182/252 (72%)
- Notes
- Embryonic remnants; relevant to thromboembolic risk and to surgical planning
Distribution. Usually one lower limb, though upper-limb, bilateral and truncal involvement occur. The capillary stain may extend onto the trunk, and visceral venous or lymphatic involvement can present with bleeding, set out under the complications.
The lateral marginal vein of Servelle. A persistent embryonic lateral leg vein, reported in fewer than 20% of patients. It produces a lateral varicosity visible from childhood and is clinically important because of venous hypertension and potentially lethal thromboembolic events (Fereydooni & Nassiri 2020). The persistent sciatic vein is the other embryonic remnant encountered.
What overgrows. The overgrowth tracks the malformation and is predominantly soft-tissue enlargement with limb elongation; girth enlargement is soft tissue. In a 17-patient series no patient had true tridimensional bony hypertrophy, and occasional limbs were even undergrown (Brandigi 2018). Length increase is real, in 80% of that series, and it is the length increase that generates limb-length discrepancy. Because the affected limb differs from its opposite side in girth as well as length, assessment records both, and the skin envelope, not just the bone, determines what surgery is safe. In the foot, macrodactyly and toe anomalies occur, including ectrodactyly and syndactyly patterns.
Symptoms beyond appearance. Pain and episodic swelling, often from thrombosis within the low-flow malformation. Lymphoedema, lymphatic leakage (lymphorrhoea) and vesicles, and superficial thrombophlebitis add to the burden, alongside the bleeding, deep vein thrombosis and recurrent cellulitis described with the complications (Asghar 2020; case literature).
Klippel-Trénaunay versus Parkes-Weber: The Critical Distinction
Parkes-Weber syndrome adds a high-flow arteriovenous malformation to capillary staining and overgrowth. Confusing the two leads to wrong imaging, wrong management and missed cardiac risk.
- Klippel-Trénaunay(-Weber)
- LOW-flow combined capillary-lymphatic-venous malformation
- Parkes-Weber syndrome
- Capillary malformation PLUS high-flow arteriovenous malformation/fistulae
- Klippel-Trénaunay(-Weber)
- No bruit, no thrill, no abnormal warmth
- Parkes-Weber syndrome
- Bruit and thrill, warm limb, bounding pulses
- Klippel-Trénaunay(-Weber)
- None from the malformation itself
- Parkes-Weber syndrome
- High-output cardiac failure in significant shunts
- Klippel-Trénaunay(-Weber)
- Lateral marginal vein (Servelle); deep system may be anomalous
- Parkes-Weber syndrome
- Dilated draining veins from shunting
- Klippel-Trénaunay(-Weber)
- PIK3CA mosaic (PROS)
- Parkes-Weber syndrome
- Classically RASA1-related (capillary malformation-AVM spectrum)
- Klippel-Trénaunay(-Weber)
- Compression, sclerotherapy/ablation, epiphysiodesis, sirolimus
- Parkes-Weber syndrome
- AVM embolisation strategies; cardiac monitoring
- Klippel-Trénaunay(-Weber)
- Low-flow; manage conservatively
- Parkes-Weber syndrome
- High-flow - the dangerous one
Both have a capillary stain and an overgrown limb. Feel and listen: Parkes-Weber is warm with a thrill and a bruit (high-flow AVM); Klippel-Trénaunay is not (low-flow CLVM). Duplex ultrasound settles it at the bedside.
Investigation & Imaging
The diagnosis is clinical, because the triad is visible. Imaging characterises the malformation, excludes a high-flow shunt, maps the venous anatomy, including whether a deep venous system is present, and quantifies overgrowth.
Duplex ultrasound is the first-line test. It confirms low-flow venous and lymphatic channels with no arteriovenous shunting, maps the lateral marginal vein, and identifies thrombosis and reflux (Ochoco 2019; Bertino 2019).
MRI with MR venography defines the extent and tissue planes of the capillary-lymphatic-venous malformation, the embryonic veins and deep-system patency, and is the roadmap for any intervention (Bertino 2019). CT venography demonstrates the marginal vein and its drainage where MRI is impractical.
Plain radiographs and scanograms document limb overgrowth and limb-length discrepancy serially, and scanograms or orthoradiographs are used to plan epiphysiodesis. Phleboliths on a plain film are a low-flow-malformation signature.
Blood tests. Three belong in the work-up:
- D-dimer (± fibrinogen) for localised intravascular coagulopathy
- Full blood count for chronic blood loss
- Coagulation profile before any procedure
Genetic testing is not required for the clinical diagnosis. When it is sought, for example before targeted therapy, it is done on affected tissue rather than blood, with deep sequencing for low-level PIK3CA mosaicism.
Management
Compression and surveillance are the treatment for most, and most patients are managed without any operation.
Before any procedure. Localised intravascular coagulopathy and thromboembolic risk shape the preparation for every intervention, vascular or orthopaedic. A D-dimer, with fibrinogen, belongs in the work-up of any child with an extensive limb malformation being considered for surgery, and LIC is corrected or anticoagulated first. Peri-procedural thromboprophylaxis is mandatory, a tourniquet where feasible in open surgery reduces bleeding, and vascular medicine is involved.
Compression. A graded compression garment on the affected limb is the hallmark of conservative management. It controls swelling, venous hypertension and lymphoedema (Gloviczki 2007).
Surveillance runs within a multidisciplinary vascular-anomalies clinic and covers:
- Limb length (scanograms)
- Spine and foot
- Skin and lymphatic complications
- D-dimer
- Psychosocial support
Symptom care. Laser therapy can lighten the capillary stain, and emollients and wound care manage lymphatic vesicles. Analgesia and LMWH treat the pain of localised intravascular coagulopathy.
Complications: Coagulopathy, Thromboembolism, Bleeding, Infection
Localised intravascular coagulopathy complicates large venous malformations - D-dimer is the marker
- Prospective two-centre study of 140 patients with venous malformations with coagulation parameters; MRI in 110.
- 59/140 (42%) had raised D-dimer; 36 of those (61%) had levels above 1.0 microg/mL; six had low fibrinogen.
- Large surface area and palpable phleboliths were independently associated with raised D-dimer on multivariate analysis.
- Severe LIC (raised D-dimer WITH low fibrinogen) clustered in extensive venous malformations of an extremity and carries a high haemorrhage risk; low-molecular-weight heparin treats LIC pain and prevents decompensation to disseminated intravascular coagulation.
Mechanism. Chronic consumption within stagnant low-flow channels raises the D-dimer, produces phleboliths (calcified thrombi, palpable and visible on plain radiographs) and causes episodic pain from local thrombosis.
Severe LIC. When the D-dimer is raised with fibrinogen falling, the risk is serious bleeding, especially with surgery or sclerotherapy. Treat with low-molecular-weight heparin, which also relieves the pain of LIC.
Guidelines, Registries & Global Practice
There is no disease-specific guideline or registry for Klippel-Trénaunay syndrome. Practice is anchored by the ISSVA classification (Wassef 2015), the International Union of Phlebology consensus on venous malformations (Lee 2014 - which covers D-dimer, anticoagulation and the marginal vein within syndrome-based malformations), and large single-centre series (Mayo). Worldwide, care is delivered by multidisciplinary vascular-anomalies teams - paediatrics, dermatology, interventional radiology, vascular surgery/medicine, haematology and orthopaedics - with diagnosis clinical, first-line imaging by duplex ultrasound and MRI, conservative management by compression and surveillance, and interventions reserved for symptoms, coagulopathy and deformity. Access to compression garments, MRI and targeted drugs varies widely; the transferable core everywhere is correct classification, low-flow confirmation, coagulation assessment and limb-length surveillance.
Mnemonics & Memory Aids
CLOVER
Hook:CLOVER: Capillary stain, Lateral vein, Overgrowth, Varicosities (low-flow), Elevated D-dimer, and remember PIK3CA not RASA1 - the high-flow Parkes-Weber mimic.
Historical primary descriptions, all pre-MEDLINE so no PMID exists: Klippel M, Trénaunay P. Du naevus variqueux ostéo-hypertrophique. Archives Générales de Médecine, 1900. Weber FP. Angioma-formation in connection with hypertrophy of limbs and hemi-hypertrophy. Br J Dermatol, 1907. Weber FP. Haemangiectatic hypertrophy of limbs - congenital phlebarteriectasis and so-called congenital varicose veins. Br J Child Dis, 1918.
MCQ Practice Points
- KTW is an ISSVA combined low-flow malformation (CLVM) + limb overgrowth; no arteriovenous shunt; caused by somatic mosaic PIK3CA mutations (PROS) - sporadic, not inherited.
- Triad frequencies (Mayo, n=252): capillary malformation 98%, varicosities 72%, hypertrophy 67%; full triad 63%.
- Lateral marginal vein of Servelle (under 20%) → venous hypertension and potentially lethal thromboembolism; image the deep system before any venous procedure.
- LIC: D-dimer raised (42% in a venous-malformation cohort), phleboliths, pain; severe LIC = low fibrinogen = bleeding risk; treat with LMWH.
- Orthopaedics: LLD in 84% of referred patients; epiphysiodesis when projected discrepancy > ~2 cm; macrodactyly debulking; scoliosis surveillance.
- Parkes-Weber = the high-flow look-alike (bruit, thrill, warmth, high-output failure) - never conflate.
- Sirolimus: partial responses in a phase-II trial; alpelisib licensed for PROS from age 2.
Clinical Decision Scenarios
Practise clinical reasoning and management decisions out loud
“A 9-year-old girl presents with an enlarged right leg since birth, a geographic purple-red stain on the thigh, and prominent varicosities along the lateral leg. The limb is not warm and there is no bruit. What is the diagnosis, how do you classify it, and what is the key differential?”
“An 11-year-old boy with Klippel-Trénaunay syndrome has a 2.3 cm leg-length discrepancy (affected side longer) that is progressing. How would you assess and manage the discrepancy, and what must you check before operating?”
Definition & genetics
- Low-flow combined capillary-lymphatic-venous malformation + limb overgrowth (ISSVA combined malformation)
- Somatic mosaic activating PIK3CA (PI3K/AKT/mTOR); sporadic; PROS; tissue testing, not blood
- Historical: Klippel & Trénaunay 1900; Parkes Weber 1907/1918 (high-flow variant)
Clinical triad (Mayo, n=252)
- Capillary malformation 98%; varicosities/VM 72%; hypertrophy 67%; full triad 63%
- Lateral marginal vein of Servelle (<20%) - venous hypertension, thromboembolism
- Persistent sciatic vein; visceral involvement → GI bleeding, haematuria
Complications
- LIC: D-dimer raised, phleboliths, pain; severe LIC = low fibrinogen → bleeding; LMWH
- VTE/DVT/PE - especially peri-procedural; prophylaxis mandatory; selective IVC filter
- Cellulitis, lymphoedema, lymphorrhoea, bleeding from varicosities
Investigations
- Duplex ultrasound first: low-flow confirmation, marginal vein, thrombosis/reflux
- MRI/MR venography: extent and deep-system patency; scanogram for limb length
- D-dimer ± fibrinogen; FBC; phleboliths on plain film
Management
- Compression garment + surveillance first; laser for the stain; LMWH for LIC
- Sclerotherapy / endovenous ablation of the marginal vein; confirm deep system first
- Epiphysiodesis for projected LLD > ~2 cm; macrodactyly debulking; scoliosis surveillance
- Sirolimus (partial responses, phase II); alpelisib for PROS from age 2
Never confuse
- Parkes-Weber = high-flow AVM: warm, thrill, bruit, high-output cardiac failure
- KTW is low-flow: no bruit, no thrill, no cardiac risk from the malformation
References
- Wassef M, Blei F, Adams D, et al; ISSVA Board and Scientific Committee. Vascular Anomalies Classification: Recommendations From the International Society for the Study of Vascular Anomalies. Pediatrics. 2015;136(1):e203-14. PMID: 26055853.
- Luks VL, Kamitaki N, Vivero MP, et al. Lymphatic and other vascular malformative/overgrowth disorders are caused by somatic mutations in PIK3CA. J Pediatr. 2015;166(4):1048-54.e1-5. PMID: 25681199.
- Mirzaa G, Graham JM Jr, Keppler-Noreuil K. PIK3CA-Related Overgrowth Spectrum. GeneReviews [Internet]. Seattle: University of Washington; 2013 (updated 2023). PMID: 23946963.
- Jacob AG, Driscoll DJ, Shaughnessy WJ, Stanson AW, Clay RP, Gloviczki P. Klippel-Trénaunay syndrome: spectrum and management. Mayo Clin Proc. 1998;73(1):28-36. PMID: 9443675.
- Gloviczki P, Driscoll DJ. Klippel-Trenaunay syndrome: current management. Phlebology. 2007;22(6):291-8. PMID: 18274338.
- Schoch JJ, Nguyen H, Schoch BS, et al. Orthopaedic diagnoses in patients with Klippel-Trenaunay syndrome. J Child Orthop. 2019;13(5):457-462. PMID: 31695812.
- Brandigi E, Torino G, Messina M, et al. Combined capillary-venous-lymphatic malformations without overgrowth in patients with Klippel-Trénaunay syndrome. J Vasc Surg Venous Lymphat Disord. 2018;6(2):230-236. PMID: 29233587.
- Dompmartin A, Acher A, Thibon P, et al. Association of localized intravascular coagulopathy with venous malformations. Arch Dermatol. 2008;144(7):873-7. PMID: 18645138.
- Fereydooni A, Nassiri N. Evaluation and management of the lateral marginal vein in Klippel-Trénaunay and other PIK3CA-related overgrowth syndromes. J Vasc Surg Venous Lymphat Disord. 2020;8(3):482-493. PMID: 32089498.
- John PR. Klippel-Trenaunay Syndrome. Tech Vasc Interv Radiol. 2019;22(4):100634. PMID: 31864529.
- Bertino F, Braithwaite KA, Hawkins CM, et al. Congenital Limb Overgrowth Syndromes Associated with Vascular Anomalies. Radiographics. 2019;39(2):491-515. PMID: 30844349.
- Ochoco GETD, Enriquez CAG, Urgel RJL, Catibog JS. Multimodality imaging approach in a patient with Klippel-Trenaunay syndrome. BMJ Case Rep. 2019;12(8):e228257. PMID: 31434664.
- Adams DM, Trenor CC 3rd, Hammill AM, et al. Efficacy and Safety of Sirolimus in the Treatment of Complicated Vascular Anomalies. Pediatrics. 2016;137(2):e20153257. PMID: 26783326.
- Hammill AM, Wentzel M, Gupta A, et al. Sirolimus for the treatment of complicated vascular anomalies in children. Pediatr Blood Cancer. 2011;57(6):1018-24. PMID: 21445948.
- Lee BB, Baumgartner I, Berlien P, et al. Guideline. Diagnosis and treatment of venous malformations: consensus document of the International Union of Phlebology (IUP), updated 2013. Int Angiol. 2014 (online ahead of print). PMID: 24961611.
- Uller W, Fishman SJ, Alomari AI. Overgrowth syndromes with complex vascular anomalies. Semin Pediatr Surg. 2014;23(4):208-15. PMID: 25241100.
- Kocaman O, Alponat A, Aygün C, et al. Lower gastrointestinal bleeding, hematuria and splenic hemangiomas in Klippel-Trenaunay syndrome: a case report and literature review. Turk J Gastroenterol. 2009;20(1):62-6. PMID: 19330738.
- Asghar F, Aqeel R, Farooque U, Haq A, Taimur M. Presentation and Management of Klippel-Trenaunay Syndrome: A Review of Available Data. Cureus. 2020;12(5):e8023. PMID: 32528762.
- Sikakulya FK, Egesa WI, Kiyaka SM, Anyama P. A neonate with Klippel-Trénaunay syndrome: a case report. J Med Case Rep. 2021;15(1):447. PMID: 34488883.
- Wei SY, Liu YP, Lin DC, Tsai PS. Klippel-Trénaunay syndrome with profound abdominal lymphatic-venous malformation in a three-day-old newborn: a case report and literature review. Front Pediatr. 2024;12:1326909. PMID: 38312923.
Historical primary descriptions, pre-MEDLINE, so no PMID exists: Klippel M, Trénaunay P. Du naevus variqueux ostéo-hypertrophique. Arch Gen Med. 1900;185:641-672. Weber FP. Angioma-formation in connection with hypertrophy of limbs and hemi-hypertrophy. Br J Dermatol. 1907;19:231-235. Weber FP. Haemangiectatic hypertrophy of limbs - congenital phlebarteriectasis and so-called congenital varicose veins. Br J Child Dis. 1918;15:13.