9 The Pathology and Treatment of Benign Paroxysmal Positional Vertigo Benign paroxysmal positional vertigo (BPPV), described by Barany in 1921,1 is the most common balance complaint encountered in practice. It is unique in that it is the only clinical form of disequilibrium that is triggered by a change in head position. True, the vertigo experience is brief (less than 1 minute), but it can be so severe during driving, bending, etc., as to be a cause of serious injury. Occasionally, patients may have such a severe episode of vertigo, nausea, and emesis that they require hospitalization. Since a tilted head position is provocative, BPPV was first assumed to be an otolith disorder. Dix and Hallpike supported this interpretation with histopathologic evidence of utricular end-organ degeneration in the temporal bone of a patient suffering from BPPV.2 Furthermore, Citron and Hallpike demonstrated that a change in head position provoked the rotatory nystagmus seen in BPPV.3 Although the use of Frenzel glasses during the Hallpike test is desirable to prevent the patient’s fixation on the surround (thus diminishing the eye response), the test may be used without enhancement to detect symptomatic BPPV.2 The subjective response without nystagmus may be used to identify patients who have a less severe response to provocation with the head in the down and to the side position.4 The typical ocular response is the onset of a rotatory and vertical nystagmus after a short (1 to 2 second) latency that has a duration of 10 to 20 seconds.2 Nystagmus re-appears briefly on the return to the sitting position. Repeat of the test will produce a reduced response and symptoms. This important feature of fatigability is indicative of a peripheral cause, rather than central cause, of the BPPV. However, focus on the role of otolith organ function in BPPV was changed by the experimental demonstrations that the nystagmus response was elicited by semicircular canal activation and not by otolith stimulation.5 These findings were supported by temporal bone histopathologic evidence presented by Lindsay and Hemenway showing complete degeneration of the superior vestibular division leaving the inferior division and its sense organs intact in a patient with BPPV after an acute episode of vestibular neuronitis. Both physiologic6 and anatomic7 laboratory observations confirmed that the posterior canal sense organ activates the vestibulo-ocular pathway to the contralateral inferior rectus and ipsilateral superior oblique extraocular muscles. These findings supported the contention that posterior canal activation was responsible for the rotatory and vertical nystagmus response characteristic of BPPV. One of the concepts based on morphologic evidence gained from human temporal bones that provided a logical explanation for symptoms was that presented by Schuknecht and Ruby.8 They found basophilic deposits embedded in the cupula of the posterior canal sense organ of a few patients who had experienced BPPV during life. Since this material stained blue with the hematoxylin and eosin stain that also stained the otoconia of the otolith organs, it was assumed the deposits were derived from otoconia. As otoconia have a high specific gravity (2.7), it was logical to conclude that the cupular mass converted the sense organ into one that was sensitive to gravity. Thus the concept of cupulolithiasis was formulated. About the same time, selective denervation of the posterior canal sense organ (singular neurectomy) of the lower ear in the provocative position completely and permanently relieved the syndrome.9,10 This result settled the question of whether it was the up- or downmost ear in the provocative position that is responsible for the clinical findings in BPPV. Later, Parnes and McClure added the observation that the free-floating particles could be seen in the limb of the posterior canal in patients undergoing occlusion of the canal for BPPV.11 The terms cupulolithiasis and canalolithiasis were coined to refer to the fixed and free-floating types of deposits in the posterior semicircular canal. Naturally, a series of head maneuvers were developed to reposition free-floating deposits from the posterior canal aupulla and/or membranous canal through the common crus and into the utricle, where they could no longer activate the canal receptor.12,13 Although the short-term relief of BPPV by these particle repositioning maneuvers was promising,14 subsequent reports with longer (> 6 months) follow-up and comparison with no treatment revealed equivalent rates of relief.15,16 Additional morphologic observations cast doubt on the validity of the lithiasis concept. Cupular deposits have been found in several temporal bones without a history of positional vertigo. Temporal bone studies describing the incidence of cupular deposits in normal pediatric17 and adult temporal bones18,19 indicated that the frequency and size of deposits increases with age. Cupular deposits therefore may be a morphologic change associated with the aging labyrinth. In one report, Parnes observed particles floating in the posterior canal limb in only one-third of 22 patients undergoing canal occlusion for BPPV that did not improve with repositioning maneuvers.20 Therefore, inactivation of the posterior canal seems to be a permanent solution to chronic (> 1 year) BPPV demonstrated by a rotatory and vertical nystagmus provoked by head down and to the side position. Positional vertigo and nystagmus following provocation may indicate similar activation of either the lateral or anterior semicircular canals. These are identified by the appropriately directed nystagmus after provocation (horizontal or vertical downbeat). The results of one form of de-activation of the posterior canal (singular neurectomy) to relieve BPPV are presented here and compared with posterior canal occlusion. We also suggest a neurologic basis for this neuropathy that may explain some inadequacies in the purely mechanistic concept of BPPV. The author performed 286 singular neurectomies over the period 1972 to 2012. The procedures were performed in 275 patients; 11 of the patients underwent sequentially a contralateral SN for bilateral BPPV. All of the patients experienced chronic (> 1 year) BPPV of the posterior canal demonstrated by a rotatory/vertical nystagmus when placed in the Hallpike provocative position and observed without Frenzel glasses or eye muscle recording. They all had contrast CT or MRI of the brain and no other neurologic deficits. Most had completed a trial of physical therapy. All had hearing tests that were normal for their age. In the group of 275 patients, there were 196 females and 79 males. The median age of the group was 59 years, with a range of 21 to 93 years. The etiologies of their BPPV fell into three groups: idiopathic (209), trauma (43), and following other surgery under general anesthesia (23). • The idiopathic group experienced a sudden onset of prolonged vertigo (hours to days) without hearing loss. BPPV followed recovery from the acute vestibular insult (vestibular neuronitis). • The trauma group suffered a concussive injury to the head with or without loss of consciousness. • The other surgery group noted onset of BPPV after abdominal, orthopedic, gynecologic, or sinus surgery, all under general anesthesia. The SN procedure may be performed under local anesthesia with sedation or under general anesthesia via intubation. The exposure is through a speculum inserted into the ear canal, with or without support by a speculum holder. After elevation of a tympanomeatal flap, the structures in the posterior half of the middle ear are exposed. Curettage of the posterior and superior bony ear canal may be required for a full view of the round window niche (RWN) and the incudostapedial joint (Fig. 9.1 and Fig. 9.2). Often there is a mucous membrane fold that may partially or completely obscure the RWN. After removal of this fold with picks or hooks, the rim of the RWN must be removed with a small (1 mm) diamond bur until a full view of the round window membrane (RWM) is obtained. This can be confirmed by downward displacement of the incudostapedial joint. The drilling on the floor of the RWN is performed with a 1-mm diamond bur. The depression created is inferior to the posterosuperior portion of the RWM. At the depth of 1 to 3 mm, the singular nerve will be encountered in one of three locations (Fig. 9.1). The most common is where the white myelinated nerve is partially exposed. Less often, the full width of the nerve may be fully exposed. Rarely, the nerve is not seen because it lies superiorly (under the RWM). This position can be confirmed by the patient’s response (if under local anesthesia) to probing with a pick or small hook. The patient will feel vertigo or pain with this stimulation. The proximal end of the singular canal is then lightly drilled with a 0.5-mm diamond bur to cause osteogenesis in the canal lumen. The tympanomeatal flap is returned to anatomic position. The patient usually stays in hospital overnight, but some patients may be discharged the same day. Confirmation of posterior canal ablation is seen with a spontaneous downbeat vertical nystagmus immediately after surgery.
Introduction
Pathology
Singular Neurectomy (SN)
Technique of Singular Neurectomy
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