Gross Anatomy, Cranial and Spine

Question 1

Does the central sulcus join the Sylvian fissure in only?

Answer 1

in only 2% of cases (i.e., in 98% of cases there is a “subcentral” gyrus).

Question 2

Br. areas 3, 1, 2: role, location:

Answer 2

Br. areas 3, 1, 2: primary somatosensory cortex, PostCentralGyrus (PostCG)

Question 3

Br. areas 41 & 42: role, location:

Answer 3

Br. areas 41 & 42: primary auditory areas; superior temporal gyrus (transverse gyri of Heschl)

Question 4

Br. area 4: role, location:

Answer 4

Br. area 4: primary motor cortex (AKA “motor strip”) - Large concentration of
giant pyramidal cells of Betz; PreCentralGyrus (PreCG);

Question 5

Br. area 6: role, location:

Answer 5

premotor area or supplemental motor area, it
plays a role in contralateral motor programming, Immediately anterior to motor strip - around PrCS (PreCentralSulcus);

Question 6

Br. area 44: role, location:

Answer 6

Br. area 44: (dominant hemisphere) Broca’s area (classically “motor speech area”), IFG: PT + POp (Inferior Frontal Gyrus: Pars Triangularis & Pars Opercularis)

Question 7

Br. area 17: role, location:

Answer 7

Br. area 17: primary visual cortex, occipital lobe, around lateral occipital sulcus (los)

Question 8

Br. area 40 and a portion of Br. area 39: role, location:

Answer 8

Wernicke’s area: (dominant hemisphere); IPL: SMG + AG (Inferior Parietal Lobe: SupraMarginal Gyrus [ls] + Angular Gyrus[sts])

Question 9

Br. area 8: role, location::

Answer 9

(frontal eye field) initiates voluntary eye movements to the opposite direction; SFG (Superior Frontal Gyrus) - anterior to the Br. area 6.;

Question 10

AC-PC line:

Answer 10

1.) Talairach definition,3 it passes through the superior edge of the AC
and the inferior edge of the PC
2.) Schaltenbrand definition: the line passing through the midpoint of the AC & PC, allowing both AC & PC to be imaged on a single
thin axial MRI slice.

The AC-PC line is used in
functional neurosurgery and is also used as the baseline for axial MRI scans (and for recent CT scanners).

Question 11

Hand “knob”:

Answer 11

The alpha motor neurons for hand function are located in the superior aspect of the precentral
gyrus which appears as a knob-like protrusion (shaped like an inverted greek letter omega Ω)
projecting posterolaterally into the central sulcus on axial imaging.

Question 12

Pterion - definition, estimated location:

Answer 12

1.) Region where the following bones are approximated: frontal, parietal, temporal and
sphenoid (greater wing).
2.) Estimated location: 2 finger-breadths above the zygomatic arch, and a
thumb’s breadth behind the frontal process of the zygomatic bone.

Question 13

Asterion - definition:

Answer 13

junction of lambdoid, occipitomastoid and parietomastoid sutures. Usually lies within a few millimetres of the posterior-inferior edge of the junction of the transverse and sigmoid sinuses.

Question 14

Vertex - definition:

Answer 14

Vertex: the topmost point of the skull.

Question 15

Lambda - definiton:

Answer 15

Lambda: junction of the lambdoid and sagittal sutures.

Question 16

Stephanion - definition:

Answer 16

Stephanion: junction of coronal suture and superior temporal line.

Question 17

Glabella - definiton:

Answer 17

Glabella: the most forward-projecting point of the forehead at the level of the supraorbital ridge
in the midline.

Question 18

Opisthion - definition:

Answer 18

Opisthion: the posterior margin of the foramen magnum in the midline.

Question 19

Bregma - definition:

Answer 19

Bregma: the junction of the coronal and sagittal sutures.

Question 20

Superior Sagittal Sinus - estimated location:

Answer 20

Although often assumed
to lie underneath the sagittal suture, the SSS lies to the right of the sagittal suture in the majority of specimens ,(but never by > 11 mm).

Question 21

Taylor-Haughton lines:

Answer 21

1. Frankfurt plane, AKA baseline: line from inferior margin of orbit through the upper margin of the external auditory meatus (EAM) (as distinguished from Reid’s base line: from inferior orbital margin through the center of the EAM)
2. the distance from the nasion to the inion is measured across the top of the calvaria and is divided into quarters (can be done simply with a piece of tape which is then folded in half twice)
3. posterior ear line: perpendicular to the baseline through the mastoid process
4. condylar line: perpendicular to the baseline through the mandibular condyle

Question 22

External landmarks to locate the motor strip (precentral gyrus) or the
central sulcus (Rolandic fissure):

Answer 22

1. method 1: the superior aspect of the motor cortex is almost straight up from the EAM near the midline
2. method: the central sulcus is approximated by connecting: a) the point 2cm posterior to the midposition of the arc extending from nasion to inion b) the point 5cm straight up from the EAM.
3. method 3: using T-H lines, the central sulcus is approximated by connecting a) the point where the “posterior ear line” intersects the circumference of the skull usually about 1cm behind the vertex, and 3–4cm behind the coronal suture), to b) the point where the “condylar line” intersects the line representing the Sylvian fissure
4. method 4: a line drawn 45° to Reid’s base line starting at the pterion points in the direction of the motor strip

Question 23

Sylvian fissure, landmarks - On the skin surface:

Answer 23

On the skin surface: approximated by a line connecting the lateral canthus to the point 3/4 of the
way posterior along the arc running over convexity from nasion to inion (T-H lines).

Question 24

Sylvian fissure, landmarks - On the skull:

Answer 24

the anterior portion of the Sylvian fissure follows the squamosal suture and then deviates superiorly to terminate at Chater’s point,

Question 25

Chater’s point - definition:

Answer 25

Chater’s point: located 6cm above the EAM on a line perpendicular to the orbitomeatal line; it is also ≈ 1.5cm above the squamosal suture along the same perpendicular line.

Question 26

ACA - segments:

Answer 26

a) A1 (precommunicating): ACA from origin to AComA

b) A2 (postcommunicating): ACA from AComA to branch-point of callosomarginal artery

c) A3 (precallosal): from branch-point of callosomarginal curving around the genu of the corpus callosum to superior surface of corpus callosum .

d) A4: (supracallosal)

e) A5: terminal branch (postcallosal)

Question 27

MCA - segments:

Answer 27

a) M1: MCA from origin to bifurcation (horizontal segment on AP angiogram). A classical bifurcation
into relatively symmetrical superior and inferior trunks is seen in 50%, no bifurcation occurs in
2%, 25% have a very proximal branch (middle trunk) arising from the superior (15%) or the inferior
(10%) trunk creating a “pseudo-trifurcation,” a pseudo-tetrafurcation occurs in 5%
● lateral fronto-orbital and prefrontal branches arise from M1 or superior M2 trunk
● precentral, central, anterior and posterior parietal arteries arise from a superior (60%), middle
(25%), or inferior (15%) trunk
● the superior M2 trunk does not give any branches to the temporal lobe

b) M2: MCA trunks from bifurcation to emergence from Sylvian fissure

c) M3–4: distal branches

d) M5: terminal branch

Question 28

PCA - segments:

Answer 28

P1: PCA from the origin to posterior communicating artery.

P2: PCA from the origin of PComA to the origin of inferior temporal arteries.

P3: PCA from the origin of the inferior temporal branches to the origin of the terminal
branches.

P4: segment after the origin of the parieto-occipital and calcarine arteries.

Question 29

ECA (external carotid artery): - branches:

Answer 29

1. superior thyroid a.: 1st anterior branch
2. ascending pharyngeal a.
   a) neuromeningeal trunk of the ascending pharyngeal a.: supplies IX, X & XI (important when
   embolizing glomus tumors, 20% of lower cranial nerve palsy if this branch is occluded)
   b) pharyngeal branch: usually the primary feeder for jugular foramen tumors (essentially the
   only cause of hypertrophy of the ascending pharyngeal a.)
3. lingual a.
4. facial a.
5. occipital a.
6. posterior auricular
7. superficial temporal
   a) frontal branch
   b) parietal branch
8. maxillary a.
   a) middle meningeal a.

Question 30

Segments of the ICA and its branches - C1:

Answer 30

C1 (cervical): begins in the neck at the carotid bifurcation where the common carotid artery
divides into internal and external carotid arteries. Encircled with postganglionic sympathetic
nerves (PGSN), the ICA travels in the carotid sheath with the IJV and vagal nerve. C1 ends where
the ICA enters the carotid canal of the petrous bone. No branches.

Question 31

Segments of the ICA and its branches - C2:

Answer 31

C2 (petrous): still surrounded by PGSNs. Ends at the posterior edge of the foramen lacerum
(f-Lac) (inferomedial to the edge of the Gasserian ganglion in Meckel’s cave). Three subdivisions:
a) vertical segment: ICA ascends then bends as the…
b) posterior loop: anterior to the cochlea, bends antero-medially becoming the…
c) horizontal segment: deep and medial to the greater and lesser superficial petrosal nerves,
anterior to the tympanic membrane (TM)

Question 32

Segments of the ICA and its branches - C3:

Answer 32

C3 (lacerum): the ICA passes over (but not through) the foramen lacerum (f-Lac) forming the lateral
loop. Ascends in the canalicular portion of the f-Lac to the juxtasellar position, piercing the
dura as it passes the petrolingual ligament to become the cavernous segment. Branches (usually
not visible angiographically):
a) caroticotympanic (inconsistent) ⇒ tympanic cavity
b) pterygoid (vidian) branch: passes through the f-Lac, present in only 30%, may continue as the
artery of the pterygoid canal

Question 33

Segments of the ICA and its branches - C4:

Answer 33

C4 (cavernous): covered by a vascular membrane lining the sinus, still surrounded by PGSNs.
Passes anteriorly then supero-medially, bends posteriorly (medial loop of ICA), travels horizontally,
and bends anteriorly (part of anterior loop of ICA) to the anterior clinoid process. Ends at
the proximal dural ring (incompletely encircles ICA). Many branches, main ones include
a) meningohypophyseal trunk (MHT) (largest & most proximal). 2 causes of a prominent MHT:
(1) tumor (usually petroclival meningioma—see below), (2) dural AVM. 3 branches:
1. a. of tentorium (AKA artery of Bernasconi & Cassinari): the blood supply of petroclival
meningiomas
2. dorsal meningeal a. (AKA dorsal clival a.)
3. inferior hypophyseal a. (⇒ posterior lobe of pituitary): post-partum occlusion causes pituitary
infarcts (Sheehan’s necrosis); however, DI is rare because the stalk is spared
b) anterior meningeal a.
c) a. to inferior portion of cavernous sinus (present in 80%)
d) capsular aa. of McConnell (in 30%): supply the capsule of the pituitary

Question 34

Segments of the ICA and its branches - C5:

Answer 34

C5 (clinoid): begins at the proximal dural ring, ends at the distal dural ring (which completely
encircles ICA) where the ICA becomes intradural

Question 35

Segments of the ICA and its branches - C6:

Answer 35

C6 (ophthalmic): begins at distal dural ring, ends just proximal to the PComA. Branches:
a) ophthalmic a.: the origin from the ICA is distal to the cavernous sinus in 89% (intracavernous
in 8%, the ophthalmic artery is absent in 3%8) and can vary from 5mm anterior to 7mm posterior
to the anterior clinoid.7 Passes through the optic canal into the orbit (the intracranial
course is very short, usually 1–2mm7). Has a characteristic bayonet-like “kink” or “L” shape
(depending on whether it passes above or below the optic nerve) on lateral angiogram
b) superior hypophyseal a. branches ⇒ anterior lobe of pituitary & stalk (1st branch of
supraclinoid ICA)

Question 36

Segments of the ICA and its branches - C7:

Answer 36

C7 (communicating): begins just proximal to the PComA origin, travels between Cr. N. II & III,
terminates just below anterior perforated substance where it bifurcates into the ACA & MCA
a) posterior communicating a. (PComA)
● few anterior thalamoperforators (⇒ optic tract, chiasm & posterior hypothalamus): below
● plexal segment: enters supracornual recess of temporal horn, ⇒ only this portion of choroid
plexus
● cisternal segment: passes through crural cistern
b) anterior choroidal artery9: takeoff 2–4mm distal to PComA ⇒ (variable) portion of optic tract,
medial globus pallidus, genu of internal capsule (IC) (in 50%), inferior half of posterior limb of
IC, uncus, retrolenticular fibers (optic radiation), lateral geniculate body; for occlusion syndromes

Question 37

“Carotid siphon”:

Answer 37

“Carotid siphon”: not a segment, but a region incorporating the cavernous, ophthalmic and communicating
segments.

Question 38

Differentiating PComA from ACh on arteriogram:

Answer 38

1. PComA origin is proximal to that of the anterior choroidal artery (ACh)
2. PComA is usually larger than ACh
3. PComA usually goes up or down a little, then straight back & usually bifurcates
4. ACh usually has a superior “hump” (plexal point) where it pass through the choroidal fissure to
   enter the ventricle