What are the differences between a 6 mm synovial cyst at the C6–C7 level and a 4 mm suspected Tarlov (perineural) cyst?

Key Differences Between Cervical Synovial Cysts and Tarlov Cysts

A 6mm synovial cyst at C6-C7 and a 4mm suspected Tarlov cyst are fundamentally different lesions with distinct anatomic origins, imaging characteristics, and clinical implications—the synovial cyst arises from facet joint degeneration while the Tarlov cyst originates from the nerve root sleeve.

Anatomic Origin

Synovial Cyst (C6-C7):

• Arises from the facet (zygapophyseal) joint capsule
• Results from degenerative joint disease and facet arthropathy
• Contains synovial fluid from the joint space
• Typically occurs in elderly patients with advanced spinal degeneration 1

Tarlov (Perineural) Cyst:

• Originates at the junction of the posterior nerve root and dorsal root ganglion
• Represents a cerebrospinal fluid-filled dilatation of the nerve root sleeve
• Benign developmental or acquired lesion 2, 3
• Can occur at any age but symptomatic cases often present in middle age

Imaging Characteristics

Synovial Cyst Features:

• Located dorsal to the neural foramen, adjacent to the facet joint
• Often 1-2 cm in diameter when symptomatic
• May show complex signal on MRI (thick wall, internal structure) in 60% of cases 1
• Fluid-density on CT
• Associated with severe ipsilateral multifidus muscle atrophy 1
• Connection to facet joint may or may not be visible 4

Tarlov Cyst Features:

• Located within or extending from the neural foramen
• Typically larger and more lobular than synovial cysts
• Pure fluid signal intensity on MRI (same as CSF on all sequences) 5, 1
• Thin-walled structures 5
• Key radiological markers include dorsal root ganglion displacement and foraminal remodeling 6
• Size alone is NOT predictive of symptoms 6

Clinical Presentation

Your 6mm Synovial Cyst:

• More likely symptomatic at this size given its location
• Presents with radicular pain from nerve root compression
• Symptoms often related to position and movement
• Typically seen in context of degenerative spine disease

Your 4mm Tarlov Cyst:

• Size is too small to be clinically significant in most cases 6
• Most Tarlov cysts are asymptomatic incidental findings
• When symptomatic (usually >1.5cm), presents with:
  • Radicular pain in the distribution of the affected nerve root 2, 3, 7
  • Pain often worse in supine position 7
  • In cervical spine: neck and arm pain, paresthesias, possible weakness 2
  • In sacral spine: sitting intolerance and sacral/perineal sensory changes are particularly discriminating features 6

Management Implications

Synovial Cyst Management:

• Often requires intervention if symptomatic
• Surgical excision is definitive treatment 4
• May respond to epidural steroid injections temporarily

Tarlov Cyst Management:

• Conservative approach is first-line for mildly symptomatic cases 2, 3
• Successful conservative treatment includes:
  • Soft cervical collar (2 weeks)
  • Oral corticosteroids (14-15 days) 2, 3
  • Activity restrictions
  • NSAIDs 3
• Repetitive transforaminal epidural steroid injections can provide sustained relief and may cause cyst shrinkage 7
• Surgery reserved for progressive neurological deficits or failed conservative management 6
• 90% symptom improvement achievable with conservative treatment alone 3

Critical Clinical Pitfall

Do not assume the 4mm Tarlov cyst is causing symptoms without careful clinical correlation. At 4mm, this cyst is likely an incidental finding. Look for alternative pain generators including:

• Disc herniation at the same or adjacent levels
• Foraminal stenosis from degenerative changes
• The 6mm synovial cyst itself as the primary pain source
• Other soft tissue pathology

The synovial cyst at 6mm is more likely to be clinically relevant than the 4mm Tarlov cyst, particularly if there is facet arthropathy and the patient's symptoms correlate with C6-C7 nerve root distribution.