Journal of Otology & RhinologyISSN: 2324-8785

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Case Report, J Otol Rhinol Vol: 3 Issue: 3

Spontaneous Size Regression of a Vestibular Schwannoma

Nicholas J Scalzitti* and Travis J Pfannenstiel
Department of Otolaryngology San Antonio Uniformed Services Health Education Consortium, San Antonio, Texas, USA
Corresponding author : Nicholas Scalzitti
2338 Jarve Valley, San Antonio, TX 78251, USA
Tel: 630-308-0359/210-916-8040; Fax: 210-916-8366
E-mail: [email protected]
Received: February 03, 2014 Accepted: April 21, 2014 Published: April 30, 2014
Citation: Scalzitti NJ, Pfannenstiel TJ, (2014) Spontaneous Size Regression of a Vestibular Schwannoma. J Otol Rhinol 3:3. doi:10.4172/2324-8785.1000155

Abstract

Spontaneous Size Regression of a Vestibular Schwannoma

Vestibular schwannomas are the most commonly occurring skull base tumors. Increasing availability of magnetic resonance imaging has allowed early recognition of these tumors and better characterization of their natural course. Recently, several series have presented data with regard to the slow growth of these tumors and challenged the need for tumor resection or radiation in cases involving small to medium-sized tumors. This is a case report of spontaneous regression of a medium-sized vestibular schwannoma occurring after initial slow tumor growth.

Keywords: Skull base tumor; Vestibular schwannoma; Tumor resection; Serial high-resolution MRI

Keywords

Skull base tumor; Vestibular schwannoma; Tumor resection; Serial high-resolution MRI

Introduction

Vestibular schwannoma (VS), also called acoustic neuroma, is a common benign tumor of the supporting cells of the eighth cranial nerve axons. VS accounts for as much as 6% of all intracranial tumors, representing about 13 cases per 1 million people per year [1]. With the increased use and improved resolution of magnetic resonance imaging (MRI), smaller and more commonly asymptomatic tumors are being discovered, and the medical and surgical paradigms for their management continue to evolve. Treatment options for vestibular schwannoma include: observation, stereotactic radiosurgery, stereotactic radiotherapy, and microsurgical resection. Conservative management with serial imaging has become more common for small and medium-sized tumors, as data demonstrating the slow growth and limited morbidity of observing these tumors over extended periods has become available. The growth rate of vestibular schwannoma has been studied extensively, and a recent meta-analysis defined the range of growth as 0.3-4.8mm per year, with a mean of 1-2 mm per year [2].
We present a patient whose vestibular schwannoma exhibited initial growth before diminishing in size over several years of observation. Previously published case series estimate from 4% to 13% of vestibular schwannomas may regress spontaneously [3]. Unique to this case is a period of slow or typical growth followed by dramatic regression in tumor size.

Case Report

A 75-year-old male was initially diagnosed via contrast-enhanced MRI with a right sided medium-sized vestibular schwannoma as part of an evaluation for unilateral profound deafness. The patient’s only symptoms relative to the VS were right sided profound hearing loss and tinnitus. He denied any imbalance, vertigo, facial nerve dysfunction, or other cranial nerve deficit. The patient’s medical history was significant for several existing comorbidities: peripheral vascular disease, chronic obstructive pulmonary disease, carotid artery stenosis, and hypertension. The three primary treatment options were presented to the patient, including: observation, microsurgical resection, and radiotherapy. He was found at the time of initial presentation to be a poor candidate for microsurgical resection secondary to his failing general health status. He declined stereotactic radiotherapy and stereotactic radiosurgery in favor of observation.
During the initial four years following diagnosis, the tumor was surveyed with serial high-resolution MRIs (Figures 1 and 2). The patient presented with and maintained a profound hearing loss on the affected side with no significant change in his contralateral hearing thresholds or discrimination. During the initial observation period, the tumor showed mild growth without brainstem compression. The patient continued to decline radiation as a treatment modality, and his health status worsened to requiring supplemental home oxygen therapy. Due to more pressing medical and social issues, the patient was lost to follow-up for a period of 4 years. The patient presented back to the Neurotology clinic due to a new symptom of infrequent right sided headache. An interval MRI examination was ordered and demonstrated a significantly smaller tumor (Figure 3).
Figure 1: High Resolution T1-weighted post-contrast MRI performed at initial diagnosis in 2004.
Figure 2: High Resolution T1-weighted post-contrast MRI in 2006 showing initial growth of tumor.
Figure 3: High Resolution T1-weighted post-contrast MRI in 2012 showing tumor regression.
The change in tumor size over its 8 year clinical history is demonstrated in Table 1. Two separate linear measurement methods for tumor size were used. The first technique measures the largest extrameatal diameter in a direction parallel to the petrous ridge, and the second employs the measurement guideline endorsed by the American Academy of Otolaryngology’s Committee on Hearing and Equilibrium in 1995 [4,5]. As seen in Table 1, the tumor exhibited mild growth from the time of its initial identification in 2004 to a follow-up MRI in 2006 (15.6% and 7.1% growth by the 2 employed measurement techniques respectively). Exams subsequent to that time have shown regression in size to its most recent state. The 2012 MRI (Figure 3) demonstrates a nearly 50% reduction compared to the tumor at its largest known size in 2006.
Table 1: Size of tumor measured by two methods at different times. Percentage in parentheses demonstrates percentage (%) of maximum tumor size.

Discussion

Size regression of a vestibular schwannoma is not a novel finding, but this case represents tumor shrinkage to a degree not previously reported. Further, the reduction in size was seen after first demonstrating mild growth (~1 mm/year). Increase in tumor diameter demonstrated on serial MRI has been suggested as a predictor of future growth; [1,6] although, not all algorithms would consider the mild growth seen with this tumor justification for intervention [7]. This initial growth did prompt a discussion with the patient regarding a need for microsurgical or radiosurgical intervention to prevent the morbidity associated with large vestibular schwannomas including: facial nerve injury, facial hyperesthesia, and other cranial neuropathies.
Few studies of tumor progression have identified reliable predictive factors. A large retrospective study by Malhotra et al. found the presenting symptom of disequilibrium, or new-onset disequilibrium during conservative management, to be significantly higher in the group requiring further intervention. They also found initial tumor size to be statistically different between the intervention and non-intervention groups, but no threshold size could be identified [8].
Several published studies have compared outcomes of conservative management of small and medium vestibular schwannomas with surgical or radiosurgical treatments. Gamma knife radiosurgery has been shown to reduce the likelihood of tumor growth with minimal impact on hearing outcomes over time relative to untreated controls [9]. Two separate studies have found a progression of hearing loss to be the natural course of vestibular schwannoma, regardless of tumor growth. This has been hypothesized to result from inner ear ischemia or protein shedding from the tumor [9,10]. Our patient did not recover hearing as the tumor regressed in size, but recovery from profound deafness regardless of cause several years after onset is extraordinarily rare.
The exact cause of this tumor’s decrease in size cannot be determined. Cyst rupture, microvascular compromise, host-immune response, or a currently undetermined process could have caused the lesion’s size regression. Serial magnetic resonance imaging of this patient did demonstrate bilateral internal carotid artery atherosclerosis and the sequelae of chronic small vessel ischemic disease. In the absence of any treatment, it is possible that tumor growth became compromised due to microvascular ischemia of the tumor itself.
Our report further supports the continued need for research into the growth behavior of these tumors, as growth is often the determining factor in the decision for treatment. Unfortunately, identifying which tumors will grow continues to be an elusive task.

Conclusion

Management of patients with vestibular schwannoma requires an extended informed consent process to provide patients with a foundation from which to determine their treatment choice. This case demonstrates a tumor exhibiting dramatic size regression following a period of slow or typical growth. This is an uncommon but not isolated phenomenon and should be considered in the informed consent discussion and as part of the natural history of the disease when designing studies of treatment efficacy.

Disclaimer

The views expressed herein are those of the authors and do not reflect the official policy or position of the San Antonio Military Medical Center, the U.S. Army Medical Department, the U.S. Army Office of the Surgeon General, the Department of the Army, Department of Defense or the U.S. Government.

Conflict of Interest

Authors do not have any conflict of interest.

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