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Posterior cerebral artery dissecting aneurysm: another cause of perimesencephalic pattern of subarachnoid haemorrhage
  1. Patrícia Pita Lobo1,
  2. Jorge Campos2,
  3. Lia Neto2,
  4. Patrícia Canhão1
  1. 1Department of Neurosciences (Neurology), Hospital de Santa Maria, Lisbon, Portugal
  2. 2Neurological Imaging Department, Hospital de Santa Maria, Lisbon, Portugal
  1. Correspondence to Dr Patrícia Canhão, Department of Neurosciences (Neurology), Hospital Santa Maria, Av Prof. Egas Moniz, Lisbon 1649-035, Portugal; pcanhao{at}

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Perimesencephalic subarachnoid haemorrhage is a distinct radiographic and clinical entity of uncertain aetiology. This syndrome is diagnosed by the characteristic pattern of extravasated blood on brain CT in combination with a negative cerebral angiography.1 Current practice requires digital subtraction angiography (DSA) to exclude an aneurysm in patients with a perimesencephalic pattern of subarachnoid haemorrhage (SAH). Although up to 96% of patients with this pattern of SAH do not have an aneurysm, and will undergo an uneventful clinical course with invariably good outcome,1 about 4% of patients might have a vertebrobasilar aneurysm requiring emergent treatment.1

We present a patient with a perimesencephalic pattern of SAH caused by rupture of dissecting posterior cerebral artery (PCA) aneurysm. To our knowledge, this is the first reported case of perimesencephalic pattern of SAH caused by a dissecting aneurysm in such a location.

Case report

A 62-year-old man presented at the emergency department because of severe headache, nausea and vomiting. The headache, initially located on the right fronto-temporal side, had developed over the course of a few minutes, while …

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  • Competing interests None.

  • Patient consent Obtained.

  • Provenance and peer review Not commissioned; externally peer reviewed.