History
A 15-year-old neutered male Persian cat was admitted for evaluation of progressive left forelimb swelling of 1 year's duration. The swelling was initially observed around the elbow joint and then progressed to include the left forelimb from the shoulder joint to carpus. The cat was housed indoors, had a current vaccination status, and had no history of illness or trauma.
Physical examination revealed a firm left forelimb swelling from the middle area of the humerus to the distal aspect of the antebrachium. The swelling was most prominent on the medial aspect of the left elbow joint; palpation of the swelling revealed fluctuance but did not elicit signs of pain. Radiographic images of both forelimbs were obtained by the referring veterinarian (HLK; Figure 1).
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Diagnostic Imaging Findings and Interpretation
Soft tissue swelling of the left forelimb extending from the middle aspect of the brachium to the carpus is evident. Bilateral periarticular new bone production with mineral fragments in the left and right elbow joints is consistent with bilateral osteoarthritis and suspected fragmented osteophytes. No bone lysis is evident. On ultrasonographic evaluation of the distal aspect of the left brachium and antebrachium, multiple, round, anechoic spaces separated by echogenic septa are evident (Figure 2).
Comments
Under ultrasonographic guidance, viscous fluid was aspirated from the cystic structures. Fluid analysis revealed a mucin-rich material with mild mononuclear reactivity, consistent with synovial fluid, and no infectious organisms or neoplastic cells. Iohexola was injected into a region of swelling at the lateral aspect of the left elbow joint (7 mL) and into a region of swelling on the lateral side of the distal aspect of the antebrachium (3 mL). Radiography (Figure 3) and computed tomographyb with 3-D reformatted images (Figure 4) confirmed the presence of contrast medium within the elbow joint and within the cavitary regions, indicating communication between the cystic structures and the elbow joint. Contrast medium failed to fill all cysts, especially distally, suggesting that not all of the cysts were communicating with the joint capsule. On the basis of these findings, a diagnosis of synovial cysts was made.
Synovial cysts have been reported for 7 other geriatric cats (10 to 16.5 years of age) that also had concomitant radiographic evidence of osteoarthritis of the elbow joint.1–3 Although osteoarthritis of the elbow joint is typically observed bilaterally, cysts are usually only found in 1 forelimb.
Differential diagnoses of limb swelling in cats include lymphedema, thrombophlebitis, abscesses, cysts, joint disease, and neoplasia.2 Definitive diagnosis of a synovial cyst requires positive-contrast arthrography to confirm joint communication without osteolysis along with histologic examination of cystic tissue. An empirical diagnosis can be made by use of ultrasonography to identify a fluid-filled swelling and to guide fine-needle aspiration of cystic contents for cytologic confirmation of synovial fluid.1,3 Synovial cysts in cats are thought to arise from distention of the joint, bursa, or tendon sheath, resulting in herniation of the synovial membrane through the joint capsule. Sections of the cystic structure may dissect between muscle bundles to expand in all directions.3
Current recommended treatments for synovial cysts include periodic drainage of cysts along with management of degenerative joint disease.1–3 In 2 of 3 affected cats in which surgical excision was elected, cysts recurred within 6 to 9 months after surgery.3 Recommendations in this cat included periodic sterile synoviocentesis to decompress the periarticular swelling and improve forelimb comfort and mobility, gabapentin administration to provide analgesia, acupuncture, passive range of motion exercises, and dietary supplementation with glucosamine, chondroitin sulfate, and polysulfated glycosaminoglycans.
Omnipaque (iohexol, 350 mg/mL), General Electric Healthcare, Amersham Health, Princeton, NJ.
Toshiba Acquilion 8, Toshiba America Medical Systems, Tustine, Calif.
References
- 1.
White JD, Martin P, Hudson D, et al. What is your diagnosis? J Feline Med Surg 2004;6:339–344.
- 2.↑
Prymak C, Goldschmidt MH. Synovial cysts in five dogs and one cat. J Am Anim Hosp Assoc 1991;27:151–154.