Benign pinealis cyst
General characteristics and Epidemiology
The most common tumor is the benign pinealis cyst, which can be found in approximately 5% of people (Lee et al. 1987). Due to the high frequency and the often-unspecific clinical presentation, even in large cystic lesions, the main role of MRI is to distinguish between cysts and pineal neoplasms.
Cysts are normally well circumscribed with a typical cystic appearance: high signal intensity on T2 and low CSF-like signal intensity on T1. Depending on the protein content of the cyst fluid, the signal can be also bright on FLAIR. The cyst wall is isointense to the normal brain tissue, and presents contrast enhancement that is normally weak and rim shaped. On late imaging, the cysts can fill with contrast media by diffusion of the contrast material. In such cases, the differential diagnosis from a malignant tumor can be difficult.
Normally the cysts are small and have no mass effect. In larger cysts, an occlusion of the aqueduct can occur with resulting clinical symptoms of hydrocephalus (Oeckler and Feiden 1991).
The main differential diagnosis of lesions in the pinealis region includes (Oeckler and Feiden 1991):
- glioma .
Germinomas are homogeneous enhancing tumors with a signal appearance similar to white matter on the unenhanced scans. Due to the lack of a capsule, these tumors are normally not well circumscribed and invade the surrounding tissue.
Metastasis has to be excluded by a whole CNS imaging procedure.
The less differentiated teratomas are usually heterogeneous on imaging because they contain neoplastic tissue, calcifications, lipids, and fluid in varied proportions.