Bilateral trochlear nerve palsies. A clinicoanatomic correlate

Area of Science:

• Neuroscience
• Neurology
• Neuroanatomy

Background:

• Trochlear nerve palsies typically result from lesions affecting the fourth cranial nerve (CN IV) pathway.
• Bilateral trochlear nerve palsies are rare and often indicate a central nervous system lesion.

Observation:

• A patient presented with bilateral trochlear nerve palsies, characterized by vertical double vision and impaired downward and inward eye movements.
• Computed tomographic (CT) brain scan revealed a lesion in the anterior cerebellar vermis.

Findings:

• The anterior cerebellar vermis lesion was compressing the brainstem region caudal to the inferior colliculi.
• This compression site is critical as it is where the fourth cranial nerves decussate (cross) and exit the dorsal brainstem.

Implications:

• The identified cerebellar lesion is the likely cause of the patient's bilateral trochlear nerve dysfunction.
• Understanding this anatomical relationship is crucial for diagnosing and localizing brainstem and cranial nerve pathologies.
• This case highlights the importance of advanced neuroimaging in identifying the etiology of complex neurological deficits.