Neuroanatomy Flashcards
Special things about CN4
Only CN that exits dorsally
Longest intracranial course
Decussates so the right nucleus of CN4 innervates the left SO
Causes of CN4 palsy:
#1: contrecoup injury from free tentorial edge
#2: ischemia
#3: idiopathic palsies
Other: hydrocephalus, vascular loops, tumors
CN6 palsy
CN6 nucleus contains interneurons which end in contra/L MR subnucleus of CN3 (conjugate eye movements)
Also means that CN6 nucleus lesion leads to ipsi/L GAZE palsy, not just ABduction deficit
MCC CN6 palsy = ischemic mononeuropathy (unless < 50 yo). No imaging if motility resolves w/in 3 mo
CN3 nuclei anatomy
CN3 subnuclei (located in midbrain) SR subnuclei crossed. Ex: Left SR subnucleus fibers cross to R SR Upper lids nuclei (single midline structure) innervates the levator OU Pupillary constrictor (parasympathetic innervation)& accommodation muscles --> under control of ipsi/L subnucleus
SO fissure divides to SR/levator (superior) and inferior (MR, IR, IO, parasympathetic axons to ciliary ganglion)
Pupillary fibers of CN3
Pupillary fibers are on the PERIPHERY of the nerve. Therefore, pupil is NOT usually involved in infarction (i.e. from DM, HTN) which affects the center.
(Therefore compressive CN3 palsy with pupil involvement is often 2/2 tumor/aneurysm. Often PAINFUL, and usually 2/2 PCOM aneurysm).
PERIPHERAL PUPILLARY FIBERS compressed by ANEURYSM. PAINFUL PCOM (MCC).
But pain is not good Sx to distinguish between compression vs. infarction.
CN3 path
1) CN3 leaves midbrain in brainstem from cerebral peduncle –> enters subarachnoid space –>
vascular supplied by terminal portion of basilar artery (at origin of superior cerebellar and posterior cerebral)
passes through these two arteries
2) travels medially along the PCOM artery and lateral to internal carotid artery
3) nerve enters cavernous sinus (lies in lateral wall superior to CN4) receives vascular supply from branches off ICA, ophthalmic artery, sup cerebellar, PCA
and then goes to SO fissure (where it divides into superior/inferior division)
4) superior division (SR and LP) and inferior (rest of EOM and Parasympathetic fibers from ciliary ganglion)
Rule of the pupil
In COMPLETE CN3 of the pupil, pupil is NORMAL if microvascular infarction. BUT, in PCOM aneurysm, anisocoria can develop at any time within 5 days of the start of diplopia
CN3 Nucleus lesions
Very rare. Ipsi/L Cn3 palsy. Ptosis OU contra/L SR palsy. OR CN3 palsy OU without ptosis OR ptosis OU alone OR any isolated palsy of muscle innervated by CN3
R CN3 nucleus innervates the RIGHT IO, IR, MR and LEFT (SR).
centrally located common CN3r subnucleus innervates levator on BOTH sides
Therefore CN3 palsy should have contralateral & ipsilateral palsy of the superior rectus and contralaterallevator palpebrae superioris.
Why lesions of CN3 nucleus also affect the ipsilateral SR considering it is innervated by the contralateral 3rd nerve nucleus?
B/C fibers from the SR subnucleus decussate and pass adjacent to the contralateral 3rd nerve nucleus. Therefore, virtually all lesions affecting the 3rd nerve nucleus will also hit fibers from the contralateral superior rectus subnucleus as they pass by in the brainstem.
Weber syndrome
Weber is WEAK
CN3 fasicle syndrome: Involvement of cerebral peduncles
ipsi/L CN3 paresis with contra/L hemiparesis
Nothnagel syndrome
Claude Nothnagel is CLUMSY
Nothnagel: CN3 fasicle syndrome: involvement of superior cerebellar peduncle
Ipsi/L CN3 paresis and cerebellar ataxia
(can also see this in Claude’s syndrome only Claude’s affects the midbrain, and ipsi/L and CONTRA/L ataxia and dysdiadochokinesis [dancing like movements])
Benedikt syndrome
CN3 fasicle syndrome: involvement of red nucleus
ipsi/L CN3 paresis with contra/L hemitremor
PCA and MCA VF defect
2/2 anatomy and vascular supply of the optic pathways, only lesions of the occipital lobe can produce a macular sparing homonymous hemianopia.
2 vascular supplies to the primary visual cortex of the occipital lobe
1) posterior cerebral artery supplies the majority of the primary visual cortex responsible for the contralateral visual hemifield
2) middle cerebral artery supplies the very posterior tip of the primary visual cortex of the occipital lobe responsible for the contralateral macular portion of the hemifield.
Therefore, a stroke of the PCA affecting the occipital lobe is the most likely cause of a macular-sparing homonymous hemianopia.
ON
intraorbital ON - some slack (none in intracranial portion) 125-1017 1 = intraocular 25 = intraorbital 10 = intracanalicular 17 = intracranial
Average optic nerve: 1.5 mm
Exits via the lamina cribosa and becomes myelinated by oligodendrocytes (NOT schwann cells as in peripheral nerves), the optic nerve size doubles to 30 mm in diameter.
sympathetic chain
Involves 3 interconnected neuron segments (1st, 2nd, and 3rd order). Throughout the entire sympathetic pathway, axons never decussate meaning that causative lesions are always SAME SIDE AS the Horner syndrome.
1st order neurons: cell bodies in the POSTERIOR LATERAL HYPOTHALAMUS descend through the brainstem to the INTERMEDIOLATERAL CELL COLUMN b/t C7 and T2 where they synapse with cell bodies of the second order neurons.
1ST ORDER HORNER CAUSES: Wallenberg (or lateral medullary syndrome) usually arises from a stroke. Other causes include: thalamic hemorrhage / stroke and tumors, cervical disc disease, demyelination, and other pathology of the cervical spinal cord.
2nd order neurons project from the INTERMEDIOLATERAL CELL COLUMN b/t C7 and T2 to the paravertebral sympathetic chain where fibers ascend to the SUPERIOR CERVICAL GANGLION and synapse with third order neurons.
2ND ORDER HONER CAUSES: apical lung malignancies (“Pancoast syndrome”), thoracic aortic aneurysms, brachial plexus injuries, and thoracic surgery with disruption of the superior portion of the paravertebral sympathetic chain.
3RD ORDER neuron cell bodies lie in the SUPERIOR CERVICAL GANGLION and pass superiorly into the cranial cavity with the INTERNAL CAROTID ARTERTY (ICA) in a fine web of nerves along the wall of the artery known as the carotid plexus. The ocular sympathetics continue with the internal carotid as it passes through the CAVERNOUS SINUS. While in the cavernous sinus, the third order neuron axons travel from the ICA to the abducens nerve before joining the NASOCILIARY BRANCH OF V1. The sympathetics then travel with the nasociliary branch of V1 into the orbit and through the CILIARY GANGLION (without synapsing) to extend to the dilator muscle of the eye.
3RD ORDER HORNER CAUSES: internal carotid artery pathology (including dissection), cavernous sinus compressive / inflammatory lesions, and trigeminal autonomic cephalgia type headaches (e.g. cluster headache, SUNCT, etc).
APD
optic tract lesion often results in an APD of the contralateral eye.
2/2 more crossed than uncrossed pupillary fibers in the optic tract.
R optic tract lesion results in decreased afferent input from both retinas but relatively-speaking there is a more marked reduction of afferent input from the contralateral eye.
ON axons
approximately 1-1.2 million ganglion cells which make up the optic nerve.
Optociliary shunt vessels
(aka retinochoroidal collaterals) are a dilation of the naturally-occurring veins that drain from the peripapillary retinal circulation into the choroidal circulation.
Similar to hemorrhoids or esophageal varices, optociliary shunt vessels evolve in response to chronically-poor drainage of the central retinal vein.
DDX: optic nerve sheath meningiomas, low-grade optic nerve gliomas, chronic papilledema, chronic glaucoma, and old central retinal vein occlusions.
Crarinopharyngioma vs pituitary adenoma VF defects
Craniopharyngiomas classically arise from ABOVE the optic chiasm and therefore classically (but not always) compress the SUPERIOR OPTIC CHIASM first. The retinal ganglion cell axons first compromised by such compression would be the superonasal fibers supplying the INFEROTEMPORAL VF in both eyes. With increasing compression more fibers become involved and the deficits may progress to a complete hemianopia.
IN CONTRAST, a compressive pituitary adenoma which classically arises from BELOW the optic chiasm and would typically START WITH SUPEROTEMPORAL VF deficits in both eyes.
dural venous sinus thrombosis (DVST)
On MRV: a DVST with a flow void (a filling defect in the venous sinus where hyperintense flow should be seen) in the transverse sinus.
DVST is one of the more common mimickers of pseudotumor cerebri and often presents acutely with one or more of the following: headache, blurred vision, papilledema, transient visual obscurations, and unilateral / bilateral sixth nerve palsy. More rarely, DVST can cause intracranial hemorrhage and stroke. Before the advent of non-invasive venography (MRV and CTV), many patients with DVST were misdiagnosed as having pseudotumor cerebri. In fact, an MRV or CTV (in addition to a brain CT or MRI) should be performed in any patient with bilateral papilledema who does not fit the typical pseudotumor cerebri profile (overweight female of childbearing age).
DVST, similar to deep venous thrombosis or pulmonary embolism, can be precipitated by acquired or hereditary hypercoaguability.
Common DVST-associated hypercoaguable states: pregnancy (and the peripartum period), OCP use, lupus, inherited coagulopathies, infection, dehydration, and acute head injury (not a remote history).
Any infection will increase the risk for DVST although middle / inner ear infections and meningitis are among the more common precipitating infections. Patients with DVST but without a clear hypercoaguable risk factor should be considered for a hypercoaguable laboratory evaluation and/or referral to a hematologist.
What structure upstream of the cavernous sinus leads to arterialization of conjunctival vessels in both low flow dural sinus fistulas (DSF) and high flow carotid cavernous fistulas (CCF)?
Elevated pressure and reduced drainage of the superior ophthalmic vein leads to arterialization of the bulbar conjunctiva.
This is an important fact to remember because one very helpful radiographic sign of a CCF or DSF is a dilated superior ophthalmic vein. This is not a specific finding of CCF / DSF, however, and can occur in other processes impeding venous drainage such as a cavernous sinus thrombosis.
Idiopathic or so called “microvascular” cranial mononeuropathies
Idiopathic or so called “microvascular” cranial mononeuropathies of cranial nerve 3, 4, or 6 are thought to be due to microvascular disease of the VASA NERVORUM, or blood supply to the peripheral nerves. Eye or periorbital pain is very common in these cases. In theory, this infarct of the nerve results in focal demyelination without permanent damage to the nerve axons allowing for full resolution with time.
MC etiology for acute onset cranial mononeuropathies of cranial nerve 3, 4, or 6 in patients with microvascular risk factors. Such risk factors include HTN, DM, peripheral vascular disease, coronary artery disease, hypercholesterolemia, smoking, and age.
Classic teaching: patients over the age of 50 (or 55 depending on the source) who develop an acute onset, isolated peripheral cranial nerve 3, 4, or 6 palsy can be observed without requiring an extensive work-up. Any cranial mononeuropathy in patients less than 50 (or 55) must be imaged and worked .
CN3 palsy - what factors to observe vs not observe
in order to observe a 3rd nerve palsy there must be NO PUPIL INVOLVEMENT AND A COMPLETE CN3 PALSY.
The definition of pupil involvement varies but includes a larger ipsilateral pupil that responds poorly to light due to impaired parasympathetic innervation. Any anisocoria is concerning while anisocoria greater than 2 mm is extremely concerning for a compressive mass of the 3rd nerve (most often an aneurysm of the posterior communicating artery).
A complete CN3 palsy means that all muscles innervated by the 3rd cranial nerve are maximally affected. Microvascular cranial mononeuropathies are either resolved or mostly resolved by 3 months. The onset is usually acute although there can be progression of the motility deficit / alignment over the first 7 days after initial onset. A progressive worsening of diplopia, motility, or alignment after the first week of symptoms is certainly an indication for a complete work-up including neuro-imaging.
MRI transverse section - midbrain
Midbrain - “mickey mouse sign” - and other structures seen well here:
Superior Ophthalmic vein starts superonasaly and passes posterolaterally (SUPERIOR to ON and INFERIOR to SR) –> exits through SO fissure and drains into cavernous sinus.
Can also see ON, Optic tract
Pupil involving CN3
Pupil involving = ASSUME acute 3rd nerve palsy from aneurysm. While saccular aneurysms can occur virtually anywhere in the cerebral circulation, aneurysms at the junction of the POSTERIOR COMMUNICATING ARTERY (PCOM) and the internal carotid artery (INTERNAL CAROTID ARTERY) often present with a pupil involving 3rd nerve palsy by compressing the 3rd nerve as it passes by in the subarachnoid space.
The parasympathetic fibers responsible for contraction of the pupillary sphincter muscle (and therefore miosis) travel in the peripheral segment of the nerve and are therefore very vulnerable to external compression.
Microvascular 3rd nerve palsies can have pupil involvement but it is a diagnosis of exclusion made only after a thorough evaluation to rule out an aneurysm.
Strokes and seizures
Hemispheric strokes can affect the afferent and efferent function of the eyes in multiple ways. General rule of stroke is that infarcted neurons do not recover function in adults.
Exception = patients with a gaze deviation towards the side of the infarct due to dysfunction of the frontal eye field (Brodmann area 8) recover quickly.
Frontal eye field exerts supranuclear control over lateral gaze towards the opposite side so an infarct of the right frontal lobe will result in a temporary right gaze deviation. A seizure, however, in the region of the frontal eye field will cause an episodic deviation towards the contralateral side.
Quick recovery from supranuclear gaze deviations caused by hemispheric strokes (usually a matter of days) hypothesis:
1) 2/2 brain compensation via other viable neurons to serve the same function.
2) brain simply “recalibrates” ocular alignment shortly after infarction of the frontal eye field.
Gradenigo’s syndrome
usually 2/2 mastoiditis–> inflammation in petrous portion of the temporal bone (affects 6 and 7 CN)
CN6 exits the ventral pons @ the pontomedullary jxn and is adjacent to the cerebellopontine angle (CPA) where CN6 and 7 exit the brainstem. Any combination of deficts suggest mass lesion in CPA (acoustic neuroma or meningoma). Large CPA masses can also affect trigeminal sensation to the face and the cornea.
SOV
Superior Ophthalmic vein starts superonasaly and passes posterolaterally (SUPERIOR to ON and INFERIOR to SR) –> exits through SO fissure and drains into cavernous sinus.
SOV enlargement: poor venous drainage through cavernous sinus. SOV enlargement - prominent feature in anteriorly draining carotid cavernous fistulas and in cavernous sinus thrombosis
Optic chiasm
Posterior portion of chiasm has a high density of macular fibers and most decussate in the posterior chiasm
53% of RGC cross in the chiasm
Chiasm lies approx 1 cm ABOVE the anterior pituitary gland
Wilbrand’s knee
Thought to be an artifact
Principal: inferior nasal retinal fibers cross in the ANTERIOR chiasm and loop anteriorly in the c/L ON before traveling posteriorly
Retrochiasmal lesion producing monocular VF defect with a single lesion alone
Temporal 30 degrees of a binocular VF = perceived by the nasal-most retina of the ipsi/L only
These “temporal crescents” represented in the most anterior portion of the occipital lobe. Therefore a lesion in this area –> monocular VF defect in the far temporal periphery of the contra/L eye, the so-called temporal crescent syndrome.
Ex: right anterior occiptal lobe lesion would –> far temporal field deficit in the left eye. Similarly a right posterior occiptal lobe lesion may spare the far temporal field in the left eye
LGN segregated based on which eye the axons orignate
RGC terminals are segregated by eye
ipsi/L ganglion cells synpase in layers 2, 3, 5 (Note 2+3 = 5)
contra/L ganglion cells synpase in 1, 4, 6
Temporal lobe lesion
formed hallucinations, partial complex seizures, olfactory hallucinations
hemianopias denser superiorly
OKN abnormalities
lesions of the parietoocciptal (slow-phase pursuit abnormalities) or the frontal lobe (fast-phase recovery abnormalities)
Although OKN asymmetry may rarely occur with occiptal lesions, this finding is generally indicative of a parietal locus of disease.
lesion in the occipital lobe
high congruity of VF
lesions in Meyer’s loop
pie-in-the-sky defects contra/L to the lesion
inferior nerve fibers from the superior retina course anteriorly in Meyer’s loop
parietal lobe lesions
agnosia = display the ability to see contours and outlines when shown an object, but they experience difficulty if asked to categorize or name objects
right-left confusion
affects slow-phase pursuit movements toward the ipsi/L side
hemianopias denser inferiorly
CN3 aberrant regeneration
Never ischemic etiology
Only: aneurysm, tumor, inflammation, trauma
classic findings: persistent vertical gaze limitation 2/2 simultaneous contraction of SR and IR
pupillary miosis w/elevation, adduction, or depression
upper eyelid retraction/lag with down-gaze
Also known as synkinetic phenomena: Following axonal damage to the 3rd nerve, aberrant re-routing of regenerating fibers causes co-contraction of muscles that typically share innervation. Because the lateral rectus is not innervated by the 3rd nerve, aberrant regeneration linking ABduction (lateral rectus) to other mechanisms is not possible.
Lesions of the cerebellopontine angle (CPA)
CN6 +/- CN5, CN7, CN8
nasopharyngeal carcinoma affects CN…
Involves numerous CN 2/2 proximity to prepontine basal cistern
MC: trigeminal involved –> facial hypesthesia or facial pain
#2: CN6
MC in chinese men, least differentiated forms aka Schmincke’s and Regaud’s tumors
cavernous sinus lesion
CN6 (because not w/in dural wall) +/- sympathethics, CN3, CN4, CN5
corkscrew conjunctival vessels - all the way to the limbus - highly suggestive of arterialization of the orbital venous system. can see in
dural low flow fistulas or carotid-cavernous fistula. See enlargement of SOV.
Cavernous sinus thrombosis - can occur in septic or aseptic pts
Si: ophthalmoplegia, orbital congestion.
Rx: Abx, anticoagulants, corticosteroids, surgery
vertical vs. horizontal gaze centers
midbrain 1 1/2 will affect vertical eye movement (remember midbrain for vertical and pons for horizontal movement)
optic canal in which bone?
Optic nerve passes through the optic canal of the sphenoid bone to exit the orbit. Of note the optic canal is formed by the lesser (not greater) wing of the sphenoid (high yield). The optic canal is thought to be the location of injury in traumatic optic neuropathy.
Other structures which pass through the optic canal include the ophthalmic artery and the sympathetic nerves traveling to the eye.
MLF anatomy and lesion
Interneurons run from the CN6 nucleus in the MID-pons to the CONTRA/L MR subnucleus of the CN3 in the rostral midbrain via the medial longitudinal fasciculus (MLF). Coordinates contraction of the medial and lateral recti to allow normal horizontal gaze.
MLF lesion disrupts coordination of the MR and LR resulting in an internuclear ophthalmoplegia (INO).
Pontine lesion of the right MLF = right INO with slowed adduction of the right eye, possible impairment of the motility of the right medial rectus (depending on the severity of the INO)
possible left beating nystagmus of the left eye on left gaze (dissociated horizontal nystagmus)
abnml ABDuction saccades
limitation of ADDuction
In addition to interneurons connecting CN3 & CN6 nuclei, the MLF also contains vestibular inputs to the brainstem nuclei affecting vertical eye movements.
Lesion here results in skew deviation.
The side of the lesion typically corresponds to the hypertropic and incyclotorted eye.
Skew deviation is very common in INO and is the first diagnosis that should come to mind when a patient with an INO has vertical binocular diplopia.
Carotid-cavernous fistula vs. dural sinus fistula
Low flow dural sinus fistulas = abnormal connection between small dural based arteries and the cavernous sinus. Usually occur spontaneously without an inciting event and can resolve spontaneously without surgical intervention whereas CCFs generally require thrombosis by interventional radiology.
High flow CCFs are usually traumatic in origin, occur in older women more than others, are much more likely to cause a cranial bruit, and involve an abnormal connection between the internal carotid artery and the cavernous sinus. Both CCFs and DSFs involve arterialization of the venous cavernous sinus. Therefore, both have similar manifestations including elevated intraocular pressure, proptosis, ocular motor palsy, arterialization and injection of the conjunctival vessels, choroidal effusions, ischemic optic neuropathy, and pain.
Considering CCFs are high flow and DSFs are low flow connections, the sequelae tend to be more severe and dramatic with CCFs. CCFs often require urgent angiography with thrombosis while DSFs can at times be observed to see if they resolve spontaneously. The urgency and need for repair must be judged on a case-by-case basis because catheter angiography carries a serious complication rate of around 1% in the literature (ischemic stroke, hemorrhage, etc).
Junctional scotoma
Diffuse visual field loss with decreased visual acuity and a contralateral deficit in the superotemporal field -accurately localized to the jxn of the optic nerve and the chiasm.
Ipsilateral optic nerve compromise results in diffuse optic nerve dysfunction / central scotoma and the contalateral visual field is compromised due to the anatomic structure known as Willbrand’s knee. Inferonasal retinal ganglion cell axons (serving the superotemporal field) decussate in the optic chiasm as they track posteriorly. Before entering the contralateral optic tract, however, they loop anteriorly for a short segment (called Willbrand’s knee) into the contralateral optic nerve. Because of this anatomy, an anterior optic chiasm or far posterior optic nerve lesion causes vision loss in both eyes in this very specific fashion.
Damaging ____ by entering the sphenoid sinus to gain access to the pituitary gland
Optic nerve exits the orbit via the optic canal. The medial wall of the optic canal is separated from the SPHENOID sinus by a very thin plate of sphenoid bone. Entering the sphenoid sinus to gain access to the pituitary gland can be complicated by damage to the adjacent optic nerve.
Lesion of: CN3 nucleus vs. fasciculus vs. CN
-nucleus is located at the level of the rostral midbrain and is made up of the 3rd nerve neuronal cell bodies. These cell bodies give off a bundle of axons known as a fasciculus that pass inferiorly through the red nucleus and adjacent to the cerebral peduncle before exiting the brainstem as the 3rd cranial nerve.
A nuclear 3rd nerve lesion causes ptosis and ipsilateral mydriasis similar to a 3rd nerve fascicular or cranial nerve lesion. The distinguishing feature is involvement of the contralateral superior rectus and levator palpebrae superioris.
Due to the close proximity of the Edinger Westphall nucleus (housing the parasympathetic preganglionic cell bodies of the eye), a nuclear lesion often results in bilateral ptosis, bilateral superior rectus dysfunction, ipsilateral mydriasis, and ipsilateral dysfunction of the medial rectus, inferior rectus, and inferior oblique muscles.
How much (measured posteriorly from the anterior tip) of the temporal lobe can be resected without causing a visual field deficit?
A: 2.5 cm
Optic radiations extend from the LGN to the ipsilateral primary visual cortex in the occipital lobe.
The fibers corresponding to the CONTRA/L superotemporal visual field pass anteriorly into the temporal lobe in a path known as the “loop of Meyer”.
This becomes important when neurosurgeons excise tissue from the temporal lobe because depending on how much tissue is excised, surgery may cause a contralateral “pie in the sky” type visual field defect by violating the loop of Meyer.
Posterior ciliary arteries and GCA
vasculitis of elastin containing large and medium-sized arteries of the head and neck.
ON head is supplied primarily by the posterior ciliary arteries which are a favorite target of GCA.
If vasculitis causes occlusion of the posterior ciliary artery supplying the optic nerve head then arteritic anterior ischemic optic neuropathy develops. If vasculitis occludes the posterior ciliary artery supplying the temporal choroid (but not the optic nerve) then there may be NO fundus findings but the FA will show dramatic filling delay as seen in this case (see FA above). In the context of an elderly patient with vision loss, findings of profound choroidal filling delay are HIGHLY suggestive of GCA.
Optic chiasm/sella turcica/pituitary gland
Optic chiasm sits approximately 10 mm SUPERIOR to the sella turcica of the sphenoid bone where the pituitary gland sits. Clinically, this is important because a pituitary adenoma must typically reach a MINIMUM size of 1 cm to threaten compression of the optic chiasm above.
Gaze-evoked AMAUROSIS
thought to occur 2/2 intermittent occlusion of retinal or optic nerve vasculature caused by intermittent compression from an orbital mass when the eye is turned in a certain position. Often times there are other accompanying signs of an orbital mass such as a motility restriction, optic disc swelling, or proptosis. The most common gaze direction to cause amaurosis is downgaze.
Adenomas - secreting and nonsecreting
Typically non-secreting adenomas present with vision loss much more commonly than secretory tumors because secretory tumors generally have systemic symptoms that allow them to be discovered before the tumor grows large enough for chiasmal compression to occur.
GH secreting adenomas result in either gigantism or acromegaly depending on whether the patient has undergone puberty prior to development of the adenoma. ACTH secreting adenomas result in Cushing’s syndrome and TSH secreting adenomas obviously result in hyperthyroidism.
Prolactinomas, particularly in men, are much more likely to present LATER with chiasmal compression. Females with prolactinomas may present with galactorrhea, amenorrhea, or other menstrual cycle abnormalities.
Prolactin secreting adenomas in men produce subtle symptoms of decreased libido and impotence.
2/2 subtle Sx (especially in men) the tumors are diagnosed at a later stage and tend to be larger at the time of Dx; it is not unusual for prolactin secreting adenomas to present with vision loss as a result.
Other syndromes caused by secretory adenomas are quite noticeable and usually prompt an early work-up before the tumor grows to sufficient size to compress the optic chiasm.
Lateral medulla supplied by what artery and occlusion of which causes which syndrome
T2 hyperintense region in the left dorsal lateral region of the medulla.
DWI sequence shows hyperintensity in the same region indicating restricted diffusion. Together these findings support the diagnosis of acute ischemic stroke of the left dorso-lateral medulla which is also known clinically as Wallenberg syndrome (WS).
WS is classically characterized by a LOSS OF PAIN AND TEMPERATURE on the CONTRALATERAL side of the body (due to impairment of the lateral spinothalamic tract) and IPSILATERAL side of the face (due to impairment of the spinal trigeminal tract).
Also IPSILATERAL Horner syndrome due to loss of ipsilateral descending sympathetic fibers. Important to remember that the sympathetic fibers throughout their 3 neuron system NEVER decussate. Therefore a lesion affecting the sympathetic pathway will ALWAYS be ipsilateral to the Horner syndrome it causes.
Damage to the inferior cerebellar peduncle as it enters the medulla results in ipsilateral ataxia (of the limbs) and ipsilateral axial lateropulsion (falling to the same side of the lesion when walking). Damage to the inferior cerebellar peduncle and the vestibular nuclei results in nystagmus. Other associated features include vertigo (from vestibular dysfunction), diplopia (from skew deviation), and uncontrollable hiccups (from vagal nerve dysfunction).
The lateral medulla is usually served by the posterior inferior cerebellar artery (PICA) so this would be the most commonly occluded vessel in cases of WS. In fact, another name for WS is posterior inferior cerebellar artery syndrome.
Aneurysms, strokes
ACOM/PCOM/MCA/PCA
Unruptured aneurysm of the anterior communicating artery (ACoM) is frequently associated with a visual field defect. (ACoM’s location above the anterior visual pathway). This type of aneurysm would cause an INFERIOR ALTITUDINAL defect 2/2 compression of the optic nerve fibers. Visual loss from chiasmal compression can occur, but is much rarer than optic nerve compression. Lastly, ACA aneurysms are the most common site of aneurysmal subarachnoid hemorrhage.
Aneurysms of the posterior communicating artery (PCoM) rarely cause visual loss because they typically point away from the optic pathways. Instead, PCoM aneurysms are classically associated with a pupil-involving CN III palsy.
Strokes and neoplasms, but not unruptured aneurysms, of the middle cerebral and posterior cerebral arteries would result in visual loss. MCA strokes/neoplasms are the most common causes of optic radiation hemianopias. PCA strokes classically cause a MACULAR-SPARING homonymous hemianopia.
optic radiations
temporal lobe: inferior retinal fibers course anteriorly around temporal horn (Meyer’s loop) to about 2.5 cm from anterior tip
Superior fibers more directly posteriorly
optic tract anatomy
crossed/uncrossed fibers together but corresponding retnal regions not together (incongrous VF defects)
pupillary fibers (mostly from M ganglion cells) branch off prior to LGN
Excitatory burst neurons for generating horizontal saccades
located in the PPRF (paramedian pontine reticular formation)
horizontal smooth pursuit eye movements arise from the nucleus of the sixth nerve.
Nucleus reticularis tegmenti pontis contains the long-lead burst cells within the brainstem
interstitial nucleus of Cajal
located in midbrain
contains inhibitory burst neurons for vertical saccades.
vertical integratetor for vertical gaze
Rostral interstitial nucleus of the medial longitudinal fasiculus
located in midbrain
vertical/torsional saccadic generator
vestiubular ocular reflex (VOR)
primarily involved in sensing angular head acceleration
conveys this info to the ocular motor centers to facilitate rapid and compensatory eye movements
allows fovea to remain on target of regard
VOR IS NOT concerned with auditory info
saccades
larger saccadic eye movements travel at a faster rate of speed than do small saccades
horizontal gaze palsy
typically: damage to the ipsi/L pontine horizontal gaze center
(R horizontal gaze center –> R gaze palsy; eyes will be deviated to the LEFT and unable to move right fully)
Gaze preferences
supranuclear lesion of frontal eye fields
R frontal lobe lesion: tendency for eyes to be deviated to the right, but this can be overcome by vestibular ocular reflex (VOR) = hence, supranuclear nature of lesion
saccadic intrusions (fast phases and no slow phases)
flutter, square waves, opsoclonus
pendular nystagmus
oculopalatal myoclonus (form of pendular nystagmus)
CPA (cerebellopontine) angle lies in close proximity to
CN8 and CN7
Embryology
7th-8th week, RGCs well-defined
7th month - myelination of axons begins, and completed by 1st postpartum month
1.2 million axons in adult ON
Optic nerve vascular supply
ON head: choroidal and posterior ciliary vessels
Circle of Zinn Haller:
laminar & pre-laminar portion of optic nerve vascular supply.
Circle of zinn-haller derived from posterior ciliary arteries, pial arterial network and peripapillary choroid
Optic canal contains
4-10 mm length
contains ON, ophthalmic artery, sympathetic plexus branches (of carotid), emninges
lateral geniculate nucleus
part of thalamus
crossed fibers: 1,4,6
uncrossed fibers: 2, 3,5
M cells (1+2 layer) and P(3 + 6 layer) cells
CN4 path
floor of cerebral aequduct –> DECUSSATE –> leave brainstem at inferior colliculi
subarachnoid (emerges from dorsal portion of brainstem) –> passes forward b/t superior cerebellar and posterior cerebral arteries
cavernous sinus: enters inferior to CN3 but then crosses
enters SO fissure OUTSIDE the Annulus of Zinn
CN6 path
o. floor of 4th ventricle (@pontomedullary jxn -in pons)
Note: facial nerves curves dorsalaterally around nucleus
MEDIAL to CN6 nucleus = MLF (part of CN6 goes here for ctrl of horizontal conjugate gaze)
passes through pons (adj to superior olivary nucleus, central tegmental/corticospinal tracts, CN5 and 7 nuceli)
vascular supply from basilar artery
o. Subarachnoid –> nerve runs along pons base LATERAL to basilar artery –> then perforates dura of clivus below crest of petrous bone
passes through inferior petrosal sinus and UNDER petroclinoid ligament (Gruber’s ligament)
o. lies w/in body of sinus (not in wall), caries sympathetic fibers briefly which then split/travel with nasociliary V1 as it enters orbit
O. Orbit: through SO fissure w/in annulus of Zinn
short posterior ciliary arteries and nerves
There are approximately 20 short posterior ciliary arteries that enter the globe in a ring around the optic nerve.
There are also 10 short posterior ciliary nerves that enter the globe in a similar fashion around the optic nerve
Where is the ciliary ganglion located?
located ~ 1 cm in front of the annulus of Zinn. It is lateral to the ophthalmic artery between the optic nerve and the lateral rectus muscle
Carries parasympathetic innervation
Short and long ciliary nerves
~ 6 to 10 short ciliary nerves from the ciliary ganglion and penetrate the posterior globe near the optic nerve - carry PARASYMPATHETIC signals and then pass anteriorly between the choroid and sclera to innervate the ciliary muscle and iris sphincter muscle.
2 to 3 long ciliary nerves that do NOT synapse in the ciliary ganglion and provide SYMPATHETIC input to the iris dilator muscle. The long ciliary nerves also carry sensory fibers from the ciliary body, iris, and cornea.
When do we have the largest number of axons achieved in the optic nerve? How many @ birth?
Largest number of axons achieved in the optic nerve is 3.7 million at 16 weeks gestation.
These nerves are pruned to approximately 1.1 million by 33 weeks gestation, which is the number of axons in the adult.
main blood supply to different portions of the optic nerve
Retrolaminar nerve – pial vessels and short posterior ciliary arteries (SPCAs)
Laminar nerve – SPCAs, branches of circle of Zinn-Haller
Prelaminar nerve – SPCAs, recurrent choroidal arteries
Nerve fiber layer – central retinal artery (CRA)
Intraorbital optic nerve – proximally - pial vessels and branches of ophthalmic artery; distally - branches of CRA
Intracanalicular optic nerve – ophthalmic artery
Intracranial optic nerve – ophtalmic artery and internal carotid artery
Retrolaminar nerve blood supply
pial vessels and short posterior ciliary arteries (SPCAs)
Laminar nerve blood supply
SPCAs, branches of circle of Zinn-Haller
Prelaminar nerve blood supply
SPCAs, recurrent choroidal arteries
Nerve fiber layer
central retinal artery (CRA)
Intraorbital optic nerve – proximally - pial vessels and branches of ophthalmic artery; distally - branches of CRA
Intraorbital optic nerve
proximally - pial vessels and branches of ophthalmic artery; distally - branches of CRA
Intracanalicular optic nerve
ophthalmic artery
Intracranial optic nerve
ophthalmic artery and internal carotid artery
ophthalmic artery is a branch of what artery?
Ophthalmic artery is a branch of the internal carotid artery (ICA) and gives rise to several important blood vessels (e.g. central retinal artery, lacrimal artery, posterior ciliary arteries). The ophthalmic artery typically branches from the ICA just after the ICA emerges from the cavernous sinus.
Prior to giving off any branches (i.e. before the Annulus of Zinn), the ophthalmic artery runs inferolaterally to the optic nerve. After the Annulus of Zinn, the ophthalmic artery turns sharply medially to run along the medial wall of the orbit.
Where is the brainstem horizontal saccadic generator located?
PPRF (paramedian pontine reticular formation) holds the excitatory burst neurons.
Vestibular ocular reflex does what?
conveys info about angular head acceleration
saccadic eye movements vary their speed in accord with the intended amplitude of the movement: true or false?
True: increasing velocity in propotion to the intended amplitude of the movement.
Larger saccadic eye mo
evements travel faster than the speed of small saccades
Hypermetric saccades (ones that overshoot their target = always abnml = indicate cerebellar dysfxn)
horizontal gaze palsy indicates the lesion is ___?
damage to the IPSI/L pontine gaze centers
Ex: R pontine horizontal gaze center lesion produces a R gaze palsy so eyes deviated to OPPOSITE side (left side)
Dense amblyopia can cause APD: true/false?
True
Interstitial nucleus of Cajal
contains inhibitory burst neurons for vertical saccades (also located in the midbrain)
vertical and torsional saccadic generator
rostral interstitial nucleus of the MLF (also located in the midbrain)
gaze preferences
supranuclear lesion of the frontal eye fields
-R frontal lobe lesion = eyes tend to be deviated to the right. Can be overcome by VOR (vestibular ocular reflex = supranuclear nature of the lesion)
blood supply to the anterior segment.
IR & SR carry the bulk of the blood supply to the anterior segment.
Each rectus muscle = 1 to 3 anterior ciliary arteries which are branches of the muscular arteries which themselves are branches of the ophthalmic artery.
lateral muscular branch supplies?
lateral muscular branch supplies the lateral rectus, superior rectus, superior oblique, and levator palpebrae muscles.
medial muscular branch supplies?
The medial muscular branch supplies the inferior rectus, medial rectus, and inferior oblique muscles.
infraorbital artery partially supplies?
Also, the infraorbital artery partially supplies the inferior oblique and inferior rectus muscles.
injury to which muscle can result in pupil sphincter changes?
Injury to the inferior oblique muscle can lead to pupillary changes since the parasympathetic innervation to the pupillary sphincter travels with the nerve of the inferior oblique.
nerves to the recti and superior oblique muscles are what distance from the muscle origin to insertion.
Actually, the nerves to the recti and superior oblique muscles are one-third of the distance from the muscle origin to insertion.
Rhodopsin is most sensitive to what wavelength?
Most sensitive to the 510 nm (green light) wavelength of the electromagnetic spectrum.
Demonstrates less absorption of blue and yellow light and cannot absorb longer wavelengths (e.g. red light). MEMORIZE!
Phototransduction cascade
- A photon of light strikes the 11-cis retinal molecule causing it to isomerize into all-trans retinal.
- This isomerization causes activation of a covalently-attached opsinmolecule which then activates multiple G-protein mediated signaling pathways.
- These signaling pathways eventually lead to closing of ion channels that prevent the influx of sodium and calcium ions.
- Thus, the photoreceptor outer segment membrane becomeshyperpolarized.
Again, only 11-cis retinal is a light sensitive molecule. Thus, the photoreceptor will eventually become light-insensitive when all the 11-cis retinal molecules are depleted (i.e. all isomerized to all-trans retinal). These 11-cis retinal molecules needed to be regenerated (via the “visual cycle”) for phototransduction to continue. The chemical reactions comprising the visual cycle are summarized in the photo below (bottom-pane). Do not worry about memorizing the specific molecules involved, but do note that regeneration of 11-cis retinal requires the retinal pigment epithelium (RPE).
cavernous sinus is continuous with which sinuses?
Cavernous sinus = continuous with the superior sagittal, transverse, straight, sigmoid, and petrosal sinuses. These are known as the “venous sinuses”. Thrombosis in any venous sinus can lead to increased intracranial hypertension and papilledema. Any young patient presenting with papilledema needs to be R/O for having a venous sinus thrombosis.
On a CT scan, what structures should you see to confirm that you have an axial cut of the optic nerve as it passes through the optic canal?
A: anterior clinoid process
What is located on either side of the sella turcica
cavernous sinus
parietal lobe stroke
The circuitry for horizontal smooth pursuit is complex. As one of many structures important for smooth pursuit, the PARIETAL LOBE PERMITS SMOOTH PURSUIT OF OBJECTS TRACKING TOWARDS THE SAME SIDE. A right parietal lobe stroke would be expected to permanently impair smooth pursuit towards the right.
Infarction of axons passing through the optic radiations
Infarction of axons passing through the optic radiations (either the temporal, parietal or occipital lobe) from the lateral geniculate nucleus to the primary visual cortex would result in a contralateral homonymous hemianopia. Such a visual field defect may improve slightly over time as the patient learns to adapt to his/her deficit but the deficit would not be expected to improve dramatically or quickly.
Cerebrum/Midbrain/Pons/Medulla cranial nerves location
Cerebrum: CN 1+2
Midbrain: CN 3+4
Pons: CN 5-8
Medulla: CN 9-12
Cavernous sinus vs CPA angle nerves
Cavernous sinus: CN 3, 4, V1+V2, 6
Cerebellopontine angle: CN 7+8
