Anything that traps fluid can restrict diffusion! Here are some tricks I use to narrow the ddx 1️⃣STROKE Cytotoxic edema due to trapped intracellular fluid leads to restriction Look for wedge shaped restriction in a vascular territory

2️⃣ABSCESS Trapped purulent material leads to LIGHT BULB BRIGHT restriction DWI is excellent for differentiating tumor from pyogenic abscess as the abscess will have CENTRAL restriction Abscess should also have vasogenic EDEMA, ENHANCEMENT, and possible dual rim sign (T2 & SWI)

3️⃣HYPERCELLULAR TUMOR (lymphoma, medulloblastoma, embryonal tumor, germinoma, glioblastoma, etc) Densely packed tumor cells trap fluid in between

Hypercellular tumor continued Primary CNS Lymphoma ▶️Central diffusion restriction ▶️Homogenous enhancement ▶️Low T2 signal (less cytoplasm and more nucleus so less water in cells and lower T2 signal) ▶️Hyperdensity on CT ▶️Periventricular location

Hypercellular tumor continued ▶️Glioblastoma or high grade glioma Variable but may have more eccentric or nodular restriction around areas of necrosis and heterogeneous enhancement

4️⃣HEMATOMA RBCs trapped in serum and fibrin can restrict on DWI (though blood can also be dark on DWI from susceptibility) Hyperdensity on CT is a giveaway but this may fade overtime or you may not have a CT Look for a rim of HYPERINTENSITY ON T1 and HYPOINTENSITY on SWI

5️⃣DEMYELINATION High signal on DWI is predominantly due to T2 SHINE THROUGH True restriction may be seen at the LEADING EDGE (along the margin) in acute demyelination possibly from cytotoxic edema, reduced fiber tract organization, or myelin fragments (This example is PML)

6️⃣EPIDERMOID CYST Tightly organized epithelial layers cause a light bulb bright restriction ADC tends to be ISOINTENSE TO BRAIN PARENCHYMA (not super dark), possibly from movement of fluid between layers (at least that’s how I think of it)

Epidermoid cyst continued ▶️CSF intensity on T1 & T2 ▶️Dirty on FLAIR ▶️DO NOT ENHANCE! (May have a tiny rim of enhancement along edge but NO CENTRAL)

Bonus cases 7️⃣SEIZURE Shows gyriform or cortical restricted diffusion (often in the mesial temporal lobe) Examples in 2 different patients

8️⃣ENCEPHALITIS Diffusion restriction in the insula and temporal lobes favors herpes encephalitis, though any encephalitis can cause restriction Herpes is usually bilateral but asymmetric and may have patchy enhancement and hemorrhage Case of herpes

9️⃣CJD Diffusion restriction is seen in the basal ganglia, thalami, and cortex. This can be asymmetric

🔟Many Toxic/metabolic disorders Hepatic encephalopathy Acute toxic leukoencephalopathy Hypoxia Methotrexate toxicity Drug abuse CO poisoning Many more

@daniel_gewolb @TheASNR I thought this thread was about how DWI helps narrow the differential diagnosis :-) just kidding awesome thread!

@aparlakmd @TheASNR Lolol yah probably not the best title choice

@daniel_gewolb @TheASNR A DWI one pager for keepsake.

@daniel_gewolb @TheASNR Marvellous. Keep it rolling.

@daniel_gewolb @TheASNR Great teaching

@daniel_gewolb @TheASNR 👏👏👏👏🙏

@daniel_gewolb @TheASNR Thank you !

@daniel_gewolb @TheASNR Great teaching don’t feel restricted to post more

@daniel_gewolb @almuftifawaz @TheASNR That’s narrowing the diff?😅

@daniel_gewolb @TheASNR Excellent thx. I had everything on my mind but you managed to organize it.

@daniel_gewolb @TheASNR Excellent thread

@daniel_gewolb @TheASNR This is a learning thread will share with my colleges

@daniel_gewolb @TheASNR In my observation while analysing DWI sequences facilitated diffusion in abnormal areas also has its diagnostic and more importantly prognostic values especially in settings of gliomas.

@daniel_gewolb @TheASNR This was actually very nice

@daniel_gewolb @TheASNR Do you take atypical cases to look at, diagnose and share? (I have one).

@daniel_gewolb @TheASNR 👏🏻👏🏻👏🏻👏🏻👏🏻

@daniel_gewolb @TheASNR Great informative thread @daniel_gewolb! Physicians from around the world post clinical findings on our physician-only network for discussion with global colleagues. We're sure they'd love seeing your educational posts. Join the conversation: https://www.g-med.com/

@daniel_gewolb @TheASNR @threadreaderapp unroll please

@daniel_gewolb @TheASNR Hi Daniel, what an impressive breakdown. Next time you wanted to refresh your mind, you might find #AskDocSplain useful. #MedTwitter #MedEd

@daniel_gewolb @TheASNR Beautifully put!

@daniel_gewolb @TheASNR Great, you can add to it when you remember, haha

@daniel_gewolb @TheASNR good

@daniel_gewolb @TheASNR Que grande!!