Vertebrobasilar Dolichoectasia in a patient with recurrent Sudden Sensorineural Hearing Loss. Diagnostic approach and dilemmas

Case Description: A fifty-five-year-old man had a recurrence of Sudden Sensorineural Hearing Loss (SSNHL) five months after the first incident which had left a residual moderate high frequency hearing loss and mild tinnitus. The recurrence involved mainly the low frequencies. He had a full audiovestibular test battery and MRI. On MRI he was diagnosed with Vertebrobasilar Dolichoectasia (VBD). Audiovestibular examination showed a cochlear hearing loss. He was treated with per os methylprednisolone. Low frequencies recovered almost fully. Discussion: Vertebrobasilar Dolichoectasia i.e. the elongation, dilatation and tortuosity of the vertebrobasilar segment can have possible impacts on the audiovestibular system either by direct nerve compression of by blood flow disturbances. A thorough audiometric and imaging investigation was done, in order to determine to what extent VBD could be the cause of a recurrent hearing loss. Conclusion: In the present case VBD looks unlikely to have caused the hearing loss. However due to being a potentially hazardous clinical entity clinical awareness is mandatory. In view of the uncommon audiological configuration and recurrence, further investigations are recommended.


Introduction
The basilar artery (BA) is the main source of posterior cerebral blood circulation. Consequently pathological entities leading to disturbance of blood flow in a vital part of the brain could be detrimental. The anatomy and normal measures of the vertebrobasilar system have been studied extensively in the past decades [1]. The most valid criteria for abnormality concerning the dimensions and location of the vertebrobasilar system, are Smoker's criteria [2] which are based on Computed tomography (CT) and Digital Subtraction Angiography (DSA) measurements, but they are practically the same for MRI [3].
Vertebrobasilar dolichoectasia (VBD) is a vascular abnormality characterized by elongation, dilatation and/or tortuosity of the vertebrobasilar segment. Estimates of the prevalence of VBD range from 0.2% to 4.4% but sound population data are lacking is the most common manifestation of VBD. A 11 year follow up study [5] reported an incidence of 48 % for stroke followed by compressive symptoms of cranial nerves at an incidence of 20% and hydrocephalus at an incidence of 1,2%. Cranial nerves can be compressed either as an effect of immediate contact with the artery or as a mass effect. The most frequently involved cranial nerve roots are the facial (VII) and trigeminal (V)triggering hemifacial spasm or trigeminal neuralgia [2]. Cases of oculomotor (ΙΙΙ) or abducens (VI) compression have been reported as well. Regarding audio vestibular nerve (VIII) compression by VBD, reports are very few. Moreover, Maruyama et al. [6] reviewing MRI findings in patients with audio vestibular symptoms who were diagnosed with VBD, introduced the question of possible existence of confounding factors leading to occurrence of Idiopathic Sudden Sensorineural Hearing Loss (ISSNHL) and/ or Canal Paresis in patients with VBD.
The present case report is aiming to present a case of a 55-year-old man with recurrent hearing loss in the left ear who was diagnosed with VBD on MRI, to exhibit the possibilities of new diagnostic MRI modalities and how to combine audiovestibular test battery and imaging in order to answer a diagnostic dilemma.

Case Report
A 55-year-old man consulted the Otorhinolaryngology practice reporting sudden hearing loss with tinnitus in the left ear. This was the second incident, a previous one having occurred five months earlier. He was then treated by another physician. Playtone Audiometry (PTA) both times showed a hearing loss of both the low and the high frequencies ( Figure 1A) preserving the mid frequencies at normal threshold. The first episode was treated by per os methylprednisolone at tapered doses. The low frequencies were restored back to normal, whereas the high frequencies improved slightly. Figure 1A shows the first and last (forty days later) audiograms of the first hearing loss incident. No imaging was done at the time of the first SSNHL episode. Four years before the first episode the patient had had an episode of Benign Paroxysmal Positional Vertigo. Playtone Audiometry at that time showed normal hearing thresholds in both ears. The patient has a history of hypertension and hyperlipidemia for which he has been on medication for the last four years.
The patient was first seen in our office when the second SSHNL incident occurred. He reported low pitched tinnitus, which was

Discussion
Sudden Sensorineural Hearing Loss (SSNHL) has been defined as the hearing loss of at least 30 dB in three consecutive frequency bands occurring over no more than 72 hours [8]. Annual incidence rate ranges from 4 cases over 100.000 population to as many as 160 cases per 100.000 population [9]. Vascular events such as vasospasm, thromboembolism, and weak blood circulation have been named among the pathomechanisms responsible for this syndrome [10]. The inner ear receives blood supply by the labyrinthine artery (or arteries as in 2/3 of individuals there are two labyrinthine arteries perfusing the inner ear) deriving from the Anterior Inferior Cerebellar Artery (AICA) and in fewer cases from the Basilar Artery [11].
In the present case the left AICA emanates in a direction perpendicular to the typical horizontal one, which could be a factor leading to blood flow disturbances. However as seen in Figure 4a the presence of anastomoses with neighboring pontine vessels, as described by the cadaveric study of Nishijima [21] could be a possible reason that a major ischemic event has not taken place. To what extent such a vascular configuration could be responsible for a moderate cochlear ischemia leading to a moderate hearing loss in a limited area of the cochlea, is highly speculative. There are references about the existence of a dominant vertebral artery more frequently on the left side [18][19][20]. Despite the fact that hyperlipidemia and hypertension were present in the patient's recent medical history, (of a few years) the lateralization of the BA being evident many years earlier (Figure 2b) is in accordance with the pathogenetic theory of a mechanism other than atherogenesis, involving a disfunction of matrix metalloproteinases leading to aberrant vascular remodeling and abnormal connective tissue in the arterial wall [3,22].
The second unique feature of the case presented is the configuration of the audiogram in the initial incident affecting the lower and higher frequencies and preserving the mid ones followed by a partial recovery, whereas recurrence affected mainly the low frequencies.
Recurrence of SSNHL is unusual and typical audiometric patterns are not available in relevant studies [12,23,24]. Cochlear hydrops cannot be precluded but high frequency involvement on the initial attack is atypical. Huh et al. [17] describe fluctuating hearing loss in one of VBD patients of their series, but they do not become more specific about the features of fluctuation. The finding of a markedly tortuous vertebrobasilar artery is a factor that has to be taken into account, but as direct nerve compression is not obvious on MRI, a further investigation with autoimmune and clotting profile of the patient should be done.

Conclusion
This is a case report adding to the few case series that already Dolichoectasia is by itself a potentially harmful clinical entity and awareness of its existence is by all means beneficiary to the patient.