MR imaging of the trigeminal ganglion, nerve, and the perineural vascular plexus: normal appearance and variants with correlation to cadaver specimens

Abstract

Background and purpose: MR imaging is the method of choice for evaluating the trigeminal nerve. Detection of abnormalities such as perineural tumor spread requires detailed knowledge of the normal MR appearance of the trigeminal nerve and surrounding structures. The purpose of this study was to clarify the normal MR appearance and variations of the trigeminal ganglion, maxillary nerve (V2), and mandibular nerve (V3) with their corresponding perineural vascular plexus.

Method: S: MR images obtained in 32 patients without symptoms referable to the trigeminal nerve were retrospectively reviewed. The trigeminal ganglion in Meckel's cave, V2 within the foramen rotundum, and V3 at the level of foramen ovale were assessed for visualization and enhancement. The configuration of the perineural vascular plexus was recorded. Correlation to cadaver specimens was made.

Results: The trigeminal ganglion and V3 were observed to enhance in 3-4% of patients unilaterally. V2 and V3 were well visualized 93% of the time. The perineural vascular plexus of V2 was observed 91% of the time, and that of V3 in 97% of instances.

Conclusion: This study characterizes the normal MR appearance of the trigeminal ganglion and its proximal branches. The trigeminal ganglion, V2, and, V3 are almost always reliably seen on thin-section MR studies of the skull base. Enhancement of the perivascular plexus is routinely seen; however, enhancement of the trigeminal ganglion, V2, or V3 alone is seen only on occasion as supported by the avascular appearance of these anatomic structures in cadaver specimens.

Fig 1.

Trigeminal ganglion in trigeminal cistern in cadaver. A, Trigeminal ganglion (TG) is crescentic in shape and proximal divisions of trigeminal nerve (V1, V2, V3) emerge from its anterolateral border. The trigeminal rootlets (*) enter the crescent-shaped TG. V1 exits the TG as the most superior branch. It lies immediately inferior to cranial nerve four (CN4). V2 leaves TG as the middle branch and V3 as the most inferior division. Venous structures are blue- and arterial red-colored silicon. An extensive pericavernous venous plexus surrounds the ganglion and each of the trigeminal nerve branches (white arrows). B, Following dissection of the pericavernous venous plexus, the avascular nature of the trigeminal ganglion and its proximal divisions (V1, V2, V3) is seen. The extent of the trigeminal ganglion (between arrowheads) and the trigeminal nerve rootlets (*) are now better delineated. The cranial nerve six (white arrow) is now visible inferior medial to V1. CN indicates cranial nerve

Fig 2.

Coronal gadolinium-enhanced T1-weighted image (TR/TE/NEX, 400/15/2) depicts the nonenhancing crescent-shaped trigeminal ganglion (arrows) and the prominent perineural venous plexus (arrowheads) superior to it. The venous plexus as well as the ganglion are symmetric in appearance.

Fig 3.

Coronal gadolinium-enhanced T1-weighted image (TR/TE/NEX, 500/15/2) illustrates the common appearance of V2 (arrows) within the foramen rotundum as central nonenhancing nerve completely surrounded by the perineural venous plexus (arrowheads).

Fig 4.

Coronal gadolinium-enhanced T1-weighted image (TR/TE/NEX, 500/15/2) illustrates the normal appearance of V3 as it exits the skull base through the foramen ovale. V3 (*) is surrounded by the venous plexus (arrowheads) on both sides at the level of the foramen ovale and over a short distance below the skull base. The perineural venous plexus (arrowheads) demonstrates the same thickness on each side of the nerve.

Fig 5.

Coronal gadolinium-enhanced T1-weighted image (TR/TE/NEX, 500/15/2) shows an incomplete perineural venous plexus within the foramen rotundum as an anatomic variant. Only small portion of the perineural venous plexus (arrowheads) is seen medial to V2 (arrows) on both sides.

Fig 6.

Coronal gadolinium-enhanced T1-weighted image (TR/TE/NEX, 400/15/2) suggests a significantly enhancing right trigeminal ganglion (right arrow). The perineural venous plexus (right arrowhead) and the trigeminal ganglion cannot be identified as separate structures. This appearance is thought to be due to obscuration of the ganglion by a more extensive perineural venous plexus than that typically seen. The subject did not have any symptoms related to trigeminal nerve or a history of malignancy. Therefore, this is considered a normal variation in imaging appearance. The contralateral side demonstrates the typical appearance of the trigeminal ganglion (left arrow) and of adjacent venous plexus (left arrowhead).

Fig 7.

Coronal gadolinium-enhanced T1-weighted image (TR/TE/NEX, 500/15/2) at the level of the foramen ovale shows a significantly enhancing V3 branch (arrow) on the left as a normal anatomic variation. The patient did not have any symptoms of V3 dysfunction. The perineural venous plexus and V3 cannot be seen as individual structures.

Fig 8.

Coronal gadolinium-enhanced T1-weighted image (TR/TE/NEX, 500/15/2) at the level of the foramen rotundum demonstrates an enhancing V2 branch on the right when compared with the left (arrows). This is considered to represent a normal anatomic variation, because the subject did not have any symptoms related to V2 dysfunction or history of malignancy. The perineural venous plexus and V2 cannot be separated from each other. This appearance might be caused by a more prominent venous plexus. On the left, the perineural venous plexus (white arrowhead) is incomplete and absent in the inferior lateral aspect. The black arrowhead indicates the bony boundary of the foramen rotundum.

Fig 9.

Coronal T1-weighted image (TR/TE/NEX, 753/14/2) through the foramen rotundum demonstrating normal appearing V2 on the left (arrow). No nerve can be visualized within the foramen rotundum on the right (arrowhead).