Hypoglossal nerveDr / Hytham Nafady

Introduction

hypoglossal nerve has only a somatic motor component (general somatic efferent) that supplies the extrinsic and intrinsic tongue muscles.

Anatomy

Segments of the hypoglossal nerve

• Hypoglossal nucleus.

Intracranial segments:

• Medullary segment.

• Cisternal segment.

• Canalicular segment.

Extracranial segments:

• Nasopharyngeal/oropharyngeal carotid space.

• Sublingual segment.

Hypoglossal nucleus, medullary & cisternal segments

Hypoglossal nucleus

• Location:

Hypoglossal colliculus of the medulla oblongata.

Medullary segment

• The fibers of the hypoglossal nerve course anteriorly lateral to the medial leminscus & lateral to the olive.

• The hypoglossal nerve exits the medulla at the pre-olivary sulcus.

Cisternal segment

• The hypoglossal nerve course laterally through the premedullary cistern, posterolateral to the vertebral artery.

PICA

Hypoglossal nerve

Vertebral arteries

Canalicular segment (hypoglossal canal)

Hypoglossal canal axial CT

Hypoglossal canal coronal CT

Persistent primitive hypoglossal artery

Interpeduncular cistern

ICA

Sigmoid sinus

IJV

Cn 12

Cn 10

Cn 9

Suprahyoid carotid space segment

• The hypoglossal nerve lies deep to the IJV, ICA & 9 & 10 cranial nerves.

• It become superficial as it courses anteriorly.

• At the level of angle of the mandible it loops anteriorly around the root of the occipital artery and lying deep to the posterior belly of digastric muscle.

Sublingual segment

• The hypoglossal nerve enters the sublingual space by crossing the lingual artery at the level of hyoid bone.

• The hypoglossal nerve lies superfical to the hyoglossus muscle & deep to the myelohyoid muscle.

suprahyoid carotid space segment

platymsa

base

Intrinsicmuscles

GG

GH

Action of genioglossus in sticking out the tongue

Tongue protrusion

Pushing the tongue into the cheek against resistance

Hypoglossal palsy

Medullary glioma

Vertebrobasilar dolichoectasia with hypoglossal nerve palsy

Meningioma

Cisternal hypoglossal schwannoma with tongue atrophy

Isolated hypoglossal palsy caused by synovial cyst

Hypoglossal schwannoma

Occipital condylar fracture

Skull base metastasis

Carotid artery dissection

Extracranial hypoglossal schwannoma with tongue hemiatrophy

Submandibular hypoglossal schwannoma