Can arachnoiditis contribute to or cause herniation, rather than just being a secondary result of herniation or microdiscectomy?

Arachnoiditis as a Potential Cause of Disc Herniation

Arachnoiditis typically occurs as a consequence of disc herniation or microdiscectomy rather than causing herniation itself, though in rare cases, the inflammatory process may contribute to structural changes that predispose to herniation.

Pathophysiology and Relationship to Herniation

Arachnoiditis is characterized by inflammation of the arachnoid membrane that surrounds and protects the spinal cord. This condition typically develops as a secondary complication rather than a primary cause of disc herniation. However, the relationship between arachnoiditis and disc herniation can be complex:

Primary Effects of Arachnoiditis

• Inflammation and scarring of the arachnoid membrane
• Formation of adhesions between nerve roots
• Potential development of syringomyelia in advanced cases 1
• Neurological symptoms including pain, sensory disturbances, and motor deficits

Potential Mechanisms for Contributing to Herniation

In certain circumstances, arachnoiditis might contribute to disc herniation through:

1. Altered Biomechanics: Severe adhesions and scarring can alter normal spinal biomechanics, potentially increasing stress on intervertebral discs 2

2. Inflammatory Processes: Chronic inflammation from arachnoiditis may extend to surrounding tissues, potentially weakening disc structures over time

3. Compensatory Movements: Patients with arachnoiditis often develop compensatory movement patterns to avoid pain, which may place abnormal stress on discs

Clinical Presentation and Diagnosis

The clinical presentation of arachnoiditis includes:

• Low back pain (80%) and leg pain (90%) 3
• Neurological deficits in approximately two-thirds of cases 3
• Sphincter disturbances (25%) 3
• Symptoms that may mimic or overlap with disc herniation

Diagnostic approaches:

• MRI is the first-line imaging modality, which may show the characteristic "scalpel sign" and associated syringomyelia 1
• CT myelography is useful when MRI findings are inconclusive 1

Risk Factors and Causative Relationships

Arachnoiditis is most commonly caused by:

• Previous spinal surgeries, particularly multiple procedures 2, 4
• Oil-based myelography contrast agents 3, 2
• Intrathecal injections of medications or other substances 5, 6
• Spinal infections
• Direct trauma to the spinal cord or nerve roots 5

Management Considerations

When evaluating patients with suspected arachnoiditis and disc herniation:

1. Determine Temporal Relationship: Establish whether arachnoiditis preceded the herniation or developed afterward

2. Imaging Studies: Comprehensive MRI to evaluate both conditions simultaneously

3. Surgical Planning: If surgery is required for herniation, consider the increased risk of worsening arachnoiditis

4. Conservative Management: Consider anti-inflammatory medications and physical therapy when appropriate

Pitfalls and Caveats

• Misdiagnosis is common as arachnoiditis can mimic other conditions including recurrent disc herniation 4
• In a study of 38 patients with postoperative epiduro-arachnoiditis, 6 myelograms simulated recurrent disc herniation 4
• Surgical intervention for patients with established arachnoiditis carries significant risk of worsening the condition 5
• Arachnoiditis is generally considered incurable, with treatment focused on symptom management 2

While arachnoiditis is most commonly a consequence rather than a cause of disc herniation or microdiscectomy, the complex interplay between these conditions warrants careful clinical evaluation and management to optimize patient outcomes.