MR imaging of CSF-like choroidal fissure and parenchymal cysts of the brain.

The purposes of this study were to delineate the MR characteristics of CSF-like parenchymal or fissural cysts of the brain and to correlate them with the clinical findings. Clinical data and MR images of 34 patients with these abnormalities were reviewed. Pathologic correlation was not available. Two types of cystic lesions were identified and separated by location: medial temporal lobe cysts arising in or near the choroidal fissure (26 patients) and parenchymal or pseudoparenchymal cysts not related to the choroidal fissure (eight patients). The choroidal fissure cysts simulated intraparenchymal cysts on axial images but their extraaxial location was well portrayed on the coronal images. Choroidal fissure cysts had a characteristic spindle shape on sagittal images. The other cysts were found in the temporal lobe (seven patients) or thalamus (one patient) and appeared parenchymal but situated close to the subarachnoid space. These lesions were round or ovoid. There was no abnormal enhancement in 10 patients studied with gadopentetate dimeglumine. Coronal images were most useful, revealing the cysts as focal CSF-intensity lesions expanding the choroidal fissure of the temporal lobe. All the cysts appeared to represent incidental findings that did not correlate with the clinical signs and/or symptoms that prompted the imaging evaluations. The MR characteristics of CSF-like cysts are important to recognize so that they are not confused with other, more serious entities, such as intraaxial cystic tumors, infarctions, or parasitic lesions.