The essential point of our method is the fast measurement of the saccule, enabling us to visualise a saccular hydrops in 84% of patients with Meniere disease, in agreement with previously published data [4,5,6,7,8,9,10,11,12,13]. In Meniere disease, the saccule appeared elongated with an increased average height, round shape, or in few cases not visualised on the side of the clinical symptoms, compared to normally shaped and sized saccules in the control group and on histological sections, where it was always visible and oval-shaped. The non-visualisation of the saccule in Meniere disease has a possible histopathological explanation. In fact, Kimura and Schucknecht  and Schucknecht and Rüther  described ruptures and fistulas of the membranous labyrinth on temporal bone sessions, which could cause this non-visualisation.
The endolymphatic hydrops associated with Meniere disease was firstly described by Hallpike and Cairns in 1938  and confirmed by Altman and Fowler in 1965 . In a more recent study on temporal bones, Rauch et al.  described the involvement of the saccule in almost all cases of endolymphatic hydrops. According to Horner , the degree of saccular dilation appeared correlated to the degree of membranous distortion towards the footplate. This was confirmed by Morita et al. , who described a saccular hydrops on the pathological side in Meniere disease patients, while the cochlear and utricular hydrops were less frequent.
To our knowledge, our study is the first one to analyse both size and morphology of the saccule in patients with Meniere disease without intravenous or intratympanic contrast material injection. Most of the authors used fluid attenuated inversion recovery (FLAIR) or three-dimensional inversion-recovery turbo spin-echo sequences, acquired 4 h after intravenous Gd-based contrast material injection [5, 6, 20,21,22,23,24]. Naganawa et al.  have been able to individualise the endolymph from the perilymph using a three-dimensional inversion-recovery turbo spin-echo sequence after intravenous injection of a Gd-based contrast material, but they were unable to separate the utricle from the saccule, contrary to Attye et al. . One of the downsides of these methods using contrast injection is the time needed for the penetration of the Gd-based contrast material in the perilymph (approximately 4 h) while the required injection also exposes the patient to potential Gd-related risks. The main advantage of the method proposed by Naganawa et al.  is given by the morphological visualisation of the anterior membranous labyrinth, although Attye et al.  gave examples of dilation of the cochlear duct in their normal population; thus, the significance of a dilated cochlear duct is uncertain. On the contrary, in our study the saccule only appeared dilated in Meniere disease and no pathological dilation of the saccule was observed in the control group.
Other authors, such as Seo et al. , Sun et al. , or Fiorino et al. , used FLAIR images acquired 24 h after intratympanic gadolinium injection. Seo et al. , using MRI images acquired 24 h after intratympanic injection, found a hydrops in 81% of their patients (21/26) with saccular involvement in the majority of the cases (19 patients, 69%).
Our method enables a fast diagnosis of Meniere disease in less than 8 minutes. Its other major strength is that it does not require intravenous or intratympanic injection of a Gd-based contrast material. The major downside of the T2-weighted gradient-echo SSFP sequence (FIESTA-C) may be its sensitivity to motion artefacts. In our study, it involved 6/128 subjects (5%), mostly related to swallowing. When compared to the literature, all sequences used for the imaging of the membranous labyrinth are quite long: 9 minutes in Attye et al.  and 14 min in Sun et al. , compared with 7 min and 49 s in our study.
Notably, three-dimensional T2-weighted turbo-spin-echo sequences (such as SPACE, CUBE, VISTA) would also work for the measurement of the saccule as long as the special resolution is sub-millimetric, but unlike gradient-echo sequences, spin-echo sequences are not sensitive to fluid composition [26, 27]. Thus, using gradient-echo SSFP sequences, such as FIESTA-C in our study, true fast imaging with steady state precession (trueFISP) sequences, or constructive interference steady state (CISS), sequences, additional information can be obtained, such as signal changes of the liquids of the inner ear that might be seen in case of schwannomas or meningiomas of the internal auditory canal, or labyrinthitis [26, 27].
To conclude, a simple 8-minute T2-weighted gradient-echo SSFP sequence (FIESTA-C), performed at 3 T, is a fast and anatomically accurate method to diagnose Meniere disease without injection of Gd-based contrast material. The measures are sub-millimetric, but the interobserver and intraobserver agreements were good, with κ ranging from 0.68 to 0.94. In Meniere disease, an endolymphatic hydrops with saccular abnormality was present in 84% of the cases, an elongated saccule (height > 1.60 mm) in 86% of the cases, an increased saccular width (>1.40 mm) in 44% of the cases (isolated in 4%), a missing saccule in 8% of the cases.