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An Atlas of Lumps and Bumps, Part 47: Popliteal Cyst

Alexander K.C. Leung, MD, MBBS, FRCPC, FRCP
Benjamin Barankin, MD, FRCPC
Joseph M. Lam, MD
Kin Fon Leong, MD
Volume 65 - Issue 1 - January 2025

Popliteal Cyst

A popliteal cyst, also known as a Baker cyst or parameniscal cyst, forms when the synovial fluid from the knee joint fills and distends a preexisting gastrocnemius-semimembranosus bursa in the popliteal fossa.1-3

The cyst is called “primary" when there is a valvular connection with the joint cavity, impeding reflux of synovial fluid from the cyst into the joint, and with no knee derangement.1 The vast majority of popliteal cysts found in children and young adults are primary.1,4

In contrast, the cyst is called "secondary" when it communicates freely with the joint cavity and is associated with an intra-articular lesion. Secondary cysts occur mainly in adults.1,5 Trauma is the most important cause.5 Meniscal tears account for at least 75% of these lesions.5,6 Popliteal cysts may also result from knee arthroscopy and knee arthroplasty.7 Other causes of popliteal cysts include osteoarthritis, rheumatoid arthritis, pigmented villonodular synovitis, and infectious arthritis.3,5,8,9

In children, popliteal cysts may occur occasionally in patients with juvenile rheumatoid arthritis and benign joint hypermobility syndrome.1-3

Plain radiographs, ultrasonography, computed tomography (CT), and magnetic resonance imaging (MRI) can be useful in the evaluation of popliteal cysts.1,3,10,11

In adults, popliteal cysts are discovered in up to 38% of patients with MRI performed in the symptomatic knee.11 The peak incidence is between 35 and 70 years of age.9 In the pediatric age group, popliteal cysts are the most common lesion behind the knee.4 (Figure 1). The condition most commonly affect children between 4 and 7 years of age.9 The male to female ratio is approximately 2:1.10

In the pediatric age group, popliteal cysts are the most common lesion behind the knee
Figure 1. In the pediatric age group, popliteal cysts are the most common lesion behind the knee

Primary popliteal cysts are often asymptomatic.4,9 On the other hand, patients with secondary popliteal cysts may complain of localized discomfort, pain, tenderness, stiffness, and reduced range of motion behind the affected knee joint.9,12 The cyst tends to be more evident when the patient is standing with full extension of the knee (Figure 2) and less evident when the knee is flexed at 45 degrees (Foucher sign).9 The cyst is nontender and transilluminates.4

The cyst tends to be more evident when the patient is standing with full extension of the knee
Figure 2. The cyst tends to be more evident when the patient is standing with full extension of the knee

Approximately 18% of popliteal cysts in the adult population may leak or rupture.13 Rupture of a popliteal cyst may result in intense sharp pain in the knee and calf, ecchymosis in the calf, and a sensation that feels like water running down the calf.9,14 Other complications include infection, compression of the surrounding blood vessels (e.g., popliteal artery and popliteal vein), entrapment neuropathy (e.g., peroneal neuropathy, tibial neuropathy), thrombophlebitis, deep vein thrombosis, and venous thromboembolism.9,11,12,15-21

AUTHORS:
Alexander K.C. Leung, MD1,2, Benjamin Barankin, MD3, Joseph M. Lam, MD4, Kin Fon Leong, MD5

AFFILIATIONS:
1Clinical Professor of Pediatrics, the University of Calgary, Calgary, Alberta, Canada
2Pediatric Consultant, the Alberta Children’s Hospital, Calgary, Alberta, Canada
3Dermatologist, Medical Director and Founder, the Toronto Dermatology Centre, Toronto, Ontario, Canada
4Associate Clinical Professor of Pediatrics, Dermatology and Skin Sciences, the University of British Columbia, Vancouver, British Columbia, Canada.
5Pediatric Dermatologist, the Pediatric Institute, Kuala Lumpur General Hospital, Kuala Lumpur, Malaysia

CITATION:
Leung AKC, Barankin B, Lam JM, Leong KF. An Atlas of Lumps and Bumps, Part 47: Popliteal Cyst. Consultant. 2025;65(1):eXX. doi: 

CORRESPONDENCE:
Alexander K. C. Leung, MD, #200, 233 16th Ave NW, Calgary, AB T2M 0H5, Canada (aleung@ucalgary.ca)

EDITOR’S NOTE:
This article is part of a series describing and differentiating dermatologic lumps and bumps. To access previously published articles in the series, visit: https://www.consultant360.com/resource-center/atlas-lumps-and-bumps.

References

  1. Leung AKC. Lumps and bumps in children: Musculoskeletal lesions. Consultant for Pediatricians. 2012;11:15-16.
  2. Herman AM, Marzo JM. Popliteal cysts: a current review. Orthopedics. 2014;37(8):e678-84. doi: 10.3928/01477447-20140728-52.
  3. Neubauer H, Morbach H, Schwarz T, Wirth C, Girschick H, Beer M. Popliteal cysts in paediatric patients: clinical characteristics and imaging features on ultrasound and MRI. Arthritis. 2011;2011:751593. doi: 10.1155/2011/751593.
  4. Harcke HT, Niedzielski A, Thacker MM. Popliteal cysts in children: another look. J Pediatr Orthop B. 2016;25(6):539-42. doi: 10.1097/BPB.0000000000000272.
  5. Lie CW, Ng TP. Arthroscopic treatment of popliteal cyst. Hong Kong Med J. 2011;17(3):180-183.
  6. Artul S, Jabaly-Habib H, Artoul F, Habib G. The association between Baker's cyst and medial meniscal tear in patients with symptomatic knee using ultrasonography. Clin Imaging. 2015;39(4):659-61. doi: 10.1016/j.clinimag.2015.03.003.
  7. Tofte JN, Holte AJ, Noiseux N. Popliteal (Baker's) cysts in the setting of primary knee arthroplasty. Iowa Orthop J. 2017;37:177-180.
  8. Adiyeke L, Bılgın E, Duymus TM, Ketencı İE, Ugurlar M. Giant Baker's cyst associated with rheumatoid arthritis. Case Rep Orthop. 2017;2017:4293104. doi: 10.1155/2017/4293104.
  9. Leib AD, Roshan A, Foris LA, Varacallo M. Baker's cyst. In: StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing; 2021 Jan–. PMID: 28613525.
  10. Alessi S, Depaoli R, Canepari M, Bartolucci F, Zacchino M, Draghi F. Baker's cyst in pediatric patients: Ultrasonographic characteristics. J Ultrasound. 2012;15(1):76-81. doi: 10.1016/j.jus.2011.06.007.
  11. Frush TJ, Noyes FR. Baker's cyst: Diagnostic and surgical considerations. Sports Health. 2015;7(4):359-65. doi: 10.1177/1941738113520130.
  12. Kuntz S, Lejay A, Rouby AF, Georg Y, Thaveau F, Chakfé N. A popliteal cyst responsible for acute lower limb ischemia. Ann Vasc Surg. 2019;60:479.e11-479.e15. doi: 10.1016/j.avsg.2019.03.029.
  13. Serrano S, Ferreira JB, Özçakar L. When "sono-palpation" becomes "sono-explosion": The Baker's cyst report. Am J Phys Med Rehabil. 2020 Oct;99(10):e125. doi: 10.1097/PHM.0000000000001380.
  14. Kano Y, Harada Y. Popliteal ecchymosis in ruptured Baker's cyst. Am J Med. 2020 Nov 2:S0002-9343(20)30926-8. doi: 10.1016/j.amjmed.2020.09.039. Online ahead of print.
  15. Cho H, Kim DR, Lee JJ, et al. Ultrasound-guided treatment of common peroneal neuropathy caused by Baker's cyst: a clinical note - A case report. Anesth Pain Med (Seoul). 2020;15(2):199-204. doi: 10.17085/apm.2020.15.2.199.
  16. Fujiyoshi K, Minami Y, Tojo T, Iwase D, Hirata M, Ako J. Lower limb ischemia due to popliteal artery compression by Baker cyst. J Vasc Surg Cases Innov Tech. 2018;4(2):99-101. doi: 10.1016/j.jvscit.2017.12.011.
  17. Koyama S, Matsuura Y, Ishikawa T, Kitamura K. A Baker cyst accompanied by venous thromboembolism. Intern Med. 2016;55(2):209. doi: 10.2169/internalmedicine.55.5807.
  18. Lee BI, Seo JH, Kim YB, Seo GW. A potential risk factor of total knee arthroplasty: an infected Baker's cyst - a case report. BMC Musculoskelet Disord. 2020;21(1):137. doi: 10.1186/s12891-020-3147-2.
  19. Moyad TF. Massive baker cyst resulting in tibial nerve compression neuropathy secondary to polyethylene wear disease. Am J Orthop (Belle Mead NJ). 2015;44(4):E113-116.
  20. Verbner JM, Pereira-Duarte M, Zicaro JP, Yacuzzi C, Costa-Paz M. Infected Baker's cyst: A new classification, diagnosis and treatment recommendations. J Orthop Case Rep. 2018;8(6):16-23. doi: 10.13107/jocr.2250-0685.1238.
  21. Zeng X, Xie L, Qiu Z, Sun K. Compression neuropathy of common peroneal nerve caused by a popliteal cyst: A case report. Medicine (Baltimore). 2018;97(16):e9922. doi: 10.1097/MD.0000000000009922.