=  from nasion to anterior angle of bregma

[bregma, Greek = top of head]

Closure:   by 3 months – 6 years of age; in up to 10% open until adulthood

Sutura frontalis persistens = metopism

=  no closure of incomplete / complete metopic suture

DDx:   anterior vertical fracture

B.  SAGITTAL SUTURE

[sagitta, Latin = arrow]

=  fibrous connective tissue joint between two parietal bones

Average width:   5.0 ± 0.2 mm (at birth), 2.4 ± 0.1 mm (1 month of age); narrowing further over time

Closure:   21–30 years of age; fusing anteriorly beginning at intersection with lambdoid suture

C.  CORONAL SUTURE

=  separates frontal from parietal bones

Average width:   2.5 ± 0.1 mm (at birth), 1.3 ± 0.1 mm (1 month of age)

Closure:   24 years of age

D.  SQUAMOSAL SUTURE

(a)  temporosquamosal suture

=  connects temporal bone squama with lower border of parietal bone; arches posteriorly from pterion (= contact point between frontal, parietal, temporal, sphenoid)

[pteron, Greek = wing]

√  often visualized at two points at CT with lambdoid suture acting as a useful posterior reference point

=  continuous posteriorly with parietomastoid suture uniting mastoid process of temporal bone with region of mastoid angle of parietal bone

(b)  sphenosquamosal suture

=  courses inferiorly from pterion separating sphenoid bone from squama of temporal bone

N.B.:   often mistaken for skull base fracture

E.  LAMBDOID SUTURE

[upper case Greek letter lambda = L]

=  connects parietal with occipital bone

Closure:   26 years of age

N.B.:   the most common site of wormian bones

F.  OCCIPITOMASTOID SUTURE

=  inferior continuation of lambdoid suture at the point where lambdoid suture intersects with temporosquamosal suture

G.  PARIETOMASTOID SUTURE

=  links temporosquamosal and lambdoid sutures

√  often not seen on axial CT images

H.  OCCIPITOMASTOID SUTURE

=  between occipital bone + mastoid process of temporal bone as a continuation of the lambdoid suture toward skull base

N.B.:   not infrequently mistaken for a skull base fracture

I.  SPHENOFRONTAL SUTURE

=  transverse suture between anterior margin of lesser sphenoid wing + posterior margin of horizontal orbital plate

√  lesser sphenoid wing (posterior to suture) is a useful landmark for suture localization

J.  ACCESSORY PARIETAL SUTURE (RARE)

=  the most common of all usually bilateral and symmetric accessory sutures

Location:   parietal and occipital bone → multiple ossification centers

K  MENDOSAL / ACCESSORY OCCIPITAL SUTURE

Frequency:   3% in an Indian subcontinent population

Closure:   in utero / first few days of life; may persist up to 6 years of age

Os incae =   large single centrally located intrasutural bone at junction of lambdoid and sagittal sutures; often forms in a persistent mendosal suture

K  SKULL BASE SUTURES

Ossification:   50% (84%) of anterior base by 6 (24) months

(a)  innominate / intraoccipital

Closure:   4 years of age

(b)  lambdoid

(c)  occipitomastoid

(d)  parietomastoid

(e)  temporosphenoidal

FORAMINA OF BASE OF SKULL

on inner aspect of middle cranial fossa 3 foramina are oriented along an oblique line in the greater sphenoidal wing from anteromedial behind the superior orbital fissure to posterolateral

mnemonic:   “rotos”

foramen rotundum

foramen ovale

foramen spinosum

Foramen Rotundum

=  canal within greater sphenoid wing connecting middle cranial fossa + pterygopalatine fossa

√  best visualized by coronal CT

Foramen Ovale

=  canal connecting middle cranial fossa + infratemporal fossa

Location:  medial aspect of sphenoid body, situated posterolateral to foramen rotundum (endocranial aspect) + at base of lateral pterygoid plate (exocranial aspect)

Foramen Spinosum

Location:  on greater sphenoid wing posterolateral to foramen ovale (endocranial aspect) + lateral to eustachian tube (exocranial aspect)

Foramen Lacerum

covered (occasionally) by fibrocartilage, carotid artery rests on endocranial aspect of fibrocartilage

Location:  at base of medial pterygoid plate

Contents:  (inconstant)

(a) nerve:   pterygoid canal n. (actually pierces cartilage)

(b) vessel:   meningeal branch of ascending pharyngeal a.

Foramen Magnum

Pterygoid Canal

=  VIDIAN CANAL

=  within sphenoid body connecting pterygopalatine fossa anteriorly to foramen lacerum posteriorly

Location:   at base of pterygoid plate below foramen rotundum

Contents:   (a)   nerves: vidian nerve = nerve of pterygoid canal = continuation of greater superficial petrosal nerve (from cranial nerve VII) after its union with deep petrosal nerve

(b)  vessel: vidian artery = artery of pterygoid canal = branch of terminal portion of internal maxillary a. arising in pterygopalatine fossa → passing through foramen lacerum posterior to vidian n.

Hypoglossal Canal

=  ANTERIOR CONDYLAR CANAL

Location:   in posterior cranial fossa anteriorly above condyle starting above anterolateral part of foramen magnum, continuing in an anterolateral direction + exiting medial to jugular foramen

Jugular Foramen

Location:   at posterior end of petrooccipital suture directly posterior to carotid orifice

(a)  anterior part:

(1)  inferior petrosal sinus

(2)  meningeal branches of pharyngeal artery + occipital a.

(b)  intermediate part:

(1)  cranial nerve IX (glossopharyngeal nerve)

(2)  cranial nerve X (vagus nerve)

(3)  cranial nerve XI (spinal accessory nerve)

(c)  posterior part: internal jugular vein

CRANIOVERTEBRAL JUNCTION (CVJ)

CRANIOCERVICAL JUNCTION: C1 (atlas) + C2 (axis) + occiput

Variants of CVJ:   precondylar tubercles, third occipital condyle, ossification of ligament of odontoid process

Craniometry:

›  LATERAL VIEW

1.   Chamberlain line

=  line between posterior edge of hard palate + posterior margin of foramen magnum (= opisthion)

√  tip of odontoid process usually lies below / tangent to Chamberlain line by > 3 mm

√  tip of odontoid process may lie up to 1 ± 6.6 mm above the Chamberlain line

2.   McGregor line

=  line between posterior edge of hard palate + most caudal portion of occipital squamosal surface

◊  Substitute to Chamberlain line if opisthion not visible

√  tip of odontoid < 4.5–5.0 mm above this line

3.   Wackenheim clivus baseline

=  BASILAR LINE = CLIVAL LINE = line along clivus

√  usually falls tangent to posterior aspect of tip of odontoid process

4.   Craniovertebral angle = clivus-canal angle

=  angle formed by line along posterior surface of axis body and odontoid process + basilar line

√  ranges from 150° in flexion to 180° in extension

√  ventral spinal cord compression may occur at < 150°

5.   Welcher basal angle

=  intersection of nasion-tuberculum line and of tuberculum-basion line (along clivus)

√  angle averages 132° (should be < 140–145°)

6.   McRae line

=  line between anterior lip (= basion) to posterior lip (= opisthion) of foramen magnum

√  tip of odontoid below this line = NO basilar invagination; if poorly seen → Chamberlain line

›  ANTEROPOSTERIOR VIEW (= “open-mouth” / odontoid view)

7.   Atlanto-occipital joint axis angle

=  formed by lines drawn parallel to atlantooccipital joints

√  lines intersect at center of odontoid process

√  average angle of 125° (range, 124° to 127°)

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