Diffusion-weighted MRI in cystic or necrotic intracranial lesions

Our purpose was to investigate the signal intensities of cystic or necrotic intracranial lesions on diffusion-weighted MRI (DWI) and measure their app arent diffusion coefficients (ADC). We examined 39 cystic or necrotic intra cranial lesions in 33 consecutive patients: five malignant gliomas, seven m etastases, two other necrotic tumours, a haemangioblastoma, three epidermoi ds, an arachnoid cyst, seven pyogenic abscesses, 12 cases of cysticercosis and one of radiation necrosis. DWI was performed on a 1.5 T unit using a si ngle-shot echo-planar spin-echo pulse sequence with b 1000 s/mm(2). The sig nal intensity of the cystic or necrotic portion on DWI was classified by vi sual assessment as markedly low las low as cerebrospinal fluid), slightly l ower than, isointense with, and slightly or markedly higher than normal bra in parenchyma. ADC were calculated in 31 lesions using a linear estimation method with measurements from b of 0 and 1000 s/mm(2). The cystic or necrot ic portions of all neoplasms (other than two metastases) gave slightly or m arkedly low signal, with ADC of more than 2.60 x 10(-3) mm(2)/s. Two metast ases in two patients showed marked high signal, with ADC of 0.50 x 10(-3) m m(2)/s and 1.23 x 10(-3) mm(2)/s, respectively. Epidermoids showed slight o r marked high signal, with ADC of less than 1.03 x 10(-3) mm(2)/s. The arac hnoid cyst gave markedly low signal, with ADC of 3.00 x 10(-3) mm(2)/s. All abscesses showed marked high signal, with ADC below 0.95 x 10(-3) mm(2)/S. The cases of cysticercosis showed variable signal intensity; markedly low in five, slightly low in three and markedly high in four.