Case 08 - Neuro-ophthalmology, orbit, and inflammation
42-year-old woman - Sudden diplopia all gaze fields - Ptosis - Fixed dilated pupil - Previously healthy
This 42-year-old woman had been in good health until today, when she suddenly developed diplopia in all fields of gaze. The photograph was taken while the patient was asked to look up.
Ptosis of the upper eyelid (levator palpebrae = CN III), 'down-and-out' globe deviation (unopposed CN IV/SO and CN VI/LR), mydriasis - large, fixed, dilated pupil (parasympathetic fibers on outer CN III surface compressed first by external pressure).
Pupil-INVOLVED = COMPRESSIVE EMERGENCY: PComm aneurysm (most common - thunderclap headache), uncal herniation, cavernous sinus pathology -> CT/CTA immediately. Pupil-SPARING + vasculopathic risk (DM/HTN) = microvascular ischemia -> observe 6-8 weeks. Pupil-sparing does NOT guarantee benign cause - image if atypical.
CN III innervates SR, IR, MR, IO, levator palpebrae, and the pupil (EW nucleus -> ciliary ganglion -> short ciliary nerves -> constriction). Complete palsy -> all lost. Parasympathetic fibers run on the OUTSIDE = compressed first by mass lesions (aneurysm); spared by ischemia (diabetic microvascular palsy).
Onset of headache - sudden 'thunderclap' or 'worst headache of life' (SAH from aneurysm rupture), neck stiffness/photophobia (meningismus), nausea/vomiting, HTN/DM/hyperlipidemia, prior TIA, trauma, malignancy, medications.
Direct (affected eye): ABSENT - sphincter cannot constrict. Consensual (light in affected -> fellow eye): PRESENT - afferent CN II and fellow CN III intact. Light in fellow -> affected: ABSENT - efferent CN III to affected eye damaged. Accommodation: ABSENT.
THE PUPIL RULE: Pupil-involved CN III palsy = PComm aneurysm until proven otherwise -> emergent CT/CTA. Parasympathetic fibers on the outer surface of CN III are compressed by mass lesions but spared by ischemia. Pupil-sparing CN III in a diabetic = microvascular; resolves in 6-12 weeks. Never send a pupil-involved CN III palsy home without neuroimaging.
Findings DDx Ptosis of the upper eyelid (levator palpebrae = CN III), 'down-and-out' globe deviation Pupil-INVOLVED = COMPRESSIVE EMERGENCY: PComm aneurysm (most common - (unopposed CN IV/SO and CN VI/LR), mydriasis - large, fixed, dilated pupil thunderclap headache), uncal herniation, cavernous sinus pathology -> CT/CTA (parasympathetic fibers on outer CN III surface compressed first by external pressure). immediately. Pupil-SPARING + vasculopathic risk (DM/HTN) = microvascular ischemia -> observe 6-8 weeks. Pupil-sparing does NOT guarantee benign cause - image if atypical. Pathophysiology General health CN III innervates SR, IR, MR, IO, levator palpebrae, and the pupil (EW nucleus -> ciliary Onset of headache - sudden 'thunderclap' or 'worst headache of life' (SAH from aneurysm ganglion -> short ciliary nerves -> constriction). Complete palsy -> all lost. Parasympathetic rupture), neck stiffness/photophobia (meningismus), nausea/vomiting, fibers run on the OUTSIDE = compressed first by mass lesions (aneurysm); spared by HTN/DM/hyperlipidemia, prior TIA, trauma, malignancy, medications. ischemia (diabetic microvascular palsy). Pupillary reflexes Direct (affected eye): ABSENT - sphincter cannot constrict. Consensual (light in affected -> fellow eye): PRESENT - afferent CN II and fellow CN III intact. Light in fellow -> affected: ABSENT - efferent CN III to affected eye damaged. Accommodation: ABSENT. TEACHING PEARL THE PUPIL RULE: Pupil-involved CN III palsy = PComm aneurysm until proven otherwise -> emergent CT/CTA. Parasympathetic fibers on the outer surface of CN III are compressed by mass lesions but spared by ischemia. Pupil-sparing CN III in a diabetic = microvascular; resolves in 6-12 weeks. Never send a pupil-involved CN III palsy home without neuroimaging.
