Peripheral trigeminal nerve injury as a consequence of dental surgery has been reported to range from 1 to 4 out of 1000 molar extractions. The most frequently injured nerves are the inferior alveolar (60%), followed by the lingual nerve. The imaging of post-surgical trigeminal neuropathy is not routinely performed and has not been described in the literature, as this is most often a clinical diagnosis.
The role of the radiologist is to understand the normal anatomy and enhancement pattern of the trigeminal nerve as to be able to discern any abnormal findings. The CN V intracranial portions include its brainstem nuclei, prepontine cistern, Meckel's cave and cavernous sinus segments. The extracranial segments are formed by V1, V2, and V3 which merge at the posterior cavernous sinus to form the trigeminal ganglion. On cadaveric specimens, the trigeminal ganglia towards the peripheral divisions are avascular in appearance, and commonly are symmetrically non-enhancing on contrast-enhanced MRI. An extensive perineural venous plexus obscures and gives the appearance of an enhancing trigeminal ganglion. Enhancement of skull base structures at the foramina also gives what appears to be an enhancement of adjacent V2 and V3 nerves. Suboptimal MR imaging parameters on top of avid venous plexus or skull base enhancement also contribute to this apparent contrast uptake. Also, trigeminal nerve enhancement without foraminal changes or nerve enlargement would point more towards a normal variant.
On the other hand, a true neuritis could produce isolated or unilateral nerve enhancement on all MR planes. Once all the possibilities of an artifactual cause of enhancement have been removed, an actual abnormality cannot be discounted when coupled with strong clinical suspicion.
Trigeminal nerve neuropathy may involve its full course. Extracranially, malignancies that produce perineural tumor spread are the most common extracranial causes. The most common intracranial causes can be discerned based on the location of abnormality (e.g. multiple sclerosis for brainstem, neurovascular compression at the cisterns, or tumors at the Meckel's cave and cavernous sinus).