Diffusion MRI of the brain: Simplified

Basics:
Bright signal on DWI (B=1000) means restricted diffusion and/or T2 effect.
On ADC, low signal in the same region means restricted diffusion, and bright or isointense signal means T2 shine through effect.
On T2,  the same area may appear bright or isointense.

Pathologies with restricted diffusion:
Acute stroke, acute stroke, acute stroke... (repeat this 10 times before proceeding to next)
Infection: Herpes encephalitis, Pyogenic infection, CJD, meningoencephalitis
Epidermoid (ADC usually cannot be calculated)

Diffuse axonal injury
Oxyhemoglobin (intracellular and hyperacute) (extracellular methHb shows increased signal on both DWI and ADC!)
A few acute MS lesions
Post-ictal
Susceptibility artefact: in inferior frontal and temporal regions should not be mistaken for restricted diffusion

Non-restricted diffusion:
Infection: HIV encepahlopathy
Tumor: primary or secondary, arachnoid cyst
Inflammation: most acute MS lesions
Chronic lesions: chronic stroke, gliosis, neuronal loss
Others: hypertensive encephalopathy, clyclosporin toxicity, hyperperfusion after endartertectomy

Sinus thrombosis

NECT:
Dense Delta sign = dense clot sign - commonly seen in SSS, can be seen in other sinuses too.
Non-arterial infarcts
Dense cortical veins = cord sign
Often a/w hemorrhage
Infarction of basal ganglia and thalami is typical of CVT (this is not a feature of arterial infarct)
Temporal lobe infarct - vein of Labbe thrombosis
Pitfalls:
Hyperdense sign can be normal in infants and neonates, in patients with increased hematocrit (dehydration, polycythemia)
Subdural hemorrhage can mimic CVT and vice versa

CECT:
Empty delta sign, commonly seen in SSS, can be seen in other sinuses too.
Enhancement of falx and tent
Pitfalls:
Intrasinus septa can mimic empty delta sign

MR:
GE images for hemorrhage
Acute: iso on T1, low on T2
Subacute: high on T1 and T2
Chronic: iso on T1 and T2
TOF - short imaging time, beware of artefacts, more false positives, false negative due to methHb
Phase contrast - artefacts due to movements and turbulent flow, no false negative due to methHb
Post-Gd venogram - less false positives, false negative due to methHb or enhancing chronic thrombus
Pitfalls:
Intrasinus septa can mimic CVT
Slow flow may mimic loss of flow void
MethHb may show increased signal on TOF

References:
Poon CS et al. Radiologic Diagnosis of Cerebral Venous Thrombosis. AJR 2007; 189:S76-S78

Pancreatitis: what every radiolgosit should know

Balthazar severity index:
CT appearance:
Normal - 0 points
Large pancreas - 1 point
Pancreatic/ peripancreatic inflammation - 2
1 fluid collection - 3
> 2 fluid collection - 4
% necrosis:
0 - 0
<> 50% - 6
Score of 0 - no mortality, score 7to10 - 17% mortality

Pancreatitis: what every radiolgosit should know

Balthazar severity index:
CT appearance:
Normal - 0 points
Large pancreas - 1 point
Pancreatic/ peripancreatic inflammation - 2
1 fluid collection - 3
> 2 fluid collection - 4
% necrosis:
0 - 0
<> 50% - 6
Score of 0 - no mortality, score 7to10 - 17% mortality

Hypothalamic lesions

1. Cranipharyngioma - solid and cystic, bimodal, enhance
2. Germinoma - upper part of infundibulum, solid, enhance, a/w pineal germinoma
3. Hypothalamic hamartoma - tuber cinerium, solid with cysts, no enhancement, no calcium
4. Osteolipoma (lipoma) - tuber cinerium, fat and osteoid
5. Dermoid cyst - midline, fat, no enhancement
6. Epidermoid cyst - parasellar, CSF signal but high signal on FLAIR, no enhancement
7. Arachnoid cyst - typical
8. Rathke's cleft cyst - variable signal, no enhancement, no calcium
9. Colloid cyst - variable signal, rim may enhance, no calcium
10. Hypothalamic chiasmatic glioma - solid, enhance
11. Ganglioglioma - solid with cystic component, nodular or solid enhancement
12. Choristoma (low grade glioma) - infundibulum, isointense, variable enhancement
13. Perisellar meningioma - typical
14. Hemangioblastoma - cyst with enhancing mural nodule, a.w VHL syndrome
15. Cavernoma - typical
16. Metastasis - intense enhancement, bone destruction, no sellar enlargement
17. Lymphoma
18. Leukemia
19. Langercells histiocytosis - paediatric, stalk > 3mm, intense enhancement
20. Hymphocytic infundibuloneurohypophysitis
21. Sarcoidosis - stalk, a/w leptomeningeal enhancement
22. Wegener's granulomatosis
23. Tuberculosis
24. Syphilis
25. Encephalitis
26. Suprasellar pituitary tumour - enhance
27. Ectopic posterior pituitary
28. Aneurysm - blood products
    
    Reference:
    Saleem SN et al. Lesions of the Hypothalamus: MR Imaging Diagnostic Features. RadioGraphics 2007;27:1087-1108