Synovial cyst mimicking an intraspinal sacral mass

Spontaneous regression of extradural intraspinal cysts in a dog: a case report

Background

Extradural intraspinal cysts are fluid accumulations that appear to be associated with increased motion at vertebral joints.

Case presentation

We report the spontaneous regression of lumbar and lumbosacral cysts (presumably synovial cysts) and the unusual occurrence of an S1–2 extradural intraspinal cyst in a dog. The dog presented with lumbosacral pain. Six extradural intraspinal cysts were observed on high-field magnetic resonance imaging from L5–6 to S1-S2. The cysts between L5–6 and L7-S1 ranged from 0.12 to 0.44cm² at their largest area. The largest cyst was located at S1–2 (left), measuring 0.84 cm² at its largest view. The dog was medically managed. A follow-up magnetic resonance imaging scan was obtained 3.5 years after the first imaging. All cysts except the one at S1–2 had reduced in size. Mean reduction in size was 59.6% (35–81%).

Conclusions

In summary, we report a case with multiple extradural intraspinal cysts that underwent spontaneous regression of all but one cyst during a 3.5-year follow-up period. Whether this is a single occurrence, or is part of the natural history of these cysts in the lumbosacral region of dogs, remains to be established. Spontaneous regression of intraspinal cysts had not been described in dogs.

Hemorrhagic lumbar synovial cyst: case report and literature review

Intraspinal synovial cysts are infrequent causes of back and radicular leg pain. Commonly associated with degenerative spinal disease, the majority of synovial cysts appear in the lumbar spine. Rarely, intracystic hemorrhage can occur through an unclear mechanism. Similarly rare, cysts may also become migratory. The pathogenesis of hemorrhagic synovial cysts remains uncertain and their potential for migration also remains unclear. A 36 year-old male presented to the clinic with 5 months of back pain and leg pain that began after a work-related injury. An initial MRI obtained by another surgeon 3 month prior demonstrated an epidural cystic mass with T1 hypointensity and T2 hyperintensity at L2-L3. With worsening pain, the patient came to our clinic for a second opinion. A second MRI demonstrated resolution of the L2-L3 epidural cystic mass and formation of a new epidural cystic mass at L3-L4 causing compression of the thecal sac. The patient subsequently underwent decompressive hemilaminectomy with cyst removal. We present a case of two lumbar synovial cysts, separated over time and a vertebral level and giving the appearance of a single, migratory cyst. This is the first case of an "occult migratory" synovial cyst with repeat MR imaging capturing spontaneous resolution of the initial cyst and formation of a hemorrhagic cyst one level below. We also present a summary of the 44 cases of hemorrhagic synovial cysts reported in the literature and propose a mechanism that may account for the hemorrhagic and migratory progression in some patients.