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General practice and family medicine
Ruptured Baker’s cyst presenting with a palpable popliteal mass and crescent sign
  1. Kenya Ie1,2,
  2. Kosuke Ishizuka3,
  3. Takuya Otsuki1,2 and
  4. Chiaki Okuse1,2
  1. 1Division of General Internal Medicine, Department of Internal Medicine, St Marianna University School of Medicine, Kawasaki, Kanagawa, Japan
  2. 2Division of General Internal Medicine, Department of Internal Medicine, Kawasaki Municipal Tama Hospital, Kawasaki, Kanagawa, Japan
  3. 3Department of General Medicine, Yokohama City University School of Medicine Graduate School of Medicine, Yokohama, Kanagawa, Japan
  1. Correspondence to Dr Kosuke Ishizuka; e103007c{at}yokohama-cu.ac.jp

http://dx.doi.org/10.1136/bcr-2023-257869

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    Description

    A patient in his 70s presented to our department with left lower leg swelling and pain. The symptoms began 1 week prior to presentation when he experienced sudden, severe pain in his left lower leg while walking. Subsequently, he became aware of the swelling at the same site as the pain. The patient had visited his primary care physician, who suspected deep vein thrombosis (DVT) and referred him to our department. His medical history included left hemiparesis due to cerebral haemorrhage and left knee osteoarthritis. Physical examination revealed swelling and tenderness in the left lower leg, a subcutaneous palpable mass in the left popliteal fossa and a crescent sign below the left ankle (figure 1). Ultrasonography revealed a Baker’s cyst without tension in the left popliteal fossa and extensive fluid accumulation between the subcutaneous tissue and gastrocnemius fascia of the flexor aspect of the left lower leg, but DVT was ruled out (figure 2). Based on these findings, diagnosis of a ruptured Baker’s cyst was made, and the patient’s symptoms improved after 3 weeks of conservative treatment.

    Figure 1
    Figure 1

    Physical examination revealing swelling and tenderness in the left lower leg and a crescent sign below the left ankle (arrow).

    Figure 2
    Figure 2

    Ultrasonography showing a Baker’s cyst without tension in the left popliteal fossa and fluid accumulation between the subcutaneous tissue and gastrocnemius fascia of the flexor aspect of the left lower leg.

    Baker’s cyst is characterised by an enlargement of the gastrocnemio-semimembranosus bursa in the posterior aspect of the popliteal fossa.1 This condition can remain asymptomatic until it ruptures spontaneously, causing swelling and pain. Its symptoms can resemble DVT; thus, it is referred to as pseudothrombophlebitis.2 Differentiating Baker’s cyst from DVT is crucial as anticoagulation for a ruptured Baker’s cyst can lead to bleeding and compartment syndrome.3 The presence of macular bleeding below the ankle joint, known as the crescent sign, is a characteristic feature of a ruptured Baker’s cyst and aids in distinguishing it from DVT, thrombophlebitis and cellulitis.4 While the crescent sign is not described in DVT patients, highlighting its diagnostic specificity for a ruptured Baker’s cyst, concurrent occurrences with DVT have been reported, emphasising the role of imaging in thorough diagnosis.5

    Ultrasonography serves as a valuable tool for identifying Baker’s cyst, offering a less invasive alternative to modalities such as CT.6 In typical cases, unnecessary radiation exposure associated with CT scans can be avoided through careful history taking, physical examination and the use of ultrasonography.

    Learning points

    • Baker’s cyst is characterised by an enlargement of the gastrocnemio-semimembranosus bursa in the popliteal fossa and can remain asymptomatic until spontaneous rupture causes swelling and pain, mimicking deep vein thrombosis.

    • Macular bleeding below the ankle joint, known as the crescent sign, aids in distinguishing a ruptured Baker’s cyst from deep vein thrombosis, thrombophlebitis and cellulitis.

    • Ultrasonography is a valuable and minimally invasive tool for identifying Baker’s cyst. In combination with careful history taking and physical examination, it avoids unnecessary radiation exposure by alternative imaging investigations.

    Ethics statements

    Patient consent for publication

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    Footnotes

    • Contributors The following authors were responsible for drafting of the text, sourcing and editing of clinical images, investigation results, drawing original diagrams and algorithms, and critical revision for important intellectual content: KIe, KIs, TO and CO. The following authors gave final approval of the manuscript: KIe, KIs, TO and CO.

    • Funding The authors have not declared a specific grant for this research from any funding agency in the public, commercial or not-for-profit sectors.

    • Case reports provide a valuable learning resource for the scientific community and can indicate areas of interest for future research. They should not be used in isolation to guide treatment choices or public health policy.

    • Competing interests None declared.

    • Provenance and peer review Not commissioned; externally peer reviewed.