Trochlear nerve palsy

November 20, 2012  |  Neurology Study

Recently, I found there was an interesting case about a male patient with trochlear nerve palsy.

The patient is a 60-year old man. Let’s call him David. 10 days ago, David got a dizziness and double vision, and the symptoms came with fatigue and bilateral hearing loss. After that he went to the hospital, there he had a head CT scan which showed “cerebral hemorrhage” (and its cause was confirmed as arteriovenous malformation).

The neurologic examination revealed that David had diplopia when his eyes moved downward and to the left. In addition, his bilateral pupils were 3 mm in size and had good light reflex. Other examinations were normal.

Figure1. David's MRI (axonal T1)

Figure 2. David's MRI (sagittal T2)

It is rare to see single trochlear nerve injury case, and David’s case happens to be an excellent opportunity to review trochlear nerve function.

A Review of trochlear nerve

In 1561, an Italian the anatomist Gabriele Falloppio first described the structure of trochlear nerve in his book Observationes Anatomicae. One hundred years later, another anatomist William Molins named the nerve “trochlear nerve”.

Figure 3. The trochlear nerve 1 (Adapted from DUUS’ Topical Diagnosis in Neurology)

Figure 4. The trochlear nerve 2 (Adapted from Symptoms and Diagnosis of the Nervous System Diseases 《神经系统疾病症候诊断学》)

The nucleus of the fourth cranial nerve lies ventral to the periaqueductal gray matter immediately below the oculomotor nuclear complex at the level of the inferior colliculi. Its radicular fibers run around the central gray matter and cross to the opposite side within the superior medullary velum. The trochlear nerve then exits the dorsal surface of the brainstem (it is the only cranial nerve that does this), emerging from the midbrain tectum into the quadrigeminal cistern. Its further course takes it laterally around the cerebral peduncle toward the ventral surface of the brainstem, so that it reaches the orbit through the superior orbital fissure together with the oculomotor nerve. It then passes to the superior oblique muscle, which it innervates. (Adapted from DUUS’ Topical Diagnosis in Neurology)

Figure 5. Diagram of eye position in the six diagnostic positions of gaze, in which weakness of one or more of the extraocular muscles can be most easily detected. (Adapted from DUUS’ Topical Diagnosis in Neurology)

Figure 6. Eye position and diplopia in trochlear nerve palsy. (Adapted from DUUS’ Topical Diagnosis in Neurology)

Patients with trochlear nerve injury can have a head tilt to unaffected side.Unfortunately, because David was not my patient, I did not see him by myself in the very end.

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1 Comment


  1. Hi Jingjing, how does head tilt in CNIV palsy help in correcting the double vision?

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