Abstract
A 12-year-old spayed Himalayan cat was presented for evaluation of unilateral forelimb swelling of three months duration. The swelling, located predominantly on the medial aspect of the left elbow, was neither hot nor painful (Fig. 1). The cat was otherwise well. Although its gait was initially considered normal, a mild lameness of the affected limb developed subsequently.
Periarticular swelling medial to the left elbow of a 12-year-old Himalayan cat (case one).
Ultrasonography revealed multiple, variably sized, sonolucent spaces separated by echogenic septae (Fig. 2). Radiographs of both elbows demonstrated changes consistent with bilateral degenerative joint disease, more severe on the left leg (Fig. 3). A large volume (>15 ml) of viscous, straw coloured fluid was aspirated using a needle and syringe (Fig. 4). At a subsequent examination, additional fluid was aspirated and submitted for laboratory investigation (Table 1).
Ultrasonography of the soft tissue swelling in case 1 demonstrating multiple anechoic spaces.
Lateral (right) and cranio-caudal (left) views of the left elbow of case one demonstrating peri-articular new bone formation consistent with degenerative joint disease. Note also the dramatic soft tissue swelling of the limb. Radiographic signs of degenerative joint disease were present, but less severe, in the right elbow.
Approximately 16 ml of blood tinged, slightly cloudy, very viscid fluid removed by needle aspiration from case one.
Fluid analysis and cytology results from a 12-year-old cat with swelling medial to the elbow
Average count 500 cells/μl.
Canfield and Martin, 1998.
Considering the history, physical findings, cytological and imaging data, what is your diagnosis?
How would you manage the case subsequently?
Answers from What is your diagnosis? Diagnosis
The specimen aspirated from the lesion is consistent with synovial fluid with erythrophagocytosis, possibly due to previous aspiration. Taken together with physical, sonographic and radiologic findings the most likely diagnosis is a synovial cyst.
The differential diagnoses for bone, joint and soft tissue swellings of the limbs are extensive and include infections, inflammatory and non-inflammatory joint disease, primary and metastatic neoplasia of the bone, cartilage, synovium and adjacent soft tissues (Sherding and Schrader, 1994). Synovial cysts should be considered the most likely diagnosis when a fluid filled swelling is palpated near the elbow joint. The cystic nature of the swellings is typically evident on physical examination (Prymak and Goldschmidt, 1991; Stead et al., 1995). Ultrasonography is helpful to confirm the fluid filled nature of the swelling and to guide needle aspiration. Radiographs that demonstrate changes typical of degenerative joint disease and exclude bone lysis associated with bone neoplasia and osteomyelitis (Konde, 1994) support a diagnosis of synovial cyst. Cytology is useful to confirm the synovial nature of the fluid and to exclude infectious or neoplastic processes.
Definitive diagnosis of a synovial cyst requires contrast arthrography, surgical excision and histopathological examination of the synovial membrane, although in many cases (such as the cat of the present report) this may not be necessary. Ultrasonography may be the screening imaging modality of choice for both human and feline patients (Handy, 2001). Debris and haemorrhage within the cyst or synovial membrane thickening may mimic a soft tissue mass on ultrasonographic examination; magnetic resonance imaging provides greater soft tissue detail but at much greater expense (Steiner et al., 1996).
Discussion
By definition, synovial cysts are lined by synovial cells, contain synovial fluid and may or may not communicate with the adjacent joint (Steiner et al., 1996). Synovial cysts have been reported infrequently in cats. Two case series include four cats with synovial cysts confirmed by histopathological evaluation of the cyst lining (Prymak and Goldschmidt, 1991; Stead et al., 1995). The aforementioned cat is one of three cases with synovial cyst(s) encountered by the authors. The salient clinical features of these three patients are summarised in Table 2. The swellings had varying characteristics on palpation; smaller cysts were described as firm, larger cysts as soft and obviously fluid filled. The palpable swelling was not attached to the overlying skin or mobile (case 2). One cat (case 3) initially presented for a periarticular swelling of the right front leg and developed a second, smaller swelling on the left front leg 15 months later (Fig. 6). Fluid analysis in all additional cases was consistent with synovial fluid. Radiographs of case three (Fig. 5) demonstrated changes consistent with bilateral degenerative joint disease although the cat was not overtly lame at the time of presentation.
Clinical features of three cats with synovial cyst(s)
Craniocaudal radiographs of both thoracic limbs of case three. Note extensive periarticular new bone formation consistent with bilateral elbow degenerative joint disease.
Periarticular swelling of the right elbow of case three.
Features common to the three cases described here and those reported previously include age and cyst location. All cats were over 10 (range 10 to 16.5 years) and the elbow was affected in all cats. Swellings were predominantly medial, although they extended cranially, distally, proximally and laterally in some cases (Prymak and Goldschmidt, 1991; Stead et al., 1995). In five cases of synovial cysts in dogs, cyst location included the hock (one dog), metatarsus (one dog) and carpus (three dogs) (Prymak and Goldschmidt, 1991).
Para-articular cysts are a common clinical problem in humans. Cysts located adjacent to the knee and arising from the gastrocnemius-semimembranosus bursa are called popliteal (or Baker's) cysts (Steiner et al., 1996). There are three proposed mechanisms for the development of popliteal cysts in human patients (1) accumulation of fluid in a bursa that does not communicate with the joint itself (2) herniation of the joint capsule because of increased intra-articular pressure and (3) distension of a bursa by fluid originating in the knee joint due to communication between it and the bursa (Liebling, 1999). In previously reported feline cases, cysts originated from the joint capsule (Prymak and Goldschmidt, 1991).
The incidence of popliteal cysts in adult humans increases with age (Handy, 2001) and they are usually considered secondary to intra-articular conditions that result in joint effusion eg meniscal tears and lesions of the articular cartilage (Rupp et al., 2002). In people, recurrence of popliteal cysts after surgical excision is common (Rauschning and Lindgren, 1979) and asymptomatic cysts do not require treatment (Steiner et al., 1996). Where possible, treatment should focus on correcting the underlying intra-articular pathology (Rupp et al., 2002).
Three of the four previously reported cats with synovial cysts were lame on the affected leg at presentation. Radiographs in these cats demonstrated soft tissue swellings, subchondral bone sclerosis and perichondral bone proliferation consistent with osteoarthritis (Allan, 1994). Surgical excision of the cysts did not improve the lameness attributed to the underlying degenerative joint disease (Stead et al., 1995). Elbow radiographs were available for two of the three cases presented here. Radiographic evidence of degenerative joint disease was present in both cases.
Degenerative joint disease is often unrecognised by cat owners and veterinarians (Hardie et al., 2002). Clinical signs may be hard for owners and veterinarians to identify due to a combination of cats' natural agility and difficulty in performing gait analysis in a veterinary hospital (Hardie, 1997; Sherding and Schrader, 1994). Other behavioural signs, for example an unkempt coat due to reduced grooming, may be more obvious (Hardie, 1997). In cats with degenerative joint disease, the elbow is consistently the most severely affected joint, both clinically and radiographically (Hardie et al., 2002). Possibly this is due to natural feline behaviours, especially jumping, placing increased compressive/percussive forces on the thoracic limbs during landing.
Treatment of synovial cysts in cats may be indicated in some cases to prevent complications such as damage to overlying skin, interference with normal range of joint motion and traumatic rupture of the cyst (Prymak and Goldschmidt, 1991). Complications associated with popliteal cysts in humans include compression of adjacent nerves (Laurencin et al., 1994) and, unusually, secondary infections resulting in abscess formation (Drees et al., 1999). Expanding, or dissecting, cysts with or without rupture can cause pain and inflammation and be misdiagnosed as thrombophlebitis (Brady et al., 1987; Katz et al., 1977). In three previously reported feline cases where the synovial cysts were surgically excised the lesions recurred within nine and six months in two of these patients, while the third cat had no evidence of recurrence six months post-operatively when he died of unrelated causes (Prymak and Goldschmidt, 1991; Stead et al., 1995). Surgical excision on three dogs was more effective, with no recurrence at six months to five years (Prymak and Goldschmidt, 1991). Given the frequency of post-surgical cyst recurrence so far reported for cats (Prymak and Goldschmidt, 1991; Stead et al., 1995), treatment for two of the three cases described here focused on drainage as required and analgesia for the underlying degenertive joint disease. Treatment options for feline degenerative joint disease include environmental modification, weight control, surgery and analgesia using non-steroidal anti-inflammatory drugs or butorphanol (Hardie, 1997). Corticosteroids are potent anti-inflammatories and provide analgesia for degenerative joint disease but can cause further cartilage deterioration (Johnston and Budsberg, 1997). Little information on the utility and side effects in cats is available. However, the use of corticosteroids may be justified in certain cases or in end stage degenerative joint disease (Lipowitz, 1993; Manley, 1995). The use of intra-articular corticosteroids avoids systemic side effects but may reduce collagen synthesis (Chunekamrai et al., 1989). Efforts should be made to eliminate potential infectious aetiologies, especially Mycoplasma sp. and anaerobic bacteria, when considering the use of corticosteroids in cats with severe degenerative joint disease.