[Metastasis in the inner auditory canal].

Metastasis in the inner auditory canal (IAC), or more precisely in the pontocerebellar angle (PCA) is extremely rare. Indeed acoustic neurinoma (AN), meningioma and other types of benign neoformations, in decreasing order, account for nearly all expansive pathologies in this anatomical region. The present paper reports a clinical case of a patient with the sudden onset of an hearing loss in the right ear. This hearing loss was promptly followed by paralysis of the homolateral facial nerve. The function of both cranial nerves worsened progressively and rapidly. Cerebral radiology, performed with MRI and the administration of gadolinium, showed a AN-compatible neoformation fundamentally affecting the IAC. However, histological tests performed after surgery indicated an adenocarcinoma. Post-operative instrumental tests identified the primary neoplasm in the lower lobe of the right lung. The purpose of this work was to highlight, in view of the literature on the topic, the main clinical aspects to consider when a malignant expansion is suspected in the PCA. Naturally there is greater basis for such suspicion when a primary malignant neoplasm has previously been diagnosed. Generally AN progresses quite gradually, in line with an extremely slow growth rate. Therefore it is normally seen in a progressive worsening of hearing, tinnitus and equilibrium disorders. Appearance of a facial nerve palsy is strictly limited to relatively large neoplasms and is encountered at a later stage. This is why a rapid progression of hearing damage accompanied, or promptly followed, by complete facial nerve paralysis must alert one to the possibility of a PCA malignancy. Imaging does not permit easy pre-operative diagnosis since the radiological signs and morphologies are often quite similar to those produced by AN. Therefore, post-operative histological examination can hold some surprises.