The cranial nerves (CNs) may be divided into segments based upon their anatomic context. Understanding the CN segments (a-nuclear, b-parenchymal fascicular, c-cisternal, d-dural cave, e-interdural, f-foraminal, g-extra-foraminal) provides a conceptual framework for understanding how best to image each portion of the CNs and allows for rapid and concise communication with referring clinicians when evaluating tumors arising from or adjacent to the CNs.The cranial nerves (CNs) span the central nervous system (CNS) and peripheral nervous system (PNS); the Obersteiner-Redlich (aka transition) zone occurs for most CNs in the cisternal (c) segment and demarcates the transition between the two. Primary tumors of the CNs differ in pathology depending upon whether they arise in the CNS or PNS. Proximal to the Obersteiner-Redlich zone gliomas may occur. Nerve sheath tumors (schwannomas and neurofibromas) on the other hand may arise at any point within the PNS.Unlike primary tumors, perineural involvement of the CNs originates uniformly within the extra-foraminal (g) segment. Perineural spread of disease occurs most frequently in skin malignancies, mucosal malignancies of the head and neck, and adenoid cystic carcinoma. Identification of perineural spread of malignancy is critical in assessing extent of disease and is often important in determining the treatment pathway.