When Bydon et al
. reviewed the surgical management of 966 spinal synovial cysts (1970–2009) in 82 studies, 96.2% were in the lumbar (75.4% at the L4–L5 level), 2.6% in the cervical, and 1.2% were in the thoracic spine.[3
Although CT studies more readily diagnose lumbar stenosis and ossification of the yellow ligament (OYL) associated with synovial cysts, MR studies better delineate the severity and extent of the cysts themselves [Figures –].
Figure 5 The axial non-contrast lumbar CT scan demonstrates marked congenital stenosis accompanied by superior facet hypertrophy. Note that air (hypodense) within the facet joints is indicative of instability. With such severe spinal stenosis, epidural steroid (more ...)
In Pirotte et al
.'s series of 46 consecutive patients (1990 and 2001), CT documented cysts in 19 of 30 cases, while MR documented all 30 cysts.[18
] Cysts predominated at the L4–L5 level (61%) and were accompanied by disc degeneration/spondylosis in 54% of cases.
Liu et al
. observed that CT scans could document cysts adjoining facet joint capsules, but noted that MR revealed more specific information [Figures –].[14
] On short TR/TE, MR images revealed slightly hyperintense (3 cases) or isointense (1 case) cysts, while long TR/TE showed hyperintensities (2 cases) or hypointensities (others).[14
] Furthermore, hypointense signals surrounding cysts often indicated rim calcification better confirmed on CT.
MR can additionally differentiate between the hyperintense signals characteristic of fluid within synovial cysts and focal hypointense signals typical of hypertrophy and/or ossification of the yellow ligament [Figures –].[11
] Unfortunately, MR scans cannot readily distinguish between the more frequently encountered gelatinous (non-aspirable) versus the rarer serosanguinous (more readily aspirated) cysts.[11
MR studies further demonstrate the large, thick, fibrous, and often calcified capsules surrounding the fluid within the synovial cysts, which are predominantly responsible for the majority of neural/dural compression and neurological dysfunction [Figures –]. Moreover, enhanced MR studies document dense adhesions between the overlying cyst capsules and the underlying dura and nerve roots, the cephalad/foraminally exiting and the caudad/lateral recess exiting nerve roots . For example, a synovial cyst at the L4–L5 level typically contributes to dural compression along with both cephalad L4 and caudad L5 nerve root compromise.
Figure 4 On the axial T1-weighted MR image, congenital lumbar stenosis is exaggerated by the presence of ossification of the yellow ligament (hypointense) resulting in marked bilateral, dorsolateral thecal sac compression. Additionally, fluid is seen in both facet (more ...)
Figure 11 Following excision of an L4–L5 massive left-sided synovial cyst extending to the L3–L4 level, this intraoperative photograph reveals the freed superiorly and foraminally exiting L4 nerve root (open arrow), and the decompressed thecal sac (more ...)
Some patients with synovial cysts exhibit no active Grade I slip (25% or less of the vertebral body width), while others exhibit instability associated with degenerative spondylolisthesis. In particular, older patients with marked degenerative changes of the facet joints accompanied by bony osteophytic bridging across facet joints and/or vertebrae on dynamic X-rays, and/or CT studies, without active motion, may not warrant fusion.
MR-documented increased fluid in the facet joints is highly correlated with degenerative spondylolisthesis and synovial cyst degeneration, and may indicate instability . Alicioglu and Sut noted that facet joint osteoarthritis was present in 30 patients with denegerative spondylolisthesis, and that synovial joint effusions occurred in 24 patients with synovial cysts.[2
] Tillich et al. documented instability in 11 (61%) of 18 patients with synovial cysts, 6 of whom also demonstrated degenerative spondylolisthesis.[25