Introduction

An intraosseous synovial cyst is relatively uncommon. Benign cyst like lesions that occur in young and middle aged adults, usually located in the end of long bones. Cyst formation is frequently encounted in osteoarthritic joints. Intraosseous synovial cyst which develops secondary to rheumatoid arthritis (RA) is a rare condition. This term is used to designate both mucoid and epiphyseal cyst like lesion in RA patient. Synovial cyst arise in close proximity to joint capsules and tendon sheaths. It must be often found in the long bones' epiphysis such as hip, ankle, knee and elbow. Intraosseous synovial cyst is quite seldomly situated in the olecranon. We aimed to present the radiological findings of a synovial cyst due to RA that was set in the olecranon.

Case Report

A 56 year old male patient who has been diagnosed as RA, was admitted with the complaint of pain and swelling on his left elbow and an insensibility in the left hand. Posteroanterior and lateral radiographs showed a smoothly marginated radiolucent lesion in the olecranon which eroded the boney cortex (Figure 1a-b).

Figure 1

Figure 1a-b: Lateral (a) and posteroanterior (b) radiograph shows a lobulated, lytic lesion in the olecranon. There are minimal sclerotic changes around the lytic lesion.

The lobulated lesion was containing septations. Magnetic resonance imaging (MRI) demonstrated a view similar to a large intraosseous synovial cyst. Extending to the proximal diaphysis in the olecranon, showing lobuler septations in T2W axial images, having peripheral enhancement after administration of contrast medium. In addition, there were some changes in the joint space these are; capsule distending, cartilages erosion over the articular faces, herniation to the periarticular soft tissue, stretching of the tendineous formations, ulnar nevre compression, reactional inflammatory enhancing in flexor carpi ulnaris, anconeous and supinator muscles of similar to the changes seen in rheumatoid synovitis (Figure 2a-b), (Figure 3a-b).

Figure 2

Figure 2a-b: Postcontrast T1 weightened axial (a) and coronal images (b) demonstrate the lobulated cystic lesion in the olecranon. This lesion contains septations and after contrast medium administration there is enhancement around the soft tissue.

Figure 3

Figure 3a-b: T2 weightened axial (a) and sagittal images (b) demonstrate the same lesion.

Discussion And Conclusion

Synovial cysts occur secondary to the trauma, degeneration and inflammation (₁). It is most often found in the popliteal region (₂). Intraosseous synovial cyst and the cysts seen in the soft tissue are histologically similar. Intraosseous synovial cyst can be called as subchondral bone cyst, intraosseous ganglion, the ganglion cyst of the bone, the ganglionic cystic defect of bone, besides the subchondral pseudocyst in the injured articulation and the lesions like giant cysts. Intraosseous synovial cyst is used to describe both the mucoid cysts and the lesions like epiphyseal cysts in the RA. But the definition of intraosseous synovial cyst must be used for geods whose wall was formed by the synovial tissue at the adjacent to the injured articulation (₃). They are must often found in the long bones' epiphysis such as hip, ankle, knee and elbow (₄). Intraosseous synovial cyst in the ulna is a very rare condition. This can be associated with RA or occur spontaneously. The lesions like subchondral cysts are pathologically formed with lax fibrose and connective tissue which are not surrounded by the epithel or synovium. They connect with the articular space through the erosions of the subchondral bone or articular cartilage (₃). Intraosseous synovial cyst or geod seen in RA is formed by the spread of articular fluid from the fragile cartilage to the fragile bone because of the increased pressure in the injured articulation, effusion, synovial hypertrophy in addition to the loss of capsular and pericapsular elasticity (₃). Histologically the osseous synovial cysts show multiloculation like soft tissue's cysts and are constituted by dense mucoid changes and fibrose tissue. Conventional radiographs demonstrate typically epiphyseal, well-marginated, lytic or lucent lesions with sclerotic rim (₃,₄,₅). Lesion may cause pathologic fracture and calcification in the lesion is uncommon (₉). On T1 weighted images, they show izointermediate signal intensity however on T2 weighted images they show high signal intensity. There are contradictory opinions about demonstration of the relation between lesion and articular space by the radiographic methods (₃,₄,₅). This situation arise from two different hypothesis for pathogenesis of the disease. According to the theory of the articular fluid pass; the articular connection, the fragments of articular cartilage in the cyst can be shown and the lesion's fluid is similar to the synovial fluid. The other theory is based on contusion of the bone; the damaged cartilage can not protect the bone and it cause focal necrosis. In this theory, there is not a direct connection between the lesion and joint. However, during the healing stage ther is a secondary articular fluid pass which is not caused by increased pressure in the articular space (₅,₆,₇,₈). In our case, typical conventional radiographs and MRI findings are seen but there is not connection between the lesion and the joint. Cystic bone lesions and the intraosseous synovial cyst is rarely reported in the olecranon (₁₀,₁₁,₁₂,₁₃). They cause spontaneon fracture and vacuum phenomenon (₁₁,₁₂,₁₃,₁₄). For this reason when the articular pain increases in a patient with RA, radiographic evaluation must be done for other probable complications thinking before exacerbation of inflammation. In our case, the radiological imaging for the investigation of articular pain revealed the intraosseous synovial cyst. The cyst caused by osteoartrit, posttravmatic cysts, simple bone cysts, epidermoid cysts, chondroblastoma, osteoblastoma, enchondroma and bone abcess should be considered in differential diagnosis. As a result, if an underlying cause is present, intraosseous synovial cyst should be considered in differential diagnosis of an epiphyseal, well- marginated, lucent bone lesions showed by direct radiography and MRI imaging is useful for the clarification.

Correspondence to

Fahrettin KUCUKAY, MD Türkiye Yüksek İhtisas Hospital, Department of Radiology, Sıhhiye 06100, Ankara / TURKEY Telephone number: + 90-312-3103080/1652 Fax: +90-312-312-4122 E-mail: fkucukay@hotmail.com