Neuroradiology
Figure 8: Axial Constructive Interference in Steady-state Image at the Level of the Inferior Olivary Nucleus Showing the Normal Left Vagus Nerve
and supplies motor fibers to the stylopharyngeus muscle. CNIX passes anterior to the choroid plexus and cerebellar flocculus. It is the only nerve that enters the jugular foramen through the pars nervosa, which is a funnel-shaped dural meatus medial to the jugular spur (see Figure 7). The inferior petrosal sinus can be used as a landmark to identify CNIX, which is anterior to the glossopharyngeal meatus.14
The Vagus Nerve
The two rootlets of the vagus nerve (large arrow) are seen posteriorly to the glossopharyngeal nerve (small arrow) entering the pars vascularis of the jugular foramen.
Figure 9: Axial Constructive Interference in Steady-state Image Showing the Oblique Course of the Hypoglossal Nerve (Large Arrow) as it Crosses the Lateral Perimedullary Cistern and Enters the Hypoglossal Canal (Small Arrow)
CNX is the longest CN. It innervates the larynx, esophagus, heart, lung, stomach, and intestines. On leaving the medulla between the ION and the inferior cerebellar peduncle, it extends through the pars vascularis of the jugular foramen, then passes into the carotid sheath to lie between the internal carotid artery and the internal jugular vein. The great majority of fibers composing CNX are afferent (sensory), conveying information from the viscera to the central nervous system. It supplies all of the intra-abdominal organs, with the exception of the adrenal glands and the distal second segment of the transverse colon. CNX is seen in its cisternal portion before entering the jugular foramen as one or two main roots (see Figure 8) at the level of the vagal trigone (a small bulge in the caudal portion of the floor of the fourth ventricle caused by the dorsal motor nucleus of CNX).14
The Spinal Accessory Nerve
CNXI has both a cranial and a spinal component. CNXI is purely motor, innervating the sternocleidomastoid and trapezius muscles. CNXI is not easily visualized, and in some situations, coronal oblique reformats are necessary. However, root bundles that enter the pars vascularis but do not join the one or two main vagal roots can be classified as CNXI. The spinal roots of CNXI are those that rise through the foramen magnum and traverse the posterior fossa to reach the pars vascularis.14
The Hypoglossal Nerve
Figure 10: Axial Constructive Interference in Steady-state Image at the Level of the Interpeduncular Fossa Showing the Usual ‘Comet Tail’ Appearance of a Dilated Perivascular Space in the Left Cerebral Peduncle
The hypoglossal nerve (CNXII) is a pure motor nerve that innervates the intrinsic and extrinsic tongue muscles (see Figure 9). The nucleus of CNXII is located medially to the dorsal nucleus of CNX and lies within the posterior and inferior aspects of the medulla oblongata. It lies close to the midline in the floor of the fourth ventricle, causing a focal bulge. CNXII exits the brainstem between the ION and the pyramid in the pre-olivary sulcus. The vertebral and posterior inferior cerebellar arteries are anterior and posterior to the cisternal portion of the CNXII, respectively.15
Cysts and Cystic Lesions
CISS is the sequence of choice to study cystic structures. Its application ranges broadly from the assessment of Virchow–Robin spaces (VRS) to the evaluation of cystic tumors such as dysembryoplastic neuroepithelial tumors (DNET).
Virchow–Robin Spaces
anterior and lateral portion of the medulla in the groove between the inferior olivary nucleus (ION) and the restiform body. It carries sensory information from the posterior third of the tongue, tonsils, pharynx, and middle ear and supplies parasympathetic stimuli to the parotid gland. Additionally, it receives sensory fibers from the carotid bodies
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VRS are an extension of the subarachnoid space that surround the walls of arteries, arterioles, veins, and venules. The VRS signal should always follow that of the cerebrospinal fluid in all pulse sequences and should not enhance. Typically, VRS can occur in three locations: along the lenticulostriate arteries, inferior to the basal ganglia at the level of the anterior perforated substance (type 1); in the path of the perforating medullary arteries in the convexities, extending into the white matter (type 2); and in the midbrain (type 3) surrounding the collicular, accessory
US RADIOLOGY
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