MR Imaging of Cysts, Ganglia, and Bursae About the Knee

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Cystic lesions around the knee comprise a diverse group of entities, ranging from benign cysts to complications of underlying diseases such as infection, arthritis, and malignancy. Their diverse causes result in varied prognoses and therapeutic options. Although the presentation of cystic masses may be similar, their management may differ, thus highlighting the importance of appropriate categorization. MR aids in the characterization of lesions by first localizing them, and then defining their relationship with adjacent structures and identifying any additional abnormalities. For the purpose of this article, the authors limit the scope of their discussion to benign cysts, ganglia, and bursae about the knee.

Section snippets

Synovial cyst

The definition of a synovial cyst is a juxta-articular fluid collection that is lined by synovial cells. It is this synovial lining that histologically distinguishes them from other juxta-articular fluid collections. A synovial cyst represents a focal extension of joint fluid that may, or may not, communicate with the joint, and may extend in any direction [1], [2]. The prototypical example of a synovial cyst is the popliteal cyst.

Ganglion

A ganglion is a cystic, tumor-like lesion of unknown origin, which is surrounded by dense connective tissue filled with gelatinous fluid rich in hyaluronic acid and other mucopolysaccharides [31]. These cysts are classified as myxoid lesions, with suggested causes including synovial herniation and tissue degeneration or repeated trauma [32], [33], [34]. The World Health Organization does not address ganglia because they are not tumors, and, therefore, no rigid classification scheme exists. The

Subchondral cyst (geode)

Subchondral lucencies are referred to by many names in the literature, including subchondral cysts, synovial cysts, subarticular pseudocysts, necrotic pseudocysts, and geodes [48]. The term subchondral cyst is not accurate technically because the cyst does not have an epithelial lining and is not fluid filled uniformly [48]. However, this term is ubiquitous in the literature, and will therefore be used in the following discussion.

OA is a process of articular degeneration characterized by

Meniscal cyst

A meniscal cyst is a focal collection of synovial fluid located within, or adjacent to, the meniscus. Various theories have been proposed regarding the etiology of these cysts, with the most widely accepted reason stating that joint fluid accumulates within a torn or degenerated meniscus, creating an intrameniscal cyst, and fluid extravasation through a meniscal tear into the surrounding soft tissues results in parameniscal cyst formation [30], [51], [52]. A horizontal component to the tear is

Bursa

Bursae are normally occurring, synovial-lined structures that function to reduce friction between moving structures, such as tendons, ligaments, and bone. Typically, they are not visible on imaging because they normally contain only limited fluid. Inflammation from local and systemic processes such as overuse, trauma, internal joint derangement, inflammatory arthropathy, and collagen vascular diseases, in addition to infection and hemorrhage, may cause thickening of the synovial lining and

Summary

Cystic lesions about the knee are common findings, representing diverse causes and, therefore, varied prognosis and therapeutic options. MR aids in the characterization of lesions by first localizing them, and then defining their relationship with adjacent structures and identifying any additional abnormalities. Cystic lesions and their relationships are best depicted on long TE/TR (fluid-sensitive) MR sequences. Careful attention to these details will allow one to provide a reasonable MR

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