Popliteal Cyst in the Child

Ovid: 5-Minute Orthopaedic Consult

Editors: Frassica, Frank J.; Sponseller, Paul D.; Wilckens, John H.
Title: 5-Minute Orthopaedic Consult, 2nd Edition
> Table of Contents > Popliteal Cyst in the Child

Popliteal Cyst in the Child
Paul D. Sponseller MD
Popliteal cyst is a painless soft-tissue mass in the medial popliteal fossa behind the knee.
  • Most common soft-tissue lesion about the knee in children
  • Affects children 2–14 years old
Incidence decreases after 9 years of age (1,2).
Twice as common in males (2)
Risk Factors
  • Most are isolated cases.
  • Juvenile rheumatoid arthritis
  • Other chronic inflammation of the knee
No Mendelian pattern is known.
  • Likely resulting from weakness in the
    posterior knee joint capsule between the semimembranosus muscle and the
    medial head of the gastrocnemius
  • Rarely related to intra-articular lesions
    Fig. 1. A diagnosis of popliteal cyst in a child may be confirmed by transillumination.
Signs and Symptoms
  • Protrusion between the medial gastrocnemius and semitendinosus muscles
  • Swelling of the medial side of the popliteal space just lateral to the semitendinosus muscle
  • Usually asymptomatic, but can cause discomfort and restrict ROM of knee if excessively enlarged
  • Usually waxes and wanes in size, depending on the child’s activity level
  • Typically present for some time before the child is brought to the physician
Physical Exam
  • Examine the affected lower limb for
    swelling of the medial side of the popliteal space just medial to the
    semimembranosus muscle.
  • Compress the cyst to check for pain.
    • Usually painless
    • The remainder of the knee examination usually is normal.
  • Examine the gait.
    • No limp should be evident.
  • Transilluminate the cyst in a darkened room with a point light source (e.g., strong penlight) (Figs. 1 and 2).
    • With the patient prone, place the light source on the skin next to the area of swelling.
    • If the mass illuminates more strongly and
      evenly than the surrounding fatty tissue, the fluid-filled nature of
      cyst is confirmed, and a diagnosis of solid tumor is excluded.
      Fig. 2. Prone 7-year-old with popliteal cyst. A: External appearance of cyst. B: After transillumination. Note that the cyst picks up light remote from the source in comparison with surrounding tissues.
  • Aspiration is not commonly performed.
  • However, if the cyst is aspirated, the cyst fluid is clear and gelatinous.
    • If the cyst fluid is not clear and
      gelatinous, send the aspirate for the following tests to rule out
      septic arthritis or soft-tissue abscess:
      • Cell count
      • Gram stain
      • Culture
  • Plain-film radiography is optional to rule out bony disorder.
  • Duplex ultrasound and MRI (rarely indicated) characterize a questionable cyst further and rule out malignancy (3).
Pathological Findings
  • Synovial fluid–filled sac in the semimembranosus-gastrocnemius interval
  • Rarely related to intra-articular lesions
Differential Diagnosis
  • Malignant disease
  • Vascular anomaly
  • Soft-tissue abscess


General Measures
  • The patient’s activity may be restricted when the cyst is large.
  • Surgical excision may be necessary if the cyst is symptomatic (rare).
    • The recurrence rate after surgical excision is 20–40% (2).
  • No treatment is required if no intra-articular lesion is present.
    • Left untreated, 70% of cysts disappear spontaneously after months to years (they may wax and wane in size) (3,4).
  • If it is desired to confirm the diagnosis
    and increase the chance of resolution, the cysts may be aspirated with
    a large-bore needle, followed by immobilization for immediate
    • However, the recurrence rate is high.
  • Excision of the cyst through a transverse incision in the posterior popliteal region:
    • May be done as an outpatient procedure
  • Immobilization for several weeks postoperatively
The rate of recurrence of the cyst after surgical treatment is ~20–40% (2).
Patient Monitoring
  • No routine follow-up is needed.
  • Instruct the parent to return if the lesion changes in symptoms or in character.
1. De Greef I, Molenaers G, Fabry G. Popliteal cysts in children: a retrospective study of 62 cases. Acta Orthop Belg 1998;64:180–183.
2. Willis
RB. Sports medicine in the growing child. Overuse injuries. In:
Morrissy RT, Weinstein SL, eds. Lovell and Winter’s Pediatric
Orthopaedics, 6th ed. Philadelphia: Lippincott Williams & Wilkins,
3. De
Maeseneer M, Debaere C, Desprechins B, et al. Popliteal cysts in
children: prevalence, appearance and associated findings at MR imaging.
Pediatr Radiol 1999;29:605–609.
4. Seil R, Rupp S, Jochum P, et al. Prevalence of popliteal cysts in children. A sonographic study and review of the literature. Arch Orthop Trauma Surg 1999;119:73–75.
727.51 Popliteal cyst
Patient Teaching
  • Inform parents about the benign nature of the condition.
  • Explain the similarity of the pathologic process to that of the Baker cyst in adults.
  • Mention the lack of underlying knee disease and the absence of increased synovial fluid production.
Q: Is MRI indicated for a popliteal cyst in a child?
A: Not unless the cyst is atypical and does not transilluminate, or separate symptoms are referable to the knee.

Q: Is follow-up needed?
A: If it is a typical cyst, no follow-up is needed unless symptoms develop.

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