Rheumatnlo N I TEaiNA~O gY I H~,L.
Rheumatol Int (1983) 3:143-144
Clinical and Experimental Investigations
© Springer-Verlag 1983
Case Report Gas-Like Radiolucencies in a Popliteal Cyst B. C. McLeod, J. R. Charters, A. K. Straus, and K. N. K u o Rush-Presbyterian-St. Luke's Medical Center, 1753 W. Congress Parkway, Chicago, Illinois 60612, USA Received April 12, 1983 / Accepted June 20, 1983
Summary. A 71-year-old m a n with r h e u m a t o i d arthritis complained o f p a i n and swelling in the left calf. X-ray examination of the calf disclosed radiolucencies suggestive o f soft tissue gas; however, subsequent investigation revealed no evidence o f infection and an a r t h r o g r a m showed a dissected popliteal cyst in the area o f the gas. Gas-like radiolucencies in a popliteal cyst are an unusual finding which has not been previously reported. Key words: Soft tissue gas - Popliteal cyst - Baker's cyst Pseudothrombophlebitis Introduction The presence o f gas in the soft tissues is a distinctive and dramatic r a d i o g r a p h i c finding. It is often attributable to severe bacterial infection which threatens life and limb, and is therefore accorded great i m p o r t a n c e in diagnosis a n d management. We wish to report an unusual case in which gas-like radiolucencies in soft tissue were detected in association with extension o f a Baker's cyst into the calf, in the absence o f any other evidence o f infection.
throgram was ordered. However, review of the venogram by a senior radiologist had disclosed soft tissue gas in the area of the fluctuant mass (Fig. 1). The radiologist was reluctant to carry out instrumentaion of a joint in close proximity to a presumed abscess cavity, and therefore the arthrogram was cancelled. Cefmandol and clindamycin were given intravenously and on the third hospital day the presumed calf abscess was incised and drained. At surgery, the lesion did not appear suppurative. There was no myonecrosis, and fascia and tissue planes were well preserved. The contents of the cyst were described as gelatinous and mucoid, and the presence of gas was not evident. Exploration of the cyst cavity suggested that it extended toward the knee. A drain was placed inferiorly through a separate stab incision and the cavity was closed. Microscopic examination of material removed from the cyst revealed only inflammatory cells and necrotic debris. No micro-organisms were seen and cultures were negative. Antibiotics were stopped on day 5 and on day 8 a left knee arthrogram was performed. Contrast material injected into the knee flowed freely into a large cavity in the upper medial calf and into the drain placed at surgery (Fig. 2). Examination of the joint fluid revealed a white blood cell count of 27 000 with 76% neutrophils. No bacteria were seen and cultures were negative. The latex test was positive at l : 2560 in the fluid. At a second operation, the cyst was excised and the defect in the knee joint capsule was closed. The patient made an uneventful recovery and has since done well on parenteral gold therapy.
Case Report A 71-year-old man entered the hospital because of the recent onset of pain and swelling in the left lower leg. There was a past history of adult onset of diabetes mellitus, controlled with diet and tolbutamide, and rheumatoid arthritis, previously confined to the hands and treated only with salicylates. He had not had injections or other instrumentation of the left knee or any other joint. He was afebrile and remained afebrile throughout his hospitalization. Swelling and limitation of motion were present in the MP and PIP joints of both hands; roentgenograms of joints showed numerous marginal erosions. There was pitting edema of the left leg up to the knee, and left calf tenderness. Thrombophlebitis was suspected clinically but an emergency venogram, performed on the evening of admission, did not show any major defects in the deep venous circulation. A CBC and urinalysis were normal. The latex test for rheumatoid factor was positive at a titer of 1:2560. Fasting blood sugars were consistently under 150 mg/dl. Conservative therapy with heat and elevation of the left leg was instituted. Generalized leg edema decreased as a result, and on the following day a 4× 8 cm fluctuant tender mass was evident in the posteromedial aspect of the left calf, just below the knee. In addition, a left knee effusion was detected. A popIiteal cyst, presenting as 'pseudothrombophlebitis' [1] was suspected and an ar-
Discussion In the absence o f prior instrumentation, the presence of gas outside the p u l m o n a r y or a l i m e n t a r y systems is a serious diagnostic sign, usually indicative o f infection, particularly with clostridial organisms, or o f a r u p t u r e d viscus. Recently, however, there have been reports o f n o n s u p p u r a t i v e gas formation following therapeutic embolization of abd o m i n a l organs. Gas formation, without other evidence o f infection, has been r e p o r t e d after transcatheter infarction o f spleen [2], k i d n e y [3], liver [4], and a d r e n a l gland [5]. In addition, it is well established that the finding o f gas in the fetus is an early r a d i o g r a p h i c indication o f fetal death [6]. In the initial m a n a g e m e n t of our patient, the p r o p e r diagnosis was entertained on clinical grounds shortly after admission, until soft tissue radiolucencies were discovered. These were considered presumptive evidence o f infection, despite the generally benign clinical presentation and the absence o f fever or leukocytosis, and this led to a delay in diagnosis and an unnecessary surgical procedure. How-
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Fig. 1. Plain film of the left lower leg taken before the venogram. Numerous radiolucent pockets are visible in the upper medial calf (arrows) Fig. 2. Double contrast arthrogram of the left knee demonstrating free flow of injected air and contrast media into the area of the medial calf where free gas was previously seen. The narrow inferior extension of contrast (arrow) is the surgical drain tract ever, it would have been difficult to justify any other course of action at that time, even though subsequent events produced no concrete evidence o f a suppurative process. Antibiotics were given before cultures of the cyst could be obtained, so that infection m a y not be totally ruled out by that single test result. Nevertheless, the preponderance of evidence from direct inspection, microscopic examination of the cyst and joint fluid, and cultures of both of these sites, supports the conclusion that infection was not present. The white cell count in the synovial fluid is compatible with either an infectious or a purely rheumatoid effusion. We are not aware of a prior report of gas in a popliteal cyst, and this event is not mentioned in an extensive review of the subject recently published [7]. Thus, the roentgenographic findings in this case are very unusual. Unfortunately, we can provide no definite explanation for the radiolucencies. The reports cited above provide some precedent for the attribution of soft tissue gas to necrosis without infection, but the mechanism of this event remains unknown. It is also possible that the lucent areas seen in the original X-ray were not due to gas at all, since gas was not appreciated in the gross examination of the cyst contents. Jayson and Dixon [8] have suggested that the contents of popliteal cysts are often isolated from the knee fluid by a one-way valve mechanism and have noted that large solid clumps of fibrinous material may accumulate in them. Per-
haps dehydrated a n d / o r lipid containing material of this sort could give rise to the radiolucent materials we observed. Since our patient was presumed to have an abscess, pathological studies focused on identification of micro-organisms. I f similar patients are seen in the future, it would be of great interest to carry out more elaborate histological and biochemical studies on the radiolucent material. References
1. Katz RS, Zizic TM, Arnold WP, Stevens MB (1977) The pseudothrombophlebitis syndrome. Medicine 56:151-164 2. Levy JM, Wasserman PI, Weiland DE (1981) Nonsuppurative gas formation in the spleen after transcatheter splenic infarction. Radiology 139:375-376 3. Rankin RN (1979) Gas formation after renal tumor embolization without abscess: a benign occurrence. Radiology 130:317-320 4. Marks WM, Filly RA (1979) Computed tomographic demonstration of intraarterial air following hepatic artery ligation. Radiology 132:665-666 5. Long JA, Dunnick NR, Doppman JL (1979) Noninflammatory gas formation following embolization of adrenal carcinoma. J Comput Assist Tomogr 3:840-841 6. Stewart AM (1961) The study of free gas in the foetus as a sign of intrauterine death. Br J Radiol 34:187-193 7. Wigley RD (1982) Popliteal cysts: variations on a theme of Baker. Semin Arthritis Rheum 12:1-10 8. Jayson M, Dixon A (1970) Valvalar mechanisms in juxta-articular cysts. Ann Rheum Dis 29:415-420