Magnetic Resonance Imaging of Extra-axial Tumor

Abstract

The first step in making decision of intra-cranial tumors is the location of tumor, whether intra- or extra-axial. After localized the lesion we make differential diagnosis that relevant to the location. Once we made the decision, we make the characterization of the tumors. With MRI it is easier to make this decision compared to CT.Meningiomas constitute the most common extra-axial tumors of the brain. Contrast-enhanced MRI can easily detect the location of the tumor, the full extension of the tumor, sinus invasion and/or thrombosis, vascularity, intra-cranial edema, and intra-osseous extension. WHO grades meningiomas in 3 types which are typical, atypical, and malignant meningioma. With structural MRI, MR Spectroscopy, MR perfusion and some methods we can grade this type.Tumors of neurogenic origin such as schwannomas, neurofibromas, neuromas may be similar in appearance. MRI can help distinguishing these tumors with meningiomas. Another extra-axial lesion located in bone or arachnoid is metastases. Contrast-enhanced T2-FLAIR can easily detect these lesions, but inflammatory lesions may also simulate dural metastase. Other extra-axial tumors are choroid plexus masses, non-neoplastic masses (epidermoids, dermoids, teratomas, lipomas). The location as well as specific appearances on imaging will guide us to a specific diagnosis.