Ptosis after motorcycle accident
A motorcycle accident precipitated by a health emergency led to loss of eye function. Advanced imaging revealed the diagnosis.
Diagnosis: Third (oculomotor) nerve palsy
This patient had a complete third nerve palsy (TNP). This is defined as palsy involving all of the muscles innervated by the oculomotor nerve, with pupillary involvement.1 The oculomotor nerve supplies motor innervation to the levator palpebrae superioris, superior rectus, medial rectus, inferior rectus, and inferior oblique muscles and parasympathetic innervation to the pupillary constrictor and ciliary muscles.2 As a result, patients present with exotropia and hypotropia on exam with anisocoria. Diplopia, ptosis, and an enlarged pupil are classic symptoms of TNP.2
Computed tomography (CT) of the brain performed immediately after this patient’s accident demonstrated a 15-mm hemorrhage within the left basal ganglia with mild associated edema, and a small focus of hyperattenuation within the right aspect of the suprasellar cistern. There was no evidence of skull fracture. CT angiography (CTA) of the brain showed no evidence of aneurysm.
Several days later, magnetic resonance imaging (MRI) of the brain confirmed prior CT findings and revealed hemorrhagic contusions along the anterior and medial left temporal lobe. Additionally, the MRI showed subtle subdural hemorrhages along the midline falx and right parietal region, as well as diffuse subarachnoid hemorrhage around both hemispheres, the interpeduncular cistern, and the suprasellar cistern (FIGURE 2). The basal ganglia hemorrhage was believed to have been a result of uncontrolled hypertension. The hemorrhage was responsible for her right-sided weakness and was the presumed cause of the accident. The other findings were due to head trauma. Her TNP was most likely caused by both compression and irritation of the right oculomotor nerve.
An uncommon occurrence
A population-based study identified the annual incidence of TNP to be 4 per 100,000.1 The mean age of onset was 42 years. The incidence in patients older than 60 years was greater than the incidence in those younger than 60.2 Isolated TNP occurred in approximately 40% of cases.2
Complete TNP is typically indicative of compression of the ipsilateral third nerve.2 The most common region for third nerve injury is the subarachnoid space, where the oculomotor nerve is vulnerable to compression, often by an aneurysm arising from the junction of the internal carotid and posterior communicating arteries.3
Continue to: Incomplete TNP
