Really easy CT/MRI cases

First a warning. If you are a health professional daily interacting with images , this post is not for you.
If you are bewildered by images and you do not know where to start , then this is for you. Basic Basic !!

Case 1- This patient presented with sudden onset difficulty in walking. Progressive deterioration in consciousness. CT brain did not show abnormality.

Axial T1 weighted image of brain  showing hypointense (dark) signal in left cerebellum.

axial T2 image showing hyperintense (bright) signal in left cerebellum.















diffusion image showing area of diffusion restriction in left cerebellum (B 1000)















What do these images suggest. Key is the last image. Bright signal in diffusion image almost always suggests recent infarct. This infarct is extending to brain stem.

Common questions .

Why CT did not show infarct..?
Infarcts are usually seen on CT after 12-24 hours. moreover in posterior fossa , CT is less sensitive due to covering bone.

How sensitive is diffusion technique in infarcts..?.
Diffusion can pick up infarcts within 2-3 hours. restriction in infarcts persists upto 2-3 weeks.
also remember that once there is bright signal in diffusion , lesion is largely irrerversible.
(exception- diffusion restriction in venous infarcts).

why is diffusion sensitive..?
In acute cell death / injury due to infarct(called cytotoxic edema) there is closure of sodium-potassium ATPase pump which  leads to diffusion restriction on MRI.

Case 2- this elderly patient presented with sudden onset left hemiparesis. Scan done 12 hours after clinical symptoms.

CT brain shows hypodensity in right fronto-parietal lobes. 

Is this lesion infarct in view of clinical history..?

No you should suspect SOL in view of edema pattern. note that hypodensity shows finger like margins preferentially involving white matter. hence contrast study is necessary.

This is the contrast study.

Within edema , an irregular area of contrast enhancement is seen. Hence this is a SOL. This was a case of metastasis from Ca lung presenting as stroke.  Hence key here is picking up different pattern of edema (called vasogenic edema )

what are different types of edema..?
cytotoxic edema which is seen in infarcts.
vasogenic edema seen associated with metastases.
interstitial edema seen around dilated ventricles , suggests acute hydrocephalus.

case 3-- no history.

i have marked a  hypodense lesion in left occipital lobe.

what is this lesion..?
This lesion is a gliotic area. because adjacent sulci , occipital horn are dilated suggestive of volume loss.
since this lesion is in PCA (posterior cerebral artery ) territory, represents an old  PCA infarct.


Contributed by Dr Krishna Kiran