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Neuroradiology Case of the Week

Case 275

Ashwani K. Sharma, MD and P-L Westesson, MD, PhD, DDS

Clinical Presentation: A 43-year-old male presented for follow-up of trigeminal neuralgia. He was diagnosed with right trigeminal schwannoma and was treated with radiosurgery. The present MRI is performed as a 5-year post-radiosurgery follow-up to look for interval change.

Imaging Findings: Varied radiological changes are observed after radiosurgery, these include increase or decrease in the size of the tumor, decrease in the contrast enhancement and cyst formation.

Diagnosis: Trigeminal schwannoma responding to radiosurgery

Discussion: Despite advances in skull base surgery techniques, complete resection of trigeminal schwannomas remains a challenge for neurosurgeons. Complete surgical removal has been associated with a significant risk of new neurological deficits and is not achieved in most cases [1]. Stereotactic radiosurgery, as an alternative or adjunct to microsurgery, has shown excellent long-term outcomes in the management of patients with vestibular schwannomas (acoustic neuromas), achieving a high rate of tumor growth control with low morbidity [2].
     While the goal of microsurgery is to remove or to decompress tumor, the goal of benign tumor radiosurgery is to control tumor growth. Tumor growth control is defined as freedom from further tumor growth, from new symptom related to growth and from the need of additional surgical treatment. Therefore, after radiosurgery, if a patient does not develop any new symptom and imaging shows no further growth, the tumor is considered controlled. Patients are given choice of tumor removal and tumor control. Patients willing to accept tumor control as successful outcome choose radiosurgery. Those patients who desire tumor removal or regression are managed by microsurgery [3].
     Modern microneurosurgery techniques have significantly decreased morbidity and mortality [4], but recent literature also reflects the application and refinement of stereotactic radiosurgery techniques [5]. Both treatment modalities have established a correlation between tumor size and associated treatment-related morbidity, but radiosurgery series have demonstrated markedly diminished cranial and noncranial nerve morbidities, even for larger tumors [6]. When compared according to treatment-related morbidity and patient satisfaction, stereotactic radiosurgery emerges as a preferred treatment by patients; it also has a higher degree of cost-effectiveness in the United States and abroad [7].
     The fundamental principle of radiosurgery is that of selective ionization of the tissue to be operated upon, by means of high-energy beams of radiation. Ionization is the production of inorganic ions which are usually deleterious to the cells, by forming free radicals that are harmful to the cellular and nuclear membranes, and even to the RNA and DNA chains of the cells, producing an irreparable damage to these structures and then the cell's death. Thus, biological inactivation is carried out in a volume of tissue to be treated, with a precise destructive effect. The radiation dose absorbed by the treated mass of tissue is what defines the degree of biological inactivation.

References:

1. Al-Mefty O, Ayoubi S, Gaber E. Trigeminal schwannomas: removal of dumbbell-shaped tumors through the expanded Meckel cave and outcomes of cranial nerve function. J Neurosurg. 2002 Mar;96(3):453-63. [Medline]
2. Andrews DW, Suarez O, Goldman HW, Downes MB, Bednarz G, Corn BW, Werner-Wasik M, Rosenstock J, Curran WJ Jr. Stereotactic radiosurgery and fractionated stereotactic radiotherapy for the treatment of acoustic schwannomas: comparative observations of 125 patients treated at one institution. Int J Radiat Oncol Biol Phys. 2001 Aug 1;50(5):1265-78. [Medline]
3. Nettel B, Niranjan A, Martin JJ, Koebbe CJ, Kondziolka D, Flickinger JC, Lunsford LD. Gamma knife radiosurgery for trigeminal schwannomas. Surg Neurol. 2004 Nov;62(5):435-44; discussion 444-6. [Medline]
4. Wiegand DA, Ojemann RG, Fickel V. Surgical treatment of acoustic neuroma (vestibular schwannoma) in the United States: Report from the Acoustic Neuroma Registry. Laryngoscope. 1996 Jan;106(1 Pt 1):58-66. [Medline]
5. Flickinger JC, Kondziolka D, Pollock BE, Lunsford LD. Evolution in technique for vestibular schwannoma radiosurgery and effect on outcome. Int J Radiat Oncol Biol Phys. 1996 Sep 1;36(2):275-80. [Medline]
6. Kondziolka D, Lunsford LD, McLaughlin MR, Flickinger JC. Long-term outcomes after radiosurgery for acoustic neuromas. N Engl J Med. 1998 Nov 12;339(20):1426-33. [Medline]
7. Pollock BE, Lunsford LD, Kondziolka D, Flickinger JC, Bissonette DJ, Kelsey SF, Jannetta PJ. Outcome analysis of acoustic neuroma management: a comparison of microsurgery and stereotactic radiosurgery. Neurosurgery. 1995 Jan;36(1):215-24; discussion 224-9. [Medline]