Mulberry that dropped the lids: A midbrain cavernoma presenting with isolated bilateral third nerve palsy

Cavernomas are uncommon vascular anomalies made up of closely packed, thin-walled vascular spaces lacking normal intervening brain tissue. These lesions often take on a mulberry-like appearance on magnetic resonance imaging (MRI) and are prone to bleeding, especially when located in the brainstem. They typically present with seizures or focal neurological deficits. However, in rare instances, they may manifest with isolated cranial nerve palsies. We present a rare case of bilateral pupil-involving third cranial nerve palsy in a young woman, secondary to a hemorrhagic midbrain cavernoma. The 28-year-old patient presented with a sudden onset of drooping of the left upper eyelid for 1 week. There were no associated systemic symptoms such as vomiting, weakness, or altered sensorium. On examination, the visual acuity was 6/6 in both eyes. Anterior segment evaluation showed ptosis in both eyes, more marked on the left, with mid-dilated pupils and restricted ocular movements consistent with bilateral third nerve involvement. MRI revealed a heterogeneous lesion, localized in the left cerebellar peduncle, suggestive of hemorrhagic cavernoma. This case highlights how isolated ocular motor findings, even in the absence of systemic symptoms, can be the first manifestation of a significant brainstem lesion, underscoring the importance of prompt neuroimaging and ophthalmologist-led evaluation. This case illustrates the key role of ophthalmologists in the early detection of intracranial lesions through ocular findings.