Pterion !

The pterion is the thin H-shaped spot on the side of the skull where four bones meet; an artery runs just inside, so a blow here can bleed over the brain.

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What it is

The H-shaped thin spot on the side of the skull where four bones meet.

What it does

The middle meningeal artery runs just inside; a blow here can cause an epidural haematoma.

Key facts

Where: H-shaped junction of the frontal, parietal, temporal squama and greater wing of the sphenoid, about 3 cm above the zygomatic arch
Function: Thinnest part of the skull side; the frontal branch of the middle meningeal artery runs beneath (epidural haematoma)

Relations

Deep: Dura with the frontal branch of the middle meningeal artery; then the lateral fissure, with the middle cerebral artery in its depth, and the inferior frontal gyrus
Superficial: Temporalis and its fascia, the superficial temporal vessels and the frontal (temporal) branch of the facial nerve crossing the temple
In front: Frontal process of the zygomatic bone and the lateral orbital rim
Below: Zygomatic arch and, below the infratemporal crest, the infratemporal fossa

How to find it

It cannot be felt as a point, because temporalis covers it. It lies in the hollow of the temple where a line going up from the middle of the zygomatic arch meets a line going back from the frontozygomatic suture.

On imaging

Skull CT with bone windows and 3D reconstruction shows the H-shaped suture junction and fractures crossing the arterial groove; the same scan in brain windows shows an epidural haematoma beneath as a bright, lens-shaped collection.

Clinical notes

An epidural haematoma from the frontal branch can enlarge over hours; drowsiness, a dilated pupil on the same side and weakness of the other side mean brain shift and call for emergency surgical evacuation
The frontal (temporal) branch of the facial nerve crosses superficially; injury in approaches here leaves the eyebrow unable to rise on that side
Small sutural bones at the pterion (epipteric bones) can be mistaken for a fracture on radiographs

Anatomical variants

Suture pattern: in most skulls the sphenoid meets the parietal (sphenoparietal type); less often the frontal meets the temporal, or all four meet at one point (stellate type)
The frontal branch of the middle meningeal artery may run in a bony tunnel rather than a groove at the pterion, which makes it easier to tear in a fracture

Development

It marks the site of the anterolateral (sphenoidal) fontanelle of the newborn, which closes in the first year.

Epidural haematoma

Test yourself

Think of the answer, then tap the question to see it.

Which bones meet at the pterion, and why is it clinically important?

Frontal, parietal, temporal squama and greater wing of the sphenoid; it is the thinnest part of the skull side, over the frontal branch of the middle meningeal artery.

What does a CT fracture line crossing the middle meningeal groove at the pterion warn of?

An epidural haematoma, even when the person looks well during a lucid interval.

Which signs show that an epidural haematoma under the pterion is causing brain shift?

Drowsiness, a dilated pupil on the same side and weakness of the other side; they call for emergency surgical evacuation.

Which nerve branch is at risk in surgical approaches at the pterion, and what is the deficit?

The frontal (temporal) branch of the facial nerve; the eyebrow cannot rise on that side.

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Educational information, not medical advice. For any symptom, see a health professional.

Its names

Official Latin (TA2): pterion TA2 421
Official Spanish (DeCS): Pterion
English (TA2): Pterion

Middle meningeal artery

Sources: Terminologia Anatomica (TA2); Anatomy, Head and Neck, Skull; Anatomy, Head and Neck, Temporal Region.

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Representative model, for educational purposes only.