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R. NICKBRYANMDS. JAMESZINREICHMD
The complete set of MRIs show bulbous enlargement of the left IAC, as well as meningeal thickening and enhancement of the left parietal convexity and the inferior left margin of the tentorium. The patient elected to undergo a translabyrinthine approach to the IAC. Intraoperative frozen section suggested malignant disease, which meant that the patient would require postoperative radiation therapy as the primary treatment modality. As complete tumor resection was impossible without sacrificing the seventh cranial nerve, a thorough, but incomplete dissection of the tumor was undertaken, which allowed the facial nerve to remain intact. Also, the dura over the posterior fossa remained completely intact, which avoided the possibility of the tumor spreading intradurally. The residual tumor was addressed with whole-brain radiation therapy.
Involvement of the IAC by a metastatic lesion may not be rare; however, an isolated lesion within the IAC, affecting no other portion of the temporal bone, is noteworthy. A study of the temporal bones of 357 subjects found microscopic evidence of metastatic tumor in 13 patients (4%).1 Gloria-Cruz et al2 screened 864 autopsy reports and subsequently studied the temporal bones of 212 patients with primary nondisseminated malignant neoplasms. Of these 212 patients, 47 (22%) were found to have microscopic evidence of metastasis to the temporal bone. The most common primary site of metastasis to the temporal bone is the breast, followed by the lung.2,3 The apex of the petrous portion of the temporal bone was the most frequently affected site, accounting for 35.6% of metastases according to 1 study. The second most common site according to the same study was the IAC, at 17.5%.4
Gloria-Cruz et al2 reported that of the 47 patients with temporal bone metastases, only 2 had isolated IAC lesions. Furthermore, one of these patients had an astrocytoma, and the other had a carcinoma of the lung that had previously involved the brain. In other words, of the 864 people whose autopsy reports were initially screened, none had an isolated IAC lesion who did not already have brain involvement.
There are 2 distinct patterns of temporal bone metastasis from noncontiguous, distant primary lesions, excluding those tumors that may affect the temporal bone via direct extension: (1) hematogenous spread of carcinoma, resulting in the seeding of petrous bone marrow spaces; and (2) tumor cell spread through the CSF. In the latter, the cells are thought to disseminate through the subarachnoid space and into the IAC.4 Breast cancer specifically has a tendency to seed the central nervous system, and anywhere from 7% to 33% of patients with breast cancer have been shown to have dural metastasis post mortem.5 Our patient's metastasis most likely is representative of the second pattern. This assumption is based on the likely parietal dural involvement with the cancer, represented by thickening on the MRIs (not all shown herein), suggesting a CSF spread rather than a hematogenous spread.
Otitis interna carcinomatosa, or the metastasis of malignancy, via the CSF to the IAC was first described in 1926.6 Symptoms of otitis interna carcinomatosa include rapidly progressive or sudden sensorineural hearing loss, tinnitus, loss of vestibular function in the form of unsteadiness rather than vertigo, poor speech discrimination, and facial palsy.3,7 However, not all metastatic lesions of the IAC are symptomatic. In fact, Streitmann and Sismanis4 reported that 32% of IAC metastases are asymptomatic, with lesions found incidentally on autopsy.
When there is a clinical picture suggestive of otitis interna carcinomatosa, a lumbar puncture and cytologic analysis of a CSF specimen can be helpful. Berlinger et al7 reported increased pressure in CSF in a patient with otitis interna carcinomatosa. They also found a high protein content, increased white blood cell count, and a strong likelihood of malignant cells. However, these are not constant findings, as was reported by Grain and Karr8 in 1955, who, after evaluating CSF specimens from 65 patients with diffuse leptomeningeal carcinomatosis, reported that it is not rare to have unremarkable findings on the CSF evaluation.
Otitis interna carcinomatosa poses a diagnostic dilemma. Magnetic resonance imaging with gadolinium contrast is an essential step in the evaluation of idiopathic sudden sensorineural hearing loss.9 Acoustic neuroma is well recognized as the most common neoplasm of the IAC.10 Consequently, the vast majority of IAC lesions that enhance on MRIs are acoustic neuromas.11 Among the rare cases in which an IAC lesion seen on MRI scan is not an acoustic neuroma, meningioma, or epidermoid cyst, metastasis represents fewer than 15% of the eventual diagnoses.11 Other possibilities include hemangioma, facial nerve sheath tumor, arteriovenous malformation, sarcoidosis, lipoma, and lymphoma.11,12 Unfortunately, some of these lesions, including metastases, will enhance similarly to acoustic neuromas on MRI scans. Therefore, the preoperative diagnosis of metastasis vs acoustic neuroma is often impossible.12
Diagnosis Radiology Quiz Case 1. Arch Otolaryngol Head Neck Surg. 2002;128(10):1215. doi:
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