Synovial Facet Cyst - Spine

Introduction

Overview
- A degenerative lesion of the lumbar spine that often presents with radicular symptoms
  - treatment involves conservative measures initially (NSAIDs, PT), followed by CT-guided rupture, lumbar decompression and cyst excision, and posterior lumbar instrumented fusion with facetectomy
Epidemiology
- incidence
  - rare
- location
  - usually in lumbar spine
    - 60% to 89% occur at the L4-L5 level (most mobile segment)
    - ~14% occurrence at L3-4
    - ~12% occurrence at L5-S1
Pathophysiology
- possible etiologies
  - trauma (controversial)
  - microinstability of the facet leading to
    - extruded synovium through joint capsules
    - myxoid degeneration of collagen tissue
    - proliferation of fibroblasts with increased hyaluronic acid production
  - cyst composition
    - ganglion cysts
    - flavum cysts
    - serous contents
    - mucoid contents
    - hemorrhagic contents
Associated conditions
- degenerative spondylolisthesis

Presentation

Symptoms
- mechanical back pain
- radicular symptoms (leg pain)
  - rapid onset or sudden deterioration suggests a facet cyst hematoma
- neurogenic claudication (buttock/leg pain with walking)
Physical exam
- neurovascular
  - may see nerve root deficits at associated spinal levels

Imaging

Radiographs
- recommended views
  - required
    - AP lateral, lateral, flexion and extension views of spine
  - findings
    - usually normal
    - look for segmental instability
MRI
- indications
  - significant leg pain
- views
  - best seen on T2 axial and sagittal images
  - traditionally hyperintense centers with hypointense rims on T2 and hypointense inner cores on T1 sequences
    - peripheral rim enhancement with gadolinium contrast
  - improved detection rate with positional MRI
    - 89% sensitivity when supine
    - 97% sensitivity when standing
      - cysts increase in size while standing
  - high-signal intensity on T2 weighted images
    - synovial content
    - higher success rate with CT guided cyst rupture
  - low-signal intensity on T2 weighted images
    - gelatinous or calcified contents
    - lower success rate with CT guided cyst rupture

Treatment

Nonoperative
- NSAIDS, rest, immobilization, physical therapy, epidural steroid injections
  - indications
    - mild symptoms
    - first-line treatment
    - radicular pain without motor weakness
  - outcomes
    - no natural history studies have been conducted to date
- CT-guided cyst rupture, facet steroid injection, cyst injection
  - indications
    - second-line management after failing conservative measures
    - radicular symptoms correlate with facet cyst location
  - outcomes
    - 50-75% pain relief at 1-year
    - approximately 39% of patients will require surgical intervention at 7 months
Operative
- laminectomy with decompression and cyst excision
  - indications
    - persistent symptoms despite non-operative management
    - unilateral symptoms
      - can be performed in patients with spondylolisthesis with unilateral symptoms as long as they are aware of the higher risk of slip progression
  - outcomes
    - high incidence of recurrent back pain and cyst formation within two years
    - 80-90% success rate in back and leg pain
    - risk of iatrogenic spondylolisthesis
- facetectomy and instrumented fusion
  - indications
    - some consider first line of surgical treatment due to high recurrance rates
    - symptomatic recurrence following laminectomy with decompression
    - bilateral symptoms
    - central canal stenosis
      - wider decompression will likely lead to iatrogenic instability
    - presence of instability (e.g. degenerative spondylolisthesis)
  - outcomes
    - demonstrated to have the lowest risk of persistent back pain and recurrence of cyst formation in recent studies
    - complete resolution of symptoms in 80-90% of patients

Techniques

NSAIDS, rest, immobilization, physical therapy, epidural steroid injections
- technique
  - recommended for 6-8 weeks prior to proceeding with surgical treatment or CT-guided rupture
CT-guided cyst rupture, facet steroid injection, cyst injection
- technique
  - fluoroscopic guidance
    - commonly used
    - secondary surgery rate roughly 50%
  - CT guidance
    - improved visualization of spinal anatomy
    - slightly improved patient outcomes compared to fluoroscopic guidance
laminectomy with decompression and cyst excision
- approach
  - posterior approach to the spine
- technique
  - unilateral laminotomy and medial facetectomy with high-speed burr
  - create plane between dura and cyst
  - grab cyst with allis clamp or forceps and apply gentle traction
  - seperate cyst from underlying dura with Epstein curet or Woodson elevator
facetectomy and instrumented fusion
- approach
  - posterior approach to the spine
- technique
  - place pedicle screws at the intersection of the superior border of the transverse process and midline of the superior process
  - perform decompressive laminectomy and facetectomy
  - excise cyst after developing interval between cyst and dura
    - partial excision in cases of cysts adherent to the dura

Complications

Cyst recurrence
- incidence
  - high incidence of recurrence with resection alone
- treatment
  - new studies favor facetectomy and fusion as first line of operative treatment
Iatrogenic spondylolisthesis
- risk factors
  - decompressive laminectomy without fusion
- treatment
  - posterior instrumented fusion +/- spondylolisthesis reduction
Dural tear
- incidence
- risk factors
  - revision surgery
  - cyst adherent to dura
    - 50-55% of cases the facet cyst is adherent to the dura
      - limited cyst resection in these cases minimizes dural tear risk
    - partial cyst excision results in 88% success rate for lumbar spinal stenosis while while minimizing risk of dural tear