Hemifacial Spasm Caused by Small Epidermoid Tumor, Misinterpreted as Delayed Secondary Hemifacial Spasm Caused by Vestibular Schwannoma Treated with Gamma Knife Surgery.

BACKGROUND: Hemifacial spasm (HFS), one of the most common hyperactive cranial rhizopathies, is a disorder characterized by spontaneous, intermittent, and repetitive contraction of unilateral facial muscle. The most common cause of HFS is a mechanical compression of the facial nerve at the root exit zone (REZ) by blood vessels located in the brainstem. The incidence of cerebellopontine angle (CPA) tumor-induced HFS ranges from 0.3%-2.5% of all patients with HFS, and the incidence of epidermoid cyst among such tumors is extremely rare (0.2% to 0.25%). We present a patient manifesting HFS induced by a small epidermoid cyst who underwent Gamma Knife surgery (GKS) for ipsilateral vestibular schwannoma (VS) more than 10 years ago. CLINICAL DESCRIPTION: A 59-year-old female was admitted to our hospital with HFS. Ten years before admission, the patient underwent GKS for ipsilateral VS. Enhanced brain magnetic resonance imaging demonstrated that the volume of VS was not increased. Also, no definitive mechanical compression of the facial nerve REZ by blood vessels was detected. We concluded that HFS was secondary to the VS treatment by GKS and decided to operate to remove the tumor and identify REZ. A standardized lateral suboccipital retrosigmoid approach was performed. The cochlear nerve was encased by a tumor mass, and the posterior inferior cerebellar artery (PICA) was displaced by the mass. During tumor excision, we ensured that the VS and displaced PICA did not directly compress the REZ. Interestingly, an unexpected lesion was found with a yellowish viscous mass located between the sixth nerve and ventral side of the seventh nerve REZ. After the tumor removal, a small piece of Teflon was inserted between the PICA and REZ of the facial nerve. Postoperatively, the patient experienced no HFS or facial nerve dysfunction. Histopathologic examination of the lesion revealed an epidermoid cyst. CONCLUSIONS: We should consider various possibilities for the cause of HFS and review brain imaging meticulously if patients were treated for CPA tumor with GKS a long time ago and the delayed HFS occurred without changes in tumor volume. HFS induced by epidermoid cyst is rare. Therefore it is critical for the neurosurgeon to ensure the absence of any abnormal contact with the REZ of the facial nerve during surgery for HFS induced by CPA tumors.

A review of treatment modalities for vestibular schwannoma.

Vestibular schwannomas are benign intracranial tumors arising from the vestibular nerve. Treatment options include observation, stereotactic radiosurgery, fractionated radiotherapy, and microsurgery. We review the evidence describing efficacy and side-effect profiles of each of these modalities. This was accomplished by outlining the results of published meta-analyses and performing a systematic search of the literature for individual studies published between 2004 and June 2009. Without intervention, 29-54% of tumors will grow and 16-26% of patients require additional treatment, with 54-63% preserving functional hearing. With radiosurgery, only 2-4% require additional treatment and hearing preservation is accomplished in 44-66% of cases. Reviewing contemporary studies, it appears that reduced marginal doses may have decreased morbidity risks associated with radiosurgery without sacrificing efficacy. With fractionated radiotherapy, 3-7% will require additional treatment and hearing preservation is reported at 59-94% of patients, although long-term outcomes are not known. Microsurgery is an alternative for eligible patients, with fewer than 2% requiring additional treatment; however, the risk of hearing loss, facial neuropathy, and other morbidities is relatively high. There are significant limitations with comparing the efficacy and morbidity rates across interventions because of selection bias and confounding factors. Additional prospective comparative trials and randomized studies are needed to improve our understanding of the relative benefits of each modality.

Fractionated stereotactic radiation therapy and single high-dose radiosurgery for acoustic neuroma: early results of a prospective clinical study.

PURPOSE: To prospectively assess the local control and toxicity rate in acoustic neuroma patients treated with linear accelerator-based radiosurgery and fractionated stereotactic radiation therapy. METHODS AND MATERIALS: We evaluated 37 consecutive patients treated with stereotactic radiation therapy for acoustic neuroma. All patients had progressive tumors, progressive symptoms, or both. Mean tumor diameter was 2.3 cm (range 0.8-3.3) on magnetic resonance (MR) scan. Dentate patients were given a dose of 5x4 Gy or 5x5 Gy and edentate patients were given a dose of 1x10 Gy or 1x12.50 Gy prescribed to the 80% isodose. All patients were treated with a single isocenter. RESULTS: With a mean follow-up period of 25 months (range 12-61), the actuarial local control rate at 5 years was 91% (only 1 patient failed). The actuarial rate of hearing preservation at 5 years was 66% in previously-hearing patients. The actuarial rate of freedom from trigeminal nerve toxicity was 97% at 5 years. No patient developed facial nerve toxicity or other complications. CONCLUSION: In this unselected series, fractionated stereotactic radiation therapy and linear accelerator-based radiosurgery give excellent local control in acoustic neuroma. It combines a high rate of preservation of hearing with a very low rate of other toxicity, although follow-up is relatively short.

Radiosurgery in intracranial tumors and vascular malformations.

In 1951 Leksell first coined the term "radiosurgery" indicating a new tool for the neurosurgeon by means of ionizing radiations. The technique consists of cross-firing a stereotactic target with several well-collimated "shots" of radiation. This produces well-defined lesions in the brain without opening the skull. After several significant improvements of this technique, now assisted by a computer, today it is possible to "tailormake" composite radiation fields for any single lesion. Some interesting clinical applications are Cushing's disease, acoustic tumors, pineal region tumors and arteriovenous malformations.

Stereotactic radiosurgery in cases of acoustic neurinoma: further experiences.

Fourteen patients with acoustic neurinomas varying in size from 7 to 30 mm were treated by stereotactic radiosurgery and then were followed for 4 years. The tumors of eight patients decreased 1 to 10 mm in diameter, no change was found in two, and the tumor increased slightly in three patients. Loss of the ability to enhance with contrast administration on computed tomographic scan was a common effect of the treatment. One patient in poor general condition died from intercurrent disease 6 months after radiosurgery. At postmortem examination, a large central necrosis was found. Among five patients with hearing before treatment, full preservation was demonstrated in one; in the other four, the mean impairment of speech discrimination score was 43%. One patient with total unilateral deafness regained hearing and achieved a discrimination score of 60% at 1 year after treatment. There was transient facial weakness in five patients, which was detectable only by electromyography in one. Facial hypesthesia appeared in two patients and was transitory in one of them. Thirteen of the patients are in good or excellent general condition. Stereotactic radiosurgery offers the only therapeutic alternative to open operation in the management of acoustic neurinomas. It is worth considering for every patient, but especially for poor risk patients and those with bilateral tumors.