2. Methods
Ethical review board approval was provided by the institutional review
board for this observational study. All examinations were performed in
concordance with the Helsinki Declaration revised 2013.
2.1. Participants
Patients with certain MD according to the AAO-HNS classification
(1995)(11) and with MR morphologic
confirmation of endolymphatic hydrops (ELH) as an equivalent to the
required histopathological findings were included in the study
(4, 12-14).
All of these patients underwent MRI on a clinical 3 Tesla scanner
investigation with a sequence protocol comprising several different MR
sequences described below. All patients gave their informed consent for
the locally enhanced inner ear MRI (LEIM). Morphometric analysis of the
VIIth and VIIIth cranial nerves was
performed retrospectively. 24 hours prior to the MRI scan a
gadolinium-based contrast agent diluted 8-fold in saline solution, was
intratympanically injected (15). After
administration, the patient remained in a supine position for another 30
minutes with the head turned approximately 45 degrees toward the
contralateral side.
Patient data consisting of CISS-0.6-sequence measurements was compared
in our previous study to clinical healthy controls
(8). In the current study we compared the
affected side with the non-affected side of unilaterally affected MD
patients as well as the bilaterally affected MD patients vs. unilateral
affected MD patients using the mentioned different MRI sequences.
2.2. Setting with MR Imaging
All MR imaging examinations were performed on a 3T MR unit (Magnetom
Verio, Siemens Healthcare, Erlangen, Germany) using a commercially
available 4-channel flexible surface coil combined with an 8-channel
head coil.
The following MR-sequences were acquired of the temporal bone:
CISS-0.6 : A strongly T2-weighted constructive interference in
steady state sequence (CISS) with the following parameters was used: TR
7.2 ms, TE 3.16 ms, flip angle of 70°, field of view of 192 x 192 mm²,
matrix size of 320 x 320, averages 1 and slice thickness of 0.6 mm.
CISS-0.4 : The second CISS had the following parameters: TR 6.24
ms, TE 2.87 ms, flip angle of 70°, field of view of 160 x 160 mm²,
matrix size of 320 x 320, averages 1 and slice thickness of 0.4 mm.
IR-0.5 : The inversion recovery sequence was acquired using the
following parameters: TR 6000 ms, TE 155 ms, flip angle of 180°, field
of view of 160 x 160 mm², matrix size of 320 x 320, averages 1 and slice
thickness of 0.5 mm.
IR-0.3 : The second inversion recovery sequence had the following
parameters: TR 6000 ms, TE 155 ms, flip angle of 180°, field of view of
160 x 160 mm², matrix size of 256 x 256, averages 1 and slice thickness
of 0.3 mm.
2.3. Design and analysis
We used a commercially available DICOM-Viewer (OsiriX v.4.0, 64-bit
version, Pixmeo, Switzerland) for measuring the diameters of the
VIIth and VIIIth cranial nerves.
Consistent windowing levels and thin slice thickness were used
performing transverse reformats at different locations throughout the
course of the nerves from the cerebellopontine angle (CPA) to the
internal auditory canal (9) fundus.
Locations of the transverse sections were defined as follows:
- VIII – CPA,
- CN, SVN and IVN - meatus of the IAC;
- VII – CPA, meatus of the IAC, fundus of the IAC.
On each transverse section the long diameter (LD), short diameter (SD)
perpendicular to LD and cross-sectional area (CSA) were measured.
Several dot-markers were positioned on the outline of the examined
nerves. These markers were linked and the CSA was calculated. All
measurements were performed by the same two readers based on consensus
readings. Both readers were blinded for the diagnosis of the patients.
All these measurements were made for the CISS-0.4, the CISS-0.6, the
IR-0.3 and the IR-0.5 sequences to investigate different nerve sizes
depending on the used MRI sequence.
All patients received locally enhanced inner ear MRI (LEIM). The study
group was subdivided into two cohorts: The first cohort consisted of
unilaterally affected MD patients; the second consisted of bilaterally
affected MD patients.
For comparing the affected and the clinically non-affected side a paired
samples (dependent) t-test was employed using MedCalc v.12.7.2 (MedCalc
Software bvba, Belgium) and SAS v. 9.4 for Windows (Copyright SAS
Institute Inc., Cary, NC, USA). After Bonferroni correction P
< 0.05 was reduced to P < 0.000595 for statistical
significance. For comparing the subgroups of different symptom duration
a two-sided independent samples t-test was used. Furthermore we used
Scatterplots, Pearson Correlation Coefficients and Bland-Altman plots
for visualization of the degree of correlation as well as measurement
differences between the employed MRI sequences.