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

ACL GANGLION

T2 SAG MRI KNEE

A patient with knee pain for MRI.  MRI of knee shows enlarged ACL with striated appearance .It is also described as drum stick appearance.Small cysts seen in femoral and tibial intercondylar articular surfaces represent intraosseous ganglia.


Contributed by Dr T N Gopinath

Aneurysmal Bone Cyst

                                                         AP and Lateral Radiographs

                                                             

STIR sagittal

                                        T1 Coronal                                         Axial T2








 10 year old girl who had a history of trauma  presented to the orthopaedic outpatient department with pain at the site of trauma. A plain radiograph was performed which show no fracture but demonstrated an eccentric expansile lucent lesion. Pt was sent for MRI for further characterization.


On the T2 and STIR sequences the eccentric expansile lesion shows hyperintense signal with multiple dependent fluid levels representing blood filled spaces. The lesion shows intermediate signal on T1


Fluid- fluid levels are characteristic of ABC but also seen in other conditions such as Giant cell tumor, telangiectatic osteosarcoma,  fibrous dysplasia.

Periventricular gliosis in fetal MRI

                                                              image A. Axial T2

image B sagittal  T2

image C axial T2

Fetal MRI showing loss of periventricular white matter , small T2 hyperintensities in periventricular white matter  .This case was referred for MRI as suspected holoprosencephaly which is not there. MRI was suggestive of periventricular gliosis , small periventricular cysts (seen in image A) and dilatation of occipital horns. Amniocentesis showed CMV (cytomegalovirus) infection. Patient had spontaneous delivery , new born did not survive.

Below are examples of normal fetal MRI brain for comparison of periventricular white matter.

image D and E.

image D

image E

Contributed by Dr Krishna Kiran