Daniel Gewolb, MD Profile picture
May 27, 2023 14 tweets 7 min read Read on X
Tips & tricks of DWI to help narrow the differential

Ddx:
Stroke
Abscess
Hypercellular tumor
Hematoma
Epidermoid cyst
Encephalitis
Seizure
Demyelination
Toxic/metabolic disorders
CJD
Other stuff I’m forgetting
#Neurology #neurosurgery #radres #MedTwitter #MedEd @TheASNR ImageImageImageImage
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 Image
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) ImageImage
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 ImageImage
Hypercellular tumor continued

▶️Glioblastoma or high grade glioma

Variable but may have more eccentric or nodular restriction around areas of necrosis and heterogeneous enhancement Image
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 ImageImage
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) ImageImage
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) Image
Bonus cases

7️⃣SEIZURE
Shows gyriform or cortical restricted diffusion (often in the mesial temporal lobe)

Examples in 2 different patients ImageImage
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 Image
9️⃣CJD
Diffusion restriction is seen in the basal ganglia, thalami, and cortex. This can be asymmetric Image
🔟Many Toxic/metabolic disorders

Hepatic encephalopathy
Acute toxic leukoencephalopathy
Hypoxia
Methotrexate toxicity
Drug abuse
CO poisoning
Many more

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More from @daniel_gewolb

Jul 19
🔷What is the most likely diagnosis and clinical syndrome in this patient with left ear pain, cranial nerve 6 palsy, and retro-orbital pain? 🧠 🤔

#Neurology #ent #neurosurgery #radres #NeuroTwitter #futureradres #MRI #Medicine @ASHNRSociety @RSNA #Ophthalmology Image
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⭐️ Answer: petrous apicitis complicated by brainstem abscess

🔷Petrous apicitis can display the clinical triad of Gradenigo’s syndrome

1️⃣Otorrhea
2️⃣Cranial nerve 6 palsy
3️⃣Pain in distribution of trigeminal nerve
▶️Petrous apicitis usually occurs as a complication of otomastoiditis when the infection spreads to the skull base.

▶️The petrous apex is in close proximity to Dorello’s canal (where cranial nerve 6 runs through) and Meckel’s cave (where the trigeminal ganglion is located)
Read 6 tweets
Jul 4
⭐️ What is the most likely diagnosis in this pregnant patient presenting with seizures? 🧠

#Neurology #medicine #radres #futureradres #Neurosurgery #MRI #FOAMed Image
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⭐️ Answer: Cortical vein thrombosis (CVT)

▶️CVT causes retrograde venous pressure leading to focal vasogenic edema

▶️Increased back pressure is characterized by dilated veins and petechial hemorrhage which can progress to large hematomas and ischemic neurological damage
🔷Two types of edema can develop:
1️⃣Vasogenic (from venous back pressure)
2️⃣Cytotoxic (ischemia)

🔷Risk factors:
💡 Up to 20% are idiopathic
1️⃣Trauma
2️⃣Tumor/malignancy (compression/invasion from meningioma)
3️⃣Infection
4️⃣Hormonal (pregnancy)
5️⃣Dehydration
Read 7 tweets
Jun 22
🔷What is the most likely diagnosis in this 70 y/o F who lives with feral cats presenting w/ vomiting, diarrhea, leukocytosis, fever for 3 days and progressive decline in level of consciousness?

🔷CSF: initially normal, repeat a few days later ⬆️ WBC (lymphocyte predominant), ⬆️ Protein, normal glucoseImage
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⭐️ Answer: Viral encephalitis (Specifically Rabies)

🔷 South Central Asia and Southeast Asia appear to have the greatest number of cases

🔷Dogs are the most common reservoir 🐶 (bats in developed countries🦇)
🔷CLINICAL:

▶️Incubation period typically 3 weeks to 2 months (range 5 days to 6 months)
▶️Prodromal symptoms: fever, malaise, anxiety,
and itching at the inoculation site

💡Once in the body, the virus begins retrograde flow to extend to the dorsal root ganglion, which may correlate with neuropathic pain

▶️CNS manifestations: Mental status changes of excessive agitation and depression with hydrophobia and aerophobia
Read 5 tweets
Jun 19
🔷35 y/o F w/ history of Li Fraumeni syndrome presents w/ intermittent left sided weakness and pain. The feeling is of heaviness, difficulty w/ grip, dropping objects and frequent falls. Episodes last for weeks to months. What is your diagnosis? 🧠

🎉Congrats to all the rad fellow matches today!!! 🍾

#Neurology #MRI #MedEd #medicine #neurosurgery #radres #futureradres #FOAMed @TheASNRImage
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⭐️ Answer: Tumefactive demyelination (MS in this case)

🔷Imaging in this case is specific enough to diagnosis with confidence but we need extra caution in patients with genetic predisposition to malignancy

💡 In cases where imaging or clinical picture are atypical or discordant for demyelination (especially if there is a genetic disorder), it is best to refer to neurology for proper work up, possible trial of steroids and short imaging follow up
🚩 Be suspicious against MS if your patient has:
1️⃣Systemic symptoms (fever, weight loss, joint or skin symptoms, etc.)
2️⃣Seizures, hearing loss, meningitis signs, movement disorder, aphasia
3️⃣”Family history”
4️⃣Age (<20 or >50)
5️⃣Lesions are symmetric
6️⃣Hemorrhage or dense on CT
7️⃣Diffusion restriction other than leading edge
8️⃣Strokes
9️⃣Cysts
🔟Cortical infiltration
Read 6 tweets
Apr 26
⭐️ What is the most likely diagnosis in this 45 y/o M found down with history of polysubstance abuse?

#Neurology #Medicine #radres #Neurosurgery #futureradres #radres #FOAMed #MRI @AlbanyMedRadRes @TheASNR Image
⭐️ Answer: Opioid-associated amnestic syndrome

🔷Toxicology was + for fentanyl and no other parts of the brain were affected on MRI

🔷Pathophys: Unclear, possibly neuronal hyper metabolism and/or ischemic component
🔷Clinical: New-onset amnesia for >24 hours

🔷Imaging:
▶️Diffuse, symmetric diffusion restriction in the hippocampi

▶️Usually mild T2/FLAIR signal in same areas
Read 7 tweets
Mar 19
⭐️ 30 y/o presents w/ R sided weakness & fall. Pt had a recent admission ~4 months ago for headache, AMS, seizure & diplopia. Clinically stable until now.

🔷LP 4 months ago: protein >600
🔷Comparison in 🧵

What is your diagnosis?

#medicine #MedEd #radres #futureradres #Neurology #Neurosurgery #FOAMed @TheASNRImage
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🔷Comparison from ~4 months ago 👇 Image
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⭐️ Hint: TB work up negative and CT chest, abdomen and pelvis also negative. The spine was imaged 👇 Image
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Read 7 tweets

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