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

Dissected uncinate fasciculus.

A, Photograph of the lateral aspect of a dissected cerebral hemisphere shows the segment of the uncinate fasciculus connecting the temporal and frontal lobes. To visualize the uncinate fasciculus, the anterior segment of the superior temporal gyrus (S), a portion of the middle temporal gyrus (M), and the temporal pole were partially removed by dissection. The insular (M2) branches of the middle cerebral artery were also removed by dissection. The horizontal segment (M1) of the middle cerebral artery was left in place as a landmark (arrowhead). The cortex of the insula and parts of the extreme capsule, the claustrum, the external capsule, and the orbital gyri were dissected away. The fiber bundles of the uncinate fasciculus (transparent red) originate in the white matter of the temporal lobe, course around the M1 segment, enter the extreme and external capsules, and continue into the orbital gyri. To visualize the underlying dissected uncinate fasciculus, we used a 10% transparent red that results in a pink appearance. I signifies the inferior temporal gyrus. To better demonstrate the dissected structures, the brain is tilted 30°, with the temporal lobe closer to the camera.

B, 3D MR rendering demonstrates the lateral surface of the dissected segment of the uncinate fasciculus (red). The uncinate fasciculus courses around the M1 segment of the middle cerebral artery and connects the temporal and frontal lobes.

Cross-sectional MR images of the uncinate fasciculus.

A, Coronal reformatted image of the specimen shows the uncinate fasciculus (red) passing from the temporal lobe lateral to the amygdala (A), through the temporal stem (green), and into the lower segment of the extreme capsule lateral to the claustrum (arrow). Coronal Talairach coordinate = −3.

B, Axial reformatted image shows segments of the uncinate fasciculus in the inferior frontal (F) and temporal (T) lobes at the level of the sylvian fissure pedicle (arrowhead). The temporal lobe segment is passing through the temporal stem. Axial Talairach coordinate = −9.

C, Oblique (+17°) axial reformatted image superior to the sylvian fissure pedicle shows the uncinate fasciculus passing from the temporal lobe through the temporal stem and into the lower region of the frontal lobe. This image is at the level of the inferior edge of the claustrum (thin arrow), putamen (P), head of the caudate nucleus (C), and anterior commissure (thick arrow). The oblique axial plane was generated at +17° to the bicommissural plane and used to better demonstrate the relationship of the dissected tracts to the anterior commissure. This oblique axial image is not in Talairach coordinates.

D, Axial image shows the most superior level at which the uncinate fasciculus (red) is present in the extreme capsule lateral to the claustrum (arrow). At its most superior level, the uncinate fasciculus is below the level of the frontal horns of the lateral ventricles. Axial Talairach coordinate = −1.

Clinical correlation of uncinate fasciculus involvement on cross-sectional MR imaging.

A, Nonenhanced parasagittal T1-weighted image in a 36-year-old woman with a temporal lobe astrocytoma extending into the frontal lobe. The region of the abnormal uncinate fasciculus (small arrows) can be identified within the low signal intensity of the tumor. It passes around the middle cerebral artery (arrowhead) into the frontal lobe, including the posterior orbital gyrus (large arrow). The relationship of the uncinate fasciculus to the middle cerebral artery is similar to that shown in the dissected specimen in Figure 2.

B, T2-weighted coronal image in a 44-year-old man with a temporal lobe astrocytoma. The tumor and edema are located adjacent to the amygdala (A). The location of the uncinate fasciculus on the coronal MR study in Figure 3A suggests the tumor is spreading out of the temporal lobe into the extreme and external capsules (arrows) via the region of the uncinate fasciculus.

C, T2-weighted axial image in a 42-year-old man with a temporal-lobe oligodendroglioma that is just beginning to spread into the extreme capsules (small arrows) via the region of the uncinate fasciculus at the level of the anterior commissure (large arrow).

D, T2-weighted axial image in a 60-year-old man with an oligodendroglioma. The tumor (small arrows), shown at the level of the anterior commissure (large arrow), has spread into the extreme and external capsules on either side of the claustrum (arrowhead) with further involvement of the orbital gyri (crossed arrow). Comparison of the images in C and D with Figure 3C illustrates the spread of the tumor from temporal to frontal lobe via the uncinate fasciculus.

Dissected inferior occipitofrontal fasciculus shown along with the uncinate fasciculus.

A, Photograph of the lateral aspect of a dissected cerebral hemisphere shows the inferior occipitofrontal fasciculus and uncinate fasciculus bridging the temporal and frontal lobes. This figure demonstrates additional dissection of the specimen in Figure 1. Further dissection of the superior (S), middle (M), inferior (I) temporal-lobe gyri and of the external and extreme capsule identified the inferior occipitofrontal fasciculus. The uncinate fasciculus (red) originates in the white matter of the temporal lobe and curves around the M1 segment of the middle cerebral artery (arrowhead), entering the extreme and external capsules. The inferior occipitofrontal fasciculus (pink), which connects the occipital and frontal lobes via the temporal lobe, passes into the extreme and external capsules adjacent and superior to the uncinate fasciculus. The inferior occipitofrontal fasciculus is a tract larger and longer than the uncinate fasciculus. In its course from the occipital to the frontal lobe, it traverses almost the entire length of the temporal lobe. To demonstrate the underlying dissected tracts, we used a 10% transparent red for the uncinate fasciculus and 10% transparent pink for the inferior occipitofrontal fasciculus. To better visualize the dissected structures, the brain is tilted 30°, with the temporal lobe closer to the camera.

B, 3D MR rendering demonstrates the surfaces of the dissected inferior occipitofrontal fasciculus (pink) and uncinate fasciculus (red). Arrowhead indicates the M1 segment of the middle cerebral artery.

Cross-sectional anatomic relationships of the inferior occipitofrontal fasciculus in sequential coronal MR planes.

A, Level of the frontal horn of the lateral ventricle and the anterior amygdala (A). This image shows the inferior occipitofrontal fasciculus (pink) in the external capsule, adjacent to the claustrum (arrow), and above the uncinate fasciculus (red); the last crosses the temporal stem (green). Coronal Talairach coordinate = −5.

B, Image at the level of the posterior amygdala and hippocampal head shows only the uncinate fasciculus in the temporal stem. The inferior occipitofrontal fasciculus is in the lower segment of the extreme capsule, lateral to the claustrum (arrow). Coronal Talairach coordinate = −7.

C, Level of the body of the lateral ventricle and the hippocampus. The inferior occipitofrontal fasciculus passes from the temporal lobe, through the temporal stem, and into the lower segment of the extreme capsule lateral to the claustrum (arrow). This level is posterior to the uncinate fasciculus. Coronal Talairach coordinate = −13.

D, The inferior occipitofrontal fasciculus crosses the temporal stem into the white matter lateral to the thalamus and lateral geniculate body (arrow). Coronal Talairach coordinate = −22.

Images of the inferior occipitofrontal fasciculus.

A, Oblique (+17°) axial image shows the inferior occipitofrontal fasciculus coursingfrom the temporal lobe through the extreme and external capsules. The most superior region of the inferior occipitofrontal fasciculus (pink) is at the level of the frontal horn (arrow) of the lateral ventricle. This image and the series of coronal images in Figure 6 demonstrate the long anteroposterior extent of the dissected segment of the inferior occipitofrontal fasciculus. The oblique axial plane was used to better demonstrate the length of the inferior occipitofrontal fasciculus.

B, Oblique (+17°) axial image. Of note is the proximity of the inferior occipitofrontal fasciculus to the anterior commissure (arrow). The anterior commissure is best demonstrated in the oblique plane. On this image, only a small segment of the inferior occipitofrontal fasciculus is adjacent to the anterior commissure.

C, Axial image shows the inferior occipitofrontal fasciculus passing from the temporal lobe into the extreme capsule via the temporal stem (green). The images in B and C show that, at the level of the anterior commissure (arrow), both the uncinate fasciculus and the inferior occipitofrontal fasciculus are present in the extreme capsule. Axial Talairach coordinate = −5. Comparison of the images in B and C demonstrates that the proximity and relationship of the uncinate fasciculus and inferior occipitofrontal fasciculus to the anterior commissure depends on the obliquity of the axial plane.

Clinical correlation of the inferior occipitofrontal fasciculus in the sagittal plane. Parasagittal T2-weighted image in a 70-year-old man with a temporal-lobe glioblastoma multiforme. The tracts shown in the anatomic dissection (Fig 5A), the 3D MR rendering (Fig 5B), and the size of the lesion above the middle cerebral artery void (arrowhead) suggest that the tumor and edema has spread into the frontal lobe via both the uncinate fasciculus and the inferior occipitofrontal fasciculus.

Clinical examples show involvement of the inferior occipitofrontal fasciculus at coronal MR planes corresponding to those in Figure 6.

A, Enhanced T1-weighted image in a 58-year old man with a recurrent glioblastoma multiforme. This image is at the level of the frontal horn of the lateral ventricle, and the amygdala (A). Comparison with Figure 6A demonstrates that the enhanced tumor is spreading out of the temporal lobe via the region of the uncinate fasciculus (large arrows). The nonenhanced edema and tumor in the extreme and external capsules, around the claustrum (arrowhead), involve the region of the inferior occipitofrontal fasciculus (small arrows). This combined involvement of the uncinate fasciculus and the inferior occipitofrontal fasciculus may vary depending on the exact location of the upper margin of the uncinate fasciculus and the lower margin of the inferior occipitofrontal fasciculus and the angulation of the section.

B, Proton density–weighted image in a 52-year-old man with a temporal lobe astrocytoma spreading into the extreme and external capsules at the posterior amygdala/hippocampal head level. Comparison with Figure 6B shows that the tumor and edema is spreading out of the temporal lobe via the region of both the uncinate fasciculus (large arrows) and the inferior occipitofrontal fasciculus (small arrows).

C, T2-weighted image in a 36-year-old woman with a temporal lobe astrocytoma spreading into the extreme and external capsules. The tumor is at the level of the body of the lateral ventricle and hippocampus. Comparison with Figure 6C, obtained at a similar coronal plane, demonstrates that the tumor and edema are spreading out of the temporal lobe via the region of the inferior occipitofrontal fasciculus (arrows).

D, T2-weighted image in a 68-year-old woman with a temporal lobe anaplastic oligodendroglioma spreading into the deep white matter lateral to the thalamus. Comparison with Figure 6D demonstrates that the inferior occipitofrontal fasciculus (arrows) is involved in the tumor and edema spread out of the temporal lobe.

Corresponding clinical examples involving the inferior occipital fasciculus in the axial plane.

A, In this 41-year-old woman, the tumor has spread to the extreme capsule. Comparison with Figure 7A shows that, at the level of the lateral ventricle, the tumor and edema is spreading out of the temporal lobe via the region of the inferior occipitofrontal fasciculus (arrows).

B, In this 61-year-old man, the tumor has spread into the extreme and external capsules around the claustrum (arrowhead). This image is at the level of the third ventricle and the anterior commissure (crossed arrow). Locations of the inferior occipitofrontal fasciculus and the uncinate fasciculus in Figure 7B and C suggest that the tumor and edema has spread out of the temporal lobe via the region of both the inferior occipitofrontal fasciculus (small arrows) and the uncinate fasciculus (large arrows). Depending on the angulation of the axial plane, or a few millimeters change in section selection, tumor spread at the anterior commissure level may involve the inferior occipitofrontal fasciculus and the uncinate fasciculus to a variable degree.

Dissected Meyer’s loop with the inferior occipitofrontal fasciculus and the uncinate fasciculus.

A, Photograph of the lateral aspect of a dissected cerebral hemisphere shows Meyer’s loop (yellow), the inferior occipitofrontal fasciculus (pink), and the uncinate fasciculus (red). This figure demonstrates additional dissection of the specimen in Figure 5A. Further dissection of the superior (S), middle (M), inferior temporal lobe gyri; the inferior occipitofrontal fasciculus; and the white matter of the temporal lobe was performed. To visualize the fiber bundles of the optic radiation, the fibers of the inferior part of the occipitofrontal fasciculus and the posterior part of the uncinate fasciculus were partially removed by dissection. The dissection demonstrates the multiple fibers of the optic radiation, which pass laterally and bend posteriorly to form the curving fiber bundles of Meyer’s loop. Of note is the proximity of the anterior commissure (arrow) to the anterior fiber bundle of Meyer’s loop, to the inferior occipitofrontal fasciculus, and to the uncinate fasciculus; the last curves around the horizontal segment of the middle cerebral artery (arrowhead). To demonstrate the underlying tracts, we used a 10% transparent red for the uncinate fasciculus, 10% pink for the inferior occipitofrontal fasciculus, and 10% transparent yellow for Meyer’s loop. To better visualize the dissected structures, the brain is tilted and angled, with the temporal lobe closer to the camera.

B, 3D MR rendering demonstrates the surfaces of the dissected Meyer’s loop, inferior occipitofrontal fasciculus and uncinate fasciculus. The inferior section of the inferior occipitofrontal fasciculus and the posterior section of the uncinate fasciculus shown in Figure 5B are not present here because they had to be removed by dissection to visualize the surface of Meyer’s loop. Arrowhead indicates the middle cerebral artery trunk.

C, 3D MR rendering of the undissected brain with the underlying dissected white matter tracts project to the cortical surface. The entire dissected surfaces of the uncinate fasciculus and inferior occipitofrontal fasciculus are shown in this image. The upper section of Meyer’s loop is not present on this image, as it is deep to the inferior occipitofrontal fasciculus.

Coronal images through Meyer’s loop.

A, Image at the level of the amygdala (A) shows the most anterior extent of Meyer’s loop (arrowhead) and its relationship to the dissected uncinate fasciculus (red) and the inferior occipitalfrontal fasciculus (pink). Coronal Talairach coordinate = −7.

B, Image at the level of the hippocampus (just anterior to the lateral geniculate body) shows Meyer’s loop superior and lateral to the temporal horn, crossing the temporal stem (green). Meyer’s loop (yellow) is located deep to the inferior occipitofrontal fasciculus (pink). This relationship is maintained throughout most of the course of these structures. Coronal Talairach coordinate = −18.

C, Image at the level of the lateral geniculate body (arrow) shows Meyer’s loop located above and lateral to the temporal horn. The inferior occipitofrontal fasciculus is not included in this image. Arrowhead indicates the hippocampus. Coronal Talairach coordinate = −23.

Axial images through Meyer’s loop.

A, Reformatted image obtained in an axial plane parallel to floor of the temporal lobe is advantageous for showing Meyer’s loop (yellow) coursing along the lateral wall of the temporal horn (T). Of note is the most anterior extent of Meyer’s loop, which is at the level of the amygdala (A) but does not reach the level of the tip of the temporal horn (compare with Fig 12A). The undissected optic radiation (arrows) is passing toward the occipital lobe. H indicates the hippocampus.

B, Oblique (+17°) axial image at the level of the lateral geniculate body (arrowhead), shows Meyer’s loop (arrow) crossing over the region of the roof of the temporal horn, which is below this image level. This relationship is more obvious on the coronal images in Figure 12B and C.

Clinical correlation of Meyer’s loop in the coronal plane. In this 51-year-old woman with a recent stroke and quadrantanopia, an ischemic lesion is present in the region of Meyer’s loop (arrow), superior to the hippocampus and temporal horn. Compare with Figure 12B

Clinical correlation of Meyer’s loop in the axial plane. In this 51-year-old woman with a recent stroke and quadrantanopia (same patient as in Fig 14), an ischemic lesion is present in the region of Meyer’s loop (arrow). Compare with Figure 13B.