Trigeminal Neuralgia from an Arteriovenous Malformation of the Trigeminal Root Entry Zone with a Flow-Related Feeding Artery Aneurysm: The Role of a Combined Endovascular and “Tailored” Surgical Treatment
Correspondence Address: Source of Support: None, Conflict of Interest: None DOI: 10.4103/0028-3886.319235
Source of Support: None, Conflict of Interest: None
Keywords: Aneurysm, arteriovenous malformation, multimodality approach, root entry zone, trigeminal neuralgiaKey Messages: Multi-modal management of the AVM-related trigeminal neuralgia with associated feeding artery aneurysm by endovascular embolization of the aneurysm, MVD with tailored AVM coagulation followed by GKS to obliterate it completely is the key to successful treatment.
Trigeminal neuralgia (TN) is characterized by paroxysmal, short-lasting, lancinating bouts of pain involving one or more of the three divisions of the trigeminal nerve. Nearly 80%–90% of these patients have a vascular loop compression over the root entry zone (REZ) leading to local demyelination and ephaptic nerve transmission.,, Very rarely, arteriovenous malformations may be the underlying cause for TN.,,,,,,,,, While the majority of these AVMs are pial AVMs sitting over the REZ, AVMs entirely or partially embedded inside the trigeminal REZ are extremely rare., Flow-related feeding artery or intra-nidal aneurysms in these situations generally lead to hemorrhagic presentations or pose a risk of subarachnoid hemorrhage if not dealt with in a timely fashion. We present here a unique case of TN where the symptoms were because of a combination of the intrinsic AVM itself and the extrinsic vascular compression by the dilated anterior inferior cerebellar artery (AICA) and its feeder into the AVM nidus. The presence of a proximal aneurysm in the second feeder from the intrinsic pontine artery (IPA) also affected the management of this patient. Herein we review the mechanisms of TN in the presence of an AVM with a feeding artery aneurysm, the management implications of these associations as well as the utility of stepwise multidisciplinary management in such patients. We also highlight the role of surgical exploration and the scope for microvascular decompression with tailored AVM coagulation without resorting to complete AVM excision in relieving neuralgic pain.
A 50-year-old female patient presented with right-sided trigeminal neuralgic pain for one year. The frequency and the intensity of the pain gradually increased despite taking increasing dosages of oral carbamazepine. From the last 1 month, there was no relief in pain even with multiple drugs. No neurologic signs were observed clinically.
On MRI, multiple vascular channels were seen around cisternal part of the right trigeminal nerve [Figure 1]a The CT angiogram revealed an abnormal vessel loop (possibly a vein) and a possible nidus near the petrous apex. A feeder was seen arising from the upper basilar trunk, and an aneurysm was seen between this feeder and the basilar bifurcation [Figure 1]b. An intra-arterial angiogram confirmed the presence of an AVM with two feeders: one from an enlarged intrinsic pontine artery and another from the anterior inferior cerebellar artery (AICA). The venous drainage was through a dilated vein which was probably draining into the superior petrosal sinus. A flow-related proximal aneurysm was also noted on the transverse pontine artery near its takeoff from the basilar trunk [Figure 1]c.
We decided to go ahead with the endovascular embolization of the feeders and the aneurysm. The transverse pontine artery feeder with an aneurysm was obliterated; however, the feeders from the AICA could not be occluded [Figure 1]d. There was a significant reduction in the size of the AVM nidus.
Post-procedure, severe pain persisted in the ophthalmic division. After discussing with the patient relatives, a decision of surgical exploration was taken as the patient wanted immediate relief of pain. Intraoperatively, we found that the AVM nidus was lying on the REZ and one of the feeders from the AICA was running on the cisternal segment before entering the embedded portion of the AVM. A dilated draining vein was also seen behind the REZ draining into an enlarged superior petrosal vein [Figure 2]a. Some part of the AVM and the draining vein was shrunken using low setting bipolar coagulation to reduce distortion of the nerve. Exercising great care, Teflon sheets were interposed between the nerve and the offending vessels [Figure 2]b. We did not attempt to resect the nidus nor divide the AICA feeder diving into the nerve. Postoperatively, there was a total pain relief with no requirement of analgesics. Later she was discharged uneventfully without any neurological deficits. Because of the residual AVM nidus inside the nerve she was referred for gamma knife surgery.
At 4 years of follow-up (after undergoing GKS dosage may be mentioned 3.5 years back), she was pain-free without any medication requirements though she has minimal numbness right side of the face.
AVMs of the posterior fossa in addition to tumors are rare causes of TN, either from the pulsatile pressure of the AVM or by its feeder/draining veins.,, Although the causative role of an intrinsic trigeminal nerve AVM has not been deciphered, one report suggests a possible neuraxial distortion as the cause of symptoms, provided co-existent neurovascular compression be ruled out. The incidence of AVM causing TN is estimated to be between 0.6-1.5%.
In a literature review, Yuan et al. noted 29 studies reporting on 40 cases of AVM associated TN till 2015. 19 of them were located in the cerebellopontine angle while 7 were intrinsic trigeminal nerve AVMs. Going by the above categorization, our patient had an intrinsic trigeminal nerve AVM. Intrinsic AVMs on the trigeminal nerve are extremely rare causes for TN. Various authors have labeled these AVMs as cryptic vascular malformations or the micro-AVMs.,
Intrinsic pontine artery usually supplies the trigeminal REZ and the adjacent brainstem via its superolateral and inferolateral branches. Generally, this vessel is not seen on the routine angiogram, but it gets dilated and tortuous in high flow states like an AVM and has been documented as a common feeder in many previous reports. Previous reports have noted that superior cerebellar artery (SCA) was a far more common feeder to these AVMs than the AICA, unlike in our case.,
Our patient additionally had a feeding artery aneurysm on the IPA. Nishino et al. noted an associated aneurysm in 5 of their patients (three on the feeding artery, two intranidal), all of whom had a hemorrhagic presentation. None of their patients who presented solely with TN (n = 3) had associated aneurysms, like in our case. The associated aneurysm must be addressed adequately before the patient is subjected to the AVM treatment as the risk of aneurysm rupture continues to be there. Surgery as well as endovascular coiling, are equally good options in dealing with the associated aneurysms. The fact that the aneurysms are located in a confined space adjacent to the brainstem with many en-passage vessels nearby, either of the modalities may be technically challenging. We favored endovascular treatment for the aneurysm as well as the significant feeder to the AVM nidus and managed to deal with the problem without any adverse consequences.
The fact that our patient had some relief of pain after embolization indicates that the AVM per se may not have been the primary underlying cause of TN. It was later found during surgery also that AICA and its feeder to the residual AVM as well as the dilated draining vein were compressing the root entry zone. Yuan et al. also highlighted that associated vascular loop compressions were the actual cause of TN. This heavily favors considering the option of surgical exploration in patients with AVM associated TN mainly if the symptoms are so severe that the patients desire immediate relief.
The critical question is whether the AVM needs to be excised or not? Those who have attempted surgical excision of the AVM nidus propose it not only for pain relief but also to reduce the future risk of hemorrhage., Edwards et al. demonstrated that it was possible to completely excise the intrinsic trigeminal nerve AVMs, although Tsubaki et al. maintained that complete extirpation of the nidus was not possible without sacrificing the nerve. Nevertheless, both the series noted a high incidence of trigeminal nerve dysfunction after surgery. Surgical excision, however, may be made easier if there is hemorrhage inside the AVM, as demonstrated by Maher et al. A tailored AVM coagulation as we did has been advocated by Sumioka et al. as well. It is said to restore somewhat the alignment of an otherwise distorted trigeminal REZ harboring an embedded AVM.
Even if the pain is relieved by the above procedures, the residual AVM may grow, cause steal syndromes and may rupture in the future. Thus, it mandates some definitive treatment. GKS provides an excellent treatment alternative for the AVM per se., Even though GKS can take care of TN (in 61-96% patients), the procedure takes time for pain relief (the median latency to response is one month) and neurological impairment, particularly, facial sensory disturbances are not uncommon. Also, cases of recurrence of pain are reported (14%–25%) as well as transient brainstem signs., So, it may not be an advisable treatment option for those who seek immediate pain relief.
AVM-related trigeminal neuralgia is due to a combination of nerve distortion, a pulsatile pressure of the AVM nidus, and compression by the dilated feeders/draining veins. The presence of a feeding artery aneurysm must be viewed as a danger sign with a potential to rupture in the future and requires addressal before targeting the trigeminal REZ. Surgical exploration with microvascular decompression and tailored AVM coagulation to correct the nerve alignment represent the most effective and prompt means of pain control. Subsequent GKS is necessary to completely obliterate the AVM nidus and eliminate the root cause of the problem.
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[Figure 1], [Figure 2]