The degree of EH in the vestibule and cochlea was assessed by visual comparison of the relative areas of the non-enhanced endolymphatic space versus the contrast-enhanced perilymph space in the axial plane, separately for the cochlea and the vestibule. The degree of cochlear hydrops was categorized as none, grade I, or grade II according to the criteria previously described by Baráth et al. [8 (link)] (Fig. 1).

Cropped axial delayed gadolinium-enhanced 3D FLAIR images at midmodiolar area of the cochlea and correlating axial cryosections with hematoxylin and eosin staining (magnification, × 7) and color overlay. a Normal cochlea: In the normal cochlea, one can recognize the interscalar septum (arrow), the scala tympani, and scala vestibuli. The scala media is normally minimally visible. b Cochlear hydrops grade I: The scala media becomes indirect visible as a nodular black cut-out of the scala vestibuli (arrow). c Cochlear hydrops grade II: The scala vestibuli (arrow) is fully obliterated due to the distended cochlear duct

However, for the degree of the vestibular hydrops, we used a modified grading system, as in our experience there were patients with subtle abnormalities who were categorized as normal according to the three-stage grading system of Baráth. We added a lower grade I vestibular hydrops in which the saccule, normally the smallest of the two vestibular sacs, became equal or larger than the utricle but is not yet confluent with the utricle. In this modified four-stage grading system, the Baráth grade I became grade II, and the Baráth grade II became grade III (Fig. 2). The visual assessment of the saccule-to-utricle ratio was done on the lowest axial images at the inferior part of the vestibule as, according to histological studies, the saccule occupies the inferior, medial, and anterior part of the vestibule [9 (link)].

Cropped axial delayed gadolinium-enhanced 3D FLAIR images at the inferior part of the vestibulum and correlating axial cryosections with hematoxylin and eosin staining (magnification, × 7) and color overlay. a Normal vestibule: The saccule (small arrowhead) and utricle (large arrowhead) are visibly separately and take less than half of the surface of the vestibule. b Vestibular hydrops grade I: The saccule (small arrowhead), normally the smallest of the two vestibular sacs, has become equal or larger than the utricle (large arrowhead) but is not yet confluent with the utricle. c Vestibular hydrops grade II: There is a confluence of the saccule and utricle (arrowhead) with still a peripheral rim enhancement of the perilymphatic space (arrow). d Vestibular hydrops grade III: The perilymphatic enhancement is no longer visible (arrowhead). There is a full obliteration of the bony vestibule. Also notice in this case, the beginning utricular protrusion in the non-ampullated part of the LSCC (arrow)

The degree of PE was also evaluated semi-quantitatively in all ears by visually comparing the degree of enhancement of the concerning ear with the contralateral ear. The degrees of enhancement both for the vestibule and cochlea were classified separately into three groups: less, equal, or more (Fig. 3). In case of a grade 3 vestibular hydrops, the evaluation of the vestibular PE is considered as non-applicable since there is no visible perilymphatic space left to evaluate.

Axial delayed gadolinium-enhanced 3D FLAIR images at the level of the inner ear in a 77-year-old woman with unilateral left-sided definite MD and cochlear hydrops grade I (small arrowhead) and vestibular hydrops grade II according to the four-stage grading system (large arrowhead). Note increased vestibular (small arrow) and cochlear (large arrow) perilymphatic enhancement (PE) on the symptomatic side compared with the normal right labyrinth. This is the signature of BPB-impairment

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