Table 1.

Patterns of discrepancy between perfusion-weighted imaging and diffusion-weighted imaging

	Pattern	Incidence %		Main etiology	Indications	Potential interventions
		< 6 h	Total
I	PWI > DWI[20,47,51-53,114,121,125,127-130,135], target mismatch	57~86	49~70	Large-artery atherosclerosis, cardioembolism, cryptogenic	Larger lesion on PWI and DWI. Part of tissue at risk and oligemia. Infarct may growth without effective therapy. More common in white patients	Reperfusion therapy: Thrombolytic therapy or angioplasty, stenting
II	PWI = DWI[20,52,125,131]	~17	~28	Cryptogenic, large-artery atherosclerosis, cardioembolism, lacunar infarction	No additional tissue at risk. Collateral flow limits the infarct volume to that depicted at DWI. Most common in patients with diabetes	Neuroprotection
III	PWI < DWI[51,52,114,123,132], inverse mismatch	~29	6~34	Cryptogenic, cardioembolism, large-artery atherosclerosis, lacunar infarction	Smaller lesion on PWI and DWI. Partial reperfusion may occur at the time of MR scan	Neuroprotection
IV	PWI (-), DWI (+)[47,114,125]	~8	~24	Single small MCA branch occlusion, small subclinical infarct	Full reperfusion may occur or due to collaterals at the time of MR scan. More common in Asian patients	Neuroprotection
V	PWI (+), DWI (-)[47,80,128,133,134], total mismatch	~8	~3	Migraine, TIA	Pure perfusion deficit (tissue at risk but not committed to infarction)	Reperfusion therapy
VI	PWI (-), DWI (-)[20,135]	~14	~18	Migraine, TIA	No abnormality on both PWI and DWI. Normal or hypoperfusion on PET	No interventional therapy
VII	PWI or DWI > 100 mL[82,112], malignant mismatch			Large-artery atherosclerosis	Poor outcome, strongly associated with reperfusion-related brain hemorrhage	Exclusion of therapy

(+): There is abnormality; (-): No abnormality; PWI: Perfusion weighted imaging; DWI: Diffusion weighted imaging; MCA: Middle cerebral artery; TIA: Transient ischemic attack; PET: Positron emission tomography.