Cystic Lesions About the Knee Workup

Updated: Dec 29, 2018
  • Author: David M Gonzalez, MD, FACS; Chief Editor: Thomas M DeBerardino, MD  more...
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Laboratory Studies

Laboratory studies are dictated by the patient's general condition. If infection is suggested, record vital signs and obtain a complete blood count (CBC) with differential and an erythrocyte sedimentation rate. Any possible undiagnosed medical condition should be investigated using appropriate laboratory and radiographic studies.


Imaging Studies

Obtain plain radiographs, and consider sonograms or any other studies as indicated. MRI is especially useful when evaluating knee cysts. [14, 18, 10, 19] However, ultrasonography is less expensive than MRI and has comparable accuracy in the evaluation of certain pathologic conditions of the knee. [20] See Baker Cyst Imaging.

MRIs may have to include intravenous contrast enhancement because high signal intensity on T2-weighted images does not necessarily mean that a structure is fluid filled.

Necrotic tissue, nerve sheath or myxoid tissue, flowing blood, and pus can all resemble cysts on T2-weighted MRIs. [21] Ultrasonography can also be used to determine if the mass is fluid filled.

Authors of a retrospective study regarding the prevalence of Baker cysts in patients with knee pain recommended that an ultrasound exam of the knee be performed in patients with painful osteoarthritis or evidence of effusion. They assessed the correlation between BC and severity of osteophytes and joint effusion and found that Baker cysts were present in 25.8% (102 of 399) of patients who had ultrasound features of osteoarthritis and joint effusion. [22]

Computed tomography scanning, knee arthrography, tomography, and bone scanning have also been used.


Other Tests

Aspiration of the cystic mass can be useful in some situations, although recurrence of the cyst is common. Bursal cysts that occur secondary to trauma often respond to aspiration and injection of corticosteroids.


Histologic Findings

The cysts are lined with an epithelium. Bursal sacs are lined with a membrane similar to synovium. A Baker cyst is the most common synovial cyst. Adventitial cysts do not have a true epithelial lining or synovial lining and usually have thickened walls. Many meniscal cysts have been shown to have a clear communication with the joint and appear to be lined with synovium.