Bilateral malignant metastases to the internal auditory canal: radiosurgical management

Abstract

Malignant melanomas constitute 1-8% of all malignant tumors and are the third most common tumor to metastasize to the central nervous system. However, metastases to the cerebellopontine angle (CPA) are rare, accounting for only 0.2 to 0.7% of the lesions identified in this location Case Report. A 62-year-old white man with a history of melanoma of the back, who had had all lesions completely excised, was reportedly tumor-free for 6 years. The patient presented bilateral metastatic CPA melanoma. Left side tumor was treated with surgery with partial resection (lost hearing) and radisorugery. Right side lesion was treated with radiosurgery and hearing preserved for 8 months, tumor controlled for 12 months, until death due to leptomeningeal carcinomatosis after 13 months of radiosurgey.

The patient underwent intensity-modulated stereotactic radiosurgery using BrainLab Iplan 4.1 for both IAC lesions, the dose was 18Gy prescribed to the 80% isodose line delivered by 11 fields. The patient presented no post-radiosurgery neurological complications. Conclusion: In patients with lesions in the CPA, a diagnosis of melanoma should be included, particularly in cases with rapid progression of symptoms. Therefore, radiosurgery is a viable treatment option since the hearing can be preserved and tumor control achieved.

INTRODUCTION

Malignant melanomas constitute 1 to 8% of all malignant tumors and are the third most common tumor to metastasize to the central nervous system. They comprise 11.7% of all cerebral metastases, can be solitary or multiple and are typically located in the gray matter,at the gray matter-white matter junction.[10] However, metastases to the cerebellopontine angle (CPA) are rare, accounting for only 0.2 to 0.7% of the lesions identified in this location. [5]

CASE REPORT

The patient, a 62-year-old white man with a history of melanoma of the back, who had had all lesions completely excised, was reportedly tumor-free for 6 years. He presented left sided hearing loss for 6 months without facial palsy.

Magnetic resonance imaging (Figure 1) revealed a hyperintense right CPA lesion on a T1-weighted sequence. Axial T1-weighted sequence MRI with contrast demonstrated an enhancing 2.5 cm tumor filling the right internal auditory canal (IAC) and a left-sided enhancing tumor of 1.4 cm.

Figure 1.

Axial T1-weighted MRI scan showing a hiperintense bilateral CPA mass lesion at presentation.

The patient was submitted to left suboccipital craniectomy. During surgery, observation verified that the tumor was quite vascular and adherent to the nerves. A subtotal resection was performed. Histopathological examination of the tumor with immunohistochemical stains confirmed the diagnosis of a malignant melanoma. The patient developed postoperative total deafness in the left ear and facial palsy. He recovered the facial function one month later.

Lumbar puncture (LP) and cytology test revealed no malignant cells in the cerebrospinal fluid (CSF). A detailed search by a dermatologist revealed no suspicious dermal, mucosal, or subungual lesion. Chest and abdominopelvic CT scans revealed no suspicious lesion.

The patient received intensity-modulated stereotactic radiosurgery for both left and right IAC lesions, the radiosurgery dose was 18Gy prescribed to the 80% isodose line delivered by 11 intensity-modulated beams (figures 2 and 3). The patient presented no postradiosurgery neurological complications.

He presented progressive right-sided hearing loss eight months later, audiometry confirmed sensorineural hearing loss in the right ear. He remained disease free for 12 months post-radiosurgery confirmed by IRM. The patient developed meningeal carcinomatosis confirmed by LP and received whole-brain irradiation. Despite aggressive treatment, he died 13 months post-radiosurgery.

DISCUSSION

Cerebellopontine angle melanoma is rare, but metastases to this location may be increasing as the incidence of melanoma increases. Brackmann & Doherty identified eight cases in more than 6,500 CPA lesions treated at the House Clinic over a 35-year period. These malignant tumors may be primary or secondary. [3,8]

In review of the literature, Gerganov et al reported 17 cases of such metastases. The average age of the patients was 49.8 years-old and their neurological signs and symptoms at presentation were related to cochlear or vestibular nerve dysfunction. [5] The mean interval from primary melanoma treatment to CPA metastasis was 7.7 years and the mean duration of survival after diagnosis of metastasis was 11 months. In contrast, for patients with primary CPA melanoma the average age was 43.5 years-old and their neurological signs were the same as a metastatic CPA melanoma. The mean duration of survival after diagnosis was 30 months.

Signs suggesting a diagnosis of CPA melanoma include a history of cutaneous or other melanoma, magnetic resonance imaging (MRI) findings and CPA syndrome with rapid progression of symptoms, including hearing loss, vertigo and facial palsy. [1] Ataxia representing cerebellar parenchymal invasion may be a prominent symptom. [4] Typically, CPA melanomas are hyperintense on T1-weighted images and hypointense or isointense on T2-weighted images and are enhanced after the administration of gadolinium. Conversely, amelanotic (i.e., nonpigmented) melanomas display isointensity to hypointensity on T1-weighted images and hyperintensity to isointensity on T2-weighted images and hyperintense on FLAIR sequences. [1,5] The neuroimaging features are not conclusive and cannot exclude the diagnosis of metastatic melanoma. The only characteristic specific to metastasis is the presence of multifocal cerebral lesions. [6]

A review of the literature, identified only 21 cases with CPA melanoma, of these only four patients received treatment by radiosurgery. Pangioutou et al reported that the treatment of cerebral melanoma metastases should be surgical. [8,7] Removal of solitary intracranial metastases was associated with a median survival of 12 months, whereas similar patients treated with radiosurgery and chemotherapy survived only 5 months. Radiosurgery is the first line of treatment only in patients with positive CSF cytology for malignant cells. [4]

Figure 2.

Radiosurgery treatment plan of the left CPA mass lesion by Brain Lab Iplan.

Figure 3.

Radiosurgery showing treatment plan of the right CPA mass lesion by Brain Lab Iplan.

Figure 4.

Axial T2-weighted MRI scan 12 months after SRS showing disappearance of the right lesion and decreased left lesion.

Brackman & Doherty reported eight patients with CPA melanoma, of these, six patients were initially submitted to surgical treatment and two patients with meningeal carcinomatosis received whole-brain radiotherapy. [3] Two patients received radiosurgery following surgical treatment.

In the present study, the diagnostic was confirmed by histopathological examination of the resected tumor. The survival of the patient post-radiosurgery was 13 months, similar to the surgical series, and he died due meningeal carcinomatosis rather than progression of the CPA lesions. In selected patients, radiosurgery should be considered as a first line treatment, because it is minimally invasive with low morbidity.

CONCLUSION

For patients with lesions in the CPA, a diagnosis of melanoma should be remembered included in the differential, particularly in cases with rapid progression of symptoms. Radiosurgery is a viable treatment option since the hearing can be preserved and tumor control achieved.