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.