Detailed MR imaging anatomy of the abducent nerve: evagination of CSF into Dorello canal.

BACKGROUND AND PURPOSE: The abducent nerve is difficult to identify reliably and consistently with conventional radiologic techniques. In this study, a 3D fast asymmetrical spin-echo MR imaging technique was used to obtain detailed images of the abducent nerve in normal volunteers. METHODS: The 3D fast asymmetrical spin-echo MR protocol was used to image the abducent nerves in 24 normal volunteers by using a 1-mm section thickness in the tilted axial and parasagittal planes. The microanatomy of the abducent nerve within Dorello's canal was also demonstrated in a cadaver study. RESULTS: In 24 normal volunteers, the anatomy of 47 abducent nerves was clearly depicted on MR images. The length of the cisternal segment of the abducent nerve, extending from the brain stem to its dural foramina, ranged from 6.7 to 19.6 mm (mean, 13.1 mm). The abducent nerves were at an angle of 5 to 90 degrees (mean, 24.5 degrees) to the clivus. CSF evagination was detected in the region of Dorello's canal in 36 (77%) of 47 abducent nerves. The length of CSF evagination varied: 0.9 mm in five nerves, 1.0 to 1.9 mm in 18 nerves, 2.0 to 2.9 mm in eight nerves, and 3.0 mm or more in five nerves. Histologic examination of serial sections of the abducent nerve revealed that the petroclival segment of the nerve was covered by an envelope composed of an arachnoid cell layer. CONCLUSION: The course of the abducent nerve was reliably identified using the 3D fast asymmetrical spin-echo MR protocol and a histologically proven arachnoid envelope around the petroclival segment of the nerve was shown as CSF evagination into Dorello's canal by MR imaging.

Fast inversion recovery magnetic resonance imaging with the real reconstruction method: a diagnostic tool for cerebral gliomas.

The fast inversion recovery (IR) technique was evaluated for the localization of gliomas. Fast IR imaging with real reconstruction and T1-weighted spin echo (SE) imaging before and after contrast administration were performed in 20 patients with gliomas. The tumor-to-white matter contrast ratio (TWCR), tumor-to-gray matter contrast ratio (TGCR), tumor-to-white matter contrast-to-noise ratio (TWCNR), and tumor-to-gray matter contrast-to-noise ratio (TGCNR) were calculated and compared. Fast IR imaging visualized tumors with significantly higher TWCR, TGCR, TWCNR, and TGCNR values (p < 0.01) than those for T1-weighted SE imaging. In particular, fast IR imaging clearly revealed seven non-enhanced tumors that were poorly visualized on T1-weighted SE imaging. Fast IR imaging showed a similar TGCR and significantly higher TWCR (p < 0.01) compared to T1-weighted SE imaging with contrast medium in 13 enhanced tumors. However, fast IR imaging showed similar TWCNR and lower TGCNR compared to T1-weighted SE imaging with contrast medium. The fast IR technique can discriminate tumors from normal cerebral tissues with high contrast and without the use of contrast medium. This technique is extremely useful for the localization of non-enhanced tumors.