RESUMO
Twenty one cases of congenital cystic intracranial lesions [having a range of age 24 days to 15 years] were subjected to CT and MRI examinations. The imaging findings were compared with the final diagnosis obtained by clinical data, operation and follow up. The lesions appeared mostly as hypodense nonenhancing masses of CSF density by CT, exerting mass effect according to the size and no surrounding edema. By MRI, they appeared hypointense in T1WI and hyperintense in T2WI. The pathological varieties encountered were; 2 cases of holoprosencephaly, 2 hydranencephaly, one porencephaly, 8 Dandy walker [DW] complex, 7 arachnoid cysts, and one epidermoid tumour. Both CT and MRI can give similar informations concerning the size, shape, rim thickness and other morphologic characteristics of cystic intracranial lesions. Additional data given by MRI are; superior visualization of cerebellar vermis in cases of Dandy Walker complex hence it could be classified into [type A] with absent vermis and [type B] with present vermis in the axial MRI cuts for the fourth ventricular level. MRI is better for detection of infection in an arachnoid cyst by the presence of high signal intensity inside the cyst, It is also able to predict the nature of the contents of the epidermoid cyst whether protein or triglycerides according to its signal intensity in both T[1] and T[2] WI. MRI can detect abnormal signal intensity in the cyst wall of a porencephalic cyst that helps differentiation from arachnoid cysts. Also MRI has a better performance specially in posterior fossa lesions as it is not affected by beam hardening artifact as CT. Other advantages of MRI include lack of ionizing radiation and direct visualization of blood flow, Muliplanar capability and high soft tissue resolution. CT is superior to MRI in the detection of calcification in certain lesions as epidermoid cyst