6. Neuro (Brain - Anatomy)

Question 1

Central sulcus (4)

Answer 1

Separates frontal lobe from parietal lobe.
Singulate gyrus seen high up on the brain, “pars bracket sign”, because the bi-heispheric symmetric pars marginalis form an anteriorly open bracket.
This bracket is immediately behind the central sulcus.
Present 95% of the time.

Question 2

Central sulcus trivia (6)

Answer 2

Superior frontal sulcus/pre-central sulcus sign: posterior end of the superior frontal sulcus joins the pre-central sulcus.
Inverted omega (sigmoid hook) corresponds to motor hand.
Bifid posterior central sulcus: posterior CS has bifid appearance 85% of cases.
Post central gyrus sign: precentral gyrus is thicker than post central gyrus (1:1.5)
Intersection - intraparietal sulcus intersects the postcentral sulcus
Midline sulcus sign: most prominent sulcus that reaches the midline is the central sulcus

Question 3

Homonculus trivia (3)

Answer 3

Inverted omega (posteriorly directed knob) on the central sulcus/gyrus designates the motor cortex controlling hand function.
ACA territory is legs, MCA is the rest

Question 4

Normal cerebral cortex (3)

Answer 4

Cortex is normally 6 layers thick, and the hippocampus is normally 3 layers thick.
Hippocampus can look slightly brighter on FLAIR compared to other cortical areas because of this

Question 5

Dilated perivascular spaces (Virchow-Robins) (10)

Answer 5

These are fluid filled spaces acompanying perforating vessels.
Normal variant and very common.
Can be enlarged and associated with multiple patholgies
- Mucopolysaccharidoses (Hurlers and Hunters)
- Gelatinous pseudocysts in cryptococcal meningitis
- Atrophy with advanced age
Don’t contain CSF, rather interstitial fluid.
Commonest locations are
- Leticulostriate arteries in the lower third of basal ganglia
- Centrum semiovale
- Midbrain

Question 6

Ventricular anatomy (6)

Answer 6

2 lateral ventricles, which communicate with third via interventricular foramen (of monroe).
This connects with the 4th via Cerebral Aqueduct of Silvius.
Fluid in the 4th ventricle escapes via the median and lateral apertures (of magendie and luschka respectively).
Small amount of fluid will pass downward into spinal subarachnoid spaces, but most rises through tentorial notch and is reabsorbed by arachnoid vili and granulations into the venous sinus system.
Blockage at any point causes non communicating hydrocephalus, as will blockage of reabsorption at the vili/granulation.

Question 7

Arachnoid granulations (4)

Answer 7

Regions where the arachnoid projects into the venous system, allowing for CSF to be reabsorbed.
Hypodense on CT (like CSF) and usually round or oval, distinguishing them from venous sinus thrombus (linear).
MR: T2 bright (iso to CSF) but can be bright on FLAIR (varied).
Can scallop the inner table, likely due to CSF pulsation.

Question 8

Cavum variants (3)

Answer 8

Cavum septum pellucidum: Seen in 100% of preterm infants, 80% at term and 15% adults. Can dilate and cause obstructive hydrocephalus
Cavum Vergae: Posterior communication of the cavum septum pellucidum (never seen without cavum septum pellucidum)
Cavum Velum Interposium: Extension of the quadrigeminal plate cistern to foramen of monro. Seen on saggital as above the 3rd ventricle, below the fornices.

Question 9

Basal cisterns (5)

Answer 9

Useful for looking at mass effect.
Suprasellar cisterns look like a pentigon, with the 5 corners of the star being landmarks.
Top corner is the interhemispheric fissue.
Anterior points are sylvian cisterns.
Posterior points are ambient cisterns.
Quadrigeminal plate looks like a smile.

Question 10

Brain development/myelination (8)

Answer 10

Baby brain has opposite signal characteristics to adult brain.
T1 pattern in baby is similar to T2 pattern in adult, and vice versa.
This is due to myelination, which occurs in a set order (inferior to superior, posterior to anterior, central to peripheral, sensory before motor)
Immature myelin has higher water content, and therefore brighter on T2 and darker on T1. Water decreases and fat increases during maturation.
T1 changes occur before T2 (age 1 vs age 2).
T1 is most useful for assessing myelination in first year, T2 in second year.
Subcortical white matter is the last part to myelinate (Occipital white matter around 12 months, frintal regions finishing around 18 months).
Terminal zones of myelination occur in subcortical frontotemporal regions, finishing at around 40 months.
Brainstem and posterior limb of the internal capsule are normally myelinated at birth.

Question 11

Corpus callosum (2)

Answer 11

Forms front to back (then rostrum last).
Hypoplasia of the corpus callosum is usually due to absent splenium.

Question 12

Brain development high yield (7)

Answer 12

Myelination occurs inferior to superior, posterior to anterior.
Corpus callosum forms front to back, rostrum last.
Anterior and posterior pituitary are bright at birth, posterior only bright 2 months to 2 years.
Calverial bone marrow will be active (t1 hypointense) in young kids, and fatty (T1 hyperintense) in older kids.
Sinuses form in the following order: Maxillary, Ethmoid, Sphenoid, Frontal.
Brain iron increases with age (Globus pallidus darkens up)

Question 13

Foramen ovale contents

Answer 13

CN V3 and Accessory meningeal artery

Question 14

Foramen rotundum contents

Answer 14

CN V2

Question 15

Superior orbital fissure contents

Answer 15

CN 3, CN 4, CN V1, CN 6

Question 16

Inferior orbital fissure contents

Answer 16

CN V2

Question 17

Foramen spinosum contents

Answer 17

Middle meningeal artery

Question 18

Jugular foramen contents (2)

Answer 18

Pars nervosa: CN 9
Pars vascularis: CN 10, CN 11, Jugular bulb

Question 19

Hypoglossal canal contents

Answer 19

CN 12

Question 20

Optic canal contents

Answer 20

CN 2 and Ophthalmic artery

Question 21

Jugular foramen (3)

Answer 21

2 parts, separated by jugular spine
Pars nervosa: anterior, contains CN 9 (glossopharyngeal nerve) and sympathetic branch, the “Jacobson’s nerve”
Pars vascularis: Contains jugular bulb, along with Vagus nerve (CN 10) along with auricular branch “Arnold’s nerve” and spinal accessory nerve (CN 11)

Question 22

Foramen spinosum and ovale (2)

Answer 22

Like a footprint of a heeled shoe, with oval part being ovale and smaller circular part the spinosum.

Question 23

Foramen rotundum (2)

Answer 23

Completely level or horizontal on sagttal view.
Coronal looks like staring onto a gun.

Question 24

Hypoglossal canal

Answer 24

Very posterior and inferior, unique for a skull base foramen.

Question 25

Cavernous sinus (4)

Answer 25

Contains CN 3, 4, V1, V2 and CN 6.
Does not contain CN 2 and CN V3.
CN 6 runs nect to the carotid, and the rest are along the wall.
Hence can get lateral rectus palsy earlier with cavernous sinus pathologies.

Question 26

Skull fusion (craniosyntosis) (5)

Answer 26

Sutures exist to allow for rapid brain growth over first few years of life.
Brain doubles in size in forst 6 months, and again by 2nd year of life.
Majority of skill growth occurs by age 3, at which time most sutures will close.
Some, like petro-occipital suture, remain open into adulthood.
Fusing too early causes problems.

Question 27

IAC - Nerve orientation (3)

Answer 27

“7 Up and Coke down”: 7th cranial nerve is superior to 8th cranial nerve (cochlear nerve component).
Superior vestibular branch is superior to the inferior one.
Ideal sequence is heavily weighted T2 sequence with thin cuts through the IAC.

Question 28

Branches of the external carotid. (8)

Answer 28

Some Anatomists Like Freaking Out Poor Medical Students
Superior thyroid
Ascending pharyngeal
Lingual
Facial
Occipital
Posterior auricular
Maxillary
Superficial temporal

Question 29

Anterior circulation anatomy (4)

Answer 29

Bifurcation of the ICA and ECA occurs around C3-C4.
Cervical ICA has no branches in the neck, so if you see branches, they’re either anomalous, or more likely this is the external carotid.
Presence of branches is what distinguishes ECA from ICA on US.
Flow reversal in carotid bulb is normal.

Question 30

C1 (cervical) ICA trivia (5)

Answer 30

Common location for atheroscloeris.
DIssection: Can be spontaneous (women) or Marfans or Ehlers danlos, can result in partial Horner’s (ptosis and miosis), followed by MCA stroke.
Can have retropharyngeal course and get “drained” by ENT accidentally.
Pharyngeal infection may cause pseudoaneurys mat this level.

Question 31

C2-C7 ICA trivia (6)

Answer 31

C2 (petrous): Sometimes aneurysms occur here
C3 (lacerum): Anatomic location is important to neurosurgeons for exposing Meckel’s cave via transfacial approach.
C4 (Cavernous): Aneurysms here strongly associated with hypertension, this segment is affected by multiple pathologies including development of cavernous - carotid fistulas.
C5 (clinoid): Aneurysm here could compress optic nerve and cause blindness.
C6 (ophthalmic - supraclinoid): common site for aneurysms. Origin at the “dural ring” is a buzzword for this artery.
C7 (communicating - terminal): Aneurysm here may compress CN 3 and cause a palsy

Question 32

Foetal origin of PCA (3)

Answer 32

Commonest vascular variant, up to 30% of general population.
Foetal PCOM is ised to refer to a situation where the PCOM is larger or same size as P1.
Foetal PCA has PCOM superior and lateral to CN3 instead of superior and medial.

Question 33

Persistent trigeminal artery (3)

Answer 33

Persistent foetal connection between cavernous ICA and basilar artery.
“Tau sign” on sagittal MRI.
Increases the risk of aneurysm (anytime there is branch points)

Question 34

Aberrant carotid artery (3)

Answer 34

Typically represents and enlarged caroticotympanic artery (with underdevelopment of the cervical ICA).
Vessel courses through the tympanic cavity and joins the horizontal carotid canal.
Causes pulsatile tinnitus.

Question 35

Anastomotic vein of Trolard

Answer 35

Connects superficial middle vein and superior sagittal sinus.

Question 36

Anastamotic vein of Labbe

Answer 36

Connects the superficial middle vein and the transverse sinus.

Question 37

Schematic for venous drainage (7)

Answer 37

Middle cerebral vein –> Cavernous sinus –> Inferior and Superior petrosal sinus
Inferior petrosal sinus –> Internal jugular vein.

Middle cerebral vein (via Anastamotic vein of Trollard) and Superior cerebral vein –> Superior sagittal sinus.
Superior sagittal sinus and Straight sinus –> Confluence of sinuses
Confluenceof sinuses and Anastamotic vein of Labbe –> transverse sinus –> Signoid sinus –> Internal jugular vein.

Superior cerebral vein –> superior sagittal sinus
Inferior sagittal sinus and Vein of galen –> straight sinus.

Question 38

Superficial vs deep veins (7)

Answer 38

Superficial
- Superior cerebral veins
- Superior anastamotic vein of Trollard
- Inferior anastamotic vein of Labbe
- Superior Middle Cerebral veins
Deep
- Basal vein or Rosenthal
- Vein of Galen
- Inferior petrosal sinus

Question 39

Collateral pathways (3)

Answer 39

Dural sinuses have accessory drainage pathways (other than jugular veins) to allow connection to extracranial veins.
These help regulate temperature and equalize pressure.
However they also allow passage of sinus infection and inflammation, resulting in venous sinus thrombosis.

Question 40

Inverse relationship (2)

Answer 40

Inverse relationship between vein of Labbe and anastamotic vein of Trollard.
As one gets larger, other gets smaller, as they drain the same territory.

Question 41

Important eponymous veins (4)

Answer 41

Vein of Labbe - Connects superficial middle vein and transverse sinus
Vein of Trolard - connects superficial middle vein and sagittal sinus.
Basal vein of Rosenthal - Deep vein passing lateral to the midbrain, through ambient cistern, and drains into vein of Galen. Similar course to PCA.
Vein of Galen: Great vein formed by union of 2 internal cerebral veins.

Question 42

Concha Bullosa (2)

Answer 42

Common variant, middle concha is pneumatised.
No clinical significance unless huge, then can cause obstructive symptoms.

Question 43

Important neuro anatomy trivia (2)

Answer 43

CN3 palsy? think posterior communicating artery aneurysm
CN6 palsy? think increased ICP.