Magnetic resonance imaging of pineal tumors and drop metastases: a review approach

Pineal region tumors represent less than 1% and 3-8% of brain tumors in adults and children respectively. There is a wide range of pineal masses, with the majority being germ cell and pineal parenchymal tumors. Magnetic resonance imaging (MRI) is the modality of choice for the assessment of pineal masses. It is considered as the gold standard for the evaluation of the central nervous system. MRI has the ability to produce very detailed images of the brain anatomy and is used to distinguish true pineal masses from parapineal with invasion of the gland. Specific MRI findings are helpful to the differential diagnosis of pineal tumors and the distinction between benign from malignant tumors. Pineal neoplasms may seed the subarachnoid space resulting in the development of intradural extramedullary metastases, known as drop metastases. MRI is the most sensitive method for the assessment of the spinal cord, meninges and nerve roots and the differentiation of the spinal lesions into intra/extra medullary and extradural. Because of its high sensitivity and the advances of the method, drop metastases can be easily diagnosed at an earlier stage than in the past, contributing to the selection of the appropriate treatment. Therefore, the entire neuroaxis should be investigated with MRI for the presence of intradural extramedullary lesions. The present study focuses on the main MR imaging characteristics of pineal masses and drop metastases with reference to the differential diagnosis. There is also a detailed approach to the MR protocol which should be obtained in order to evaluate the lesions.