What imaging modality is recommended to assess the trigeminal nerve (cranial nerve V) roots?

From the Guidelines

To assess trigeminal nerve roots, I recommend high-resolution magnetic resonance imaging (MRI) with thin-slice sequences through the brainstem, cerebellopontine angle, and skull base, as it provides the best visualization of the nerve and its potential pathologies, according to the most recent guidelines 1. The trigeminal nerve is a complex structure that requires detailed imaging to evaluate its entire course, from the brainstem to its peripheral branches.

• High-resolution MRI with thin-slice sequences is essential for visualizing the cisternal and root entry zone segments of the trigeminal nerve, where compression or pathology often occurs.
• The use of T1-weighted images with and without gadolinium contrast, T2-weighted images, and constructive interference in steady state (CISS) or fast imaging employing steady-state acquisition (FIESTA) sequences provides excellent visualization of the nerve and its surrounding structures.
• MRI is preferred over CT because it offers superior soft tissue contrast for evaluating nerve structures and can detect vascular compression, demyelination, tumors, and inflammatory changes affecting the trigeminal nerve, as stated in the guidelines 1.
• In cases where vascular compression is suspected, MR angiography (MRA) may be added to better visualize the relationship between blood vessels and the nerve, as recommended in the guidelines 1. Some key points to consider when ordering imaging for trigeminal nerve roots include:
• The importance of using high-resolution techniques to visualize the nerve and its surrounding structures.
• The need to evaluate the entire course of the nerve, from the brainstem to its peripheral branches.
• The use of MRI as the preferred modality, due to its superior soft tissue contrast and ability to detect various pathologies.
• The potential addition of MRA in cases where vascular compression is suspected, as supported by the guidelines 1. It is also important to note that, if the patient has contraindications to MRI, such as certain implanted devices or severe claustrophobia, high-resolution CT with contrast can be considered as an alternative, although it provides less detailed information about the nerve itself, as mentioned in the guidelines 1.

From the Research

Imaging Modalities for Trigeminal Nerve Roots Assessment

To assess the trigeminal nerve roots, the following imaging modalities can be considered:

• Magnetic Resonance Imaging (MRI) with specific sequences such as:
  • Thin-sliced, axial T2-weighted imaging 2
  • Coronal constructive interference in steady-state (CISS) sequence 2, 3
  • 3D T2-weighted driven equilibrium (DRIVE) 4
  • 3D time-of-flight (TOF) magnetic resonance angiography (MRA) 4, 3
  • 3D T1-weighted gadolinium-enhanced sequences 4
• High-resolution 3T MRI for detailed anatomy and neurovascular relationships 4

Key Imaging Findings

Key imaging findings for trigeminal nerve roots assessment include:

• Delineation of the main trigeminal sensory root and its divisions 2
• Identification of the accessory sensory and motor rootlets 2
• Visualization of the neurovascular relationships, including contact between the sensory root and surrounding vessels such as the superior cerebellar artery (SCA) and the anterior inferior cerebellar artery (AICA) 4, 3
• Assessment of the degree of compression exerted on the root 4

Clinical Applications

These imaging modalities and findings have clinical applications in:

• Diagnosing trigeminal neuralgia and other diseases affecting the trigeminal nerve 4, 5
• Preoperative planning for microvascular decompression and other surgical procedures 4
• Evaluating the anatomy and pathology of the trigeminal nerve and its branches 5, 6