Saturday, 26 September 2015

xrayoftheweek 38: a classic brain MRI finding

The #xrayoftheweek is this axial image from a brain MRI. 

(1) Which MRI sequence is this?
(2) What is the finding and the significance?
(3) Can you guess how this person presented?

I'll address the latter 2 questions first. This is a diffusion weighted image showing high signal (i.e. bright) in the cortical and subcortical parts of the right occipital lobe. Take a look at my previous posts on diffusion weighted imaging to recap the principles of the technique and the significance of the various signal changes. On this image, this signal change signifies cellular swelling secondary to ischaemia - this is a posterior cerebral artery territory infarct.

This image of the optic pathways and which visual field defects occur due to insults to various parts of the pathway shows that a homonymous hemianopia is caused by damage to either the optic tracts or the occipital lobes. When the optic radiations are damaged, the field defects may be limited to quadrants rather than halves. This person presented with a left homonymous hemianopia due to a right posterior cerebral artery territory infarct.

Visual field defects associated with hemianopia. From Polaski and Tatro, 1996.
Keep an eye our future #xrayoftheweek posts for more diffusion weighted imaging cases.

#FOAMed #FOAMrad