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Posterior cerebral artery infarcts associated with brainstem shift have been traditionally associated with uncal herniation. We describe the first case of a peduncular infarct due to lateral brainstem displacement.
A 64-year-old man with a putaminal haemorrhage into the left putamen presented with eye opening to pain, localisation to pain, pupil anisocoria but intact pupil and corneal reflexes, gaze preference to the left and right hemiplegia. CT scan showed significant mass effect and early oedema. He became more drowsy and could not protect the airway which led to endotracheal intubation. MRI 2 days after admission showed lateral brainstem displacement but no uncal herniation. Surgical evacuation was considered but fluctuating level of consciousness (at times eye opening to strong voice) together with uncertainty of improved outcome after surgical evacuation prompted medical management only. Follow-up MRI 5 days later showed similar lateral brainstem displacement but a new infarct in the ipsilateral peduncle had appeared (fig 1). No uncal herniation was again noted. MR angiography (MRA) was normal. The patient improved gradually over 5–7 days. Lack of speech and flaccid hemiplegia made rehabilitation difficult and he was transferred to a nursing home.
COMMENT
Cerebral haemorrhage may displace brain tissue and distort the brainstem. During this process, the uncus of the temporal lobe may be pushed forward and herniate into the tentorial incisura. Posterior cerebral artery compression may cause a calcarine territorial infarct.1 To our knowledge, this is the first MR documentation of a peduncular infarct associated with brainstem shift. Although we could not appreciate displacement of the posterior cerebral artery on MRA, we explain our case as a disruption of the mesencephalic branch of the posterior cerebral artery from brainstem displacement.
The anatomical changes associated with acute mass effect remains largely unexplained. Traditional explanations such as uncal herniation have been challenged by CT and MRI studies and de-emphasised herniation (uncal or central) as a clinical phenomenon.2 3 Pupil anisocoria or dilated pupil has been explained by traction or compression of the third cranial nerve but a nuclear origin has been considered. One study suggested that even the changes in pupil responses with brainstem displacement may be of ischaemic origin.4
Acknowledgments
This article has been adapted from Wijdicks E F M. Acute brainstem displacement without uncal herniation and posterior cerebral artery injury Journal of Neurology, Neurosurgery and Psychiatry 2008;79:744
Footnotes
Competing interests: None.
Patient consent: Informed consent was obtained for publication of the case details in this report.