MRI detection of cerebral lesions in post-traumatic anisocoria: specificity and prognostic significance

To identify whether increased numbers of brainstem lesions are found in the presence of a post-traumatic pupillary function disturbance and classify them anatomically.

In this study, a diagnostic magnetic resonance imaging (MRI) examination was performed within 8 days after traumatic brain injury (TBI) in patients who had been unconscious for more than 24 hours post-TBI. The Glasgow Outcome Scale was evaluated 6 months after TBI. The data obtained from 140 consecutively enrolled patients between 2005 and 2011 were analysed. The clinical study parameter comprised the development of post-traumatic anisocoria at least once over the course between onset of trauma and diagnostic MRI, as a yes/no decision. Significance was presumed at p≤0.05.

A total of 57 patients (41%) were found to have a lesion at MRI without involvement of the brainstem; in 83 (59%) the brainstem was (multiple) affected. Of the latter, 66 (46%) of patients had lesions in the midbrain, 38 (27%) in the pons, and seven (5%) in the medulla oblongata. By the time of MRI, anisocoria had been diagnosed in 45 (32%) patients. Mortality was highest, at 58%, in patients with anisocoria and a midbrain lesion, whilst it was 23% in those with anisocoria and no lesion in the midbrain. Mortality was 33% in relation to a midbrain lesion without anisocoria.

Overall, the study demonstrated that there is a significant correlation between midbrain lesions and post-traumatic anisocoria in unconscious trauma patients. A brainstem lesion in this case can be assumed to be a pathomorphological correlate of anisocoria. The rate of damage to the midbrain was approximately 50% in cases of transient anisocoria. It can be assumed in this situation that there are functional disorders of the peripheral oculomotor nerve or identifiable/unidentifiable lesions of the brainstem.