Learning objectives
1.
To present an optimum imaging protocol for hypoglossal nerve imaging.
2.
To review the normal course of the hypoglossal nerve using a segmental approach.
3.
To present a pictorial overview of pathologic conditions affecting the hypoglossal nerve in each of its four segments.
Background
The twelfth cranial nerve or hypoglossal nerve is an entire motor nerve,
controlling the intrinsic and extrinsic muscles of the tongue,
as well as the infrahyoid strap muscles through an anastomosis with the cervical plexus,
called the ansa cervicalis.
Damage to the hypoglossal nerve produces characteristic clinical and radiological manifestations of which unilateral tongue atrophy is the most common.
Dysfunction of the hypoglossal nerve may be a consequence of supranuclear,
nuclear or infranuclear disease.
The nuclear and infranuclear hypoglossal nerve can be divided into four...
Imaging findings OR Procedure details
MRI is the imaging modality of choice for the study of a patient with hypoglossal nerve palsy.
It supplies superior soft-tissue contrast and allows direct visualization of the different segments of the nerve.
Multiple sequences are available to study the nerve and each has specific advantages according to the segments being studied.
For the intra-axial segment or above (nuclear or supra-nuclear lesions) a brain protocol is used with fast spin-echo (FSE) T2WI of the brain and T1WI of the skull base.
After intravenous injection of...
Conclusion
MRI is the preferred imaging technique to visualize the hypoglossal nerve.
For the radiologist approaching a patient with hypoglossal nerve damage,
a segmental anatomical approach and knowledge of the most common pathologic conditions occurring in each segment will narrow the differential diagnosis.
References
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Hypoglossal nerve palsy: a segmental approach.
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Cranial nerve XII: The hypoglossal nerve.
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Lemmerling M,
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Traumatic dissection of the internal carotid artery as an unusual cause of hypoglossal nerve dysfunction.
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