Complications of Various Treatment Options for Trigeminal Neuralgia

Highlights

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Complications after treatment of trigeminal neuralgias are rare, but they are debilitating when they occur.
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Facial numbness and masseter weakness are common complications after all treatment modalities.
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Stereotactic radiosurgery is least invasive and is associated with fewer complications but with higher recurrence rates.
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Microvascular decompression is invasive but is associated with fewer complications and higher success rates.

Introduction

Trigeminal neuralgia (TN) is a chronic debilitating disease characterized by paroxysmal lancinating pain along the distribution of trigeminal nerve. Compression at the root entry zone (REZ) of the trigeminal nerve is the most common proposed pathogenesis, but a definite compression may not be found in a large subset of patients. Historically, section of the nerve at the extracranial location was the most commonly practiced method to alleviate the pain, but it was associated with complete loss of nerve function. Over the years, multiple treatment methods have evolved, including various percutaneous ablation methods [retrogasserian glycerol rhizotomy (RGR), balloon compression rhizotomy (BCR), radiofrequency rhizotomy (RFR)], stereotactic radiosurgery (SRS), and microvascular decompression (MVD). All the treatment methods have been compared with one another and have their own merits and demerits. Ablation methods are less invasive, but the overall efficacy depends on the size of the lesion created during the ablation procedure; therefore adequate pain relief is associated with a greater degree of facial numbness and keratitis. SRS is least invasive but requires a longer time for pain relief and is associated with a higher recurrence rate. MVD relieves the compression at the REZ and hence is associated with immediate pain relief; therefore it is considered the most effective and gold standard modality. However, it requires a craniotomy and general anesthesia with the associated risks and complications. Recently, less invasive methods have been developed, including endoscope-assisted MVD, which requires a small burr hole for the whole procedure; however, it is still associated with the complications related to microsurgery itself.

Complications After Treatment of Trigeminal Neuralgia

The complication profiles for each procedure are different and are related to the approach and technical details. However, few complications are common for each procedure and are better discussed collectively and comparatively.

Complications Common to Each Treatment Method

The trigeminal nerve is a mixed nerve carrying both sensory and motor nerve fibers. The sensory nerve fibers include pathways carrying pain as well as touch and proprioception. The mechanism of pain relief in all the treatment modalities except MVD involves the manipulation of the nerve conduction by producing lesions to ablate the pain pathway using different methods. Therefore all these methods are expected to produce some degree of nerve dysfunction that involves not only pain pathway but also other sensory and motor function. MVD essentially relieves the compression at the REZ by separating the offending artery or vein from the trigeminal nerve. Direct manipulation of the nerve is usually avoided, though many surgeons prefer some degree of nerve massaging for optimal pain relief. Therefore the incidence of nerve dysfunction is much less with MVD.

Sensory Dysfunction

The rates of postoperative dysesthesia are mostly comparable among the three percutaneous ablation methods. The rate of dysesthesia after BCR ranges from 1.5% to 19% and is related to the compression time. Similar rates have been reported after RFR (1%–15.2%). Facial numbness is considered as a predictor of pain relief after RGR, and some degree of sensory loss is always expected for an adequate pain relief. Most of the series have reported dysesthesia in the range of 1% to 11.7% ; however, a few series have reported much higher rates (49%–53%). Corneal hypoesthesia is a common complication after RFR because the V1 segment is mostly targeted during the ablation. Corneal complications can occur in 1% to 20% of patients after RFR. Though similar rates are observed after RGR (0%–16%), this complication is particularly rare after BCR (nearly 0%). This is due to the observation that balloon compression selectively spares the small fibers carrying the corneal reflex. Pain over the area of numbness, also called anesthesia dolorosa, is fairly common after RFR. In a series of 1600 patients of TN treated by RFR by Kanpolat et al., this was the most common complication encountered, occurring in as many as 12% of cases. However, anesthesia dolorosa is rare after RGR (0%–5%) and BCR (0%–0.6%).

Sensory dysfunction is the most common complication after SRS and is related to the radiation dose and location of the isocenter. The rates of sensory dysfunction range from 6% to 42% among most of the series. A higher radiation dose is thought to be associated with higher rates of sensory dysfunction. In a study by Pollock et al., sensory dysfunction was noted in more than half of the patients who received 90 Gy, which dropped to 15% in patients receiving 70 Gy. Similarly, facial numbness is more common when the target is closer to the brainstem. In a study by Xu et al., the rate of facial numbness in patients with a proximal target was significantly higher (53%) than in those with distal targets (25%). Postoperative anesthesia dolorosa is rare after SRS and reported only in less than 1% of cases. MVD is associated with the least incidence of facial numbness. In the largest series of 1204 patients by Barker et al., only 11 (0.01%) patients developed severe facial numbness after first surgery ; however, there was an increase in rate to 0.08% (11 of 132 patients) in patients undergoing reoperation. In a recent study, Theodros et al. reported facial numbness in up to 1% of their surgically treated patients.

Motor Dysfunction

The most common motor dysfunctions after treatment of TNs are diplopia and masseter weakness. Diplopia occurs in 0% to 3% of patients after BCR, which is a little higher than for RFR (0%–0.8%). Similarly, the rates of masseter weakness are higher after BCR and RFR, ranging from 3% to 29% and 6.2% to 33%, respectively. In a prospective study of 105 patients, the rate of mandibular weakness was as high as 50% after BCR. RGR is thought to be associated with less motor nerve dysfunction, with rates of diplopia and masseter nerve dysfunction being 0% to 0.2% and 0% to 4%, respectively. Motor weakness after SRS or MVD is extremely rare and has been reported in less than 1% of cases.

Complications Specific to Each Treatment Method

Percutaneous Ablation Procedures

The percutaneous procedures are associated with complications inherent to their techniques. The usual site of access in all three type of percutaneous procedures is the foramen ovale, which is surrounded by important neurovascular structures. All the access methods are landmark based and are relatively blind; therefore they can be associated with disastrous complications. Puncture of the internal carotid artery in the neck or in the skull base can lead to neck hematoma or internal carotid artery dissection. Similarly, inadvertent puncture of the jugular foramen, which lies just posterolateral to foramen ovale, can lead to venous bleeding and cranial nerve palsies. Other possible complications are reactivation of herpes labialis, subdural hematoma (venous injury), occlusion of cavernous sinus, ocular motor nerve palsies (cannulation of superior orbital fissure or nerve injury at the ganglion), optic nerve injury leading to blindness, and brainstem injury. Sudden cardiac arrest may occur during engagement of foramen ovale and has been reported in two patients. Meningitis is another serious complication after percutaneous accesses and has been reported in up to 6% of cases in some series. Mortality during the procedure is rare and has been reported in only two cases of BCR. One patient developed hemorrhage after puncture of the arteriovenous fistula, and the other developed brainstem hematoma.

Stereotactic Radiosurgery

SRS is one of the safest treatment options for TN. Acute complications apart from frame-related complications are rare and mostly due to the immediate effect of radiation on the brainstem. Higher doses on the brainstem may produce brainstem edema, which may be prevented in some cases with the use of steroids. Delayed parenchymal changes applicable to any radiosurgery, including postradiation malignancy and vascular occlusion, are also potential complications.

Microvascular Decompression

MVD is one of the safest, albeit invasive, procedures in microneurosurgery. Complications after MVD have been dramatically reduced over the years, with the lowest rates reported in high-volume centers. Specific complications may include cranial nerve dysfunctions during manipulation of the nerves in the cerebellopontine angle. Some degree of hearing loss is not infrequent after MVD; in most cases it is due to conductive impairment secondary to fluid ingression into the middle ear cavity through the mastoid bone. This hearing problem is transient and improves over 2 to 3 weeks. Sensory neural hearing loss is troublesome and should call for more attention. It is the possible result of retraction injury of the cochlear nerve or may be secondary to vasospasm of the anterior inferior cerebellar artery (AICA) during separation of the vessel. Facial nerve paresis, tinnitus, and vertigo are the other few reported cranial nerve complications. Another important complication during surgery is venous bleeding while coagulating the petrosal vein or venous loop over the trigeminal nerve. Though not frequent, the bleeding can sometimes be troublesome and can lead to postoperative cerebellar or brainstem edema. Injury to the transverse or sigmoid sinus during craniotomy and cerebellar contusion during retraction are some important avoidable intraoperative complications. Postoperative complications include cerebrospinal fluid (CSF) leak, wound infection, and CSF rhinorrhea.

Red Flags

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Percutaneous treatment: indistinct radiologic landmarks, skull base anomalies, abnormal curvature of extracranial internal carotid artery
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SRS: no specific risk factors; short cisternal segment of trigeminal nerve may pose problem in appropriate fixing of target
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Microvascular surgery: previous radiosurgery, previous MVD, vascular malformation in the cerebellopontine angle
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Previous medical therapy (especially prolonged dopamine agonist therapy)
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Lesions invading the cavernous sinus