Clinical diagnosis
Case 278
【Progress】
The patient returned to local orthopedic clinic with radiological findings.
【Discussion】
There are four kinds of fluid retention on knee joint: intracapsular fluid, synovial cyst, bursitis and ganglion. Articular joint is covered with capsule, composed of synovial cells that secrete fluid to avoid friction and induce smooth motion (1). When capsule injures or inflames, intracapsular fluid increases, called synovitis, capsulitis or arthritis. Synovitis is a synonym as capsulitis which induce joint fluid increase (1).
Synovial cyst is covered with synovial membrane. Synovial cyst is defined as fluid retention secreted from auricular synovial cells. The most known synovial cyst is Baker cyst or popliteal cyst with communication with intracapsular lumen. It emerges in case of arthritis, rheumatoid arthritis, meniscus tear and anterior cruciate ligament tear (2, 3). It arises at between medial head of gastrocnemius muscle and semi-membranous muscle, probably fragile site when intra-capsular pressure elevates. It also situates at the posterior to medial condyle.
Parameniscal cyst, one of the synovial cysts, usually occur with horizontal meniscal tear. Fluids come from teared meniscus that contain hyaluronic acids and protein probably due to healing process (4-6).
Auricular bursa is separated from joint space and present at friction site between bone and tendon, and between tendon and skin to make friction damages less and to slide smoothly. It is known that there are seven knee bursitis: suprapatellar bursitis, prepatellar bursitis, superficial infrapatellar bursitis, deep infrapatellar bursitis, medial collateral ligament bursitis, pes anserinus (goose foot) bursitis and iliotibial band bursitis (4-8). There is a patella tendon between superficial infrapatellar bursa and deep infrapatellar bursa. When medial cystic lesion of knee joint is encountered, the differential interpretation is important among medial ligament bursitis, pes anserinus bursitis, medial parameniscal cyst. When lateral cystic lesion of knee joint is present, that is important to differentiate between ilio-tibial band bursitis and lateral meniscal cyst.
Pes anserinus (Goose foot) bursa is present near the attachment of tendons of three muscles: sartorius, gracilis and semitendinosus. It usually situates at below knee joint. Then, when cystic lesion at medial and below knee joint is demonstrated on MRI, goose foot bursitis should be listed one of the differential diagnosis. (9, 10)
Ganglion occurs in anywhere and include lateral & medial meniscal cysts, anterior & posterior cruciate cysts and perineural cysts. Ganglion cyst surface does not include synovial cells. They leak synovial fluids from joint space. It is known that possible stalk is possibly present in ganglion between from knee joint and cyst (1, 6). However, it is often hard to find out because of minute leak. The difference between synovial cyst and ganglion cyst is presence or absence of synovial cells on cyst epithelium. Hence, it might be meaningless whether meniscus cyst is categorized to synovial cyst or ganglion, or whether cruciate ligamentum cyst is synovial cyst or ganglion.
【Summary】
We presented a fifty four-year-old male presented in our hospital for a painful mass-like lesion at the medial side of the right knee. MRI depicted cystic lesion crossing beyond knee joint along with medial collateral ligament plus horizontal tear of medial meniscus indicating imaging diagnosis of medial parameniscal cyst. It is borne in mind that cystic fluid lesion of the knee is categorized into synovial cyst, bursitis and ganglion. Ganglion has no synovial cells on its epithelial layer. When cystic lesions at anterior to knee joint surrounding patella are found out, suprapatellar bursitis, prepatellar bursitis, infrapatellar bursitis (superficial and deep) should be differentiated. At posterior to knee joint, Baker cyst (popliteal cyst) is listed. At medial site, medial collateral ligament bursitis, pes anserinus bursitis, medial parameniscal cyst should be differentiated. At lateral site, iliotibial band bursitis and lateral parameniscal cyst should be differentiated.
【References】
1.Vanhoenacker F, et al. Common Mistakes and Pitfalls in Magnetic Resonance Imaging of the Knee. J Belg Soc Radiol. 2016; 100(1): 99
2.Miller TT, et al. MR imaging of Baker cysts: association with internal derangement, effusion, and degenerative arthropathy. Radiology. 1996;201 (1): 247-50. Radiology (abstract) - Pubmed citation
3.Toussaint SP, et al. Baker's cyst imaging. Int J Emerg Med. 2010;3 (4): 469-70.
4.Chatra PS. Bursae around the knee joints. Indian J Radiol Imaging. 2012 Jan-Mar; 22(1): 27–30.
5.Campbell S, et al. MR Imaging of Meniscal Cysts: Incidence, Location, and Clinical Significance. AJR Am J Roentgenol. 2001;177(2):409-13.
6.Tschirch F, et al. Prevalence and Size of Meniscal Cysts, Ganglionic Cysts, Synovial Cysts of the Popliteal Space, Fluid-Filled Bursae, and Other Fluid Collections in Asymptomatic Knees on MR Imaging. AJR Am J Roentgenol. 2003;180(5):1431-6.
7.Steinbach, LS et al. Imaging of cysts and bursae about the knee. Radiol Clin North Am 2013; 51(3): 433–454
8.Murphy BJ, et al. Iliotibial Band Friction Syndrome: MR imaging findings. Radiology 1992: 185: 569-571.
9.Moschowitz E. Bursitis of the Sartorius bursa: an undescribed malady simulating chronic arthritis. JAMA 1937; 109:1362.
10.Forbes RJ, Celms CA, Janzen DL. Acute Pes Anserine Bursitis: MR Imaging. Radiology 1995; 194:525-527.
2022.9.22