Malignant Peripheral Nerve Sheath Tumors of the 8th Cranial Nerve Arising without Prior Irradiation

Background/Objectives Malignant peripheral nerve sheath tumors (MPNST) of the eighth cranial nerve are exceedingly rare. To date the literature has focused on MPNSTs occurring after radiation therapy for presumed benign vestibular schwannomas (VS), while MPNSTs arising without prior irradiation have received little attention. The objectives of the current study are to characterize the epidemiology, clinical presentation, disease course, and outcome using a large national cancer registry database and a systematic review of the English literature. Additionally, a previously unreported case is presented.

Methods: Analysis of the Surveillance, Epidemiology, and End Results (SEER) database, systematic review of the literature, and case report. Data from all patients identified in the SEER database with a diagnosis of MPNST involving the eighth cranial nerve, without a history of prior radiation, were analyzed. Additionally, all cases reported in the English literature between January 1980 and March 2015 were reviewed. Finally, one previously unreported case is presented.

Results: The SEER registries identified 30 cases between 1973 and 2012. The average incidence was 0.017 per 1 million persons per year (range 0.000 – 0.0687). The median age at diagnosis was 55 years, and 16 (53%) were women. Fourteen cases were diagnosed upon autopsy. Of the 16 cases diagnosed while alive, the median follow-up was 118 days, with 3 (19%) deaths observed. When compared with the incidence of benign VS, 1,041 VSs present for every one MPNST arising from the eighth cranial nerve. Including a previously unreported case from the authors’ center, a systematic review of the English literature yielded 24 reports. The median age at diagnosis was 44 years, 50% were women, and the median tumor size at diagnosis was 3cm. Eleven (46%) patients reported isolated audiovestibular complaints typical for VS while 13 (54%) exhibited facial paresis or other signs of a more aggressive process. Treatment included microsurgery alone, microsurgery with adjuvant radiation or microsurgery with chemoradiation. 61% of patients receiving treatment experienced recurrence, 22% of which were diagnosed with drop metastases to the spine. Ultimately 13 (54%) patients died of progressive disease at a median time of 3 months following diagnosis. The ability to achieve gross total resection was the only feature that was associated with improved disease-specific survival.

Conclusions: MPNSTs of the eighth nerve are extremely rare and portend a poor prognosis. Nearly half of patients initially present with findings consistent with a benign VS often making an early diagnosis challenging. In light of these data, early radiologic and clinical follow-up should be considered in those who elect non-operative treatment, particularly in patients with a short duration of symptoms or atypical presentation. These data also provide a baseline rate of malignancy that should be considered when estimating risk of malignant transformation following stereotactic radiosurgery for VS.