Neurosurgical Skull Landmarks
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Neurosurgical Skull Landmarks (Localization)
- Nasion: located at the midline frontonasal suture.
Nasion - Pterion: located at the junction of the frontal,
parietal, temporal, and greater wing of sphenoid
bones It is located two fingerbreadths above the
zygomatic arch and a thumb’s breadth behind
the frontal process of the zygomatic bone.
Pterion - Asterion: located at the junction of the lambdoid,
occipitomastoid, and parietomastoid sutures. It
lies on top of the lower half of the transverse/
sigmoid sinus junction.
Asterion
- Lambda: located at the junction of the lambdoid
and sagittal sutures.
Lambda
- Bregma: located at the junction of coronal and
sagittal sutures.
Bregma
- Inion: located at the indentation under the
external occipital protuberance that overlies the
torcula.
Inion - Opisthion: located at the posterior margin of the foramen magnum in the midline.
Opisthion
- Sylvian fissure: located by
a. marking the 75% point on a line over the superior sagittal sinus from the nasion to the inion;
b. marking the frontozygomatic point, which is 2.5 cm up along the orbital rim past the zygomatic
portion; and
c. the Sylvian fissure extends along the line connecting the 75% point and the frontozygomatic
point. The pterion is located 3 cm behind the frontozygomatic point along the sylvian line.
Sylvian fissure
- Rolandic fissure: located by a. the upper rolandic point, with is 2 cm posterior to the 50% point of the midline nasion/inion
line; and
b. the lower rolandic point is at the junction of the line from the upper rolandic point to the midzygomatic arch and the Sylvian fissure line as previously defined. The rolandic fissure lies between
these two points. The lower rolandic point is also 2.5 cm behind the pterion along the sylvian
line. The motor strip is usually 4 to 5.4 cm behind the coronal suture.
Rolandic fissure
- Angular gyrus (part of Wernicke area): usually just above the pinna, although it is quite variable.
Angular gyrus
