Trigeminal Nerve Involvement with ICA Junction Aneurysms
Yes, left-sided trigeminal nerve involvement can occur with Internal Carotid Artery (ICA) junction aneurysms, particularly when the aneurysm is large and projects posteriorly or medially to compress the trigeminal nerve in the cavernous sinus or at its root entry zone.
Anatomical Basis for Trigeminal Involvement
The trigeminal nerve (CN V) provides general sensation to the face and divides into three main branches: ophthalmic (V1), maxillary (V2), and mandibular (V3) divisions 1. The meningeal branch of the mandibular nerve re-enters the cranium through the foramen spinosum to provide sensory innervation to the dura mater of the middle cranial fossa 1.
ICA aneurysms can compress the trigeminal nerve through two primary mechanisms:
- Cavernous sinus compression: When aneurysms extend into or compress the cavernous sinus, where the trigeminal nerve and its branches traverse 2
- Direct trigeminal root compression: Large aneurysms projecting posteriorly or medially can directly compress the trigeminal root at the pons 2
Clinical Presentation Patterns
Aneurysms at the ICA junction causing trigeminal symptoms typically present with specific characteristics:
- Mean aneurysm size of 24.7mm (range 7-40mm), with 87.5% projecting posteriorly 2
- Atypical trigeminal neuralgia (continuous pain with exacerbating fits) in 87.5% of cases, rather than classic TGN 2
- Absence of trigger points in 87.5% of cases 2
- Most common pain distribution: V2 alone, followed by V1-2, then V1-2-3 2
Associated Cranial Nerve Findings
Abducens nerve palsy (CN VI) frequently accompanies trigeminal involvement with ICA-persistent primitive trigeminal artery (PPTA) junction aneurysms, as documented in multiple case reports 3, 4. This occurs because both nerves traverse the cavernous sinus in close proximity to the ICA.
Critical Diagnostic Considerations
When evaluating for ICA junction aneurysms with trigeminal symptoms, look for:
- Large aneurysm size (typically >20mm) with posterior-medial-inferior projection 2
- Cavernous sinus extension or compression on imaging 2
- Continuous facial pain rather than paroxysmal attacks 2
- Absence of typical TGN trigger points 2
- Associated oculomotor or abducens nerve dysfunction 3, 4
Imaging Approach
For suspected ICA junction aneurysms causing cranial nerve symptoms:
- CTA with 3-dimensional reconstruction, MRA, or DSA are all reasonable initial screening modalities 5
- If initial imaging is negative but clinical suspicion remains high, conventional angiography may be reasonable 5
- DSA offers diagnostic advantage for small aneurysms (<3mm) but carries <1% complication risk 5
Common Pitfalls to Avoid
Do not dismiss atypical facial pain patterns in patients with large ICA aneurysms, as trigeminal involvement presents differently than classic TGN (continuous pain, no triggers, multiple divisions involved) 2.
Consider persistent primitive trigeminal artery (PPTA) variants, as aneurysms at the ICA-PPTA junction have particular propensity for causing both trigeminal and abducens nerve symptoms 3, 4, 6, 7.
Recognize that standard ICA occlusion may be inadequate for PPTA-associated aneurysms, as continued blood supply via the PPTA from the vertebrobasilar system can maintain aneurysm filling 6, 7.
Treatment Implications
Surgical aneurysmal clipping has been the most frequent treatment for ICA junction aneurysms causing trigeminal symptoms, providing complete trigeminal pain relief in all reported cases with good neurological outcomes (average mRS score of 1) 2. Flow-diverter stents represent an emerging alternative, particularly after PPTA embolization when applicable 4.