We report a case of a cerebellopontine angle cholesteatoma whose initial sign was benign paroxysmal positional vertigo (BPPV). Positional vertigo caused by a central pathology is extremely rare and is usually accompanied by other suspicious features. In this case, there were no additional neurotologic symptoms or signs. The only abnormalities were seen on Dix-Hallpike testing, but because they were not consistent with a diagnosis of BPPV, the decision was made to proceed to imaging. Diagnostic rigor is required when evaluating positional vertigo, as with all symptoms of imbalance, if such cases are not to be overlooked.
The most common cause of positional vertigo is benign paroxysmal positional vertigo (BPPV). In most patients, BPPV initially manifests in the fourth to seventh decade of life, and the condition has a slight predisposition to women. Patients typically report brief episodes of rotary vertigo, which are provoked when they assume certain positions--specifically, lying down, rolling to the affected side, and leaning forward or backward. [1-4]
The condition is diagnosed by observing the characteristic nystagmus on Dix-Hallpike testing.  Norre  found that one-third of patients with BPPV reported atypical vertigo, so Dix-Hallpike testing was the only way to confirm the diagnosis. The characteristics of BPPV on Dix-Hallpike testing are a latent period before the onset of nystagmus, a rotary nystagmus beating toward the under ear that lasts for less than 40 seconds, a reversal of nystagmus upon sitting up, and fatiguing of response on repeat testing. Electronystagmographic findings in BPPV have been well documented by Baloh et al  and Katsarkas. 
The pathophysiologic mechanism of BPPV is presumed to involve canalothiasis  or cupulolithiasis.  Most cases of BPPV are idiopathic and believed to be the result of spontaneous degenerative changes in the maculae of the utricle or saccule. In approximately 20% of patients, the condition is secondary to a labyrinthine concussion, chronic suppurative otitis media, or ear surgery--stapes surgery, in particular. BPPV usually resolves spontaneously, but treatment of persistent cases with repositioning maneuvers and exercise therapy has been relatively successful.[9, 10] In those rare cases that fail to respond to these conservative measures, good results have been reported with posterior canal occlusion. 
Positional vertigo and nystagmus demonstrated on the Dix-Hallpike test that does not fit the characteristics of BPPV raises the suspicion of other diseases. Other vestibular labyrinthine causes exist, such as positional alcoholic nystagmus, but of greater concern is central vestibular system pathology.
Patients with BPPV account for 20% of referrals to specialized vertigo clinics. [12, 13] Central pathologies manifesting as BPPV are extremely rare, but when they do occur, they should become apparent on Dix-Hallpike testing. Positional nystagmus has been reported in patients with a cerebellopontine angle tumor, Arnold-Chiari malformation, multiple sclerosis, lateral medullary infarction, or brainstem contusion. [14, 15] Given these possible causes, it is of the utmost importance to investigate those features on Dix-Hallpike testing that deviate from the normal presentation of BPPV.
In this article, we describe the case of a patient who complained of positional vertigo (which was presumed to be BPPV based on the reported symptoms) and who had unusual findings on Dix-Hallpike testing. The patient was found to have a large cerebellopontine angle cholesteatoma.
A 31 -year-old woman had a 2-year history of positional rotary vertigo. Her episodes were precipitated by lying down or by looking up. Their duration was reported to range from a few seconds to several minutes. She also experienced a slight loss of balance when she walked quickly or engaged in exercise. Based on this history alone, the consulting ENT physician made a preliminary diagnosis of BPPV and planned to treat the patient with a repositioning maneuver. However, the physician deferred a final decision until the rest of the examination was completed. The evaluation continued, and the woman's clinical examination was unremarkable. The results of her cranial nerve and tandem gait tests were normal, and her Romberg and Unterberger tests were negative. However, the results of her positional testing were abnormal, as the Dix-Hallpike test provoked a marked rotary nystagmus bilaterally. This nystagmus was of immediate onset, prolonged ([greater than]1 min), and did not fatigue with repeat testing. These findin gs led to the suspicion of a central cause, and the planned repositioning maneuver was not performed.
Pure-tone audiometry revealed normal thresholds ([less than]20 dB) bilaterally across the frequency range of 250 to 8,000 Hz. Speech audiometry was normal, with 100% discrimination at 40 dB bilaterally. The results of auditory brainstem response testing were normal in the right ear, but abnormal in the left. In the left, the latencies of waves III and V were delayed, and the interpeak latencies between waves I and III and between waves I and V were prolonged beyond normal limits. The difference between the absolute latency of wave V from the left and right ears was abnormal (0.39 msec).
On electronystagmography, there was no spontaneous or gaze nystagmus (horizontal or vertical) with eyes open or closed. Random horizontal saccade testing showed a normal amplitude, velocity, and latency of saccades in both directions of movement. Smooth-pursuit testing showed abnormalities across the frequency range of 0.2 to 0.7 Hz; at all frequencies, saccadic intrusions were present in excess of those that would be expected in someone of this patient's age.
On Dix-Hallpike testing, nystagmus was elicited with the head turned to the right and to the left. The right Dix-Hallpike provoked a fine right-beating and down-beating nystagmus that had a torsional (clockwise) component; there was no latent period before the nystagmus appeared, and repeat positioning did not result in any fatigue of the response. The left Dix-Hallpike provoked a fine left-beating and down-beating nystagmus that also had a torsional (counterclockwise) component; again, there was no latent period before the nystagmus appeared, and repeat positioning did not result in any fatigue of the response.
These findings prompted an order for magnetic resonance imaging, which detected the presence of a mass in the left cerebellopontine angle, that measured approximately 4.5 cm in its maximum linear dimension (figure). A significant displacement of the brainstem to the right was observed, but the ventricular cistern was not effaced and there was no evidence of hydrocephalus. The mass extended into the prepontine cistern, as evidenced by the displacement of the basilar artery away from the clivus and sella turcica. The anatomic distribution and signal characteristics were those of a left cerebellopontine angle cholesteatoma that had extended into the left internal auditory meatus.
After the patient was counseled regarding the relative risks and benefits of surgery, the cholesteatoma was removed with a retrosigmoid craniotomy.
A variety of conditions can cause positional vertigo, one of the most common being BPPV. The recent abundance of reports documenting the effectiveness of repositioning maneuvers in the treatment of BPPV has renewed interest in this condition.  Nevertheless, it is important that this enthusiasm does not lead us to neglect diagnostic rigor, because positional vertigo can be caused by far less benign conditions. This case study shows that symptoms that mimic BPPV can mislead the clinician and result in an incorrect presumptive diagnosis. The careful examination of eye movements on Dix-Hallpike testing is of the utmost importance in establishing whether vertigo is of peripheral or central origin.
Our patient did not exhibit the classic characteristics of BPPV on Dix-Hallpike testing. She had no latent period before the onset of nystagmus, she had a prolonged duration of nystagmus, and she manifested no fatiguing of the response with repeat positioning. It is worthy of note that a patient could report symptoms that are so entirely compatible with BPPV but whose Dix-Hallpike testing differed in such a manner.
Positional vertigo of a central character is indicative of a posterior fossa lesion. The probable locations are the caudal brainstem and the vestibulocerebellum.  Brandt has suggested that the pathogenesis of the nystagmus is the result of a "disinhibition" of the normal vestibular reflexes.  When the head is moved to an off-vertical or lateral position, the otolith organs change their neural firing rate and the disinhibition of this end-organ signal causes nystagmus and vertigo. According to Brandt's theory, then, it is therefore not the head position resulting in dislocation of the mass and intracerebral structures that causes nystagmus. Kattah et al have suggested, however, that nystagmus is caused by the compression of a tumor mass coupled with the force that the mass exerts when the head is in the position that elicited nystagmus on the Dix-Hallpike test.  Evidence for both of these possibilities is provided by Katsarkas. 
Epidermoid cysts (primary cholesteatomas) arise from cell rests in either the fourth ventricle, in the cerebellopontine angle, or within the temporal bone. Cerebellopontine angle cholesteatomas grow slowly and stretch the cranial nerves in the region, eventually compressing the brainstem and cerebellum. The initial features reported in one series were hearing loss and tinnitus in 80% of patients, with gait disturbance and headache in the remaining 20%.  Less common initial features are intention tremor, facial numbness, facial spasm, facial palsy, impaired sense of taste, impaired lacrimation, dysarthria, dysphasia, tongue deviation, and loss of consciousness. [20,21] It is well known that some form of dizziness or unsteadiness is often present, but positional vertigo as an initial symptom is rare.
In our case, no other neurologic, auditory, or vestibular symptom was present. Pure-tone audiometry was normal, but auditory brainstem responses strongly indicated a retrocochlear lesion. Further examination by electronystagmography gave no indication of any peripheral vestibular pathology (symmetrical caloric responses present), but it did provide evidence of central vestibular system dysfunction in terms of smooth-pursuit abnormalities. These findings suggested the presence of a brainstem and/or a cerebellar lesion.
Electronystagmography also replicated the clinical findings on caloric testing. Although these further tests clearly indicated the presence of a central lesion, the physician's diagnostic strategy should not necessarily require such a weight of evidence before the physician pursues a definitive investigation with magnetic resonance imaging. It is the view of this department that the abnormalities on Dix-Hallpike testing alone were sufficient to warrant such investigation.
In the midst of the renewed interest in BPPV and in light of its successful treatment by repositioning maneuvers, this case serves as a reminder that central causes of positional vertigo do exist. They might usually be associated with additional auditory or neurologic features, but not always, as this case illustrates. Diagnostic rigor is therefore required in assessing positional vertigo, as it is with all symptoms of imbalance, if such cases are not to be overlooked.
From the Department of Audiology (Mr. Beynon and Mr. Baguley) and the Department of Neuro-Otology (Mr. Moffat), Addenbrooke's Hospital, Cambridge, U.K., and the Department of Otolaryngology, University Hospital, Birmingham, U.K. (Dr. Irving).
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