What type of Magnetic Resonance Imaging (MRI) is used to assess anisocoria (unequal pupil size)?

From the Guidelines

To assess anisocoria, an MRI of the orbits without and with contrast is the optimal imaging modality. This is because anisocoria can be caused by various conditions, including mass lesions, vascular abnormalities, or inflammatory processes affecting the pupillary pathways, and MRI provides improved soft tissue characterization 1. The MRI should include T1-weighted, T2-weighted, and contrast-enhanced sequences, and thin-slice imaging through the orbit is particularly important to evaluate the oculomotor nerve pathway.

Some key points to consider when assessing anisocoria with MRI include:

• The use of diffusion-weighted imaging (DWI) to detect acute ischemic changes 1
• The evaluation of the brainstem, orbit, and cavernous sinus to identify potential causes of anisocoria
• The consideration of magnetic resonance angiography (MRA) to evaluate vascular structures, particularly if an aneurysm is suspected
• The importance of a thorough clinical history and ophthalmologic investigation, including ophthalmoscopy, to guide the imaging evaluation

In patients with anisocoria, it is essential to consider the possibility of underlying conditions such as Horner's syndrome, third nerve palsy, or other neurological conditions, and the MRI findings should be interpreted in the context of the clinical presentation 1. An MRI of the orbits without and with contrast is the preferred initial imaging modality, and additional imaging modalities, such as CT or MRA, may be added as needed to further evaluate the extent of disease or to assess for specific conditions.

From the Research

MRI Assessment for Anisocoria

To assess anisocoria, a diagnostic magnetic resonance imaging (MRI) examination can be performed, particularly in cases of post-traumatic anisocoria. The study 2 suggests that MRI can help identify cerebral lesions, specifically in the brainstem, which may be associated with anisocoria.

Key Findings

• The study 2 found that 59% of patients with post-traumatic anisocoria had brainstem lesions, with 46% having lesions in the midbrain, 27% in the pons, and 5% in the medulla oblongata.
• The presence of a midbrain lesion was significantly correlated with post-traumatic anisocoria, with a mortality rate of 58% in patients with anisocoria and a midbrain lesion.
• The study 2 suggests that a brainstem lesion, particularly in the midbrain, can be a pathomorphological correlate of anisocoria.

MRI Examination

• The MRI examination should be performed as soon as possible after the onset of anisocoria, ideally within 8 days after traumatic brain injury (TBI) 2.
• The MRI examination can help identify lesions in the brainstem, which can be associated with anisocoria, and provide valuable information for prognosis and treatment.