What is the mechanism by which a C5/6 disc extrusion causes headaches throughout the skull?

Mechanism of C5/6 Disc Extrusion Causing Headaches

A C5/6 disc extrusion is unlikely to directly cause headaches throughout the skull, as this level is below the typical anatomical pathways responsible for cervicogenic headache, which primarily involve the upper cervical spine (C1-C3) and their convergence with trigeminal pathways.

Anatomical Basis for Cervicogenic Headache

The established mechanism for cervicogenic headache involves the trigeminocervical nucleus, where upper cervical afferents from C1, C2, and C3 spinal nerves converge with trigeminal nerve afferents in the upper cervical cord 1. This functional convergence allows bidirectional referral of pain to the occipital, frontal, temporal, and orbital regions 1. The International Headache Society defines cervicogenic headache as secondary to disorders of cervical spine elements, typically accompanied by neck pain 2, 3.

Why C5/6 is Atypical

• C5/6 is anatomically distant from the trigeminocervical nucleus convergence zone that mediates typical cervicogenic headache 1
• The pathophysiologic mechanism requires upper cervical nerve involvement (C1-C3) to access the trigeminal sensory pathways 1
• Only one case report exists of a C5 nerve root schwannoma causing cervicogenic headache, representing an exceptional circumstance 4

Potential Indirect Mechanisms at C5/6

If headaches are truly related to C5/6 pathology, consider these alternative explanations:

• Referred myofascial pain: Chronic neck pain from C5/6 disc extrusion may cause secondary muscle tension and spasm in cervical musculature, which can refer pain cephalad 1
• Cervical range of motion limitation: Patients with cervical spine disorders and limited ROM have higher rates of associated headache (66.7% prevalence) 1
• Biomechanical compensation: Altered cervical mechanics at C5/6 may create abnormal stress on upper cervical segments, indirectly affecting C1-C3 structures 1

Clinical Risk Factors Supporting Association

Studies demonstrate that cervical spine disorders requiring surgery have associated headache when these features are present:

• Neck pain (86.7% of patients with cervicogenic headache have concurrent neck pain) 1
• Limited cervical ROM (66.7% association) 1
• High Neck Disability Index scores 1
• Cervical spondylotic myeloradiculopathy (60% prevalence of cervicogenic headache, highest among cervical disorders) 1

Diagnostic Considerations

The diagnosis remains challenging due to heterogeneous clinical presentations, overlapping symptoms with other headache disorders (particularly migraine), and lack of definitive radiological findings 2, 3. Importantly, abnormal imaging findings are common in asymptomatic patients, making it difficult to establish causation 2, 3.

Critical Pitfall to Avoid

Do not assume all headaches in patients with cervical spine pathology are cervicogenic. The prevalence of true cervicogenic headache in patients with cervical spine disorders requiring surgery is only 21.4% 1, much lower than previously reported. Consider alternative primary headache disorders (migraine, tension-type headache) that may coexist with or be exacerbated by cervical pathology 2.

Diagnostic Approach

• MRI is the most sensitive imaging modality for detecting soft tissue abnormalities with 90.6% sensitivity and 95.4% specificity 3
• Percutaneous interventions (such as nerve blocks at suspected levels) serve both diagnostic and therapeutic purposes in confirming cervical origin 2, 3
• Evaluate for upper cervical pathology (C1-C3) that may be the actual source despite prominent C5/6 findings 1