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.
OBJECTIVE
The purposes of this study were to evaluate the prevalence and determine the size of meniscal cysts, ganglionic cysts, synovial cysts of the popliteal space, fluid-filled bursae, and other fluid collections on MR images of asymptomatic knees.


METHODS
MR images of 102 asymptomatic knees were evaluated with regard to the prevalence of meniscal cysts, ganglionic cysts, synovial cysts of the popliteal space, fluid-filled bursae, and other fluid collections. The MR examinations were performed in patients (mean age, 42.8 years; age range, 18-73 years) with clinically suspected meniscal lesions in the contralateral knee. The craniocaudal, anteroposterior, and mediolateral diameters of detectable abnormal fluid collections were measured.


RESULTS
Medial meniscal cysts (mean size [craniocaudal x anteroposterior x mediolateral], 9 x 6 x 13 mm) were found in four asymptomatic knees. Neither lateral meniscal cysts nor ganglionic cysts of the cruciate ligaments were identified. Twenty-six synovial cysts of the popliteal space (Baker's cyst)-consisting of 11 gastrocnemius portions (mean size, 19 x 8 x 10 mm) and 15 semimembranosus portions (mean size, 20 x 7 x 9 mm)-were found in 19 knees. Twenty-four (92%) of these cysts had a maximal diameter of 30 mm or less. Fluid-filled bursae were found in 49 knees. The deep infrapatellar bursa was most commonly involved (42 knees; mean size, 6 x 3 x 5 mm). Fluid-filled anserine bursae (mean size, 27 x 12 x 10 mm) were detected in five knees.


CONCLUSIONS
Meniscal cysts may be present in asymptomatic knees, at least on the medial side. Synovial cysts of the popliteal space can be found in approximately one fifth of asymptomatic knees. Their maximal diameter is usually smaller than 30 mm.
Tschirch
Frank T C
FT
Department of Radiology, Orthopedic University Hospital Balgrist, Forchstrasse 340, CH-8008 Zürich, Switzerland.
Schmid
Marius R
MR
Pfirrmann
Christian W A
CW
Romero
José
J
Hodler
Juerg
J
Zanetti
Marco
M
D000328:Adult; D001826:Body Fluids; D001845:Bone Cysts / Q000453:epidemiology / Q000473:pathology; D002061:Bursa, Synovial; D003560:Cysts / Q000453:epidemiology* / Q000473:pathology*; D006801:Humans; D007592:Joint Diseases / Q000453:epidemiology / Q000473:pathology; D007717:Knee / Q000473:pathology*; D008279:Magnetic Resonance Imaging; D008297:Male; D008592:Menisci, Tibial; D008875:Middle Aged; D011151:Popliteal Cyst / Q000453:epidemiology / Q000473:pathology; D015995:Prevalence; D013581:Synovial Cyst / Q000453:epidemiology / Q000473:pathology