Case Presentation: An 80-year-old Korean gentleman with a past medical history of hypertension and dyslipidemia presented with a one week history of right eye ptosis and diplopia. He denied head/eye trauma, headaches or loss of consciousness. Also denied focal weakness of limbs, numbness/parasthesias, speech changes, or seizure activity. He reported no other symptoms. Distant smoking history of 5 pack years.Physical exam was remarkable for right eye ptosis and inability to move the eye medially or up with visual tracking, but other extra-ocular movements were intact. His right eye was 5mm and reactive but sluggish, left eye 4mm and reactive. There was no nystagmus. No other neurological deficits were noted. Lab studies were unrevealing. Non-contrast computed tomography (CT) head and orbits and magnetic resonance imaging (MRI) brain and orbits were unremarkable. CT angiogram (CTA) head revealed a tiny right posterior communicating (PCOMM) infundibulum as well as a small fenestration within the proximal basilar artery; no evidence of aneurysm, significant stenosis, or vascular malformation as shown in figure 1 and figure 2. CTA images were reviewed by neurosurgery who recommended conservative management and non-urgent outpatient follow-up.

Discussion: A PCOMM artery infundibulum is a relatively common symmetric, conical, and often congenital, outpouching of the artery. It may progress to an aneurysm but rarely does so, and even more uncommon is the risk of rupture.[1] According to a study done by Fang et. Al., the most common causes of cranial nerve (CN) III palsy were presumed microvascular (42%), trauma (12%), compression from neoplasm (11%), post-neurosurgery (10%), compression from aneurysm (6%), stroke (4%), undetermined (4%), pituitary apoplexy (2%), Tolosa-Hunt syndrome (2%), giant cell arteritis (1%), and other (5%).[2] Previous reports have shown anisocoria ≤1 mm in patients with microvascular dysfunction.[2]
In this case, our patient was completely asymptomatic for other causes of CN III palsy. It is unclear if his symptoms are related to the PCOMM infundibulum due it’s miniscule size; it is more likely to be related microvascular causes for which the management is mainly conservative as symptoms may spontaneously resolve over weeks to months.

Conclusions: Isolated CN III palsy is rare and thorough evaluation and diagnostic investigation is required to determine the cause and rule out those which are life threatening. Although symptoms may be concerning, it may be reassuring that presumed microvascular disease is relatively benign and can be managed conservatively.

IMAGE 1: Figure 1

IMAGE 2: Figure 2