Appearance of Normal Cranial Nerves on Steady-State Free Precession MR Images

Abstract

As radiologic imaging technology improves and more intricate details of the anatomy can be evaluated, images provide more precise diagnostic information and allow better localization of abnormalities. For example, standard T2-weighted magnetic resonance (MR) imaging sequences adequately depicted only the larger cranial nerves, whereas current steady-state free precession (SSFP) sequences are capable of depicting the cisternal segments of all 12 cranial nerves. SSFP sequences provide submillimetric spatial resolution and high contrast resolution between cerebrospinal fluid and solid structures, allowing the reconstruction of elegant multiplanar images that highlight the course of each nerve. These sequences have become a mainstay in the evaluation of the cerebellopontine angles and inner ear. Usually referred to by their trade names or acronyms (eg, constructive interference steady state, or CISS, and fast imaging employing steady-state acquisition, or FIESTA), SSFP sequences allow precise differentiation between branches of the facial and vestibulocochlear nerves, accurate detection of small masses in the cerebellopontine angles and internal auditory canals, and detailed evaluation of endolymph and perilymph within the inner ear. To take full advantage of these imaging sequences, radiologists must be familiar with the appearances of similar anatomic details of all 12 cranial nerves on SSFP MR images.

Visualization of the Peripheral Branches of the Mandibular Division of the Trigeminal Nerve on 3D Double-Echo Steady-State with Water Excitation Sequence

“…Following the entire course of the cranial nerves, including the extracranial segments, however, is still a diagnostic challenge in routine clinical practice. 1,2,[11][12][13][14][15][16] Intracranial segments of the cranial nerves, particularly the cisternal segments, are readily detected by using high-resolution heavily T2-weighted imaging. 14,15 Without the high-signal background from the CSF, however, heavily T2-weighted imaging has not proved to be very useful in visualizing the extracranial segments of the cranial nerves.…”

“…With increasing spatial and contrast resolution of cross-sectional imaging, better visualization of the cranial nerves and their major branches has become possible, but the delineation of the entire course of the extracranial segments of the cranial nerves still remains a diagnostic challenge. [11][12][13][14][15][16][17] The trigeminal nerve has the largest distribution of innervation among all the cranial nerves in the suprahyoid neck. Even though the mandibular nerve (V3) is the largest division of the trigeminal nerve, there have been only limited studies investigating the visualization of the extracranial segments of V3 with MR imaging.…”

MRI Findings in Patients with a History of Failed Prior Microvascular Decompression for Hemifacial Spasm: How to Image and Where to Look

“…[17][18][19][20] The use of SSFP imaging has been shown to predict vascular compression of the facial nerve with sensitivities of 75%-93% and specificities of 29%-75% for blinded observers. 21 In light of this higher sensitivity and lower specificity, the decision to operate is supported by imaging, but imaging results are never the sole factor in determining whether to offer MVD to a patient.…”

MRI Sequences in Head & Neck Radiology – State of the Art

“…high-resolution dark signal of cranial nerves and very high signal of liquor in SSFP [20] labyrinthitis lower signal intensity than liquor on SSFP [22] menière's disease endolymphatic hydrops as ratio of high post-gadolinium 3D-FLAIR signal intensity in the perilymphatic space and the high signal in MRI cisternographic sequences in both endolymph and perilymph: vestibule (mild: 34 -50 %, significant: > 50) cochlea (mild: extrusion of the scala media, significant: scala media larger than scala vestibuli) [25] 3D-TOF, TWIST/ TRICKS angiography, DCE vascular contact syndromes point, longitudinal and loop compression as well as indentation of cranial nerves on 3D-TOF [26] infantile hemangioma arterial enhancement on TWIST with gadofosveset trisodium [30] venous malformation venous enhancement on TWIST with gadofosveset trisodium [30] lymphatic malformation no enhancement on TWIST with gadofosveset trisodium [30] arteriovenous malformation arterial and venous enhancement on TWIST with gadofosveset trisodium [30] hypoxia low K trans [32] bone do not cause severe artifacts (as typically seen in computed tomography CT), which makes MRI a superior image modality for delineating tumors in the oropharynx and oral cavity [5]. The ability to discriminate fluid and mucus from soft tissue is extremely helpful in the imaging of sinonasal tumors.…”

“…SSFP has become essential in identifying the vestibular cochlear nerves before cochlear implant surgery. It allows for the accurate detection of small masses such as schwannomas in the cerebellopontine angles and internal auditory canals, and detailed evaluation of the labyrinth of the inner ear [20,21]. In addition to a high signal in T1wC+, labyrinthitis may show a lower signal than fluid on SSFP [22].…”