Unilateral cerebellar hypoplasia and mesencephalic malformation in a Hanoverian foal.

This study presents a unique case of a Hanoverian foal exhibiting progressive ataxia, a symptom of neurological problems, which upon investigation was found to have an uncommonly seen malformation involving a unilateral absence of a cerebellar hemisphere and an abnormal mesencephalon. These neurological malformations were not associated with any common infectious diseases, suggesting other potential causes such as an ischemic event or a primary retrocerebellar cyst.

Case Presentation and Diagnosis

• The foal began showing signs of progressive ataxia, or lack of muscle control. As ataxia impacts coordination and balance, this signaled a potential neurological problem.
• A neurological examination revealed unilateral hypermetria, a sign of cerebellar dysfunction.
• A complex diagnostic procedure called a cisternography was performed on the foal’s head, which led to the suspicion of a cerebellar malformation.
• The prognosis was poor, and the foal was euthanized. A necropsy later confirmed a unilateral absence of a cerebellar hemisphere and a malformation of the contralateral mesencephalon.

Additional Findings

• A cystic formation replaced the missing areas of the right cerebellar hemisphere, while the left part of the mesencephalic lamina quadrigemina was reduced in size, and the corpus callosum was underdeveloped.
• Microscopic examination revealed a number of anomalies like angiofibrosis, abnormal positioning of cerebellar neurons, thickening in the cerebellar cortex, focal proliferation of meningeal cells, and mild inflammation around blood vessels.
• There was no detection of common infectious agents, such as Borna disease virus, rabies virus, and equine herpesvirus.

Possible Causes

• Due to the lack of infectious agents, the malformation could have been caused by a destructive event that resulted in reduced blood supply, known as an ischemic event. This type of event could result in tissue death and lead to malformations.
• An alternative possibility suggested by the author is a primary retrocerebellar cyst affecting surrounding tissue, which may have led to the observed abnormalities. This could be a result of a pre-existing condition or a symptom of a broader health issue.

Conclusion

• The research highlights the importance of considering malformations when dealing with neurological patients, as these may not always be due to common infectious diseases or traumas.
• The findings expand the existing range of possible neuropathological lesions, providing clinicians with additional understanding of complex unilateral neurological scenarios.