Trigeminal neuropathy after tooth extraction
An elderly woman presented with severe right facial pain after a recent upper molar tooth extraction.
MR of the brain with gadolinium and thin sections of the cerebellopontine angle
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Thin axial T2-weighted images of the cranial nerve V course shows no evidence for vascular compression or mass lesion, particularly on the right side. Upon contrast administration, avid enhancement of the intracranial right trigeminal nerve from its origin at the pons, at its cisternal segment, to the trigeminal ganglion and likely at the cavernous sinus is appreciated. There is also abnormal enhancement of the meninges along the right Meckel's cave. The left trigeminal nerve course shows no abnormal signal change or enhancement.
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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).
- Williams LS, et al. 2003. MR imaging of the trigeminal ganglion, nerve, and the perineural vascular plexus: normal appearance and variants with correlation to cadaver specimens. AJNR 2003 24: 1317-1323.
- Majoie CB, et al. 1995. Trigeminal neuropathy: evaluation with MR imaging. Radiographics. July 1995, Volume 15, Issue 4. DOI: http://dx.doi.org/10.1148/radiographics.15.4.7569130
- Saremi F, et al. 2005. MRI of cranial nerve enhancement. AJR 2005; 185:1487-1497. DOI: 10.2214/AJR.04.1518.
- Robert RC, Bacchetti P, Pogrel MA. 2005. Frequency of trigeminal nerve injuries following third molar removal. J Oral Maxillofac Surg. 2005 Jun;63(6):732-5