術前に鼓索神経腫瘍が疑われた鼓室内炎症性偽腫瘍例

Inflammatory pseudotumor (IPT) is a rare, benign or intermediate pathological lesion that can occur in any of various organs. Some cases of IPT of the temporal bone have been reported, but it is not fully elucidated how it should be managed or treated. We report the case of a 47-year-old man who presented to us with left-sided tinnitus. Pure-tone audiometry revealed no hearing impairment. CT showed no erosion of either the ossicular chain or the external auditory canal in the left temporal bone. T1-weighted MRI indicated an iso- to low- intensity mass in the left mesotympanum, with fluid collection in the hypotympanum. Non-echo-planar diffusion MRI did not demonstrate any mass, which is atypical for cholesteatoma. Because a rare entity such as tumor of the chorda tympani was suspected at first, we performed tympanoplasty. The mass was successfully removed from the chorda tympani without safety margins, preserving the chorda tympani. Postoperative histopathological examination showed an heterogeneous inflammatory lymphatic cell infiltration with fibrous tissue, consistent with the diagnosis of IPT. IPT usually has a good prognosis, but the risk of recurrence and rare fatal outcome warrant careful postoperative observation.