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| Journal of the New Zealand Medical Association,
27-August-2010, Vol 123 No 1321
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Until now, imaging of the inner ear has been by computed
tomograpy (CT) scanning which can delineate its bony borders, defects and
congenital abnormalities. Because of their size, imaging of internal structures
has not been possible. Therefore much inner ear pathology has been elucidated
from post-mortem histology.
It is 70 years since temporal bone histology demonstrated
that in Meniere’s disease the fundamental abnormality is an excess of
fluid in the endolymphatic compartment, called endolymphatic hydrops. The
official definition of “definite” Meniere’s disease is attacks
of vertigo accompanied by documented fluctuating hearing and/or aural fullness
in the affected ear, whereas “certain” Meniere’s disease
requires a post-mortem to prove the
hydrops.1
In animal models it had been shown, with long scanning
times, that intratympanic delivery of gadolinium selectively enhances perilymph,
delineating it from endolymph.2 In humans,
medical resonance imaging (MRI) inner ear studies have been limited by the
spatial resolution of 1.5 Tesla scanners. Intratympanic gadolinium was shown to
enter the human ear on 1.5 Tesla scanner in
2005.3
Newer scanners with greater magnetic strength and improved
image sequencing have made ultrastructural detail achievable. On 3 Tesla scans,
human endolymphatic hydrops has been clearly
demonstrated.4–7 The dosage, timing of
administration and safety have been established, and a grading system has been
suggested.8
PatientsMRI inner ear scanning was conducted on two patients: (1) an
80-year-old male with vertigo attacks and mild right ear hearing loss,
experiencing no aural symptoms and not fulfilling the AAOHNS criteria for
Meniere’s disease; and (2) a 46-year-old male year with a 2-year ear
history of vertigo attacks accompanied by progressive hearing loss, tinnitus and
aural fullness in the right ear fulfilling the criteria for Meniere’s
disease.
Twenty-four hours before the scan, multihance gadolinium 1.6
ml in 10 ml saline was introduced to the right middle ear through a small
myringotomy (and replenished 4 to 5 times, a total of 1.0–1.5 ml over 45
minutes with the patient lying to the opposite side).
Images were obtained on a 3 Tesla Magnet (General Electric
HDX). Two inversion recovery sequences were obtained with inversion times of T1
1000 (endolymph) and 2500 (perilymph) in addition to routine 3D Fiesta imaging
of the inner ear/IAMs.
Patient 1. Normal inner ear: no hydropsFigure 1. Perilymph sequence. The cochlea,
vestibule and one semicircular canal are labelled.
 P=perilymph, E=endolymph.
Figure 2. Perilymph sequence. Basal turn of the
cochlea, with normal endolymphatic compartment; no hydrops.
 P=perilymph, E=endolymph.
Patient 2. Meniere’s disease: significant hydropsFigure 3. Perilymph sequence. Significant
enlargement [33–50%] of the endolymphatic compartment in the cochlea; in
the vestibule and semicircular canal endolymphatic hydrops [>50%] has
displaced almost all perilymph.
 P=perilymph, E=endolymph.
Figure 4. Endolymph sequence. Enlargement of
the endolymphatic compartment in the cochlea; endolymph fills the
vestibule.
 E=endolymph.
DiscussionIn these two subjects, MRI inner ear scanning was normal in
Patient 1 and clearly showed endolymphatic hydrops in Patient 2 with a history
fulfilling the AAOHNS criteria for a diagnosis of “definite”
Meniere’s disease.1
The recently proposed hydrops grading
system8 is simple: none, mild, significant. In
the vestibule an endolymph/perilymph ratio of one-third=none; one-third to
one-half=mild; and >50%=significant. In the cochlea, no Resisner’s
membrane displacement=none; Resisner’s membrane displacement with the area
of the endolymphatic compartment not exceeding the area of the scala vestibuli
(perilymph)=mild; the endolymphatic space exceeds the area of the scala
vestibuli (perilymph)=significant.
Early human studies established that intratympanically
administered gadolinium enhances cochlear perilymph within 4
hours6 and the perilymph in all areas by 24
hours.3 In three patients scanned at 6 days the
gadolinium and had almost disappeared.3 In
animal studies a 8-fold dilution of gadolinium had no adverse affects on the
stria vascularis9, and there have been no
reports of it causing hearing loss or aggravating tinnitus.
In Japan, Nakashima et al10
have used MRI imaging to study 73 patients with inner ear diseases including
Meniere’s disease, idiopathic sudden sensorineural hearing loss, and
fluctuating hearing loss without vertigo. They used 3D-real IRI (a 3-dimensional
technique) MRI which gives clearer visualisation of the perilymph space than the
2-dimensional technique used in New Zealand.
MRI scanning of the inner ear is an exciting new development
in the diagnosis of inner ear conditions. Correlation of symptoms with imaging
should significantly contribute to the understanding of inner ear diseases. For
example, recurrent non-positional attacks of vertigo similar to Meniere’s
disease without hearing loss may be due to endolymphatic hydrops, or have an
entirely different pathology.
Conversely, fluctuating hearing loss, tinnitus and aural
fullness often occur without vertigo. Do these people have endolymphatic hydrops
confined to the cochlea? Although patients with unilateral inner ear symptoms
usually receive MRI scanning to exclude vestibular schwannoma/acoustic neuroma,
both this and intratympanic gadolinium are mildly invasive.
Rigorous clinical research will be required to delineate the
role of this new technology in the management of Meniere’s disease and
other inner ear conditions.
Author information: Jeremy Hornibrook and
Philip Bird, Otolaryngologists, Christchurch Hospital, Christchurch; Mark Coates
and Tony Goh, Radiologists, Christchurch Hospital and Christchurch Radiology
Group, Christchurch; Philip Bird, Senior Lecturer, Department of Surgery,
University of Otago, Christchurch
Correspondence: Jeremy Hornibrook,
Department of Otolaryngology-Head and Neck Surgery and Audiology, 2 Riccarton
Avenue, Christchurch 8011, New Zealand. Fax: +64 (0)3 3642073; email: jeremy@jhornibrook.com
References:
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