The diagnosis of classical TN was made through patients records according to the International Headache Society, whether the neuralgia was purely paroxysmal (typical TN) or with concomitant continuous pain (atypical TN). All patients who underwent posterior fossa exploration have at least 2 years of proved refractory to or intolerance to of the usual medical therapies for TN such as carbamazepine, phenytoin, baclofen, gabapentin or other drugs used either alone or in various combinations and sent to us for the neurologist after failed medical treatment. We prefer to operate the patients in phase of trigeminal pain attacks, avoiding surgery in periods of remission. The senior author (EU) has operated at the Donostia University Hospital and Policlinica Gipuzkoa on 52 patients for primary trigeminal neuralgia by microsurgical suboccipital exploration as described by Jannetta11 and Sindou.12 All patients underwent preoperative CT Scan and magnetic resonance imaging (MRI). In 42 patients we found an artery as the major offending vessel, specially the superior cerebellar artery. During the surgical exploration, venous contact without arterial compression was noted in 8 (15.38%) cases and no offending vessel in 2, all of them were included in this study.

This is a retrospective analysis of the 10 consecutive patients without a visible microsurgical trigeminal arterial contact in which we applied the technique of trigeminal root arachnoidal liberation, venous cut and divided if needed, and massage without interposition of any implant material.

The clinical characteristics of the patients are summarized in Table 1. No patient had multiple sclerosis.

Basically we performed microsurgical exploration of the trigeminal root in two different positions: semisitting and supine with the affected side up, shoulder elevation, head rotation to the opposite side and chin flexed. Sometimes we used intraoperative neuromonitoring: facial nerve electromyography and brainstem auditory evoked potentials (Fig. 1A). We utilize the conventional retrosigmoid approach described by Jannetta13 and Samii, with some personal modifications. A linear or slightly curved skin incision extending superiorly 2cm behind the pinna, passing through the asterion and terminating 2cm medial to the mastoid tip. Mannitol is administered intravenously at the time of the skin incision. The burr hole is made in the asterion, and then a 2–3-cm retromastoid craniectomy or sometimes craniotomy toward the transvers and sigmoid sinus and the squamous part of the occipital bone. A high-speed diamond drill is used to expose the borders of the transvers sinus, the superolateral corner of the transverse-sigmoid sinuses, and the sigmoid sinus. Bone wax is used to pack the mastoid air cells and the emissary vein. The dura is opened under magnification using an operating microscope in a C-shape, some millimeters medially along the transverse and sigmoid sinus, followed by opening the cerebellomedulary cistern; CSF is withdrawn until cerebellar relaxation is achieved. Through the supracerebellar-infratentorial route we reach the petrotentorial corner to gain access to the trigeminal root entry zone (TREZ). During the approach we try to preserve the superficial petrosal vein, but it was coagulated and divided when it clearly participates in compressive neurocontact or when it riskily obstructs the lane to widen exposure to the trigeminal root. The arachnoid overlying the superior pontocerebellar cistern was fully opened, the fifth nerve was exposed, the vein was coagulated and divided; finishing the operation applying a slight gentle intermittent compressive massage along the length of the trigeminal root with the microforceps or the microdissector, which we call trigeminal root massage (TRM), without interposing any material (Fig. 1). As important as the surgical opening and microsurgical procedure, an exquisite closure technique to avoid postoperative complications is mandatory. Hemostasis is achieved with the utmost care. At the end of the procedure, jugular vein compression is performed by the anesthesiologist to search for possible venous bleeding and to confirm a clean surgical field. The dura is closed in a watertight fashion with sutures and epidural sealant. The mastoid cells are covered with muscle and fibrin glue. Cranioplasty is performed with the bone chips taken from the craniectomy and mixed with fibrin glue molding it to the cranial contour. The neck muscles are sutured back, respecting the anatomical layers. No drains are used. A compressive bandage is used after the skin closure. We routinely perform a postoperative CT scan during the day after surgery on all patients operated on cerebellopontine angle, independently of its type, and emergently when recovery from anesthesia was delayed or when the patient's condition deteriorated.

Fig. 1.

Case 6. Patient position and intraoperative neuromonitoring. Different steps microsurgery technique. Leyends (more description) in the text.

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The two principal intraoperative findings in this series of ten patients without arterial contact were venous or/and thick arachnoid adhesions involved in root compression. We have adopted the Sindou classifications for both the petrosal venous systems and the degrees of compression to the trigeminal root: grade I is a simple but clear contact, grade II for displacement or distorsion, and grade III in cases of marked grooving in the root with a more or less focal demyelination under the form of a grayish aspect.14

8 of our cases had a pure venous conflict, one of grade III, 3 grade II and 4 grade I. We found conflicting veins either of the superficial superior petrosal vein system (sSPVS) in 7 cases and/or of the deep superior petrosal vein system (dSPVS) in three cases. Only in 2 patients we found no clear vascular contact and, after arachnoid decompression, we finished surgery with TRM in both cases (Fig. 2).

Fig. 2.

Case 7. Intraoperative photographs in a patient without any vascular contact. (A) The entire course of the cisternal TR is exposed after arachnoidal resection. (B) Final trigeminal root massage was used with microdissector.

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5 cases presented with thick arachnoidal membrane, more or less adherent to the V nerve, 4 cases with some compressive veins that we coagulated and then cut. As in our case 1: After thick arachnoidal section we expose a venous grade III TR compression, which was coagulated and divided, observing finally the trigeminal indentation as a collar around the TR and its grayish color (Fig. 3).

Fig. 3.

Case 1. Patient in semisitting position. (A) Photograph showing a thick arachnoidal adhesions (Arach. Adh.) covering the V nerve and compressive grade III deep superior petrosal venous system (dSPVS). r: retractor. (B and C) dSPVS veins coagulation. (D) Indentation of the V nerve with grayish color. E and F: final trigeminal root massage with microdissector.

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Sometimes we can find a prominent suprameatal petrous bone obscuring the vision of the porus trigemini. This part of the petrous bone was called suprameatal tubercle by Rhoton,15 which blocks the view of the Meckel's segment of the trigeminal root, and can be drilled away if needed to enlarge access to this part of the nerve, which increases the surgeon's work space.16 As in our case 10, in which during the exploration of the TR, a big prominence of the suprameatal tubercle obscure the direct vision of the distal portion of the TR, deciding to drill away to see the root entrance in Meckel cave and entirely expose the TR, a dSPVS grade II compressing the nerve was observed, and finally coagulated and divided to free the root, finishing with TRM without interposition of any material (Fig. 4).

Fig. 4.

Case 10. A big tubercle prominence was found (arrow) and drilled away (B and C) to expose a dPVS compressing the V nerve. (E) Coagulation and cutting the vein. (F) Gentle intermittent trigeminal root massage with the microforceps.

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Trigeminal root massage is not an alternative to microvascular decompression, it is just a complementary and simple maneuver during microsurgical exploration of the trigeminal root without a clear neurovascular compromise, avoiding other options such as partial sensory rhizotomy or more complicated and time consuming like nerve combing. When arterial compression is not evident during microsurgical exploration of the trigeminal root in the superior cerebellar-pontine cistern, the neurosurgeon is in an engaged situation, because there are not well-established surgical strategies. To improve the operative outcomes in these cases, some authors have tried to refine the operative techniques and paid great attention to patient selection for MVD.32,34 We use trigeminal root massage as the final step of the decompressive exploration of the TR only in cases without arterial contact and after trigeminal root liberation from the adhesive arachnoidal and/or venous compression.

MR imaging is useful in evaluating neurovascular conflict of the trigeminal nerve at the REZ and helpful as a preoperative tool when trigeminal neuralgia is diagnosed by patients’ records. During the last years, high-resolution MRI techniques and different sequences as 3D-T2, 3D-TOF and 3D-T1 with gadolinium, have been developed to detect the offending vessel(s) in patients with neurovascular compression and trigeminal neuralgia.35 This is important preoperative information for better selection of patients for arterial MVD, but not in most cases of venous contact or with simple arachnoid adhesions in which the MRI cannot detect a clear neurovascular contact, these symptomatic patients can also benefit from trigeminal nerve microsurgical exploration. Even more, the absence of vascular compression in patients with trigeminal neuralgia has been described in the literature and the existence of cases without vascular conflict, which were cured after MVD complicated the dilemma. On the other hand, vascular compression of the trigeminal nerve is a frequent anatomical variant and MRI finding in people with no symptoms of trigeminal neuralgia.36–38 That is why we think that based only on MRI images, this is not enough to decide surgical indication for MVD, because trigeminal neuralgia is a clinical diagnosis that does not depend exclusively on the presence of imaging of neurovascular conflict. According to Rasche et al.,29 the decision for microvascular decompression operation is still based on clinical findings and not on neuroradiological findings.

How to deal with the TN patients without trigeminal root arterial compression or with venous neurovascular conflict is a challenge for all neurosurgeons. There are some surgical options depending on the operative findings. The most simple is a wide opening of the arachnoid adhesions to free the root, in some cases very adherent to the TR. But if a trigeminal root venous compression exists, the indication and management for these veins is still controversial. The decision to coagulate and cut the vein/s is risky; nevertheless it is an alternative choice for venous cases.32

Rogelio Revuelta et al.,7 described his technique in 3 steps: first, a meticulous dissection of the arachnoid to expose the entire trigeminal root, followed by slight compression (neuroapraxia) with bipolar tips on the trigeminal REZ (second step), and finally, the third step was the isolation of the TR with fragments of Teflon. Such a technique has been used by other authors.34 Our TRM procedure is similar: after arachnoid trigeminal liberation and compressive vein coagulation and section, we apply a slight gentle intermittent compressive massage along the length of the trigeminal root three or four times with the microforceps or the microdissector, but we ended up with the second step, after the final root massage, without interposing any material implant.

Partial sensory rhizotomy (PSR) is a classical alternative technique used in absence of arterial contact.9,39 The outcome of PSR reported by Young and Wilkins was excellent in 48% of patients, good in 22% and poor in 30%, and the failure rate was 17% for the 1st year.39 Sensory loss is an inevitable and irreversible side effect after PSR and it has been reported to a lesser degree of patient satisfaction.1

Another option is nerve combing, also called internal neurolysis, is a procedure in which all or portions of the trigeminal nerve are divided longitudinally by microneedle along its fibers into several fascicles between the pons and the porus trigemini.10,40 Postoperative numbness and facial hypoesthesia is consubstantial with the combing technique, carries the risk of anesthesia dolorosa and the rate of dysesthesias or deafferentation pain is 16%.10,40 Comparing to these techniques, we have no case of postoperative anesthesia dolorosa whatsoever.

Based on the proposed mechanisms of production of trigeminal neuralgia related to the compression of the sensitive trigeminal root of the 5th nerve in its intracranial route, non-destructive open surgical techniques have historically been directed toward a decompression of the trigeminal nerve at some point in its intracranial trajectory. In 1955, Shelden et al.,41 advised that the common denominator to all procedures is operative trauma, introducing a new technique such as pressing with a blunt dissector the portio major nerve fibers of the trigeminal nerve surgically exposed through a middle cranial fossa approach, suggesting that the compression of the trigeminal fibers during the operation is the factor that relieves the pain. Jannetta using microneurosurgical techniques, considers that vascular compression of the trigeminal root is the principle cause of TN, expanded the concept of this neurovascular compression theory, popularizing the MVD operation procedure.11 Since then, some authors, skeptical and critical of the microvascular decompression procedure, started a controversial discussion and hypothesis about the mechanisms of trigeminal pain disappearance after the MVD operation and suggests an alternative view as surgical trauma.8,42

Without getting into sterile controversies and in these cases without a clear arterial TR compression, and always after a careful trigeminal root liberation from the adhesive arachnoidal and/or venous compromise, we used the final maneuver of gentle TR intermittent compression called massage for some reasons. Mainly because after surgery the trigeminal pain immediately disappears and we considered that a little microsurgical manipulation of the TR can have an effect for initial pain disappearance, while the TR arachnoidal and venous decompression can influence in maintaining long term pain relief. TRM avoids the definitive and irreversible trigeminal nerve side effects such as facial sensory loss produced by other techniques such as rhizotomy. And finally, because it allows other types of surgery if there is pain recurrence.

In summary, whatever mechanism makes the trigeminal neuralgia disappear, one of the best moments for the patient and for the neurosurgeon is when the patient awakes from the anesthesia without trigeminal pain and free of symptoms: that is the most satisfactory moment after MVD and TRM, which we always try to achieve in cases without TR arterial compression. But also we always take into consideration in the patient's satisfaction and the final results throughout the next few years, because we know that only 60% of our cases have excellent results after a average follow-up of 5 years: which means that there are no perfect surgical techniques at the moment for permanent cure of trigeminal neuralgia without arterial compression.