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Ultrasonographic demonstration of popliteal cysts in rheumatoid arthritis.

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Ultrasound scanning techniques detected popliteal cysts in 14 of 24 knees affected with rheumatoid arthritis and associated with an anterior effusion.
Serial scans demonstrated the persistence of cysts when
effusion was not controlled by intraarticular steroid
and lidocaine, and regression of cyst following control of effusion with anterior synovectomy. As the
technique is noninvasive, painless, and reproducible,
ultrasound scanning should be the technique of choice
for the detection and assessment of popliteal cysts.
Popliteal cysts occur with great frequency in
patients with rheumatoid arthritis (1,2). Yet, clinically,
their presence may be overlooked or even misdiagnosed as an acute thrombophlebitis (3), vascular malformation, or tumor (4). Confirming diagnostic techniques include direct needle aspiration, arthrography
with contrast material (2), and scintography with
intravenous or intraarticular injections of isotopes
From the Department of Medicine, Division of Rheumatology, Harbor General Hospital Campus, UCLA School of
Medicine, 1000 West Carson, Torrance, California
Charles P. Moore, M.D.: Fellow in Rheumatology,
Harbor General Hospital Campus, UCLA School of Medicine
(present address: University of Washington, Seattle, Washington); Dennis A. Sarti, M.D.: Department of Radiology, Harbor
General Hospital Campus, UCLA School of Medicine; James
S. Louie, M.D.: Assistant Professor, Harbor General Hospital
Campus, UCLA School of Medicine.
Address reprint requests to Dr. J. Louie.
Submitted for publication October 7, 1974; accepted
December 31, 1974.
Arthritis and Rheumatism, Vol. IS, No. 6 (November-December 1975)
(5,6), all of which are invasive procedures with potential risk. This study extends the successful use of a
noninvasive technique, ultrasound B-scanning (7,8),
in demonstrating popliteal cysts and monitoring responses to therapeutic trials.
Seventeen patients with definite o r classic rheumatoid arthritis were examined specifically for the presence
of knee effusions and popliteal masses a n d were referred
for ultrasound B-scanning.
T h e patients were studied prone with their p o p
liteal fossae coated with mineral oil. A Picker Electronics
Echoview VIIJ with a 5 mHz transducer was used at two
sensitivity settings: An initial scan a t normal sensitivity outlined the popliteal anatomy, a n d a subsequent scan a t a
higher sensitivity differentiated fluid-filled spaces from surrounding tissue.
All knees were scanned i n two planes. Sagittal scans
were obtained parallel to the long axis of the leg a t 1 - a n
intervals beginning a t the medial aspect of the knee. Transverse scans were recorded perpendicular to the long axis a t
1-cm intervals with the popliteal crease as the reference
Several patients were studied serially following arthrocentesis a n d a) immobilization by casting, b) intraarticular instillation of lidocaine, o r lidocaine and prednisolone, 40 mg (Hydeltra TBA), and c) anterior synovectomy.
Seventeen patients were scanned bilaterally
for cysts. Of the 24 knees with apparent effusion, 14
Fig 1. Ultrascan of popliteal cyst extending into right calf. Patient R N . A. Prone sagittal (scale markers of 1 c m are seen in upper
right). B. Prone transverse.
were found to have an associated popliteal cyst. I n
the 10 knees without effusion, one cyst was detected
in a patient with a transverse popliteal scar through
which a cyst had been excised 5 years earlier.
Though most patients with effusion complained
of knee pain, only 4 patients localized the pain to
the popliteal fossa. These patients clearly had palpable cysts upon examination. I n other patients, palpation consistently failed to predict cyst presence.
(Figure 4). Direct aspiration of the sonolucent area
returned a grossly bloody effusion with crenated RBC
and ghost forms, and subsequent instillation of contrast material confirmed extravasated fluid (Figure 5).
Following immobilization by casting, the superficial
sonolucent area regressed although a small cyst persisted. Subsequent synovectomy again controlled the
effusion and allowed further regression of cyst size.
Response to Therapy
Popliteal cysts, first described by Adams (9) and
Baker (lo), arise from the semimembranosogastrocnemius bursa by virtue of a) a valvular anatomic communication from the anterior joint space, and b) an
intraarticular lesion that produces a chronic knee
effusion. Anatomic studies of cadaver dissections suggest that 40-50% of normal knees will demonstrate
this valvular communication (1 l), which allows effusion to go from knee to bursa but not vice versa.
Cysts have been described in association with a variety
of lesions but are especially common in patients with
rheumatoid arthritis. T h e cysts may appear as asymptomatic or symptomatic popliteal masses and occasionally may extend deep into the calf or rupture
into the soft tissue planes producing a swollen painful
limb that mimics thrombophlebitis.
T h e various techniques for demonstrating popliteal cysts are often insensitive, technically difficult,
time consuming, and potentially hazardous. Thus,
direct aspiration of the popliteal cysts may lacerate
vessels or produce a chronic fistula.
Nine of the knees with effusion were aspirated
and injected intraarticularly with lidocaine, or a lidocaine-prednisolone combination, some on multiple
occasions. Despite subjective improvement in all, effusions and cysts persisted at 2-6 weeks.
Two patients presented with acute calf pain
and were initially treated with anticoagulants for
thrombophlebitis. T h e initial patient, RN, was found
to have a 16-cm-long cyst deep into the calf by scan
(Figure 1). An arthrogram confirmed the cyst presence but not the extent (Figure 2). When intraarticular injections did not control the effusion and
associated cyst and symptoms continued, the patient
underwent synovectomy with control of effusion and
regression of cyst. I n the other patient, JS, ultrasound
again demonstrated a large cyst extending deep into
the calf. Peculiarly, the sonolucent area was situated
just beneath the skin (Figure 3). Joint aspiration returned a clear effusion. Arthrograms again confirmed
a small cyst but did not outline the sonolucent mass
Fig 3. Ultrascan of popliteal cyst (ruptured) with sonolucent
area just beneath the skin. Patient IS. Right leg. Prone sagittal
(popliteal crease identified by vertical line).
Fig 2. Arthrogram of popliteal cyst, incompletely outlined.
Patient R N .
Arthrography requires the intraarticular instillation of contrast material and air and subsequent
knee movements of flexion-extension or walking and
squatting to impel the mixture into the posterior
space (4). Occasionally, the contrast material may not
traverse posteriorly to outline adequately the cyst,
especially when patient cooperation is compromised
by calf pain or when the communication is obstructed
by loose bodies. Thus, both patients with acute calf
pain showed large cysts by scan but not by arthrogram.
Arthroscintography has proved useful i n delineating synovial inflammation. Yet intravenous
may fail to demonstrate cysts as
effectively as intraarticular instillation of 1311-IHSA
(6), another invasive procedure and one that requires
a 24-hour wait.
T h e authors of this article have found ultrasound B-scanning to be a n ideal technique for the
demonstration and sequential evaluation of popliteal
cysts. T h e limit of resolution is theoretically set by
the transducer diameter. A 5-mHz transducer, as used
in the present study, has a diameter of 7 mm. However, the practical limits of resolution are in the
range of 1.5 cm.
A cystic structure can be differentiated from a
solid soft tissue tumor by using the following criteria:
a) At normal sensitivity, a cyst will have no internal echoes, whereas a solid tumor will have a
few internal echoes.
b) At high sensitivity, the cyst will fill in from
the periphery, whereas the solid tumor will fill
in centrally.
c) T h e posterior wall of a cyst is more sharply
seen than in a solid structure.
Using the B-mode of scanning, cysts were
demonstrated in rheumatoid knees with effusion in
a frequency approaching that reported for the presence of an anatomic communication between joint
space and bursa. This result supports the concept that
cyst formation is dependent both on a valvular communication and on a source of chronic effusion. I n
addition, in 2 patients with acute calf pain, scanning
clearly differentiated popliteal cyst formation from
thrombophlebitis. I n one instance, an associated cyst
rupture was suggested by the superficial placement of
the sonolucent mass.
Several potential diagnostic possibilities exist
in using ultrasound B-scanning for examining the
popliteal fossa. T h e popliteal artery has been identified on B-scan and confirmed by pulsations using the
A-mode. A popliteal artery aneurysm can potentially
be diagnosed by finding a sonolucent area with an
artery leading into or from it. Popliteal cyst puncture
directed by ultrasound, as has been performed in
renal cyst puncture, is also feasible. Finally, the ability
Fig 5. Direct instillation of contrast material into sonohcent
area. Superficial location and slight feathering suggest extravasated fluid. Patient J S .
Fig 4. Arthrogratn
popliteal cyst, poorly outlined. Patient J S .
t o do reproducible, painless, a n d noninvasive serial
studies allowed assessment of various therapeutic
maneuvers, a n d supported t h e concept that control
of effusion by anterior synovectomy is a proper recommendation for popliteal cyst.
T h e early encouragement and assistance of Dr.
Dennis McQuown is acknowledged.
1. Genovese GR, Jayson MIV, Dixon ASJ: Protective value
of synovial cysts in rheumatoid knees. Ann Rheum
Dis 31:179-182, 1972
2. Taylor AR: Arthrography of the knee in rheumatoid
arthritis. Br J Radiol 42:493-497, 1969
3. Hench PK, Reid R T , Reames PM: Dissecting popliteal
cyst simulating thrombophlebitis. .4nn Intern Med 64:
125F1264, 1966
4. Gerber NJ, Dixon ASJ: Synovial cysts and juxta-
articular bone cysts (geodes). Semin Arthritis Rheum
3:323-348, 1974
5. Levin MH, Nordyke RA, Ball JJ: Demonstration of
dissecting popliteal cysts by joint scans after intraarticular isotope injections. Arthritis Kheum 14:591598, I97 1
6. Hays M T , Green FA: T h e pertechnetate joint scan.
Ann Rheum Dis 31:272-282, 1972
7. McDonald DG, Leopold GR: Ultrasound B-scanning
in the differentiation of Baker’s cyst and thrombophlebitis. Br J Radiol 45:729-732, 1972
8. Meire HB, Lindsay DJ, Swinson DR, et al: Comparison
of ultrasound and positive contrast arthrography in
the diagnosis of popliteal and calf swellings. Ann
Rheum Dis 33:221-224, 1974
9. Adams M: Chronic rheumatic arthritis of the knee
joint. Dublin J Med Sci 17:52&528, 1840
10. Baker WhI: T h e formation of abnormal synovial cysts
in connection with the joints. St Bartholomew’s Hosp
21:177-190, 1885
11. Wilson PD, Eyre-Brooke AL, Francis JD: Clinical and
anatomical study of the semimembranosus bursa in
relation to popliteal cyst. J Bone Joint Surg [Am] 20:
963-984, 1938
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popliteal, demonstration, ultrasonography, arthritis, rheumatoid, cysts
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