Pinning Down the Site of Infarct in a Woman With Altered Consciousness

Figure 1. Brain CT scan on presentation.

Figure 2. Diffusion-weighted imaging (DWI) sequence.

Figure 3. Apparent diffusion coefficient (ADC) mapping sequence.

A 53-year-old woman presents to the emergency department (ED) with altered consciousness. Seen in Figure 1 is the brain CT scan obtained at ED presentation. The diffusion weighted imaging (DWI) sequence obtained on MRI (Figure 2) was obtained 12 hours following the CT scan. Figure 3 is an apparent diffusion coefficient (ADC) mapping sequence on MRI, also obtained 12 hours following the CT. (Please click on images to enlarge)

After studying these 3 images, what is your diagnosis?

A. Right parietal acute to early subacute infarct and left frontoparietal chronic infarct.

B. Right parietal chronic infarct and left frontoparietal acute to early subacute infarct.

C. Right parietal cerebral abscess and left frontoparietal chronic infarct.

D. Right parietal intraparenchymal cerebral hemorrhage and left frontoparietal acute to early subacute infarct.

Answer: B. A right parietal chronic infarct and a left frontoparietal acute-to-early subacute infarct is the correct imaging diagnosis.

Discussion

As in this case, acute to early subacute infarcts (0-10 days following onset) can present on CT as focal or territorial mild hypoattenuation, often extending to the cerebral cortex; however, they can also be occult depending on their chronicity and size at presentation. 

Seen on MRI, infarcts in this period exhibit hyperintense signal on DWI sequences and hypointense signal on ADC mapping sequences, reflecting restricted diffusion.

Chronic infarcts (several months following onset) will typically exhibit more pronounced hypoattenuation on CT as encephalomalacia and gliosis occur. On MRI, chronic infarcts will demonstrate hyperintense signal on ADC and variable signal intensity on DWI depending on the nature of the involved brain tissue. 

In this case, the cystic encephalomalacia of the right parietal lobe creates hypointense signal on the DWI sequence.

References:

Allen LM, Hasso AN, Handwerker J, Farid H. Sequence-specific MR imaging findings that are useful in dating ischemic stroke. Radiographics 2012;32:1285-1297.