What is the recommended Magnetic Resonance Imaging (MRI) protocol for diagnosing Trigeminal Neuralgia?

From the Guidelines

MRI is the preferred imaging modality for diagnosing trigeminal neuralgia, and a high-resolution MRI with thin-slice sequences focused on the posterior fossa is recommended. This recommendation is based on the most recent and highest quality study available, which suggests that MRI is useful for directly imaging the trigeminal nerve and assessing for neurovascular compression, demyelination, tumors, or other structural abnormalities 1.

Key Considerations for MRI

• The scan should include specialized sequences like FIESTA (Fast Imaging Employing Steady-state Acquisition), CISS (Constructive Interference in Steady State), or 3D TOF (Time-of-Flight) MR angiography to better visualize the trigeminal nerve and surrounding vascular structures 1.
• The MRI should cover the entire course of the trigeminal nerve from the brainstem to the peripheral branches to identify any potential compression, demyelination, tumors, or other structural abnormalities 1.
• Pre- and postcontrast imaging provides the best opportunity to identify and characterize a lesion, although noncontrast MRI may also be an alternate option for this clinical scenario 1.

Important Details

• Patients should inform their doctor about any metal implants, pacemakers, or claustrophobia before undergoing MRI.
• The procedure is non-invasive and typically takes 30-60 minutes to complete.
• Advanced MRI techniques, including diffusion tensor imaging (DTI), functional MRI, and voxel-based morphometry, are being used to research the pathophysiology of trigeminal neuralgia and may be useful for making treatment decisions 1.

Clinical Context

• Trigeminal neuralgia is often caused by vascular compression of the trigeminal nerve, typically by the superior cerebellar artery.
• Imaging evidence of vascular trigeminal nerve root compression, the degree of compression, location of contact, and nerve volume may have prognostic value 1.
• MRI is supportive rather than diagnostic in selecting candidates for microvascular decompression and should be interpreted in the context of the site of symptoms 1.

From the Research

MRI for Trigeminal Neuralgia

• High-resolution MRI can be used to identify neurovascular compression in patients with trigeminal neuralgia, with a study finding that 93% of patients had one or several vascular structures in contact with the trigeminal nerve or close to its origin in the pons 2.
• MRI studies, including T1, T1 enhanced, and T2-SPIR, with axial, coronal, and sagittal simultaneous visualization, can be used to assess the anatomy of the trigeminal nerve, brain stem, and vascular structures related to this nerve 2.
• High-resolution trigeminal sequences should be performed as part of the diagnostic work-up for trigeminal neuralgia 3.
• MRI can help identify secondary causes of trigeminal neuralgia, including multiple sclerosis, and can be used to evaluate patients with neurovascular conflict before surgery 4.
• The use of MRI to identify neurovascular compression of the trigeminal nerve is supported by some studies, but there is insufficient evidence to fully support or refute its usefulness 5.

Types of MRI

• High-resolution MRI can provide exquisite anatomic detail and allow radiologists to scrutinize the entire course of the trigeminal nerve 4.
• T1, T1 enhanced, and T2-SPIR sequences can be used to assess the anatomy of the trigeminal nerve, brain stem, and vascular structures related to this nerve 2.
• High-resolution trigeminal sequences should be performed as part of the diagnostic work-up for trigeminal neuralgia 3.

Diagnostic Criteria

• New diagnostic criteria for trigeminal neuralgia subclassify the condition based on the presence of trigeminal neurovascular conflict or an underlying neurological disorder, and can help with decision-making regarding medical and surgical treatments 3.
• Trigeminal sensory deficits, bilateral involvement of the trigeminal nerve, and abnormal trigeminal reflexes are associated with an increased risk of symptomatic trigeminal neuralgia and should be considered useful in distinguishing it from classic trigeminal neuralgia 5.