Download MRI appearance of the normal and diseased hypoglossal nerve

MRI appearance of the normal and diseased hypoglossal
nerve
Poster No.:
C-1971
Congress:
ECR 2013
Type:
Educational Exhibit
Authors:
I. De Kock , B. Smet , M. Lemmerling ; Ghent/BE, Gent/BE,
1
2
3 1
2
3
Beervelde/BE
Keywords:
MR, Neuroradiology brain, Head and neck, Structured reporting,
Technical aspects, Pathology
DOI:
10.1594/ecr2013/C-1971
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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
segments: the medullary, cisternal, skull base and extracranial segments. Because each
segment is usually affected by different disorders, localizing a lesion to a particular
segment allows the radiologist to narrow the differential diagnosis.
ANATOMY:
The cortical centre for lingual movement is located within the precentral gyrus, which
sends fibers to the hypoglossus nucleus. The paired hypoglossus nuclei are located
on the floor of the fourth ventricle, within the medulla oblongata. This is the medullary
segment. The fibers course anteriorly, lateral to the medial lemniscus, to exit the medulla
in the preolivary sulcus. The rootlets lie posterolateral to the vertebral artery within the
premedullary cistern. This is the cisternal segment. Then the rootlets merge to form the
hypoglossal nerve within the hypoglossal canal of the occipital bone. This is the skull
base segment (Fig. 1). Emerging from the hypoglossal canal, the hypoglossal nerve
begins its extracranial course as it enters the nasopharyngeal carotid space. As the
nerve passes inferiorly, it comes to lie between the internal jugular vein and the carotid
artery, superficial to the vagus nerve (Fig. 2). At the level of the angle of the mandible
it then takes an anterior course, lying at the inferior border of the posterior belly of
the digastric muscle. After exiting the carotid space the nerve continues anteriorly and
inferiorly towards the hyoid bone, crossing the lingual artery to run along the surface of
the hyoglossal muscle. This segment of the hypoglossal nerve lies within the sublingual
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space (Fig. 3). The nerve then continues forward to supply the genioglossus muscle to
the tip of the tongue.
As already mentioned, the hypoglossal nerve not only supplies motor innervation to the
intrinsic and extrinsic muscles of the tongue but also contributes motor innervation to the
infrahyoid strap muscles (sternohyoid, sternothyroid and omohyoid muscle) through the
ansa cervicalis. The ansa cervicalis is made up of fibers from the first to third cervical
nerves (C1-C3) that course through the carotid space together with the hypoglossal nerve
(Fig. 4).
Images for this section:
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Fig. 1: On this axial T2WI through the skull base the dots indicate the hypoglossal
nuclei. The hypoglossal nerve roots exit the medulla oblongata and pass through the
premedullary cistern (arrow heads) toward the hypoglossal canal (asterisk).
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Fig. 2: On this axial T2WI at the level of the oropharyngeal carotid space the arrows
indicate the position of the hypoglossal nerve between the internal jugular vein and the
internal carotid artery.
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Fig. 3: On this axial T2WI at the level of the sublingual space the dots indicate the position
of the hypoglossal nerve lateral to the hyoglossus muscle (H). The hypoglossal nerve
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runs forward into the sublingual space, lying between the paired genioglossus muscles
(G) and the mylohyoid muscles (M).
Fig. 4: This schematic drawing nicely illustrates the consecutive segments of the course
of the hypoglossal nerve (medullary, cisternal, skull base, carotid space, sublingual
space). The anastomosis via the ansa cervicalis is also shown.
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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 gadolinium T1WI are repeated. High resolution T1W images preand post-contrast with fat suppression allow further anatomical characterization of the
remaining segments. The use of contrast is especially useful in infectious/inflammatory
pathology where abnormal enhancement of the nerve may be the only presentation of
the disease.
The hypoglossal nerve should be routinely studied in the axial and coronal plane.
Sometimes the sagittal plane may be useful, e.g. for distal lesions involving the floor of
the mouth or the tongue base.
The imaging approach of a patient with hypoglossal nerve palsy consists of analyzing the
different anatomical segments of the nerve and recognizing the most common differential
diagnosis in each. The most common diseases affecting each segment are discussed
below and are listed in table 1.
Unilateral atrophy of the tongue musculature is the most important radiologic feature of
hypoglossal nerve palsy. Imaging changes in the tongue after damage to the hypoglossal
nerve vary according to the time gone by between the initial nerve lesion and the imaging
examination. MRI is the most useful imaging modality to characterize these various
muscle changes. In the subacute phase of denervation, the tongue is hyperintense on
T2WI and hypointense on T1WI, mainly due to edema. Enhancement of the denervated
part can be seen after intravenous gadolinium administration. In the chronic phase, as
fatty infiltration progresses, the tongue volume on the affected side will decrease. On MRI
the affected tongue will have high signal on both T1WI and T2WI.
Once tongue atrophy is identified at imaging, systemic evaluation of the hypoglossal
nerve should be performed.
MEDULLARY SEGMENT:
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Pathology of this segment of the nerve is frequently associated with damage to other
nuclei, resulting in a complex lower cranial neuropathy. Disease that involves both
hypoglossal nerve nuclei leads to bulbar palsy with complete paralysis of the tongue.
The most common pathology in this region is infarction, due to ischemia or hemorrhage.
Neoplasms are also among the most common causes and may be primary or secondary.
Most frequent are metastases followed by gliomas. Metastases have a variety of imaging
appearances but should always be thought of. Gliomas are heterogeneous lesions with
high signal intensity on T2WI, causing expansion of the brainstem (Fig. 5). Other less
common pathologic processes of inflammatory, infectious or demyelinating nature may
also occur, such as multiple sclerosis, amyotrophic lateral sclerosis or poliomyelitis.
CISTERNAL SEGMENT:
As described in the anatomical layout of the hypoglossal nerve, there is a close
relationship between the nerve and the vertebral artery. Thus, vertebrobasilar pathology
or anatomic variants may cause compression of the rootlets resulting in paralysis. Other
pathologic entities in this region include skull base bony pathology such as clival tumors,
meningioma, osteomyelitis or pathology involving the odontoid such as rheumatoid
arthritis, trauma or Chiari malformation (Fig. 6). Basal meningitis or subarachnoidal
hemorrhage with exsudation and organization can also compromise the nerve. Primary
tumors of the hypoglossal nerve, although uncommon, may also affect the cisternal
portion of the nerve.
SKULL BASE SEGMENT:
Tumors, both benign and malignant, and trauma may damage the hypoglossal nerve
along its course through the skull base. Tumors of the skull base may affect the
hypoglossal canal by expansion or destruction. The most common malignant tumors are
metastasis from breast, lung and prostate cancer and direct extension of nasopharyngeal
carcinoma through the skull base. Benign tumors include peripheral nerve sheath tumors
(such as schwannoma), glomus tumors, and meningiomas (Fig. 7). Primary bony tumors
such as giant cell tumors or osteogenic sarcomas may also involve the hypoglossal canal.
Infection of the skull base (pseudomonas infection, tuberculous osteomyelitis) is even
much rarer, but should also be included in the differential diagnosis, especially in the
diabetic or immunocompromised patient.
EXTRACRANIAL SEGMENT:
•
Carotid space segment:
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In the carotid space the hypoglossal nerve lies in close contact with the internal carotid
artery and internal jugular vein. As a result, ectasia and aneurysm of the carotid artery,
as well as arterial dissection and jugular thrombosis can compress the nerve and lead
to palsy (Fig. 8). However, the most common cause of hypoglossal nerve palsy in the
carotid space are malignant tumors, both primary and secondary pathologies, including
squamous cell carcinoma, lymphoma, salivary gland tumors and metastatic disease.
Benign tumors such as paragangliomas and lipomas should also be in the differential
diagnosis.
Iatrogenic lesions (endarterectomy, vascular punction) or trauma (stab, gunshot wounds
or infection spreading from other neck spaces) may also cause dysfunction of the twelfth
cranial nerve.
•
Sublingual segment:
The most common cause of dysfunction in this segment is nerve damage due to
squamous cell carcinoma of the base or lateral regions of the tongue (Fig. 9).
Odontogenic lesions such as abscesses or iatrogenic damage after tooth extraction are
other causes to be considered.
Images for this section:
Table 1: Segmental differential diagnosis of hypoglossal palsy.
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Fig. 5: These consecutive T2WI and postgadolinium T1WI in a 40-year-old female
glioma patient with impaired sensibility and motor dysfunction of the left half of the
tongue shows a T2 hyperintense mass in the left half of the pons and in the left
hemicerebellum extending into the medulla oblongata. Heterogeneous enhancement is
noted after gadolinium injection.
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Fig. 6: Three consecutive T1WI are shown in a 52 year-old male with right sided
hypoglossal nerve paralysis and rectal cancer in the previous history. A hypointense lytic
metastasis is shown in a right paraclival location, extending to the hypoglossal canal on
the right side (thick arrows) and to the foramen magnum (thin arrows).
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Fig. 7: Three consecutive T2WI and T1WI are shown (before and after intravenous
injection of gadolinium) in a 49-year-old male with left sided atrophy of the tongue.
A dumbbell-shaped mass is seen (arrows) in the left hypoglossal canal, extending
into the cistern anterior to the medulla oblongata. The mass is hyperintense on T2WI,
hypointense on T1WI, and enhances heterogeneously after intravenous injection of
gadolinium: schwannoma.
Fig. 8: On these T1WI in a 37-year-old female with sudden left sided partial Horner's
syndrome a semilunate T1 hyperintensity is seen (arrows) in the wall of the internal carotid
artery on the left side, indicative of dissection of the artery.
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Fig. 9: T1WI in a 62-year-old male with left sided paralysis of the tongue and dysphagia
show a hypointense squamous cell carcinoma posterolaterally in the left half of the
tongue (thick arrows), with beginning extension to the left sublingual space. On the
fat-suppressed T1WI after intravenous injection of gadolinium moderate enhancement
is noted (thick arrows), and it is obvious that the genioglossus muscle is spared (thin
arrows).
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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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Loh C, Maya MM, Go JL. Cranial nerve XII: The hypoglossal nerve. Semin.
Ultrasound CT MR 2002;23(3):256-65.
Lemmerling M, Crevits L, Defreyne L, Achten E, Kunnen M. Traumatic
dissection of the internal carotid artery as an unusual cause of hypoglossal
nerve dysfunction. Clin Neurol Neurosurg. 1996;98(1):52-4.
Personal Information
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