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MR Anatomy of the Proximal Cisternal Segment of the Trochlear Nerve: Neurovascular Relationships and Landmarks¹

¹ From the Depts of Neuroradiology (I.Y., T.A.Y.) and Neurology (M.D.), Klinikum Grosshadern, Munich, Germany; Dept of Anatomy, Ludwig-Maximilians Universität, Munich, Germany (B.M.); Neurosurgical Unit, Klinik Im Park, Zürich, Switzerland (U.D.S.); and Depts of Radiology and Neurosurgery, Mount Sinai School of Medicine, New York, NY (T.P.N.). Received Mar 15, 2001; revision requested May 3; revision received Aug 13; accepted Sep 9. Address correspondence to T.A.Y., Lysholm Department of Radiology, National Hospital of Neurology and Neurosurgery, Queen Square, London WC1N 3BG, England (e-mail: T.yousry@ion.ucl.ac.uk).

View larger version (138K): [in a new window]   Figure 1. Schematic illustration of the segments of the trochlear nerve: 1 = nucleus and central segment, 2a = visible part of cisternal segment, 2b = subtentorial part of cisternal segment, 3 = cavernous (within-wall) segment, 4 = orbital segment. Anatomic landmarks: AC = ambient cistern (cerebrospinal fluid), BA = basilar artery, Cer = cerebellum, CS = cavernous sinus, DP = dural pore, IC = inferior colliculus, Ped = cerebellar peduncle, SOF = superior orbital fissure, TE = tentorial edge, Ve = velum.

View larger version (150K): [in a new window]   Figure 2a. Normal anatomic relationships. (a) Transverse, (c) parasagittal, and (d) coronal 3D CISS MR images (12.25/5.90), as well as (b) corresponding transverse 3D TOF source MR image (31/7) from a nonenhanced MR angiogram, obtained in a 59-year-old woman. In a, the proximal cisternal segment of the trochlear nerve can be identified with certainty on both sides (arrowheads) at the level of the triangular (ie, tent-shaped) superior medullary velum (long arrow). On the right, the SCA (short arrow) is anterior to and in direct contact with the nerve. In b, the SCA (arrow) can be identified on the right side, but the trochlear nerve cannot. In c, the trochlear nerve (arrowhead) is visible inferior to the inferior colliculus (arrow). In d, the proximal cisternal course of the trochlear nerve can be identified on both sides (arrowheads). On the right, the SCA (solid arrow) is inferior and anterior to the trochlear nerve and in direct contact with it. The inferior colliculus (open arrow) also is identified.

View larger version (139K): [in a new window]   Figure 2b. Normal anatomic relationships. (a) Transverse, (c) parasagittal, and (d) coronal 3D CISS MR images (12.25/5.90), as well as (b) corresponding transverse 3D TOF source MR image (31/7) from a nonenhanced MR angiogram, obtained in a 59-year-old woman. In a, the proximal cisternal segment of the trochlear nerve can be identified with certainty on both sides (arrowheads) at the level of the triangular (ie, tent-shaped) superior medullary velum (long arrow). On the right, the SCA (short arrow) is anterior to and in direct contact with the nerve. In b, the SCA (arrow) can be identified on the right side, but the trochlear nerve cannot. In c, the trochlear nerve (arrowhead) is visible inferior to the inferior colliculus (arrow). In d, the proximal cisternal course of the trochlear nerve can be identified on both sides (arrowheads). On the right, the SCA (solid arrow) is inferior and anterior to the trochlear nerve and in direct contact with it. The inferior colliculus (open arrow) also is identified.

View larger version (125K): [in a new window]   Figure 2c. Normal anatomic relationships. (a) Transverse, (c) parasagittal, and (d) coronal 3D CISS MR images (12.25/5.90), as well as (b) corresponding transverse 3D TOF source MR image (31/7) from a nonenhanced MR angiogram, obtained in a 59-year-old woman. In a, the proximal cisternal segment of the trochlear nerve can be identified with certainty on both sides (arrowheads) at the level of the triangular (ie, tent-shaped) superior medullary velum (long arrow). On the right, the SCA (short arrow) is anterior to and in direct contact with the nerve. In b, the SCA (arrow) can be identified on the right side, but the trochlear nerve cannot. In c, the trochlear nerve (arrowhead) is visible inferior to the inferior colliculus (arrow). In d, the proximal cisternal course of the trochlear nerve can be identified on both sides (arrowheads). On the right, the SCA (solid arrow) is inferior and anterior to the trochlear nerve and in direct contact with it. The inferior colliculus (open arrow) also is identified.

View larger version (128K): [in a new window]   Figure 2d. Normal anatomic relationships. (a) Transverse, (c) parasagittal, and (d) coronal 3D CISS MR images (12.25/5.90), as well as (b) corresponding transverse 3D TOF source MR image (31/7) from a nonenhanced MR angiogram, obtained in a 59-year-old woman. In a, the proximal cisternal segment of the trochlear nerve can be identified with certainty on both sides (arrowheads) at the level of the triangular (ie, tent-shaped) superior medullary velum (long arrow). On the right, the SCA (short arrow) is anterior to and in direct contact with the nerve. In b, the SCA (arrow) can be identified on the right side, but the trochlear nerve cannot. In c, the trochlear nerve (arrowhead) is visible inferior to the inferior colliculus (arrow). In d, the proximal cisternal course of the trochlear nerve can be identified on both sides (arrowheads). On the right, the SCA (solid arrow) is inferior and anterior to the trochlear nerve and in direct contact with it. The inferior colliculus (open arrow) also is identified.

View larger version (126K): [in a new window]   Figure 3. Transverse 3D CISS MR image (12.25/5.90) obtained in a 57-year-old woman. The proximal cisternal courses of the left and right trochlear nerves can be identified at the level of the triangular (ie, tent-shaped) superior medullary velum (long arrow). The right trochlear nerve (arrowhead) passes laterally in the more classic pattern, whereas the left nerve (open arrow) follows an oblique anterolateral course. The SCA (short solid arrows) is anterior to and in direct contact with the trochlear nerve on both sides.

View larger version (145K): [in a new window]   Figure 4a. Right superior oblique myokymia in a 39-year-old man. (a) On the transverse 3D CISS MR image (12.25/5.90), the trochlear nerve can be identified on both sides (arrowheads). On the right, a medial SCA branch (arrow) is located at the REZ of the trochlear nerve. The nerve itself can be identified as a separate structure in its distal portion. The proximal portion of the trochlear nerve cannot be distinguished from the artery, however. This finding is consistent with a vascular compression of the nerve. (b) Transverse source image from a nonenhanced 3D TOF MR angiogram (31/7) confirms that the structure that is in close contact with the trochlear nerve at the REZ is an artery (arrow), which is indistinguishable from the trochlear nerve.

View larger version (135K): [in a new window]   Figure 4b. Right superior oblique myokymia in a 39-year-old man. (a) On the transverse 3D CISS MR image (12.25/5.90), the trochlear nerve can be identified on both sides (arrowheads). On the right, a medial SCA branch (arrow) is located at the REZ of the trochlear nerve. The nerve itself can be identified as a separate structure in its distal portion. The proximal portion of the trochlear nerve cannot be distinguished from the artery, however. This finding is consistent with a vascular compression of the nerve. (b) Transverse source image from a nonenhanced 3D TOF MR angiogram (31/7) confirms that the structure that is in close contact with the trochlear nerve at the REZ is an artery (arrow), which is indistinguishable from the trochlear nerve.