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A 70-year-old woman presented to the emergency room with a 1-day history of right periorbital pain, ptosis and binocular horizontal diplopia when looking to the left. Visual acuity was 20/20 in both eyes and external examination revealed partial right ptosis. Assessment of ocular motility revealed a mild limitation of elevation, depression and adduction in the right eye only (figure 1). Pupils were of equal sizes and reactive to light (figure 1). Cranial nerve function and neurological examination were otherwise normal. CT angiography (CTA) of the brain was performed, demonstrating an intracranial aneurysm.
Where is the most likely location of an aneurysm causing this condition?
Posterior cerebral artery at the junction of the posterior communicating (Pcomm) artery.
Pcomm artery at the junction of the internal carotid artery (ICA).
Cavernous carotid artery.
C. Pcomm artery at the junction of the internal carotid artery (ICA).
The combination of right ptosis and limitation of elevation, depression and adduction of the right eye indicates dysfunction of the third cranial nerve (CN3), which innervates the levator palpebrae superioris, superior rectus, inferior rectus and medial rectus muscles.
A third nerve palsy (3 NP) may be the presenting sign of an intracranial aneurysm, and a CTA of the brain is required in all new cases.1 This patient had an aneurysm at the junction of the Pcomm artery and the ICA, which is the most common location for those causing 3 NP (figure 2).2 When aneurysms cause new neurological symptoms, it suggests that their morphology is changing and they are at high risk of rupture.2
The presence of pupillary dilation in the setting of a 3 NP is highly indicative of a compressive lesion involving CN3. However, an aneurysm may present with normal pupils especially when the 3 NP is partial.3 Urgent neuroimaging (CTA or magnetic resonance angiography) should be performed in all suspected cases of 3 NP regardless of the pupillary examination. The Pcomm-ICA aneurysm usually extends inferolaterally to compress the dorsomedially located pupillary fibres on CN3. Pupil sparing may be explained by more laterally placed parasympathetic fibres or aneurysms approaching the nerve inferiorly or superiorly.3
Contributors Conception and design: JMK and JAM; data acquisition: JMK and JAM; manuscript preparation: JMK; critical revision: JAM; final approval: JMK and JAM.
Funding The authors have not declared a specific grant for this research from any funding agency in the public, commercial or not-for-profit sectors.
Competing interests None declared.
Patient and public involvement Patients and/or the public were not involved in the design, or conduct, or reporting, or dissemination plans of this research.
Patient consent for publication Obtained.
Provenance and peer review Not commissioned; internally peer reviewed.