الفهرس 
Diffusion MR imagingOnly 14 pages are availabe for public view
 |  | from | 184 |  |  |
| | | from | 184 | | |
Abstract
Intracranial cystic mass lesions include true cysts linedby epithelial, ependymal or meningothelial cells, dermoid and epidermoid cysts, parasitic cysts (cysticercosis, hydatid cysts) or may be pseudocystic neoplastic or inflammatory lesions (abscesses) secondary to accumulation of necrotic, intercellular mixed or proteinaceous material.
The differential diagnosis of various intracranial cystic lesions is sometimes difficult on the basis of CT or MRI findings. DWI is useful as additional diagnostic modalities in their differentiation. Combination of DWI with calculated ADC values added more information to MRI in the differentiation of intracranial cystic mass lesions.
Diffusion-weighted imaging (DWI) is based on the irregular diffusion motion of water molecules and provides more detailed information at the cellular level than conventional magnetic resonance imaging (MRI). Since it is non-invasive and relatively low cost, DWI has been widely
Applied to the diagnosis of various diseases including the detection of abscesses from cystic tumors, and distinguishing epidermoid from arachnoid cysts. DWI has also been explored as a rapid method for the grading of brain tumours, and differentiates recurrent gliomas from radiation necrosis.
DWI is helpful in distinguishing between brain abscesses and necrotic and cystic neoplasms on MRI. This differentiation is still a challenge on both clinical and radiological setting. The abscesses have a high signal on DWI and a reduced (ADC) within the cavity. with the ADC values lower than (0.9 to 0.13 ×10ˉ³ mm²/s). By contrast, necrotic
and cystic tumors display a low signal on DWI (similarto the CSF in the ventricles) with an ADC value of (2.2 ± 0.9 ×10ˉ³mm²/s). as well as isointense or hypointense DWI signal intensity in the lesion margins. DWI has high sensitivity and specificity for the differentiation of brain abscess from other non abscess intracranial cystic lesions.
Criterion for diagnosis of benign cysts is the hypointensity on DWI, with the ADC comparable to that of the CSF. All arachnoid cysts show hypointensity on DWI, and all of the epidermoid cysts show hyperintensity.
DWI differentiates recurrent gliomas from radiation necrosis. As radiation necrosis shows as heterogeneous intensity whereas recurrent tumor appears as predominantly hyperintensity. Mean ADC values of the recurrent tumor 1.18 × 10ˉ³ while that of radiation necrosis is 1.4×10ˉ³ mm²/s showing that the ADC values of the recurrent tumor is significantly lower than those of radiation necrosis.
Diffusion-weighted imaging is highly reliable and practical because of its short duration, especially in the setting of neurological emergencies. For this reason, other techniques that may also be useful such as perfusion or spectroscopy are sometimes used to solve this diagnostic dilemma.