Medial acoustic neuromas: clinical and surgical implications

Clinical article

Ian F. DunnDepartment of Neurosurgery, Brigham and Women's Hospital, Harvard Medical School, Boston, Massachusetts;

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Wenya Linda BiDepartment of Neurosurgery, Brigham and Women's Hospital, Harvard Medical School, Boston, Massachusetts;

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Kadir ErkmenDepartment of Neurosurgery, University of Texas Medical School at Houston, Texas;

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Paulo A. S. KadriDepartment of Neurosurgery, Federal University of Mato Groso do Sul, Campo Grande, Brazil;

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David HasanDepartment of Neurosurgery, University of Iowa Carver College of Medicine, Iowa City, Iowa;

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Chi-Tun TangDepartment of Neurological Surgery, Tri-Service General Hospital/National Defense Medical Center, Taipei, Taiwan; and

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Svetlana PravdenkovaArkansas Neuroscience Institute, St. Vincent Infirmary, Little Rock, Arkansas

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Ossama Al-MeftyDepartment of Neurosurgery, Brigham and Women's Hospital, Harvard Medical School, Boston, Massachusetts;

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Object

Medial acoustic neuroma is a rare entity that confers a distinct clinical syndrome. It is scarcely discussed in the literature and is associated with adverse features. This study evaluates the clinical and imaging features, pertinent surgical challenges, and treatment outcome in a large series of this variant. The authors postulate that the particular pathological anatomy with its arachnoidal rearrangement has a profound implication on the surgical technique and outcome.

Methods

The authors conducted a retrospective analysis of 52 cases involving 33 women and 19 men who underwent resection of medial acoustic neuromas performed by the senior author (O.A.) over a 20-year period (1993–2013). Clinical, radiological, and operative records were reviewed, with a specific focus on the neurological outcomes and facial nerve function and hearing preservation. Intraoperative findings were analyzed with respect to the effect of arachnoidal arrangement on the surgeon's ability to resect the lesion and the impact on postoperative function.

Results

The average tumor size was 34.5 mm (maximum diameter), with over 90% of tumors being 25 mm or larger and 71% being cystic. Cerebellar, trigeminal nerve, and facial nerve dysfunction were common preoperative findings. Hydrocephalus was present in 11 patients. Distinguishing intraoperative findings included marked tumor adherence to the brainstem and frequent hypervascularity, which prompted intracapsular dissection resulting in enhancement on postoperative MRI in 18 cases, with only 3 demonstrating growth on follow-up. There was no mortality or major postoperative neurological deficit. Cerebrospinal fluid leak was encountered in 7 patients, with 4 requiring surgical repair. Among 45 patients who had intact preoperative facial function, only 1 had permanent facial nerve paralysis on extended follow-up. Of the patients with preoperative Grade I–II facial function, 87% continued to have Grade I–II function on follow-up. Of 10 patients who had Class A hearing preoperatively, 5 continued to have Class A or B hearing after surgery.

Conclusions

Medial acoustic neuromas represent a rare subgroup whose site of origin and growth patterns produce a distinct clinical presentation and present specific operative challenges. They reach giant size and are frequently cystic and hypervascular. Their origin and growth pattern lead to arachnoidal rearrangement with marked adherence against the brainstem, which is critical in the surgical management. Excellent surgical outcome is achievable with a high rate of facial nerve function and attainable hearing preservation. These results suggest that similar or better results may be achieved in less complex tumors.

Abbreviations used in this paper:

AICA = anterior inferior cerebellar artery; CN = cranial nerve; IAC = internal auditory canal; PICA = posterior inferior cerebellar artery.
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