Epipteric bones in the pterion may be a surgical pitfall.

Background: The pterion, the most commonly used neurosurgical landmark, is defined as the junction of frontal, parietal, and greater wing of the sphenoid and the squamous part of temporal bones. Our aim was to identify the variations of the pterion which may be a potential surgical pitfall.
Methods: Both sides of 300 adult skulls were examined but 110 sides were eliminated since their pterion could not be identified owing to a damage. The shortest distance between the lateral orbital rim and the most anterior junction of the four bones forming the pterion was measured on all sides.
Results: Out of 490 sides the pterion was found to contain epipteric bones in 44 (9 %), and in these skulls the most anterior junction of the bones may be as close as 16 mm to the lateral orbital rim.
Conclusion: In skulls with an epipteric bone variation, particularly the anterius and proprium types; the pterion can mistakenly be assessed to be at the most anterior junction of bones and a burr hole placed over there may cause inadvertent penetration into the orbit.