![]() ![]() CISS was taken in every patient for evaluation of cranial nerve segments. Head coil was used 5 mm thick FSE PD-T2W, FLAIR and T1W axial images, 4 mm FSE coronal T2W & 0.4-0.5 mm thick 3D CISS axial sequences were taken. MRI was done on a 1.5-T Siemens Magnetom Symphony Vision in patients with strong clinical suspicion of intracranial nerve involvement. Axial post contrast 0.5 mm thick VIBE image shows bilateral hypoglossal nerve (thin arrow) surrounding by venous structures in jugular fossa (thick arrow) & faint glossopharyngeal vagus nerve (white arrowheads). Axial 0.5mm thick SSFP image shows oblique course of hypoglossal nerve (white arrowhead) in lateral cerebellomedullary cistern and vertebral arteries (thin white arrow) anterior to the nerve B. The identification rate of each cranial nerve is related to difference in its anatomic characteristics, most importantly nerve diameter and intracranial course.ĭepending on the diameter cranial nerves can be divided into three groups, first group consist CN’s I & II, the second group consist of the CN’s III, V, VII, VIII and the lower nerve complex (IX & XI) and the third group consist of the CN’s IV, VI, and XII ( Tables 1-3). There are 12 paired intracranial nerves, the intracranial segment of paired 12 cranial nerves consists of nuclear, parenchymal fascicular, cisternal, dural cave and interdural segments. On these sequences the intracranial nerve are seen as black structures surrounded by high signal intensity gadoliniumfilled venous structures. Contrast-enhanced T1-weighted images (VIBE-Volumetric Interpolated Breath-Hold Examination) specially help to see the nerves and its branches or segment which are surrounded by venous plexus (III to VI in the cavernous sinus, VI behind the clivus in the basilar plexus, IX to XI in the jugular foramen, XII in the hypoglossal canal). While the interdural and foraminal segments of the CNs are revealed better after the administration of intravenous contrast. The root entry zone, cisternal and intracanalicular segment of each individual nerve is best delineated by non-contrast SSFP sequences. 3D sequences provide submillimetric spatial resolution and high contrast resolution between cerebrospinal fluid and solid structures thus allowing the reconstruction of elegant multiplanar images that highlights the entire course of an individual nerve. Ĭonventional Magnetic Resonance (MR) imaging sequences provide excellent soft-tissue resolution but may lack the spatial resolution which is required for clear depiction of tiny intracranial structures. Casselman et al., first introduced the three-dimensional constructive interference of steady state (3D CISS) sequence for imaging the inner ear and the cerebello-pontine angle. High-resolution Steady-State Free Precession (SSFP) sequences with a heavily T2-weighted appearance are mainstay of visualization of the cisternal component of the CNs since their introduction by Casselman and colleagues. The anatomic visualization of various intracranial nerves largely depends on the nerve diameter, course of the individual nerve as well as on the amount of CSF surrounding it. ![]()
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