![]() ![]() Table 1 lists the location of the FNSs and basic clinical data of the cases. The involved portions of the facial nerve by these lesions were divided into the following 8 segments: cerebellopontine angle cistern segment, internal auditory canal segment, labyrinthine segment, geniculate fossa, greater superficial petrosal nerve involvement, tympanic segment, mastoid segment, and extracranial segment. In 12 cases, both CT and MR imaging were performed. The imaging examinations were collected from 1986 to 2000 and consisted of CT (18 studies 75%), MR imaging (17 studies 77%), and high-resolution MR imaging with thin sections through the temporal bones (11 cases 46%). Seventeen (71%) of these 24 lesions were pathologically confirmed, while the others were determined intraoperatively or diagnostically by the presence of both enlargement of the facial nerve canal and enhancement on contrast-enhanced MR imaging examinations. One patient presented with bilateral lesions and had a known history of neurofibromatosis type II. The clinical and pathologic records and imaging studies of 23 patients with 24 FNSs within the temporal bone were retrospectively reviewed. Finally, a mastoid segment FNS could break into adjacent mastoid air cells, thereby appearing as an aggressive tumor, especially on MR imaging. A tympanic segment FNS often lobulated into the middle ear cavity, losing its tubular configuration. When a FNS extended along the greater superficial petrosal nerve, a round middle cranial fossa extra-axial mass was seen. FNSs centered in the geniculate fossa most commonly conformed to the classic tubular description of the lesion or were seen as round masses enlarging only the fossa itself. Cerebellopontine angle-internal auditory canal (CPA-IAC) FNSs were indistinguishable from acoustic schwannomas if they did not enter the labyrinthine segment of the facial nerve canal. ![]() 3 This retrospective review of the clinical and radiologic records of 24 FNSs was undertaken to determine whether this classic radiologic description accurately applies to all FNSs.Īlthough the classic description of FNS was identified, 5 additional distinct imaging appearances were seen along the course of the facial nerve. 1, 2 The lack of a large radiologic series of these lesions has resulted in a uniform imaging description of an enhancing tubular mass (using MR imaging) in a smoothly enlarged facial nerve canal (using CT). When the mastoid segment of the facial nerve is involved, irregular and “invasive“ tumor margins seen on MR can be explained on CT as tumor breaking into surrounding mastoid air cells.įacial nerve schwannomas (FNSs) are rare lesions that can arise anywhere along the course of the facial nerve, from its origin in the cerebellopontine angle to its extracranial ramifications in the parotid space of the extracranial head and neck. FNS of the tympanic segment of the facial nerve preferentially pedunculate into the middle ear cavity, clinically presenting as a middle ear mass. When FNSs track along the greater superficial petrosal nerve, they may present as a round mass projecting up into the middle cranial fossa. Lesions traversing the labyrinthine segment can demonstrate a dumbbell appearance. Modern imaging techniques, however, demonstrate the importance of the surrounding anatomic landscape, leading to various imaging appearances. The most common clinical presentation was facial neuropathy (42%).ĬONCLUSION: The classic description of FNS on enhanced T1 MR is that of a well-circumscribed fusiform enhancing mass along the course of the intratemporal facial nerve with bone algorithm CT showing sharply defined bony canal enlargement. The most common location was in the geniculate fossa (83%), followed by the labyrinthine and tympanic segments of the facial nerve (both 54%). Eighteen (71%) of the 24 FNSs were pathologically confirmed, while the others were determined intraoperatively or diagnostically by the presence of both enlargement of the facial nerve canal and enhancement on contrast-enhanced T1 MR examination. RESULTS: The average age at time of first imaging was 39 years (age range, 10–70 years). The lesions were cataloged by facial nerve segment with the imaging characteristics of each segment described. Each FNS was evaluated for location along the facial nerve. MATERIALS AND METHODS: The clinical, pathologic, and radiologic records of 24 FNS in 23 patients were retrospectively reviewed. The purpose of this study is to identify how often the FNS imaging findings conform to this description and determine whether there are underlying anatomic explanations for the discrepant imaging appearances identified. BACKGROUND AND PURPOSE: The imaging appearance of facial nerve schwannomas (FNSs) has been described as an enhancing tubular mass (using T1-enhanced MR) within an enlarged facial nerve canal (using CT). ![]()
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