Midline shift refers to the displacement of anatomical structures that separate the cerebral hemispheres along an imaginary midline within the cranial cavity.

Imaging

In CT or MRI images, the midline shift appears as a curvature of otherwise straight boundary structures.

Midline shift on a CT — Midline shift (marked by the red arrows) caused by an acute subdural hematoma.

Causes

Any space-occupying process in the brain can lead to a midline shift, such as:

A chronic or acute subdural hematoma
Intracerebral hemorrhage
Brain tumors
Cerebral edema

Clinical Relevance

Depending on the extent, a midline shift can be life-threatening and lead to herniation syndrome. The extent of an acute midline shift correlates with the level of consciousness[^1]:

Extent of Midline Shift	Level of Consciousness
0–3 mm	Alert
3–4 mm	Drowsy
6–8.5 mm	Stuporous
8–13 mm	Comatose

It is important to note that this can vary from patient to patient and can be significantly influenced by pre-existing spatial conditions such as brain atrophy[^2].