Resolution of Trigeminal Neuralgia Following Cerebellar AVM Embolization With Onyx

Abstract

Intracranial arteriovenous malformation (AVM) is a rare cause of trigeminal neuralgia (TN). Successful resolution of AVM-related TN following embolization surgery using Onyx has not been reported. In this case report, a posterior fossa AVM was embolized in two separate, staged endovascular surgeries using Onyx. The AVM was reduced in size, and the TN resolved. The patient subsequently underwent radiosurgery for the small, residual AVM, and he has maintained an uneventful follow-up. A thorough literature review was also performed for AVM-associated TN. Fifty-nine reports of AVM-related TN have been described to date, of which only three were treated with embosurgery. None of the prior two embosurgical reports utilized Onyx, and no AVM was obliterated with embosurgery alone. TN secondary to AVM can be resolved with embosurgery utilizing Onyx; however, complete elimination of the underlying AVM requires adjuvant surgery.

Trigeminal neuralgia (TN) is an infrequent but important cause of facial pain, having an incidence of 4.7/100 000 (1). Although a large percentage of patients have no discernable cause for their TN, some signal underlying neoplasia or trigeminal nerve compression by an ectatic basilar or superior cerebellar artery. An underlying arteriovenous malformation (AVM) is rarely identified as the cause of TN. In cases with AVM-related TN, successful management requires invasive surgical AVM extirpation or less commonly reported stereotactic irradiation (radiosurgery) (2, 3). Endovascular embolization (embosurgery) offers the patient a third option, usually as an adjuvant treatment to reduce the AVM size prior to craniotomy or radiosurgery. Improving rates of success in obliterating cerebral AVMs with embosurgery using cohesive Onyx glue have recently been reported (4). As regards AVM-related TN, however, only two prior reports exist for embosurgery (5, 6). Of these, one was successful in eliminating the TN, which occurred with the use of embolic coils. The current report details the first case of AVM-related TN resolved with endovascular injection of Onyx.

Case report

A 55-year-old White man presented with a 6-month history of severe right-sided jaw pain for which he had originally sought care from his dentist. Having found no underlying cause of the symptoms, and telling the patient that he suspected TN, the dentist referred the patient to a neurologist. A more detailed history revealed that the patient complained of sudden attacks of severe, lancinating and slightly throbbing pain in the third trigeminal division, arising from the right base of the tongue, running along the inside of the mouth at the lower gum line. These paroxysms lasted 20 s at a time and had increased in frequency from twice a week to the current three or four times a day. The patient himself noticed that the attacks occurred only when he moved his tongue, especially while talking or singing. He also experienced intermittent episodes of occasional numbness and a burning sensation at the right corner of his mouth. He was never awakened from sleep by the pain. The patient was neurologically intact on physical examination. He was prescribed gabapentin but he never filled the prescription. Magnetic resonance imaging and angiography of the brain were ordered. The images showed a right cerebellar AVM, subsequently confirmed by catheter angiography. Altogether, the studies indicated that the cisternal segment of the right trigeminal nerve was squeezed between an enlarged right superior cerebellar artery and a vein that drained a 3.8-cm posterior fossa AVM (Figs 1, 2). The patient elected to have embosurgery. This was performed in two staged procedures that were performed 19 days apart. Both surgeries entailed endoarterial, microvascular exploration of the vertebrobasilar vasculature in conjunction with a total volume injection of 5.4 ml ethylene vinyl alcohol copolymer (Onyx; Micro Therapeutics, Irvine, CA, USA) into five pedicles of the right posteroinferior cerebellar artery and two pedicles of the right superior cerebellar artery (Fig. 3). The nidus was reduced to < 2 cm, but no further embolization could be safely done without significant risk of infarction to the rhombencephalon. Postoperatively, the patient had no neurological deficits, but complained of initial worsening of his right facial pain that soon improved and completely resolved over 4 months. He remained pain free for > 1 month prior to undergoing radiosurgery 6.5 months after his second embosurgery. Three months after radiosurgery, he denied any new complaints and continued to enjoy freedom from pain.

Figure 1

Baseline lateral right vertebral angiogram. The arterial phase (A) demonstrates an enlarged right superior cerebellar artery (arrow) coursing downward into the vicinity of cisternal portion of the trigeminal nerve. Note the posterior fossa arteriovenous malformation, which is supplied by several branches of the posteroinferior and superior cerebellar arteries. On the venous phase (B), several sizable draining veins converge adjacent to the cisternal trigeminal nerve.

Figure 2

Magnetic resonance angiography source images, before (A), 3.5 months after embosurgery (B), and 3 months following radiosurgery (10 months after embosurgery) (C). Note the decreasing sizes of both the enlarged superior cerebellar artery (arrowhead) and the laterally located draining vein (arrow) following embosurgery (B) and adjuvant radiosurgery (C). The cisternal segment of the right fifth cranial nerve can be faintly seen coursing between these two vessels.

Figure 3

Frontal (A) and lateral (B) skull radiographs following embosurgery show the radiodense Onyx glue within the cerebellar arteriovenous malformation.

Discussion

TN affects approximately 1 million people worldwide, while women outnumber men by a 3 : 2 ratio. TN results from irritation of, or compression upon the fifth cranial nerve, and is classified as either classical or symptomatic (7). Although classical and symptomatic TN presents with identical symptoms, namely unilateral, paroxysmal attacks of pain lasting from a fraction of a second to 2 min and affecting one or more divisions of the trigeminal nerve, these TN subtypes differ by underlying cause. Specifically, whereas classical TN is often due to compression of the fifth cranial nerve by an adjacent vessel (usually the superior cerebellar artery), the source of symptomatic TN is from any causative lesion other than vascular compression. Consequently, cross-sectional imaging should be performed to exclude a structural mass lesion as the cause in any patient who presents with TN. In the current case report, the patient technically had classical TN because of the vascular compression upon the trigeminal nerve by the AVM's feeding vessel and draining vein. However, not categorizing this patient with symptomatic TN is somewhat tenuous, since ultimately the causative reason for the enlarged vessels is an adjacent AVM. Any future revisions to the classification criteria of classical and symptomatic TN should clarify this dilemma.

A variety of treatment options are available for TN. Pharmacological intervention remains the first line of therapy, especially anticonvulsants such as carbamazepine derivatives. Gabapentin and baclofen may also provide adequate pain relief, although patients may seek invasive treatment owing to intolerable medication side-effects or because the neuralgia becomes recalcitrant to therapy.

The surgeon can approach primary TN in several ways. Trigeminal tractotomy and retrogasserian neurotomy have fallen out of favour in response to lesser invasive surgical methods including stereotactic radiosurgery and percutaneous trigeminal rhizotomy (PTR). PTR utilizes balloon compression, radiofrequency ablation or glycerol injection of the trigeminal nerve, offering satisfactory or complete long-term pain relief in 75% of patients, whereas stereotactic radiosurgery completely relieves neuralgia in 58% of patients at 2 years (8). Craniotomy with microsurgical vascular decompression of the trigeminal nerve root perhaps remains the gold standard with immediate and long-term success rates exceeding 92% and 80%, respectively (9).

In a review of mass lesions including congenital Chiari-1 malformations that cause TN, Papanastassiou et al. found that 0.8–5.7% of patients with TN signal neoplasms that directly affect the trigeminal nerve (10). Aside from trigeminal nerve involvement by intracranial or skull base neoplasia, post-herpetic neuralgia, multiple sclerosis, aneurysms, cysts, or ectatic but otherwise normal posterior fossa vasculature, other causes of TN remain infrequent. An important but uncommon cause of TN includes the vascular malformation subtypes. With the exception of capillary telangiectasia, TN has been found in conjunction with neighbouring vascular malformations including cavernous haemangioma or cavernous malformation (cavernoma), venous developmental anomaly (venous angioma), dural arteriovenous fistula (AVF) and AVM (11–13). Cavernomas, AVM and AVF comprise an overwhelming majority of the reported cases of TN in this category. Reviewing the past 75 years' worth of published data in the English literature, only 59 patients including the current case study have been cited with pure AVM-associated TN (2, 3, 5, 6, 14–41). These 59 patients represent a greater number than that preliminarily described in a recent literature review (42).

In reviewing past reports, accurate terminology is at times problematic, in that the term AVM is not uniformly applied. Some terms possibly misconstrued for an AVM have been found, including ‘vascular malformation’, ‘angioma’ and ‘cavernous angioma’. In Dandy's 1934 report of five patients with cavernous angiomas and TN, it is inferred that these patients had cavernous malformations, not AVMs (43). Taarnhoj mentioned in his operative series of 350 patients with TN that five patients had an underlying angioma (44). Since details of the exact pathology were not provided, these patients are not included in the current report's summary. On the other hand, the term ‘arteriovenous aneurysm’ was used to describe AVM and AVF in some of the earlier reports of the mid 1900s. If the descriptions or images were consistent with AVM, then they were included in this review. Buettner reports TN as being caused by ‘malformations’ that are in fact non-AVM vascular variants including vascular ‘loops’, basilar ‘elongation’ or ectasia, and hypertension-related ‘coiling of the distal vertebral and basilar arteries’ (45). Also, an erroneously increased number of patients with AVM-related TN was encountered during the literature search given the practice of duplicating patient case reports of AVM-related TN in more than one article, or inaccurately referring to prior reports of AVM-related TN that in fact did not exist or were reported by the referenced author in a different manuscript (27, 21, 46, 47). The latter was frequently encountered in references to Olivecrona's 1949 article regarding cerebellopontine angle cholesteatomas, in which he mentions that ‘arteriovenous aneurysms’ could present with TN (48). He rightly states this because a year earlier in 1948, Olivecrona and Riives did report the first case of AVM-related TN in their large series of AVM patients (34).

AVF may masquerade as an AVM during surgery. In the study of Tsubaki et al., there were five TN patients with histologically proven microscopic AVM and three TN patients with medium to large AVMs, but the other two TN patients with observed arterialized petrous veins probably harboured dural AVF and not AVM—an argument supported by Edwards et al. (3, 40). Verbiest cited one patient with TN due to a mixed dural AVF and pial AVM; this patient is unique in the literature and is not included in the current report's summary of the pure AVM-related TN cases (49).

Several of the historically reported AVMs eluded preoperative diagnosis by either cross-sectional imaging or angiography, but at craniotomy were generally found to be cryptic or microscopic, and intimately involved with the fifth cranial nerve. Overall, TN heralds an underlying intracranial AVM 0.22–1.8% of the time, whereas in published series of patients with posterior fossa AVM, the incidence of TN is 3.1–9.8% (20, 29, 35).

Treatment considerations may be less straightforward in patients with AVM-related TN than in patients who present with either classical TN or asymptomatic AVM alone. The decision to obliterate an intact AVM completely, as opposed to simply intervening enough to relieve the AVM-related TN, depends upon numerous factors including patient age, Spetzler–Martin AVM grade and medical comorbidities. In unruptured but large AVMs, reducing the size of the feeding pedicles may resolve the TN, as illustrated in this case report. Although obliteration of the AVM will jointly eliminate the TN and also remove the potential risk of future debilitating or fatal AVM haemorrhage, the surgical risk of complications should be weighed against the likelihood of complete AVM cure. Onyx glue offers controlled embolization with deep penetration of the nidus that if not obliterated, may be reduced sufficiently in size to allow radiosurgery or an otherwise less complicated surgical extirpation.

Conclusions

TN secondary to AVM can be resolved with embosurgery utilizing Onyx. Complete elimination of the underlying AVM requires adjuvant extirpative surgery or radiosurgery.