Synovial Cysts

As previously mentioned, the z-joints are diarthrodial synovial joints characterized by an articular surface covered by hyaline cartilage and surrounded by a joint capsule, which is lined by synovium. Similar to other synovial joints, diverticula may form, known as synovial cysts. These cysts may emanate from the inferior recess and protrude posteriorly (extracanalicular). In this location they typically do not cause symptoms in and of themselves, but serve as a marker of underlying osteoarthritis. When synovial cysts emanate from the superior recess, they tend to protrude anteriorly into the vertebral canal or medially underneath the ligamentum flavum (these are often referred to as intraspinal or intracanalicular). When large, these cysts compromise the lateral recess or neural foramen and can produce radicular symptoms mimicking a disc herniation clinically. Cross-sectional imaging (CT or MR) will show a rounded lesion in the lateral recess or neural foramen in close proximity to the z-joint (49,50). On MR imaging synovial cysts typically follow fluid signal intensity. However, they may be complicated by hemorrhage (51) and the wall may calcify (Fig. 13). The lumbar spine is the most common location, but these have been described in the thoracic spine (52,53).

The synovial cyst is a lesion that can be treated by z-joint intra-articular injections as an alternative to surgery. This technique was described in three patients who were treated with complete relief in two and partial relief in the third (54). No complications were identified. A retrospective series (55) treating 30 patients with radiculopathy secondary to lumbar z-joint synovial cysts found that about one-third of the patients had long-term relief greater than six months. A more recent series of 12 patients (56) with clinical and imaging follow-up found a correlation between excellent pain relief and resolution of the synovial cyst by imaging. In this

FIGURE 13 Lumbar synovial cyst. Postinjection computed tomography image shows intra-articular contrast in an osteoarthritic zygapophyseal joint (large arrow) and opacification of a synovial cyst that is causing right lateral recess stenosis (small arrow). Note that the cyst wall is also hyperattenu-ating, but not as dense as the contrast reflecting that it is calcified (small arrowhead). Note also the contrast extravasation into the posterior musculature (large arrowhead).

study, 75% (9 of 12 patients) had excellent pain relief, which makes this procedure an attractive treatment option prior to surgical intervention. The three patients with no or only partial relief showed a persistent synovial cyst at followup imaging. As mentioned previously, the wall of the synovial cyst may calcify and while not addressed in the literature, it is this author's experience that cysts with calcified walls are more resilient to injection treatment, but this is not an absolute contraindication. Given the simplicity and low morbidity of this technique, it is considered a suitable first-line therapy despite the possibility of symptomatic recurrence. Also, in the author's experience, if temporary or partial relief is achieved with a single injection, then a repeat in a couple or a few weeks may enhance or augment the therapeutic effect similar to a partial response to an epidural steroid injection. Postprocedure CT imaging is not routinely performed but may be useful if one is uncertain on fluoroscopic imaging that an intra-articular injection was performed (Fig. 13).

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Responses

  • semolina
    Are all synovial cysts syptomatic of arthritis?
    10 months ago

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