Imaging the cranial nerves: part II: primary and secondary neoplastic conditions and neurovascular conflicts

Abstract

There have been unprecedented improvements in cross-sectional imaging in the last decades. The emergence of volumetric CT, higher field MR scanners and higher resolution MR sequences is largely responsible for the increasing diagnostic yield of imaging in patients presenting with cranial nerve deficits. The introduction of parallel MR imaging in combination with small surface coils allows the depiction of submillimetric nerves and nerve branches, and volumetric CT and MR imaging is able to provide high quality multiplanar and curved reconstructions that can follow the often complex course of cranial nerves. Seeking the cause of a cranial nerve deficit is a common indication for imaging, and it is not uncommon that radiologists are the first specialists to see a patient with a cranial neuropathy. To increase the diagnostic yield of imaging, high-resolution studies with smaller fields of view are required. To keep imaging studies within a reasonable time frame, it is mandatory to tailor the study according to neuro-topographic testing. This review article focuses on the contribution of current imaging techniques in the depiction of primary and secondary neoplastic conditions affecting the cranial nerves as well as on neurovascular conflicts, an increasingly recognized cause of cranial neuralgias.

Visualization of the Peripheral Branches of the Mandibular Division of the Trigeminal Nerve on 3D Double-Echo Steady-State with Water Excitation Sequence

“…We evaluated the capability of detecting the V3 branches with a 5-point scale with the criteria as follows: excellent (4), both the proximal and distal portions of the nerve identified; good (3), both the proximal and distal portions of the nerve identified but not continuous; fair (2), only the proximal portion of the nerve identified; poor (1), only the proximal portion of the nerve identified but not continuous; and none (0), the nerve not identified. The average scores for each reader, in addition to the average score from all 3 readers for the 6 branches of the V3, were calculated.…”

“…Following the entire course of the cranial nerves, including the extracranial segments, however, is still a diagnostic challenge in routine clinical practice. 1,2,[11][12][13][14][15][16] Intracranial segments of the cranial nerves, particularly the cisternal segments, are readily detected by using high-resolution heavily T2-weighted imaging. 14,15 Without the high-signal background from the CSF, however, heavily T2-weighted imaging has not proved to be very useful in visualizing the extracranial segments of the cranial nerves.…”

Pathology of the Ocular Motor Nerves III, IV, and VI

“…11) or leptomeningeal carcinomatosis secondary to solid tumors. 52 Although lymphoma and leukemia are the most common malignancies seeding to the CSF, only a minority invokes a leptomeningeal reaction visible on imaging. The most common finding in childhood leukemia is enlargement of the ventricles, possibly representing hydrocephalus secondary to occult disease involvement.…”

“…50 On CT, schwannomas generally are of lower attenuation than brain parenchyma and show moderate enhancement. 52 The MRI appearances of schwannomas are variable but generally of well-circumscribed lesions isointense or slightly hypointense to brain parenchyma on T1-weighted (T1-w) images and isointense or heterogeneously hyperintense on T2-w images. 32,47,52,53 The heterogeneity tends to increase with increasing tumor size and may be the result of regions of different histology (hypercellular Antoni A tissue appearing isointense and hypocellular Antoni B tissue appearing hyperintense) or cystic change.…”

MRI of Lateral Skull Base Lesions

“…New strict criteria have been developed for the diagnosis of neurovascular conflict that in appropriate clinical setting, the vessel should be an artery, site of contact must be the root entry zone with the vessel crossing the nerve perpendicularly, and the nerve must be deviated or indented by the offending vessel or compressed or encased between two or more vessels. 56,57 Newer MR pulse sequences, like CISS, thin T2-weighted sequences and MR angiography, help to image this condition. 58,59 As surgical intervention is highly successful, imaging plays a crucial role in the identification of this pathology.…”