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Case 93

MRI and MRA of a man with left-sided homonymous hemianopia

Acute right PCA infarct

Ozgur Kilickesmez

This 62-year-old man presented with left sided homonymous hemianopia and confusion. MRI and then MRA of the cranium were performed. What is the diagnosis? What are the hyperintensities observed in the lateral ventricle atria? Is there any pathology demonstrated on MRA image?

Findings

T1, T2 and FLAIR images show the right PCA distribution infarct. The hyperintensities observed in the lateral ventricle atria observed on the second FLAIR image are consistent with CSF related motion artifact. On the MRA image the right P1 is occluded.

Diagnosis

Acute right PCA infarct

Discussion

Most commonly, the PCAs are formed by the bifurcation of the basilar artery. Generally the PCA supplies the inferior aspect of the temporal lobe, the posterior one third of the cerebral convexity, and the occipital lobe. Its ganglionic branches supply the caudal half of the thalamus and much of the midbrain. The calcarine artery is a branch of major importance because it supplies the primary visual cortex. Thus occlusion of the PCA or calcarine artery produces a contralateral homonymous hemianopia. Vascular occlusive disease is common at the basilar tip and can result in bilateral PCA territorial infarcts. Anatomic localization of the point of vascular occlusion in PCA infarcts may be simplified into the following 2 categories: (1) deep or proximal PCA strokes, causing ischemia in the thalamus and/or midbrain (regions supplied by P1 and P2), as well as in the cortex (regions supplied by P3 and P4); and (2) superficial or distal PCA, involving only cortical structures (P3, P4 branch areas).

Patients with PCA infarcts present with symptoms including the following: acute vision loss, confusion, new onset posterior cranium headache, paraesthesias, limb weakness, dizziness, nausea, memory loss, language dysfunction.

Commonly used MR imaging techniques are the following:
T1-weighted images (T1-WI) in which cerebrospinal fluid (CSF) has a low signal intensity in relation to brain tissue, T2-weighted images (T2-WI) in which CSF has a high signal intensity in relation to brain tissue, spin density-weighted images in which CSF has a density similar to brain tissue, gradient echo imaging, which has the highest sensitivity in detecting early hemorrhagic changes, diffusion-weighted images (DWI) in which the images reflect microscopic random motion of water molecules, perfusion-weighted images (PWI) in which hemodynamically weighted MR sequences are based on passage of MR contrast through brain tissue.

References

1. Brandt T, Steinke W, Thie A, Pessin MS, Caplan LR. Posterior cerebral artery territory infarcts: clinical features, infarct topography, causes and outcome. Multicenter results and a review of the literature. Cerebrovasc Dis. 2000 May-Jun;10(3):170-82. PMID: 10773642
2. Georgiadis AL, Yamamoto Y, Kwan ES, Pessin MS, Caplan LR. Anatomy of sensory findings in patients with posterior cerebral artery territory infarction. Arch Neurol. 1999 Jul;56(7):835-8. PMID: 10404985
3. Steinke W, Mangold J, Schwartz A, Hennerici M. Mechanisms of infarction in the superficial posterior cerebral artery territory. J Neurol. 1997 Sep;244(9):571-8. PMID: 9352455
4. Servan J, Verstichel P, Catala M, Yakovleff A, Rancurel G. Aphasia and infarction of the posterior cerebral artery territory. J Neurol. 1995 Jan;242(2):87-92. PMID: 7707096

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