Trigeminal Neuralgia (TN) is defined as a shooting pain in the distribution of the trigeminal nerve.
Diagnosis of Trigeminal Neuralgia
Trigeminal neuralgia, a painful condition of the face, is characterized by stereotypic symptoms and (absence of) signs that usually allow its clinical diagnosis. The average age of onset is around 50 years. Pain is in the distribution of one or more divisions of the trigeminal nerve and is labeled as V1, V2 or V3 neuralgia (Fig. 1).
The pain is lancinating and described as “shock like”, “bolt out of the blue”, “shooting pain” etc. It is brief in duration, lasting for few seconds to couple of minutes. In a typical trigeminal neuralgia, the patient is pain free between the attacks. The pain is precipitated by triggers. These include simple actions like brushing the teeth, washing face, mere touch or even a breeze of air. During the acute attacks, the pain is severe enough to compromise hygiene or diet. In some patients the pain is so excruciating that they start considering the idea of suicide. In a typical case of trigeminal neuralgia, the disease is characterized by remissions with or without medical treatment. The period of remission is variable and after a few years of disease the remissions do not occur. Patients with trigeminal neuralgia should not have neurological deficits, and if such is present a CT scan or MRI should be carried out to rule out other pathology. CT/MRI should also be performed if the pain is atypical. 1% of patients with multiple sclerosis (MS) develop trigeminal neuralgia and 3% of trigeminal neuralgia patients suffer from MS.
Pathological changes in Trigeminal Neuralgia
In patients suffering from trigeminal neuralgia there is extreme hypermyelination, demyelination, and tortuousity of hypertrophied axons. Kerr observed that the myelin disintegration is far more pronounced in the patients with trigeminal neuralgia than normal patients. These changes are noted at the level of peripheral branches of trigeminal nerve, gasserian ganglion and trigeminal rootlets and also in descending spinal trigeminal tract. Though the cause of this is not known vascular compression of the trigeminal rootlets by either artery or veins at the level of the root entry zone is put forward as one of the cause.
Radiology in Trigeminal Neuralgia:
In patients with typical trigeminal neuralgia, radiological investigations are not necessary. However, when performed, MRI (Cis images) may reveal vascular loop adjacent to the trigeminal nerve root entry zone on the affected side. However, this is not a diagnostic finding for trigeminal neuralgia, as in many cases patients suffer from trigeminal neuralgia even in the absence of the vascular loop. In patients desirous of undergoing Microvascular decompression, demonstration of the loop increases the chance of success.
There are several websites focusing on medical treatment of trigeminal neuralgia. As a result, we will focus on the surgical treatment available at our centre.
Role of peripheral Neurectomies
The common practice of peripheral neurectomies of mandibular and maxillary of the trigeminal nerve is highly discouraged. Peripheral neurectomies carry a high rate of recurrence. Beside , they also have a very high incidence of causing deafferentation pain which is one of the worst pain to manage ,requiring aggressive therapies like gasserian ganglion stimulation or motor cortex stimulation. The only place a peripheral neurectomy should be performed is in a case of V1 neuralgia as other therapies have higher incidence of side effect.
The two most common form of surgical treatments are :
Microvascular Decompression MVD
Peter Janetta was the pioneer to popularize this surgery. He postulated that the constant pulsations transmitted by a vascular loop overlying or underlying the trigeminal root entry zone results in demyelination.However , this is highly controversial as in one paper Janetta noted that in cadaver dissection of patients who never suffered from TN there was no vascular compression , but the same group later on published an incidence of 35% of vascular compression in asymptomatic patients. The MVD surgery involves posterior fossa exploration through a small opening next to the mastoid process. Under magnification, the offending vascular loop is dissected free of the root entry zone and a Teflon graft is interposed. It has been found that in patients in whom arterial compression is identified the recurrence rate is 30% but in those patients where the conflict was either venous or none , the recurrence rate was high as 70%. The side effects of this surgery include damage to 7th and 8th nerve, and other complications like CSF leak, infection, haematoma etc (Table 1).
Radiofrequency thermocoagulation RFTC
Radiofrequency rhizotomy is based on temperature dependent selective destruction of pain transmitting C fibres whiles sparing the A-delta fibres. We recommend RFTC for most patients undergoing their first surgical treatment for typical trigeminal neuralgia, trigeminal neuralgia in multiple sclerosis and patients who have failed Mircovascular decompression. This is a day care procedure. Preoperative workup involves evaluation for fitness to undergo short general anaesthesia. Patient is explained the procedure in detail and what to expect during the procedure so as to ensure adequate cooperation. The procedure involves retrogasserian needle placement by percutaneous technique. Needle is introduced through a point 2.5 cm lateral to the angle of the mouth on side of the lesion. It is passed medial to the mandible and aimed in the direction of the petrous bone and clivus junction, seen on lateral fluoroscopic view (Fig. 2). Medial part of the foramen ovale is entered. Oblique view localizing the foramen is useful in case of difficult penetration (Fig. 3).
Once the needle is in position, the appropriate trigeminal division is stimulated using the current from the radiofrequency lesion generator (Fig. 4). Patient typically experiences paraesthesia in the territory of his pain. In case he does not feel the paraesthesia in the desired territory, the needle position is adjusted. Once the distribution of the paraesthesia is confirmed a short general anaesthetic is administered and the division is lesioned using 70oC current for 60 sec (Fig. 5). The patient is woken up while the needle is still in place. He is asked to check if he has got adequate pain relief. This procedure is suitable for the second and third division trigeminal neuralgia. For the first division trigeminal neuralgia supraorbital block and if successful followed by supraorbital neurectomy.
Results of RFTC
We have been performing RFTC for last 15 years . We have compared our results with those published in the literature (Table 2).
Treatment of Trigeminal Neuropathy
Gasserian Ganglion Stimulation
Patients with pain secondary to the damaged nerve or ganglion as occurs after some poorly performed surgery for trigeminal neuralgia or in cases of nerve infiltration by tumors, experience burning or nagging pain in the distribution of the trigeminal nerve. This is known as trigeminal neuropathy. Neuromodulation of gasserian ganglion stimulation or motor cortex stimulation is the only sensible alternative for treating this pain if the medical treatment fails. This involves implantation of the electrode at the target site and delivering current to the target nerve or cortex through a pacemaker.It is presumed that this will either increase their pain threshold or block the painful impulses from the periphery to relieve pain. This is a highly advanced form of treatment available at only select centres like Jaslok Hospital.