Introduction An endolymphatic sac tumour (ELST) is a rare form of a locally invasive very slowly growing papillary epithelial neoplasm originating from the endolymphatic sac and/or duct ( Wick et al., 2015 ). This single case study exemplifies the usefulness of delayed intravenous gadolinium-enhanced magnetic resonance imaging (iMRI) of the inner ear for differentiation of divers vestibular pathologies in complex cases of dizziness ( Nakada et al., 2014 ). Case report & methods A 48-year old, highly burdened right-handed female patient who had been operated on an ELST in the right petrosal bone presented with three different vestibular symptoms: (i) a persistent to-and-fro vertigo since 20 years, (ii) reproducible position-dependent short vertigo attacks accompanied by an inconsistent nystagmus when laying down on her side (R > L), and (iii) spontaneous rotational vertigo attacks for several hours associated by ear pressure, nausea, vomiting, and diarrhea. The diagnostic work-up included a careful neurootological and neuro-orthoptic assessment, videooculography during oculomotor examination (VOG), caloric stimulation (caloric) and head-impulse (HIT), audiometry, as well as an iMRI 4 h after injection of i.v. contrast agent ( Nakada et al., 2014 ). Endolymphatic hydrops (ELH) was characterized by criteria previously described ( Barath et al., 2014 ). Volumetric assessment used manual segmentation in combination with machine learning and automated local thresholding algorithms ( Gurkov et al., 2015 ). Results The structural MRI showed a focal defect zone in the right cerebellar hemisphere. In line, the neuro-orthoptic examination revealed a cerebellar syndrome with downbeat-nystagmus (DBN) that increased when lying down on her R > L side. Furthermore, a right-sided audio-vestibular peripheral deficit was disclosed (HITmean gain: R = 0.66, L = 0.98; caloricsmean[°/s]: R = 4, L = 11; audiometrymean [dB]: R = 50, L = 15). The iMRI revealed a high-grade unilateral right-sided ELH (R = 87 mm3, Rcochlea(=c) = grade II-III, Rvestibule(=v) = grade III), whereas the left ear showed normal values (L = 32 mm3, Lc/v = grade 0). Discussion On the basis of these results the (i) ongoing vertigo with (ii) exacerbation when lying down on the side could be assigned to a DBN syndrome with central positional vertigo due to the cerebellar lesion. The spontaneous attacks (iii) were caused by a secondary right-sided ELH. The differentiation of aetiologies allowed a stepwise treatment with a combination of 4-aminopyridine (5 × 5 mg/d) to improve the DBN and betahistin (3 × 48 mg/d) to improve the ELH. Both medications lead to a considerable clinical benefit. Here, iMRI was crucial in assigning a complex symptomatology to different central and peripheral vestibular pathologies resulting in a successful treatment ( Brandt and Dieterich ).