3D CRANI, a novel MR neurography sequence, can reliable visualise the extraforaminal cranial and occipital nerves

Abstract

Objectives: We aim to validate 3D CRANI, a novel high-field STIR TSE, MR neurography sequence in the visualisation of the extraforaminal cranial and occipital nerve branches on a 3-T system. Furthermore, we wish to evaluate the role of gadolinium administration and calculate nerve benchmark values for future reference.

Methods: Eleven consecutive patients underwent MR imaging including the 3D CRANI sequence before and immediately after intravenous gadolinium administration. Two observers rated suppression quality and nerve visualisation using Likert scales before and after contrast administration. Extraforaminal cranial and occipital nerves were assessed. Nerve calibers and signal intensities were measured at predefined anatomical landmarks, and apparent signal intensity ratios were calculated.

Results: The assessed segments of the cranial and occipital nerves could be identified in most cases. The overall intrarater agreement was 79.2% and interrater agreement was 82.7% (intrarater κ = .561, p < .0001; interrater κ = .642, p < .0001). After contrast administration, this significantly improved to an intrarater agreement of 92.7% and interrater agreement of 93.6% (intrarater κ = .688, p < .0001; interrater κ = .727, p < .0001). Contrast administration improved suppression quality and significant changes in nerve caliber and signal intensity measurements. Nerve diameter and signal intensity benchmarking values were obtained.

Conclusion: 3D CRANI is reliable for the visualization of the extraforaminal cranial and occipital nerves. Intravenous gadolinium significantly improves MR neurography when applying this sequence. Benchmarking data are published to allow future assessment of the 3D CRANI sequence in patients with pathology of the extraforaminal cranial and occipital nerves.

Key points: • MR neurography using the 3D CRANI sequence is a reliable method to evaluate the extraforaminal cranial and occipital nerves. • Gadolinium contrast administration significantly improves suppression quality and nerve visualisation. • Benchmarking values including apparent signal intensity ratios and nerve calibers depend on contrast administration and might play an important role in future studies evaluating extraforaminal cranial and occipital neuropathies.

Keywords: Cranial nerves; Magnetic resonance imaging; Neuroimaging.

Fig. 1

ROI measurements on the 3D CRANI sequence of the midpoint of the lingual nerve. Using the magnifying tool (red box at top inset) the nerve diameter (blue ROI line) can be accurately measured in a coronal view. To measure signal intensity, a ROI is placed at predefined landmarks within the nerve contour (upper green ROI circle). A 1 cm² ROI circle is used to measure muscle signal intensity in an axial view (right masseter muscle: lower green ROI circle) and air signal intensity within the right maxillary sinus (not illustrated here)

Fig. 2

a Axial view of the 3D CRANI sequence immediately after contrast administration illustrating the ophthalmic division of the trigeminal nerve (white arrows) entering the orbit. b Axial view of the 3D CRANI sequence immediately after contrast administration illustrating the maxillary nerve (second division of the trigeminal nerve) starting at Meckel’s cave and its infraorbital branch coursing inferior to the optic nerve towards the infraorbital foramen

Fig. 3

a Oblique coronal view of the 3D CRANI sequence immediately after contrast administration illustrating the lingual nerve (long arrow) and inferior alveolar nerve (short arrow) running lateral to the pterygoid muscles on an oblique coronal viewing plane. Barium filled bags were used to fixate the patient’s head and further improve the suppression quality of surrounding tissues. b Third division of the trigeminal nerve in an axial view. This illustrates the ability of the 3D CRANI sequence to visualise the buccal (arrowhead), deep temporal (small short arrow), auriculotemporal (small long arrow), and masseteric (large arrow) nerves

Fig. 4

a Visualization of facial (VII), hypoglossal (XII), accessory (XI) and glossopharyngeal-vagus (IX-X) nerves on a coronal 3D CRANI sequence immediately after contrast administration. b Greater occipital (long arrow) and lesser occipital nerves on an axial 3D CRANI viewing plane

Fig. 5

a Venous plexus artefacts before contrast administration limiting the visualization of the third division of the trigeminal nerve in the area of the pterygoid muscles and plexus. b Same patient as in Figs. 1, 2, 3, 4 and 5 after gadolinium contrast administration. Remarkable improvement in suppression quality and nerve visualisation. Some lymph nodes remain poorly suppressed (white arrow)

Fig. 6

Qualitative nerve visualisation scores as assessed by both observers using a 5-point scale (4, excellent: both proximal and distal portion identified; 3, good: both portions identified but not continuous; 2, fair: only proximal portion identified; 1, poor: only proximal portion identified but not continuous; 0, nerve could not be identified). Most nerves were rated as good to excellent visualization (green cut-off line)