Imaging Modalities
MRI
MRI has superior soft tissue contrast resolution with better assessment of soft tissue spatiality and extension and bone marrow involvement compared to CT27,28. MRI with post contrast T1WI with fat saturation is the imaging modality of choice for evaluation of perineural tumor spread although gross perineural spread may be seen with contrast-enhanced CT30,31. MRI sequences for skull base protocol should include T1WI and T2WI with FS and contrast-enhanced T1WI with FS in axial and coronal planes. Precontrast T1WI without FS allows for assessment of bone marrow replacement and abnormalities of adipose tissue within the extracranial spaces adjacent to skull base tumors as well as detection of intrinsic T1 hyperintensity if present. Intrinsic T1 hyperintensity within tumors may be secondary to intratumoral hemorrhage, fat, mineralization or melanin 32. Images should be obtained with thin slices (slice thickness <3 mm). Sagittal images provide additional information regarding craniocaudal extension of the lesions. Detailed evaluation of cranial nerves is required for skull base and temporal bone tumors; dedicated MR sequences including high-resolution 3D T2WI, pre- and post-contrast 3D T1WI with multiplanar reformations of cranial nerves are recommended at the temporal bone and skull base33,34. Entire brain imaging is necessary to assess the integrity of the subjacent brain and dura. The role of advanced MRI techniques such as DWI, MR perfusion, or MR spectroscopy remains under investigation in research 35. MRA and MRV (or CTA/CTV) are adjunctive radiological exams that can be used to assess vascular anatomy (compression, displacement, invasion)23.