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AJNR - American Journal of Neuroradiology

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American Journal of Neuroradiology 25:677-691, May 2004
© 2004 American Society of Neuroradiology

BRAIN

MR Imaging of the Temporal Stem: Anatomic Dissection Tractography of the Uncinate Fasciculus, Inferior Occipitofrontal Fasciculus, and Meyer’s Loop of the Optic Radiation

E. Leon Kier^a, Lawrence H. Staib^a,b,c, Lawrence M. Davis^a and Richard A. Bronen^a,d

^a Department of Diagnostic Radiology, Yale University School of Medicine, New Haven, CT
^b Department of Biomedical Engineering, Yale University School of Medicine, New Haven, CT
^c Department of Electrical Engineering, Yale University School of Medicine, New Haven, CT
^d Department of Neurosurgery, Yale University School of Medicine, New Haven, CT

Corresponding author: E. Leon Kier, MD, Yale University School of Medicine, 333 Cedar Street, New Haven, CT 06520-8042

BACKGROUND AND PURPOSE: The MR anatomy of the uncinate fasciculus, inferior occipitofrontal fasciculus, and Meyer’s loop of the optic radiation, which traverse the temporal stem, is not well known. The purpose of this investigation was to study these structures in the anterior temporal lobe and the external and extreme capsules and to correlate the dissected anatomy with the cross-sectional MR anatomy.

METHODS: Progressive dissection was guided by three-dimensional MR renderings and cross-sectional images. Dissected segments of the tracts and the temporal stem were traced and projected onto reformatted images. The method of dissection tractography is detailed in a companion article.

RESULTS: The temporal stem extends posteriorly from the level of the amygdala to the level of the lateral geniculate body. The uncinate and inferior occipitofrontal fasciculi pass from the temporal lobe into the extreme and external capsules via the temporal stem. Meyer’s loop extends to the level of the amygdala, adjacent to the uncinate fasciculus and anterior commissure. These anatomic features were demonstrated on correlative cross-sectional MR images and compared with clinical examples.

CONCLUSION: This study clarified the MR anatomy of the uncinate and inferior occipitofrontal fasciculi and Meyer’s loop in the temporal stem and in the external and extreme capsules, helping to explain patterns of tumor spread. The inferior occipitofrontal fasciculus is an important yet previously neglected tract. These results provide a solid anatomic foundation for diffusion tractography of the normal temporal stem and its tracts, as well as their abnormalities in brain disorders such as epilepsy, postoperative complications, trauma, schizophrenia, and Alzheimer disease.