Case of trigeminal neuralgia due to venous compression by the lateral pontine vein — courtesy of Dr. Eytan Raz

Occasionally (for example a scenario of venous congestion) even venous compression can cause trigeminal neuralgia.  Of course, arterial compression is better known, but veins can be responsible also.  In this patient, a dural fistula opens directly into the petrosal vein (P); I believe this is taking place because the superior petrosal sinus, which must have originally drained the fistula, has occluded.  From the petrosal vein, the fistula drains retrogradely via the lateral pontine vein (J), also known as the vein of the pontocerebellar sulcus (Rhoton) into an inferior hemispheric cerebellar vein (X).  The fistula is primarily supplied via the artery of Bernasconi-Cassinari (BC), seen in this case via the Foramen Rotundum (FR) branch of the IMAX

Postcontrast T1 MRI of the patient with the same veins marked:

There is obvious compression of the left trigeminal root zone (yellow), which is flattened and anteriorly displaced.  Notice a tiny, physiologically normal lateral pontine vein ventral to the right of CN V on CISS and T1-postcontrast images.

Relevant diagrams are shown here:

For further reading, check out:

Mitsuhashi Y, Aurboonyawat T, Pereira VM, Geibprasert S, Toulgoat F, Ozanne A, Lasjaunias P. Dural arteriovenous fistulas draining into the petrosal vein or bridging vein of the medulla: possible homologs of spinal dural arteriovenous fistulas. Clinical article.  http://www.ncbi.nlm.nih.gov/pubmed/19425886