Patient one

A 73-year-old male presented with left-sided non-pulsatile tinnitus and otalgia in 2014. Pure tone audiogram showed bilateral high frequency sensorineural hearing loss. An MRI scan of the IAM revealed a 3 mm vestibular schwannoma on the left side. Patient one was referred to the skull base team. Since then, he has been monitored with annual MRI of the IAM. In 2017, the scan showed that the vestibular schwannoma had increased in size to 3.9 mm. It was decided to continue active monitoring with annual MRI of the IAM.

Patient two

A 61-year-old female presented with left-sided unilateral non-pulsatile tinnitus in 2015. An MRI scan of the IAM revealed a 4 mm vestibular schwannoma on the right side (contralateral to the patient's symptoms). Pure tone audiogram showed symmetrical hearing within the normal range. The patient was referred to the skull base team, where she has been monitored with annual MRI of the IAM. There has been no growth of the vestibular schwannoma.

Patient three

A 45-year-old female presented with left-sided non-pulsatile tinnitus and otalgia in 2014. An MRI revealed a 5.1 mm vestibular schwannoma on the left side. Pure tone audiogram showed symmetrical hearing within the normal range. The patient was referred to the skull base team, where she has been monitored with annual MRI. There has been no growth of the vestibular schwannoma.

Overall findings

Our detection rate for vestibular schwannoma in patients investigated with unilateral non-pulsatile tinnitus was extremely low. One vestibular schwannoma was detected on the contralateral side to the tinnitus (patient two) and was therefore an incidental finding, which would lower the detection rate further to just 0.3 per cent. Patients one and three also had the additional symptom of otalgia alongside the unilateral non-pulsatile tinnitus. All three patients have been managed conservatively, undergoing annual MRI. Only one vestibular schwannoma (patient one) has shown growth (of 0.9 mm) since detection over four years ago.

There have only been two published series reporting detection rates for vestibular schwannoma in patients with unilateral tinnitus. Dawes et al., in Sunderland, UK, reported a vestibular schwannoma detection rate on MRI of 0.5 per cent.^{Reference Dawes and Basiouny12} The Michigan Ear Institute found a 0 per cent detection rate for vestibular schwannoma in patients scanned for unilateral tinnitus.^{Reference Robinette, Benscoter, Trenkle, Alapati, Jackson and Babu13} Our figure of 0.3 per cent is in keeping with these findings, and an overall detection rate of 0.2 per cent can be established. Published data in the UK have revealed a vestibular schwannoma detection rate of 1.6–4 per cent for all MRI scans of the IAM ordered.^{Reference Amiraraghi, Lim, Locke, Crowther and Kontorinis7,Reference Sheppard, Milford and Anslow11,Reference Harcourt, Vijaya-Sekaran, Loney and Lennox14}

As current national UK guidelines state that patients who present with unilateral tinnitus should undergo MRI, failure of the clinician to order this could be difficult to defend medicolegally.^{5,Reference Nouraei, Huys, Chatrath, Powles and Harcourt8} It presents a challenge, and may lead to clinicians simply ordering the MRI both to reassure and to protect themselves against litigation. It is difficult to put a value on reassuring patients; however, clinical acumen is paramount, unnecessary imaging is putting an ever-increasing strain on our health service, and it is our duty to improve resource utilisation. A careful history eliciting whether the tinnitus is constant or occasionally present and its relationship to factors such as stress, and clinical examination along with audiological screening, in the absence of other signs and symptoms of a cerebellopontine angle lesion, does not require MRI investigation.

Vestibular schwannomas have been associated with a range of vestibular symptoms, which sometimes can be vague, from light-headedness and disequilibrium to true rotatory vertigo mimicking either benign positional paroxysmal vertigo or Ménière's disease.^{Reference Harcourt, Vijaya-Sekaran, Loney and Lennox14} Unilateral tinnitus alone is an uncommon presenting symptom of vestibular schwannoma. Morrison and Sterkers found that just 2.8 per cent of their series of vestibular schwannoma actually presented with tinnitus.^{Reference Morrison and Sterkers15} Lustig et al. found that 5 per cent of vestibular schwannoma patients had normal or symmetrical pure tone audiograms between 0.5 and 4 kHz.^{Reference Lustig, Rifkin, Jackler and Pitts16}

Several protocols have been devised to try to rationalise and aid the decision as to which patients from the large population with audiovestibular symptoms warrant an MRI, to improve detection rates. Harcourt et al. have devised a protocol for the degree of hearing threshold asymmetry.^{Reference Harcourt, Vijaya-Sekaran, Loney and Lennox14} Sheppard et al. have set an age limit (70 years) for screening with MRI.^{Reference Sheppard, Milford and Anslow11} Dawes and Basiouny limited MRI to patients without significant co-morbidities that would prevent them from having surgery.^{Reference Dawes and Basiouny12} Previously, auditory brainstem response (ABR) testing had been used to detect a vestibular schwannoma.^{Reference Hentschel, Scholte, Steens, Kunst and Rovers17} However, one-third of the intracanalicular vestibular schwannoma patients had normal ABRs; therefore, this was not an appropriate primary test to screen for vestibular schwannoma.^{Reference Anderson, Loevner, Bigelow and Mirza18} Anderson et al. found 7 incidental vestibular schwannomas per 10 000 MRI studies (0.07 per cent).^{Reference Anderson, Loevner, Bigelow and Mirza18} Vestibular schwannoma can cause indistinct symptoms and occasionally be asymptomatic; therefore, the only way to identify every single vestibular schwannoma would be to perform MRI in all patients presenting with any audiovestibular symptoms, which would amount to a population-level screening programme.^{Reference Nouraei, Huys, Chatrath, Powles and Harcourt8}

We have shown a large number (24 per cent) of incidental findings detected on MRI scans of the IAM. This has warranted in some cases unnecessary investigations and referral to other medical teams, causing anxiety and stress for the patient involved and further cost pressures on the NHS. Patients often find the process of undergoing an MRI scan unpleasant, causing symptoms of claustrophobia. There is also a potential adverse reaction to the gadolinium contrast given.

In the current environment, we need to improve our resource utilisation within the NHS. The average cost for an MRI scan of the IAM is £200. Our department has spent £113 200 on investigating patients with unilateral non-pulsatile tinnitus in the five-year period investigated, and this does not include the costs for scan reporting, follow-up appointments and further investigation into the 134 incidental findings discovered on MRI.

Study limitations

The large series was reviewed and analysed by three authors to minimise bias. The data were collected retrospectively. Our study is single-centred, which limits the generalisability of our findings. We aim to collaborate with other ENT departments to develop a multi-centre study.