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“Unravelling a Bundle of Nerves” ASNR 2016 Electronic Educational Exhibit Saunders D, Adams B, Craven IJ, Warren DJ, Macmullen-Price J, Currie S Department of Neuroradiology, Leeds Teaching Hospitals Trust, Leeds UK eEdE#: eEdE-174 Disclosures • We, the named have authors have no disclosures of conflicts of interest Oh the nerves, the nerves; the mystery of this machine called Man! Charles Dickens - The Chimes (1844) Objectives • This educational resource is designed to use pathology to help better understand the anatomy of the cranial nerves as seen on cross-sectional imaging • Each nerve is described in relation to its course, any special considerations when evaluating individual nerves and some select pathological cases that can be diagnosed radiologically (primarily on MRI) • The user has the option of working through each nerve in turn or alternatively, if time is short focusing on specific nerves by utilising the hyperlinks on the following slide. There are also multiple hyperlinks within the presentation to allow the user to view additional information, images and illustrations • The eventual aim is to adapt this resource to be used in both an undergraduate and postgraduate setting to complement established anatomical and pathological teaching models Contents • CN I – Olfactory • Pathology • Pathology • CN II – Optic • CN VIII –Vestibulocochlear • Pathology • Pathology • CN III – Oculomotor • Pathology • CN IX – Glossopharyngeal • Pathology • CN IV – Trochlear • Pathology • CN X – Vagus • Pathology • CN V – Trigeminal • Pathology • CN XI – Spinal Accessory • Pathology • CN VI – Abducens • Pathology • CN VII – Facial • CN XII - Hypoglossal • Pathology Appendix of images, diagrams and further information Olfactory Nerve (I) Course • Origin: olfactory bulb – cribiform plate • Course and pathway: – Primary neurosensory cells in the roof of both nasal cavities – Efferent axons pass through the cribiform plate to synapse with the olfactory bulb – Pass posteriorly deep within the olfactory grooves inferior to the gyri recti – Enter the inferior frontal regions via medial and lateral olfactory striae – Medial striae – subcallosal medial frontal lobe – Lateral striae – Inferomedial temporal lobes • Tertiary pathways: – Orbitofrontal cortex – Hypothalamus (via septum pellucidum) – Limbic system CONTENTS Olfactory Nerve (I) Notes – Olfactory nerves are white matter tracts not surrounded by schwann cells (unlike most other CNs) – The limbic responses to olfaction are derived through connections to the hypothalamus, habenular nucleus, reticular formation, and cranial nerves controlling salivation, nausea and GI motility. CONTENTS Olfactory Nerve (I) Pathology • Presentation: Anosmia, Parosmia, Phantosmia • Most commonly caused by damage at the olfactory bulb level – Trauma – Upper respiratory tract infection – Nasopharyngeal neoplasm • Central causes described include: – Temporal lobe epilepsy (Usually transient) – Parkinson’s disease CONTENTS I – Olfactory groove meningioma 46F presenting with altered sense of smell. Triplanar MRI demonstrates the typical well circumscribed and homogenously increased T1/T2 signal intensity lesion within the olfactory groove causing elevation of the gyri recti and compression of CN I CONTENTS I – Olfactory groove meningioma This case of a different patient with a larger olfactory groove meningioma demonstrates the typical well defined and homogenously enhancing CT appearances of a meningioma CONTENTS I - Neuroblastoma 32F with nasal discharge and altered sense of smell. In contrast to the previous well defined benign meningioma which was seen to displace structures, this case of neuroblastoma appears much more aggressive with invasion and destruction of the cribiform plate CONTENTS I - Schwannoma 53M – headache and altered sense of smell. These images demonstrate a more in-homogenous but still well defined lesion, demonstrating intense enhancement. This was a rare case of schwannoma affecting the olfactory nerve – remember the olfactory nerves are white matter tracts and are not associated with Schwann cells! CONTENTS Optic Nerve (II) Course • The optic pathway consists of nerves, chiasm, tracts and radiations • The optic nerve has 4 main segments – Retinal: Leaves globe through lamina cribrosa sclerae – Orbital/Retrobulbar: Surrounded by dural sheath, visible through fat filled orbit – Canalicular: Within the optic canal beneath the ophthalmic artery – Cisternal: Suprasellar cistern leading to optic chiasm • The optic nerve terminates at the chiasm. Bilateral nerves meet, decussate and form optic tracts • The optic tracts pass around the cerebral peduncles and enter the lateral geniculate body (LGB) of thalamus • From LGB the optic radiations loop around the occipital horns of the lateral ventricles to enter the visual cortex of the occipital lobe CONTENTS Optic Nerve (II) Notes • Optic nerves are white matter tracts with no surrounding Schwann cells • The canalicular portion of the nerve is frequently overlooked and should be a review area in cases of visual disturbance • Important relations of the suprasellar segment: – Anterior cerebral artery – Infundibulum – Mamillary bodies (posteriorly) CONTENTS Optic Nerve (II) Pathology • • • • • Enlargement of an optic nerve has a large differential The commonest ‘tumours’ are meningioma and glioma – NF1 – increased incidence of glioma – NF2 – increased incidence of meningioma The nerve is covered with dura therefore hydrocephalus and raised ICP can manifest as swelling of the optic nerve (and papilloedema) Other causes of nerve enlargement include, but are not limited to: – Optic neuritis – Orbital pseudotumour – Direct extension of retinoblastoma – Lymphoma and leukaemia – Metastases – Sarcoidosis and other granulomatous diseases. The chiasm can also be compressed by pituitary tumours and the optic radiations can be compromised by infarction, masses and demyelination CONTENTS II – Optic glioma 8M – Known history of Neurofibromatosis 1 and new onset eye pain with decreased visual acuity in the left. Imaging demonstrates gross fusiform enlargement of the left optic nerve in comparison to the right with marked peripheral enhancement typical of an optic glioma which show significantly increased prevalence in patients with NF1. CONTENTS II – optic chiasm glioma 7F: Gliomas can also be very large at presentation as is the case in this young patient who had bilateral visual symptoms and was demonstrated as having a very extensive, avidly enhancing glioma centred on the optic chiasm and extending posteriorly to involve the proximal optic radiations. On axial, post-contrast imaging the basic outline of the chiasm is still vaguely apparent owing to the initially fusiform type enlargement CONTENTS II - meningioma 61F: Meningiomas can occur anywhere where there is meninges as in this case of one affecting the Planum Sphenoidale. Even on precontrast T1 imaging the proximity to the right optic nerve within the optic canal (small arrows) is evident. Imaging characteristics are again typical of meningioma with prominent but homogenous enhancement. CONTENTS Oculomotor Nerve (III) Course • The oculomotor nuclei lie: – Deep to superior colliculus – Ventral to cerebral aquaduct – Inferior to pineal gland • Course: • Root entry zone in interpeduncular cistern • Travels in pre-pontine cistern between superior cerebellar and posterior cerebral arteries • Most superior nerve along the lateral wall of the cavernous sinus • Enters orbit through the superior orbital fissure • Splits into superior and inferior divisions lateral to the optic nerve • A smaller parasympathetic branch accompanies the motor branch to control pupillary constriction and accommodation CONTENTS Oculomotor Nerve (III) Notes • In most cases, to easily identify CN III look: – For the root entry within the interpeduncular cistern – Between the superior cerebellar and posterior cerebral arteries in the coronal plane • The Oculomotor nerve innervates all the extra-occular muscles except the superior oblique and lateral rectus: Denervation therefore results in the resting eye position being down and out CONTENTS Oculomotor Nerve (III) Pathology • The commonest cause of a CN III palsy is secondary to focal ischaemia/infarction affecting the nucleus and is seen more commonly in the presence of diabetes • Note: When secondary to ischaemia the pupillary reflex is usually spared but when secondary to compression pupillary reflex tends to be involved • CN III can be compressed anywhere along it’s path: – Interpeduncular: PCOM aneurysm; basal meningeal (usually > 1 CN affected) infection, inflammation (Sarcoidosis) and neoplastic infiltration. – Cavernous: Pituitary macroadenoma, meningioma, trigeminal schwannoma; Diffuse inflammation (Tolosa-Hunt) – Orbital: Usually have other orbital signs CONTENTS III - Infarct 50F patient with diabetes presented with an acute onset of diplopia. Clinical examination demonstrated reduced eye movements with the globe fixed in downward, lateral gaze. MRI demonstrated increased signal on B1000 sequences with corresponding low signal on ADC map in keeping with acute diffusion restriction within the left oculomotor nucleus consistent with acute infarction. CONTENTS III – PCOM aneurysm In cases of isolated CN III palsies, especially if the onset is sudden and painful, rapid expansion of a Berry aneurysm (most commonly PCOM) should be excluded as was the case in this 68yo female with a large right PCOM aneurysm CONTENTS Trochlear Nerve (IV) Course • Originates from the posterior (dorsal) midbrain • Curves forwards to pass over the superior cerebellar peduncle • Runs alongside CN III between superior cerebellar and posterior cerebral arteries • Pierces dura to enter cisterna basalis between the free and attached borders of the tentorium • Courses immediately inferiorly to CN III within the lateral wall of the cavernous sinus • Enters the orbit through the superior orbital fissure to supply the superior oblique extra-occular muscle CONTENTS Trochlear Nerve (IV) Notes • Named trochlear after the pulley system (fibrous trochlea) that the superior oblique muscle passes through • The trochlear nerve is the only cranial nerve with a root entry zone on the dorsum of the brainstem (midbrain) – The cisternal segment is therefore generally most readily identifiable postero-laterally • CN IV has the longest intracranial course of the cranial nerves • Is the smallest cranial nerve in terms of number of axons • Innervates the contralateral superior oblique muscle (fibres cross in the midbrain before exiting) • For a variable part of its course the trochlear nerve lies between dural layers making it difficult to identify on cross sectional imaging CONTENTS Trochlear Nerve (IV) Pathology • Isolated CN IV pathology is rare and the commonest cause is trauma – Congenital defects/absence can also cause these symptoms but seen very infrequently • Other causes include (normally not isolated IV palsies): – Any cause of stretching: hydrocephalus, oedema, haemorrhage (Abducens normally the 1st nerve affected) – Infections (herpes) – Demyelination – Cavernous sinus disease – Tumours – Infarction CONTENTS IV - Epidermoid 55F presenting with left sided diplopia on vertical gaze. MRI demonstrates typical imaging appearances for an epidermoid lying within the right ambient cistern and compressing the trochlear nerve. A cystic-looking lesion on T1 and T2 but devoid of attenuation on FLAIR. No enhancement but diffusion restriction. CONTENTS Trigeminal Nerve (V) Course • • • • Course Large sensory root runs medial to smaller motor root Originates from the mid-pons laterally Travels through the prepontine cistern to enter Meckel’s cave through the porus trigeminus • It adopts a ‘mesh like’ form within Meckel’s cave • Anteriorly, within Meckel’s cave it forms the Trigeminal (Gasserian) ganglion before dividing into 3 divisions: – V1 – Ophthalmic nerve moves medially and exits through the superior orbital fissure – V2 – Maxillary nerve moves medially and exits through the Foramen Rotundum – V3 Mandibular (+motor branches) travel inferiorly to exit through the Foramen Ovale CONTENTS Trigeminal Nerve (V) Notes • CN V is the largest cranial nerve – Due to its size and anterior course it is normally easily visualised on MRI • Meckel’s cave is a CSF filled ‘pouch’ in the middle cranial fossa that should be readily identifiable on fluid sensitive sequences CONTENTS Trigeminal Nerve (V) Pathology • CN V is the largest cranial nerve and has multiple nuclei and a large number of sensory, motor and parasympathetic divisions. • The range of pathology is vast but can be grossly divided into: – Trauma: particularly of the skull base exit foramina – Infection: Post-viral, direct spread from the face through the cavernous sinus – Inflammation and demyelination – Vascular: Aneurysmal or aberrant artery (SCA) causing compression; infarction of the trigeminal nuclei – Neoplasia: Infiltration or compression within the skull base foramina or elsewhere along it’s course CONTENTS V - Metastasis 66F with previous history of endometrial carcinoma presented with right trigeminal nerve symptoms affecting all branches. MRI demonstrated an irregular, ring enhancing lesion with associated vasogenic oedema centred over the trigeminal nucleus consistent with an intracranial metastasis CONTENTS V - Lipoma Young patient with left trigeminal nerve sensory symptoms due to compression by a small lipoma at the left root entry zone Axial CISS, T1 and T2, coronal CISS and FLAIR demonstrate the small lesion to be hyper-intense across all sequences with corresponding negative HU on CT consistent with fat CONTENTS V - Schwannoma 48F with sensory disturbance within the right face (mainly V2/3). Axial T2, Sagittal FLAIR and Coronal T1 pre and post gadolinium MR images demonstrate a very large right sided mass showing intense enhancement with some central cystic areas. It causes marked expansion of the Foramen Ovale (best appreciated on sag) and Foramen Rotundum. CONTENTS V – Perineural spread of neoplasia 68M with a known right adenoid cystic carcinoma and right trigeminal signs. T2 fat saturated and contrast enhanced T1 images demonstrate marked peri-neural thickening and enhancement of the right trigeminal nerve CONTENTS Abducens Nerve (VI) Course • Nuclei – anterior to the fourth ventricle • Travels anteriorly through the pons to enter the prepontine cistern at the pontomedullary junction • Crosses the prepontine cistern and then travels vertically up the posterior aspect of the clivus through Dorello’s canal (a fibrous sheath) • Passes over the medial petrous apex • Travels through the medial cavernous sinus • Enters the orbit through the superior orbital fissure • Innervates the lateral rectus muscle of the eye CONTENTS Abducens Nerve (VI) Notes • In isolated CN VI palsy important review areas include: – The petrous apex – The clivus (CN VI travels over almost its entire length) • The cisternal portion of CN VI and the anterior inferior cerebellar artery can appear similar – they are easily distinguishable as they travel in orthogonal directions with CN VI running laterally from posterior - anterior CONTENTS Abducens Nerve (VI) Pathology • CN VI has the longest sub-arachnoid course and is therefore prone to stretching injuries at its entry to Dorello’s canal due to any cause of raised ICP • Other causes are similar to those of all the CNs: – Abnormal subarachnoid space: haemorrhage, infection, tumour – Infection/inflammation: post viral, diabetes – Demyelination – Trauma – Pontine neoplasia CONTENTS VI - Abducens nucleus demyelination 45M Presented with left sided diplopia on a background of several previous transient neurological symptoms for which an underlying demyelination was suspected. T2 and FLAIR images demonstrated a small focus of signal hyper-intensity within the left abducens nucleus consistent with demyelination CONTENTS VI - Chordoma 17M presenting with bilateral 6th nerve palsies, the right more pronounced than the left Axial T2 and sagittal T1 images demonstrate an aggressive, destructive lesion within the clivus at the level of Dorello’s canal bilaterally with consequent neural compromise CONTENTS Facial Nerve (VII) Course • The facial nerve has both sensory and motor components. It primarily supplies the facial and auricular muscles, gives parasympathetic supply to some of the salivary glands and supplies taste to the anterior two thirds of the tongue • During its course, the facial nerve traverses the posterior cranial fossa, internal acoustic meatus, facial canal, stylomastoid foramen of the temporal bone, and parotid gland. • After traversing the internal acoustic meatus, the nerve proceeds a short distance anteriorly within the temporal bone and then turns abruptly posteriorly to course along the medial wall of the tympanic cavity. The sharp bend is the geniculum of the facial nerve. • While traversing the temporal bone within the facial canal, the nerve gives rise to the greater petrosal nerve, nerve to the stapedius and chorda tympani. • Then, after running the longest intraosseous course of any cranial nerve, it emerges from the cranium via the stylomastoid foramen; gives off the posterior auricular branch and enters the parotid gland, forming the parotid plexus, which gives rise to the following five terminal motor branches: temporal, zygomatic, buccal, marginal mandibular, and cervical. • • • For a diagrammatic representation of CN VII’s course click here For more information on the function of this nerve click here For more information on the nuclei that form this nerve please click here CONTENTS Facial Nerve (VII) Pathology Pathologies that affect the facial nerve include facial schwannoma, congenital absence, compression by vascular loops, inflammation and Moebius syndrome. This 32 year old female presented with right hemifacial spasm. Axial T2 and TOF sequences through the level of the IAM’s demonstrate prominent arteries closely associated with the intracanalicular VII and VIII cranial nerves bilaterally. The branches extend through the porus acousticus into the internal auditory meatus and appear to be the anterior inferior cerebellar arteries on the angiographic images. CONTENTS Vestibulocochlear Nerve (VIII) Course • The vestibulocochlear nerve (CN VIII) emerges from the junction of the pons and medulla and enters the internal acoustic meatus. Here it separates into the vestibular and cochlear nerves. • The vestibular nerve is concerned with equilibrium. It is composed of the central processes of bipolar neurons in the vestibular ganglion; the peripheral processes of the neurons extend to the maculae of the utricle and saccule (sensitive linear acceleration relative to the position of the head) and to the ampullae of the semicircular ducts (sensitive to rotational acceleration). • The cochlear nerve is concerned with hearing. It is composed of the central processes of bipolar neurons in the spiral ganglion; the peripheral processes of the neurons extend to the spiral organ. • • For a schematic of the course and MRI images of the normal nerve click here For more information on the function and nuclei of this nerve click here CONTENTS Vestibulocochlear Nerve (VIII) Pathology • • The most common pathology to affect the vestibulocochlear nerve is a vestibular schwannoma (a.k.a. acoustic neuroma). This schwannoma arises from the inferior vestibular nerve in the vast majority of cases. It presents with unilateral sensorineural hearing loss, on the right side in the case shown below. On imaging, it appears as a slightly T1 hypointense, T2 hyperintense soft tissue lesion arising from the internal acoustic canal (IAC) and extending into the cerebellopontine angle. It demonstrates avid enhancement with contrast. A meningioma is a consideration in the differential but this will have a wide dural base and doesn’t tend to cause erosion and widening of the IAC, which is considered highly specific for an acoustic neuroma. CONTENTS Vestibulocochlear Nerve (VIII) Pathology • This patient presented with bilateral sensorineural hearing loss. Indistinct additional soft tissue is seen on the axial T2-weighted imaging, which demonstrates avid enhancement postcontrast. The patient was found to have metastatic melanoma and the imaging appearances below are thought to be metastatic leptomeningeal disease. CONTENTS Glossopharyngeal Nerve (CN IX) Course • The glossopharyngeal nerve emerges from the lateral aspect of the medulla and passes anterolaterally to leave the cranium through the anterior aspect of the jugular foramen. • CN IX follows the stylopharyngeus, the only muscle the nerve supplies, and passes between the superior and the middle constrictor muscles of the pharynx to reach the oropharynx and tongue. It contributes sensory fibres to the pharyngeal plexus of nerves. • CN IX is afferent from the tongue and pharynx and efferent to the stylopharyngeus and parotid gland. • • For a schematic of the nerve course and MRI of the normal appearances click here For more information on the function and nuclei of this nerve click here CONTENTS Glossopharyngeal Nerve (CN IX) Pathology Pathologies involving the glossopharyngeal nerve include glomus tumours and glossopharyngeal neuralgia. This case is that of a clival chordoma, which extends into the jugular foramen and has caused a left CNIX palsy. Classically, they have very high T2 signal and intermediate T1 signal with heterogenous enhancement in a honeycomb pattern. They can also cause blooming on gradient echo due to their propensity to bleed. CONTENTS Glossopharyngeal Nerve (CN IX) Pathology 12 year old male with a mature teratoma. Presented with multiple left lower cranial nerve palsies – left VII, IX, X especially . Axial T2 and coronal STIR images demonstrate a large mixed solid/cystic tumour centred on the left cerebellopontine angle cistern. •The white arrow shows left internal auditory canal filled with tumour. The blue arrows show tumour extension through the left jugular foramen and the bottom right axial T2 image shows tumour extension into the left carotid and parapharyngeal spaces. CONTENTS Vagus Nerve (X) Course • The vagus nerve (CN X) has the longest course and most extensive distribution of all the cranial nerves, most of which is external to the head. The term vagus is derived from the Latin word vagari meaning “wandering”. • It arises by a series of rootlets from the lateral aspect of the medulla that merge and leave the cranium through the jugular foramen positioned between CN IX and CN XI. What was formerly called the cranial root of the accessory nerve is actually a part of the vagus nerve. It has a superior ganglion in the jugular foramen that is mainly concerned with the general sensory component of the nerve. Inferior to the foramen is an inferior ganglion (ganglion nodose) concerned with the visceral sensory components of the nerve. • In the region of the superior ganglion are connections to CN IX and the superior cervical (sympathetic) ganglion. CN X continues inferiorly in the carotid sheath to the root of the neck, supplying branches to the palate and pharynx. • The course of CN X in the thorax differs on the two sides, a consequence of rotation of the midgut during development. CN X supplies branches to the heart, bronchi, and lungs. The vagi join the oesophageal plexus surrounding the oesophagus, which is formed by branches of the vagi and sympathetic trunks. This plexus follows the oesophagus through the diaphragm into the abdomen, where the anterior and posterior vagal trunks break up into branches that innervate the oesophagus, stomach, and intestinal tract as far as the left colic flexure. • • For a diagram of the course of CN X click here For more information on the function and nuclei of this nerve click here CONTENTS Vagus Nerve (X) Pathology Pathology affecting the vagus nerve includes schwannomas, neurofibromas, traumatic injuries and direct infiltration by skull base lesions. The example below is of a glomus jugulotympanicum paraganglioma. The patient presented with hoarseness due to vocal cord palsy and tinnitus. The imaging demonstrates a high T2, low T1 signal lesion involving both the middle ear and jugular foramen with intense enhancement following contrast. A “Salt and pepper appearance” is the classical MRI characteristics CONTENTS Vagus Nerve (X) Pathology • This 35 year old female presented with multiple lower cranial nerve palsies on the left. Imaging demonstrates bilateral paragangliomas. The patient was found to have a succinate dehydrogenase complex subunit D (SDHD) gene mutation, which predisposes to paragangliomas. CONTENTS Spinal Accessory Nerve (XI) Course • Spinal portion – arises from the upper spinal cord, specifically the C1-C5/C6 nerve roots. These fibres coalesce to form the spinal part of the accessory nerve, which then runs superiorly to enter the cranial cavity via the foramen magnum. The nerve traverses the posterior cranial fossa to reach the jugular foramen. It briefly meets the cranial portion of the accessory nerve, before exiting the skull (along with the glossopharyngeal and vagus nerves). Outside the cranium, the spinal part descends along the internal carotid artery to reach the sternocleidomastoid muscle, which it innervates. It then moves across the posterior triangle of the neck to supply motor fibres to the trapezius. • Cranial portion – arises from the lateral aspect of the medulla oblongata. It leaves the cranium via the jugular foramen, where it briefly contacts the spinal part of the accessory nerve. Immediately after leaving the skull, the nerve combines with the vagus nerve (CN X) at the ganglion nodose. The fibres from the cranial part are then distributed through the vagus nerve. For this reason, the cranial part of the accessory nerve is considered as part of the vagus nerve. – – For a diagram of the normal course click here For more information on the function and nuclei of this nerve click here CONTENTS Spinal Accessory Nerve (XI) Pathology • The most common spinal accessory nerve pathologies are similar to those for XI and X with much of the pathology being centered on the jugular foramen e.g. glomus jugulare tumours. CONTENTS Hypoglossal Nerve (XII) Course • The hypoglossal nerve (CN XII) arises as a purely motor nerve by several rootlets from the medulla and leaves the cranium through the hypoglossal canal. • After exiting the cranial cavity, it is joined by branches of the cervical plexus conveying general somatic motor fibres from C1 and C2 spinal nerves and general somatic sensory fibres from the spinal ganglion of C2. These spinal nerve fibres “hitch a ride” with CN XII to reach the hyoid muscles, with some of the sensory fibres passing retrogradely along it to reach the dura mater of the posterior cranial fossa. • CN XII passes inferiorly, medial to the angle of the mandible and then curves anteriorly to enter the tongue. • It ends in many branches that supply all the extrinsic muscles of the tongue, except the palatoglossus (which is actually a palatine muscle). • • For more information on the function and nuclei of this nerve click here For a diagram of the nerve course and MRI image of a normal nerve click here CONTENTS Hypoglossal Nerve (XII) Pathology • Hypoglossal nerve pathologies include hypoglossal schwannoma and Collet-Sicard syndrome (secondary to a glomus jugulare tumour). Below is a rare case of a left hypoglossal nerve palsy. The CISS sequence demonstrates the left XII nerve as it exits the medulla and the post contrast sequences show an enhancing structure compressing the nerve in the hypoglossal canal. CE-MRA confirms this to be a left internal carotid artery aneurysm. CONTENTS Hypoglossal Nerve (XII) Pathology • Another case referred for MRI due to a left-sided tongue palsy reveals a well-defined lesion arising from the cisternal segment of nerve root that is isointense on T1 and hyperintense on T2 (not shown), with avid homogenous enhancement post contrast. These appearances are in keeping with a hypoglossal schwannoma • Schwannomas are slow-growing lesions. Surgery is the treatment of choice. As schwannomas do not infiltrate the parent nerve, they can usually be separated from it. Recurrence is unusual, even after complete resection. They almost never undergo malignant change CONTENTS Appendix • Further detail on selected cranial nerves • Images CONTENTS Facial Nerve (VII) Functions •Sensory – Special afferent - Fibres carried by the chorda tympani join the lingual nerve to convey taste sensation from the anterior two thirds of the tongue and soft palate. – General somatic afferent - Some fibres arising from facial nerve supply a small area of the skin of the concha of the auricle, close to external acoustic meatus. •Motor – Branchial motor - As the nerve of the 2nd pharyngeal arch, the facial nerve supplies striated muscles derived from its mesoderm, mainly the muscles of facial expression and auricular muscles. It also supplies the posterior bellies of the digastric, stylohyoid, and stapedius muscles. – Parasympathetic - The facial nerve provides presynaptic parasympathetic fibres to the pterygopalatine ganglion for innervation of the lacrimal glands and to the submandibular ganglion for innervation of the sublingual and submandibular salivary glands. The pterygopalatine ganglion is associated with the maxillary nerve (CN V2), which distributes its postsynaptic fibres, whereas the submandibular ganglion is associated with the mandibular nerve (CN V3). Parasympathetic fibres synapse in these ganglia, whereas sympathetic and other fibres pass through them. •Proprioception to innervated musculature BACK KEY CONTENTS Facial Nerve (VII) Nuclei Nuclei: – Motor nucleus of the facial nerve - a branchiomotor nucleus in the ventrolateral part of the pons. – Spinal nucleus of the trigeminal nerve - (pain, touch, and thermal) from around the external ear end here. – Tractus solitarius – neurons associated with the sensation of taste terminate here. • The facial nerve (CN VII) emerges from the junction of the pons and medulla as two divisions, the motor root and the intermediate nerve. • The larger motor root innervates the muscles of facial expression, and the smaller intermediate nerve (L. nervus intermedius) carries taste, parasympathetic, and somatic sensory fibres. BACK KEY CONTENTS Vestibulocochlear Nerve (VIII) Function and Nuclei • Function: Special afferent - special sensations of hearing and equilibrium. • Nuclei: Four vestibular nuclei are located at the junction of the pons and medulla in the lateral part of the floor of the 4th ventricle; two cochlear nuclei are in the medulla. BACK KEY CONTENTS Glossopharyngeal Nerve (CN IX) Function and Nuclei • Sensory – Special afferent - Taste fibres are conveyed from the posterior third of the tongue to the sensory ganglia. – General visceral afferent • The carotid sinus nerve to the carotid sinus, a baroreceptor sensitive to changes in blood pressure, and the carotid body, a chemoreceptor sensitive to blood gas (oxygen and carbon dioxide levels). • The pharyngeal, tonsillar, and lingual nerves to the mucosa of the oropharynx and isthmus of the fauces, including palatine tonsil, soft palate, and posterior third of the tongue. In addition to general sensation (touch, pain, temperature), tactile stimuli determined to be unusual or unpleasant here may evoke the gag reflex or even vomiting. • Motor – Branchial motor - Motor fibres pass to one muscle, the stylopharyngeus, derived from the 3rd pharyngeal arch. – Parasympathetic - Following a circuitous route initially involving the tympanic nerve, presynaptic parasympathetic fibres are provided to the otic ganglion for innervation of the parotid gland. The otic ganglion is associated with the mandibular nerve (CN V3), branches of which convey the postsynaptic parasympathetic fibres to the parotid gland. – Nuclei: Four nuclei in the medulla send or receive fibres via CN IX: two motor and two sensory. Three of these nuclei are shared with CN X. BACK KEY CONTENTS Vagus Nerve (X) Function and Nuclei Functions: • Sensory – General visceral afferent and General somatic afferent • Sensory from the inferior pharynx, larynx, and thoracic and abdominal organs – Special afferent - Sense of taste from the root of the tongue and taste buds on the epiglottis. Branches of the internal laryngeal nerve (a branch of CN X) supply a small area, mostly general but some special sensation; most general and special sensation to the root is supplied by CN IX. • Motor – Branchial motor - Motor to the soft palate; pharynx; intrinsic laryngeal muscles (phonation); and a nominal extrinsic tongue muscle, the palatoglossus, which is actually a palatine muscle based on its derivation and innervation. – Parasympathetic to thoracic and abdominal viscera. – Proprioception to innervated musculature – BACK Nuclei: Four nuclei of CN X in the medulla send or receive fibres via CN IX; two motor and two sensory. Three of these nuclei are shared with CN IX. KEY CONTENTS Spinal Accessory Nerve (XI) Function and Nuclei • Functions: – Branchial motor to the striated sternocleidomastoid and trapezius muscles. • Nuclei: The spinal accessory nerve arises from the nucleus of the accessory nerve, a column of anterior horn motor neurons in the superior five or six cervical segments of the spinal cord . BACK KEY CONTENTS Hypoglossal Nerve (XII) Function and Branches Functions: • General somatic efferent to the intrinsic and extrinsic muscles of the tongue (styloglossus, hyoglossus, and genioglossus). Branches: – A meningeal branch returns to the cranium through the hypoglossal canal and innervates the dura mater on the floor and posterior wall of the posterior cranial fossa. The nerve fibres conveyed are from the sensory spinal ganglion of spinal nerve C2 and are not hypoglossal fibres. – The superior root of the ansa cervicalis branches from CN XII to supply the infrahyoid muscles (sternohyoid, sternothyroid, and omohyoid). This branch actually conveys only fibres from the cervical plexus (the loop between the anterior rami of C1 and C2) that joined the nerve outside the cranial cavity, not hypoglossal fibres. Some fibres continue past the descending branch to reach the thyrohyoid muscle. – Terminal lingual branches supply the styloglossus, hyoglossus, genioglossus, and intrinsic muscles of the tongue. BACK KEY CONTENTS Key Afferent • Special afferent • General somatic afferent • General visceral afferent Efferent • Branchial motor • Parasympathetic • General somatic efferent CONTENTS Olfactory Bulb Patrick J. Lynch, medical illustrator – 23/12/06 Back to text CONTENTS Olfactory nerve course www.studyblue.com Back to text CONTENTS Courtesy of http://ueu.co/ovid-clinically-oriented-anatomy-9/c Back to text CONTENTS Courtesy of http://ueu.co/ovid-clinically-oriented-anatomy-9/ Optic pathway www.studyblue.com Back to text CONTENTS Optic nerve • Superior view of dissected robot showing the four anatomical parts of the optic nerve. Courtesy of Dr. John B. Selhorst. Back to text CONTENTS Bilateral CN III entering cavernous sinuses Courtesy of http://ueu.co/ovid-clinically-oriented-anatomy-9/c Back to text CONTENTS Courtesy of http://ueu.co/ovid-clinically-oriented-anatomy-9/ Diagram of nuclei of cranial nerves (numbered). Image created by Patrick J. Lynch, medical illustrator. Back to CN IV or CN VI CONTENTS Back to text Courtesy of http://ueu.co/ovid-clinically-oriented-anatomy-9/c CONTENTS Courtesy of http://ueu.co/ovid-clinically-oriented-anatomy-9/ Courtesy of http://ueu.co/ovid-clinically-oriented-anatomy-9/c Back to text CONTENTS Courtesy of http://ueu.co/ovid-clinically-oriented-anatomy-9/ These sagittal and axial CISS image shows nerves VII and VIII in the IAC VII Anterior Courtesy of http://ueu.co/ovid-clinically-oriented-anatomy-9/c Back to text Courtesy of http://ueu.co/ovid-clinically-oriented-anatomy-9/ Superior Bill’s Bar Sagittal section of IAC VIII Sup Transverse Crest VIII Coch VIII Inf CONTENTS Courtesy of http://ueu.co/ovid-clinically-oriented-anatomy-9/c Back to text Courtesy of http://ueu.co/ovid-clinically-oriented-anatomy-9/ This is an axial CISS image showing the cisternal segments of the IX and X as they enter the pars nervosa of the jugular foramen. Contrast this appearance with the next case of a chordoma involving the left jugular foramen. CONTENTS Courtesy of http://ueu.co/ovid-clinically-oriented-anatomy-9/c Back to text Courtesy of http://ueu.co/ovid-clinically-oriented-anatomy-9/ CONTENTS Courtesy of http://ueu.co/ovid-clinically-oriented-anatomy-9/c Back to text CONTENTS Courtesy of http://ueu.co/ovid-clinically-oriented-anatomy-9/ Courtesy of http://ueu.co/ovid-clinically-oriented-anatomy-9/ Courtesy of http://ueu.co/ovid-clinically-oriented-anatomy-9/c Back to text CONTENTS