Stress caused by tissue within the incisura can compromise the midbrain, oculomotor nerve, and posterior cerebral artery leading to isolated pupils resulting in ONP. Transtentorial herniation occurs when increased cranial pressure displaces brain tissue toward the tentorial notch. Transtentorial herniation from hemorrhage, as in our case, can be another cause. Kwon and Jang reported a 50-year-old man who developed ONP after right thalamic intracerebral hemorrhage, but in this case, the midbrain's effect was due to perilesional edema. Regarding indirect causes other than brainstem stroke or aneurysm, several case reports with ONP after various types of hemorrhage are presented in Table 1. Considering the anatomical pathway of the oculomotor nerve, stroke involving the midbrain or brainstem and direct compression from an aneurysm, with or without rupture, are considered medical emergencies. Numerous etiologies are known to be related to ONP, and oculomotor nerve can be affected both directly and indirectly. The effect on the midbrain was also revealed on MRI-SWI as presentation of isolated microbleed in the substantia nigra region. The intracerebral hemorrhage in our patient did not directly involve the brainstem however, CT images revealed that the size of the lobar bleeding led to subtentorial herniation, thereby compressing the midbrain. As it leaves the midbrain, the oculomotor nerve passes between the posterior cerebral artery and superior cerebellar artery and travels parallel to the posterior communicating artery. Nerve fascicles pass through the red nucleus and the substantia nigra, to finally exit the brainstem via the inter-peduncular fossa. The oculomotor nerve originates from the oculomotor nucleus in the midbrain. Presentation of ONP showed no significant improvements and continued to show complete ptosis, mydriasis, exotropia-type strabismus on primary gaze, limited ocular movement, and subjective complaints of dizziness due to diplopia ( Fig.
#Cn iii compression and fixed dilated pupil download
MRI, magnetic resonance imaging SWI, susceptibility-weighted images CT, computed tomography.Ĭlick for larger image Download as PowerPoint slideĪfter two months of the onset, the patient was admitted to our hospital for rehabilitation following an apparent hemorrhage. The nerve nucleus originates in the midbrain, nerve fascicles pass through the red heart, substantia nigra (blue circle), and finally exit the brainstem via the inter-peduncular fossa.
(B) Oculomotor nerve pathway and location of patient's microbleed. (A) Axial T2-weighted MRI-SWI demonstrated cerebral microbleed in the region of substantia nigra of the midbrain (blue arrow) that were not revealed on the initial CT. Written informed consent was obtained from the patient.īrain MRI obtained after 6 days following the onset day of intracranial hemorrhage. Herein, we report a case of isolated ONP following a massive temporoparietal lobar hemorrhage without usual causes. Cerebrovascular accidents in the brainstem, direct compression from an aneurysm or neoplasm, and subarachnoid hemorrhage are other common causes of ONP. In cases of stroke-related ONP, it is necessary to consider the anatomic pathway of the oculomotor nerve from the nerve nucleus within the brainstem to the innervation of extraocular and ciliary muscles. Although the mechanism of acquired ONP is not well established, ischemic change of microvasculature with hypertension or diabetes is considered a major cause. In oculomotor nerve palsy (ONP), common presentations include symptoms such as ptosis, mydriasis, strabismus, and diplopia. The oculomotor nerve (third cranial nerve CN III) innervates the majority of extraocular muscles, sphincter pupillage, and ciliary muscles, controlling extraocular movements, pupil constriction, and visual accommodation.
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