Baker cyst
Updates to Article Attributes
Baker cysts (or popliteal cysts) are fluid-filled distended synovial-lined bursa arising in the popliteal fossa between the medial head of the gastrocnemius and the semimembranosus tendons via a communication with the knee joint. They are usually located at or below the joint line.
Epidemiology
Two peaks are described at 4-7 years and 35-70 years 7.
Clinical presentation
Baker cysts are most often found incidentally when the knee is imaged for other reasons.
Symptomatic presentation may be acute when rupture occurs, in which case the chief differential diagnosis is deep venous thrombosis. Chronic/subacute presentation can be with a popliteal fossa mass or with pain.
Pathology
Two pathological processes are described 7:
- valve-like connection between the knee joint and the gastrocnemio-semimembranosus bursa, resulting in fluid being squeezed in one direction
- no connection with primary gastrocnemio-semimembranosus bursitis
Associations
- degenerative arthropathy 2
- rheumatoid arthritis
- Charcot joint: involving knee 3
- post-traumatic in athletes 6
Radiographic features
Ultrasound
Normally the first line investigation:
- well-defined cyst with a 'neck' at its deepest extent, extending into the joint space between the semimembranosus tendon and the medial head of the gastrocnemius
- identification of a fluid-filled structure at the posteriomedial knee is suggestive of a popliteal cyst, but identification of the 'neck' between the tendons is necessary for a definitive diagnosis.
- usually anechoic, but may contain internal debris
MRI
Exquisitely outlines the cyst as a high T2 signal content mass extending from the joint space.
Complications
Recognised complications include:
- dissection: cyst usually dissects inferomedially but can occurs proximal, anterior, intermuscular or intramuscular
- rupture: leaking of cyst fluid into the popliteal fossa, between fascial planes and surrounding the hamstrings and medial gastrocnemius muscles; moreover there is oedema of the soft tissue and irregularity of the cyst wall
- compression: of the popliteal vessels and tibial nerve
-
compartment syndrome:
: cancan be either anterior or posterior
Treatment and prognosis
In children they can be common, with most spontaneously resolving by 10-20 months. Aspiration may be undertaken, with steroid injection shown to be beneficial in reducing Baker's cyst size and improved symptoms 5-6, 10. If the symptoms persist and/or the cyst is very large, surgical excision is an option.
Differential diagnosis
On ultrasound consider:
- large parameniscal cyst
- liquified haematoma in popliteal fossa
History and etymology
It was first described by Adams and its intra-articular origin described by Baker 6.
See also
-<p><strong>Baker cysts</strong> (or <strong>popliteal cysts</strong>) are fluid-filled distended synovial-lined <a href="/articles/bursa">bursa</a> arising in the <a title="Popliteal fossa" href="/articles/popliteal-fossa">popliteal fossa</a> between the medial head of the <a href="/articles/gastrocnemius-muscle">gastrocnemius</a> and the <a href="/articles/semimembranosus-muscle">semimembranosus</a> tendons via a communication with the knee joint. They are usually located at or below the joint line.</p><h4>Epidemiology</h4><p>Two peaks are described at 4-7 years and 35-70 years <sup>7</sup>.</p><h4>Clinical presentation</h4><p>Baker cysts are most often found incidentally when the knee is imaged for other reasons.</p><p>Symptomatic presentation may be acute when rupture occurs, in which case the chief differential diagnosis is <a href="/articles/deep-vein-thrombosis">deep venous thrombosis</a>. Chronic/subacute presentation can be with a popliteal fossa mass or with pain.</p><h4>Pathology</h4><p>Two pathological processes are described <sup>7</sup>:</p><ul>- +<p><strong>Baker cysts</strong> (or <strong>popliteal cysts</strong>) are fluid-filled distended synovial-lined <a href="/articles/bursa">bursa</a> arising in the <a href="/articles/popliteal-fossa">popliteal fossa</a> between the medial head of the <a href="/articles/gastrocnemius-muscle">gastrocnemius</a> and the <a href="/articles/semimembranosus-muscle">semimembranosus</a> tendons via a communication with the knee joint. They are usually located at or below the joint line.</p><h4>Epidemiology</h4><p>Two peaks are described at 4-7 years and 35-70 years <sup>7</sup>.</p><h4>Clinical presentation</h4><p>Baker cysts are most often found incidentally when the knee is imaged for other reasons.</p><p>Symptomatic presentation may be acute when rupture occurs, in which case the chief differential diagnosis is <a href="/articles/deep-vein-thrombosis">deep venous thrombosis</a>. Chronic/subacute presentation can be with a popliteal fossa mass or with pain.</p><h4>Pathology</h4><p>Two pathological processes are described <sup>7</sup>:</p><ul>
-</ul><h5>MRI</h5><p>Exquisitely outlines the cyst as a high T2 signal content mass extending from the joint space.</p><h4>Complications</h4><p>Recognised complications include</p><ul>- +</ul><h5>MRI</h5><p>Exquisitely outlines the cyst as a high T2 signal content mass extending from the joint space.</p><h4>Complications</h4><p>Recognised complications include:</p><ul>
-<strong>compartment syndrome</strong>: can be either anterior or posterior</li>- +<strong>compartment syndrome:</strong> can be either anterior or posterior</li>
Image 5 MRI (T2) ( update )
Image 6 Ultrasound (Longitudinal) ( update )
Image 7 MRI (PD FS) ( update )
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