What is a Perineural Neuroforaminal Cyst?
A perineural neuroforaminal cyst (also known as a Tarlov cyst) is a cerebrospinal fluid-filled sac that develops at the junction of a dorsal root ganglion and posterior nerve root, typically located within or near the neural foramen of the spine. 1
Anatomical Characteristics
- Location: These cysts most commonly occur in the sacral region, though they can develop in cervical, thoracic, or lumbar spine locations 1, 2, 3
- Structure: They are thin-walled sacs filled with clear cerebrospinal fluid (CSF) that communicate with the subarachnoid space 1, 4
- Size: Cysts can range from a few millimeters to several centimeters in diameter 1
Clinical Presentation
Asymptomatic Cases
- Most perineural cysts are asymptomatic and discovered incidentally during routine spine imaging 1, 5
- These incidental findings typically require no treatment 5
Symptomatic Cases
When symptomatic, clinical manifestations depend on location:
- Sacral/lumbar cysts: Most commonly present with sciatica, low back pain, or claudication 1, 5
- Cervical cysts: Can mimic cubital tunnel syndrome with motor weakness of finger muscles, hypoesthesia in the hypothenar region, and radicular pain 2, 3
- Thoracic cysts: May cause intermittent intercostal neuralgia corresponding to specific dermatomes 4
- Severe cases: Rarely present with cauda equina syndrome requiring urgent intervention 5
Imaging Characteristics
MRI Findings
- Cysts appear isointense to CSF on all MRI sequences 6
- No enhancement after gadolinium administration 6
- The cyst wall is typically not visible on standard imaging 6
- Extra MRI sections through the neural foramen or extraforaminal area may be needed for visualization 2
Myelography/CT Findings
- Classic finding: Delayed filling with contrast medium on myelography, distinguishing them from meningeal diverticula 4
- Atypical presentation: Some cysts show selective filling of contrast medium immediately after injection, suggesting CSF inflow exceeds outflow 4
- Contrast enhancement typically equalizes with the thecal sac within 3 hours and becomes undetectable by 24 hours 4
Pathophysiology
The mechanism of symptom development involves an imbalance between CSF inflow and outflow, causing intermittent elevation of pressure within the cyst 4. This pressure fluctuation leads to:
- Nerve root compression
- Radicular pain patterns
- Potential motor or sensory deficits
Management Algorithm
Conservative Management
- Asymptomatic cysts require only patient counseling and reassurance 6
- For nonspecific symptoms, obtain two sequential scans approximately 1 year apart to demonstrate stability 6
- Long-term imaging follow-up is unnecessary once stability is confirmed 6
Medical Treatment
- Repetitive transforaminal epidural steroid injections (TFESI) can provide incremental relief lasting more than 6 months 3
- Intercostal nerve blocks are effective for thoracic cysts causing neuralgia 4
- Corticosteroids should be administered perioperatively to decrease brain edema if surgery is planned 6
Surgical Indications
Surgery is indicated only for symptomatic cysts that fail conservative management:
Diagnostic cyst aspiration should be performed first 1
Microsurgical cyst fenestration is the preferred surgical approach 1
Alternative surgical options include excision with duraplasty 5
Common Pitfalls
- Avoid preoperative antiparasitic drugs as they may cause cyst disruption 6
- Nonspecific headaches unrelated to hydrocephalus are not well-accepted indications for surgical intervention 6
- Patients who decline surgery after positive aspiration may show symptom progression (4 of 10 patients in one series) 1