DISCUSSION
CE-3D-GRE is able to visualise the normal facial nerve in the geniculate
ganglion, and the tympanic and mastoid segmentswith high resolutionand
moderate signal intensitydue to the presence of the intrinsic
plexus.5,6In pathological conditions, includingRamsay
Hunt syndrome and Bell’s palsy,the facial nerve is intensely enhanced
because disruption of the blood–nerve barrier causes leakage and
further accumulation of contrast material inside the Fallopian
canal.5
We performed CE-3D-GRE at 3.0 Tesla on four patients with otologic
manifestations of AAV as the major initial symptoms. In this study,
intense enhancement in the tympanic and mastoid segments of the
Fallopian canal was clearly associated with development of otologic
symptoms, including external otitis, otitis media, and SNHL. The
enhancement was attenuated to the normal level in accordance with
clinical improvement after immunosuppressive treatment. The results
suggestthat intense enhancement of the Fallopian canal reflects disease
activity of vasculitis in the ear and can be used as a surrogate marker
of otologic involvement of AAV. It is clinically important because the
imaging method may enable early diagnosis, monitoring, and therapy
optimisation of otologic involvement of AAV in a less invasive manner.
The findings in this study provide further insights into the
pathophysiology of vasculitis of the ear. The SMA enters the Fallopian
canal and predominantly supplies the mastoid and tympanic segment of the
facial nerve,4,7 giving off numerous branches to the
mastoid, tympanic cavity, and the posterior wall of the external ear
canal, which are in line with frequent otologic manifestations in AAV.
Our findings on CE-3D-GRE were consistent with pathologic evidence of
vasculitis in the mastoid and tympanic segments in patients with
GPA3and polyarteritis nodosa,8 which
is also known to present with otitis media and facial paresis. We
therefore consider that otologic involvement of AAV is at least in part
caused by vasculitis of the SMA and imaging shows intense enhancement in
the mastoid and tympanic segments of the Fallopian canal on CE-3D-GRE.
Furthermore, our results support vasculitis in the cochlea as anetiology
of SNHL,3 rather than eight-cranial-nerve
neuropathy.2We could not find significant enhancement
in the geniculate ganglion or internal auditory canal on CE-3D-GRE(Fig.
1A). One possible mechanism of nerve involvement in AAV is vasculitis
originating in arterio–venous anastomoses (AVAs), which are 7 m in a
diameter9 and exist only in the stria vascularis and
spiral ganglion of the cochlea9 and the Fallopian
canal7 in the temporal bone. This hypothesis is able
to explain several features of otologic manifestations of AAV. First,
microembolism of AVAs in the stria vascularis and spiral ganglion may
cause a reduction in the endocochlear potential and reversible
SNHL.3Second, vertigo is less frequent and less severe
compared to SNHL,2,3due to the lack of AVAs in the
periphery of both the macular and
crista.10Progression
of the vasculitic process may cause arterial embolism and subsequent
ischaemic necrosis of the peripheral organs. Lastly, facial paresis is
not always in concert with vasculitis in the Fallopian canal, probably
due to occasional connections between AVAs and the vasa nervorum of the
facial nerve.7
This study had limitations due to its study design and the small number
of included patients. Despite this, we showed a clear relationship
between clinical presentations and radiological findings using 3D MRI
acquired at 3.0 Tesla. Further studies are necessary for assessment of
the sensitivity and specificity of the imaging protocol using more
patients and comparison with other ear diseases.