70 Management of Pre- and Posttreatment Trigeminal Neuralgia in Vestibular Schwannoma

10.1055/b-0039-169224

70 Management of Pre- and Posttreatment Trigeminal Neuralgia in Vestibular Schwannoma

Ramsey Ashour, Siviero Agazzi, and Harry van Loveren

70.1 Introduction

Patients with vestibular schwannoma (VS) occasionally present with trigeminal neuralgia secondary to the tumor itself, or, more rarely, develop trigeminal neuralgia as a complication after radiosurgical treatment of the tumor. For the former group, the presence of “pretreatment trigeminal neuralgia” may impact the strategy for tumor management. For the latter group, the plan and resulting outcome of radiosurgical treatment can impact the management strategy for “posttreatment trigeminal neuralgia.” In this chapter, we review the management of pre- and posttreatment trigeminal neuralgia in patients with VS.

70.2 Pretreatment Trigeminal Neuralgia

70.2.1 History

Early 20th century reports of trigeminal neuralgia in the setting of a posterior fossa tumor were provided by Krause,s. Literatur Lexer,s. Literatur Oppenheim,s. Literatur and Weisenburg.s. Literatur However, it was Cushings. Literatur who provided the clearest early description of VS case presentations in his 1917 monograph, some of whom also presented with trigeminal neuralgia. He noted that, “in true tic douloureux, unmodified by operation, there is no cutaneous hypoesthesia, whereas in the painful neuralgia from pressure of a tumor some sensory loss is demonstrable, and the conditions may thus be easily distinguished.”

We once agreed with Cushing that the so-called secondary trigeminal neuralgia associated with a tumor could always be distinguished by the presence of a detectable neurologic deficit specific to the tumor (e.g., hearing loss, vestibulopathy, trigeminal numbness, and sensorimotor disturbances) that was caused by brainstem compression. We later disagreed with this premise after encountering a number of patients who had classic trigeminal neuralgia, that is, an occurrence characterized by no detectable neurologic deficit in spite of nerve distortion by tumor as the probable cause.

During his era, Cushing also documented the occasional manifestation of trigeminal neuralgia contralateral to the side of large tumors, and highlighted the high incidence of trigeminal neuropathy in VS patients. He then pointed out that, in association with cerebellopontine angle tumors, neurotrophic keratitis can develop because of trigeminal nerve compression; however, he stated that this “never occurs in true trigeminal neuralgia except as the result of the loss of sensitivity of the cornea following a neurectomy.” Interestingly, Cushing emphasized that trigeminal neuralgia “is rarely if ever a significant symptom of a VS.” Careful review of his classic monograph reveals a relatively high incidence (8/33 cases) of VS-related trigeminal “neuralgic” pain, perhaps reflecting the large tumor sizes at the time of diagnosis during this early era.

70.2.2 Epidemiology and Clinical Features

Trigeminal neuralgia can be attributed to the presence of tumor in 2 to 10% of cases, most often meningiomas, epidermoids, or VSs.s. Literatur ^, s. Literatur ^, s. Literatur ^, s. Literatur ^, s. Literatur ^, s. Literatur ^, s. Literatur Although pretreatment trigeminal neuralgia has been reported to affect 3.5 to 7% of VS patients, its true incidence is often hindered and likely overestimated by a failure to distinguish between trigeminal neuralgia and trigeminal neuropathy.s. Literatur ^, s. Literatur ^, s. Literatur

Tumor-related trigeminal neuralgia shares the same features as non–tumor-related trigeminal neuralgia. Both are characterized by paroxysmal, intense, shock-like pains in one or more ipsilateral trigeminal distributions that are often triggered by cutaneous stimulation of the affected areas, such as by touch or common oral activities. Atypical trigeminal neuralgia can also occur, characterized by concomitant background “aching” facial pain in addition to the neuralgic pains. On the other hand, compressive trigeminal neuropathy in the setting of tumor results in facial numbness and associated paresthesias and dysesthesias, and has been reported to affect almost half of large VSs.s. Literatur ^, s. Literatur

Even patients with non–tumor-related trigeminal neuralgia can experience subtle changes in facial sensation and/or complain of facial numbness especially when in the midst of a series of painful attacks.s. Literatur Therefore, it is difficult to distinguish between tumor- and non–tumor-related trigeminal neuralgia on clinical grounds alone.s. Literatur This difficulty supports obtaining an MRI whenever possible before treatment in patients with trigeminal neuralgia to elucidate any primary disorders (e.g., tumor, vascular malformation, multiple sclerosis) that might affect treatment strategy. In VS patients, vestibulocochlear nerve dysfunction (i.e., hearing loss) drives the diagnosis, but the presence of trigeminal neuralgia does not appear to result in earlier diagnosis of VS.s. Literatur

70.2.3 Pathophysiology

Although it seems obvious that the cause of tumor-related trigeminal neuralgia is tumor contact with the nerve,s. Literatur Cushings. Literatur realized that the extent of tumor compression alone could not explain the development of trigeminal neuralgia. He explained, “In the case of the trigeminus … neuralgic pain such as one would expect is relatively uncommon. This is more remarkable when one realizes how flattened and elongated the nerve becomes as it is crowded aside by the growth.”

Jannettas. Literatur pioneered the concept of neurovascular conflict, specifically, a blood vessel contacting the trigeminal root in either non–tumor-related or tumor-related trigeminal neuralgia. In his series of trigeminal neuralgia patients with posterior fossa tumors, vessels compressing the nerve were found in all 21 patients in whom the nerve root entry zone was examined.s. Literatur In his hypothesis, the tumor either pushes a vessel against the nerve or the nerve against a vessel, thus reproducing a classic neurovascular conflict and therefore a classic trigeminal neuralgia. Some authors have also documented vascular compression of the trigeminal nerve root in cases of tumor-related trigeminal neuralgia,s. Literatur ^, s. Literatur ^, s. Literatur ^, s. Literatur whereas others searched for but did not find vascular compression in such cases.s. Literatur ^, s. Literatur ^, s. Literatur Recall that even in non–tumor-related classic trigeminal neuralgia, vascular conflict is not universally present (Fig. 70‑1 , Fig. 70‑2 ).

**Fig. 70.1** Axial T2-weighted images of a right vestibular schwannoma in a patient with medically intractable right trigeminal neuralgia and right-sided hearing loss. (a) At the level of the internal auditory canal. (b) Above level of the internal auditory canal, demonstrating where the tumor reaches the level of the trigeminal nerve. At surgery, the trigeminal nerve was deep to the tumor and a large loop of the superior cerebellar artery was found compressing the nerve from above.

**Fig. 70.2** Postcontrast T1-weighted images in a vestibular schwannoma patient with hearing loss and trigeminal neuralgia. (a) Axial view shows a prominent vertebrobasilar complex abutting the ventromedial aspect of the tumor. At surgery, multiple arterial loops were found to be compressing the trigeminal both from above and below. (b) Coronal view demonstrates tumor extending superiorly up to the petrotentorial junction in close proximity to the trigeminal nerve.

70.2.4 Management

Medical Therapy

Standard pharmacotherapy for non–tumor-related trigeminal neuralgia includes carbamazepine, oxcarbazepine, lamotrigine, or baclofen.s. Literatur Alternatives include gabapentin, pregabalin, topiramate, and older anticonvulsants. When medications prove ineffective at achieving adequate pain control or cause intolerable side effects to the patient, neurosurgical interventions (e.g., microvascular decompression, percutaneous ablative procedures, radiosurgery) are considered.s. Literatur

Trigeminal neuralgia caused by VS is not in and of itself an absolute indication for VS treatment. This is the case when the neuralgia is well controlled by medical therapy with tolerable side effects, and the tumor is otherwise without evidence of active growth. In the majority of patients, tumor treatment whether by radiosurgery or surgery will achieve excellent relief of the associated trigeminal neuralgia so long as either treatment is specifically designed to address both disorders simultaneously. Percutaneous radiofrequency rhizotomy and glycerol rhizotomy are also part of the surgical armamentarium and should not be forgotten; however, both have been largely set aside because they address only the trigeminal neuralgia component and ignore the tumor.

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