From the Guidelines
Horner's syndrome, or small pupil nerve palsy, is primarily caused by conditions such as tumors, trauma, subarachnoid hemorrhage, viral illnesses including COVID-19, demyelinating disease, and leptomeningeal disorders, as well as vasculopathic events like stroke or carotid artery dissection 1. The causes of Horner's syndrome can be diverse and complex, involving various pathways and conditions.
- Key causes include:
- Tumors, such as meningioma, schwannoma, and metastatic lesions
- Trauma
- Subarachnoid hemorrhage
- Viral illnesses, including COVID-19
- Demyelinating diseases
- Leptomeningeal disorders
- Vasculopathic events, such as stroke or carotid artery dissection When diagnosing Horner's syndrome, it is crucial to consider the possibility of a compressive lesion, such as an aneurysm involving the posterior communicating artery, which requires urgent medical attention 1. The diagnostic approach should involve neuroimaging, including MR imaging with gadolinium and magnetic resonance angiography (MRA) or computed tomography angiography (CTA), to rule out compressive lesions or other serious conditions 1. If the initial neuroimaging results are normal but there is a high suspicion for an aneurysm, further diagnostic steps, such as a catheter angiogram, should be considered after thorough evaluation, including brain MR imaging with and without contrast, with specific attention to the affected nerve 1.
From the Research
Causes of Small Pupil Nerve Palsy (Horner's Syndrome)
The causes of small pupil nerve palsy, also known as Horner's syndrome, can be varied and complex. Some of the possible causes include:
- Aneurysms, such as internal carotid-posterior communicating artery aneurysms 2, 3
- Midbrain hemorrhage 4
- Neurovascular conflicts, such as direct compression of the oculomotor nerve by the posterior cerebral artery 5
- Diabetes mellitus 4, 6
- Tumors, such as cavernous sinus tumors 6
- Pituitary lesions 6
- Central nervous system infections 6
- Subarachnoid hemorrhage 6
- Ischemic injury 3
- Infarction 4
Specific Cases
Some specific cases of small pupil nerve palsy have been reported, including:
- A case of transient pupil-sparing oculomotor nerve palsy caused by an aneurysm at the junction of the internal carotid and posterior communicating arteries 2
- A case of isolated oculomotor nerve palsy caused by a midbrain hemorrhage 4
- A case of complete oculomotor nerve palsy caused by direct compression of the oculomotor nerve by the posterior cerebral artery 5
- A case of oculomotor nerve palsy with referred tooth pain caused by a posterior communicating artery aneurysm 3