neuroradiosurgery Flashcards
- A 37 year old man has a tonic – clonic seizure and is found to have an unruptured 2 cm AVM located in the sensorimotor cortex. Angiography shows that there are no associated aneurysms and it has both superficial and deep venous drainage. The patient alects to unergo radiosurgery for his Spletzer – Martin Grade III AVM. The 3.6 cc AVM volume was treated with 20 Gy to the 50% isodose line. Which of the following is the MOST likely clinical outcome :
A. Radiation induced deficit
B. Hemorrhage induced deficit
C. Complete AVM obliteration
D. Subtotal AVM obliteration
C. Complete AVM obliteration
The most likely outcome is complete obliteration with no new deficits. The main factor that predicts AVM obliteration after radiosurgery is radiation dose. The chance of obliteration is approximately 90%, 80%, and 70% for AVM margin doses of 20 Gy, 18 Gy, and 16 Gy, respectively. The chance of radiation related complications is related to the AVM location, AVM volume, and radiation dose. For larger AVM volumes, the radiation dose is typically decreased to keep the chance of radiation relatedcomplications less than 5%. The primary disadvantage of AVM radiosurgery compared to surgical resection is that patients continue to have a hemorrhage risk until the AVM is completely obliterated. The latency interval after radiosurgey until AVM obliteration is typically between one and for years. Although deficit related to hemorrhage is possible in this case, it is likely in patient who presented with seizures and does not harbor peri-nidal aneurysms.
- A 45 year old woman with medically refractory trigeminal neurlgia chooses raiosurgical therapy. Which of the following is the MOST appropriate maximum radiation dose for trigeminal neuralgia radiosurgery :
A. 20 Gy
B. 40 Gy
C. 60 Gy
D. 80 Gy
E. 100 Gy
D. 80 Gy
The appropriate maximum dose for trigeminal neuralgia radiosurgery is 80 Gy. Although some of the first radiosurgical procedures were for trigeminal neuralgia, the inability to clearly image the trigeminal system limited the usefulness of this technique. However, with the advent of MRI, physicians are able to visualize the trigeminal root for radiosurgery dose planning. A prospective , multi-institusional dose escalation trial showed that patients receiving a maximum radiation dose of 70 Gy or more had a significantly greater chance of complete pain relief compared to patients receiving less than 70 gy. Later studies showed that the chance of bothersome facial numbness was significantly higher for patients treated at doses above 90 Gy. Consequently, most radiosurgical centers limit the dose for trigeminal neuralgia radiosurgery to 80 gy in the hope of achieving better facial pain outcomes than reported with 70 Gy with an acceptable incidence of new facial sensory loss. Other factors that have been associated with improved facial pain outcomes are normal pre-operative facial sensation, increased dose to the brainstem and absence of prior surgery. Negative predictors for pain relief after radiosurgery has included patients with trigeminal neuralgia related to multiple sclerosis or patients with a constant pain component.
- A 56 year old man with history of renal cell carcinoma presents with localized back pain but without myelopathy. Radiographs showed normal alignment and no evidence of instability. MRI showed a dorsal, enhancing paraspinal mass with extension into the spinal canal. Which of the following is the MOST likely outcome of stereotactic radiosurgery for the spine metastasis :
A. Tumor stabilization but persistent back pain
B. Tumor stabilization with an improvement in back pain
C. Tumor stabilization with new onset myelopathy
D. Tumor progression causing spinal cord compression
E. Tumor progression causing vertebral collapse
B. Tumor stabilization with an improvement in back pain
The most likely outcome after stereotactic radiosurgery of this spine metastasis is tumor stabilization with an improvement in back pain. Utilizing the general concepts developed over 30 years of intracranial radiosurgery, it has become possible to perform high – dose, single fraction (radiosurgery) radiation delivery to spinal and para – spinal lesions. Although the follow up available after spine radiosurgery is limited, spine radiosurgery has been shown to be feasible, safe, andeffective. Tumor control is achieved in the majority of patients, and improvement in axial and radicular symptoms has been noted in more 90% of affected patients. Contraindications to spine radiosurgery include mechanical instability. The chance of radiation – induced myelopathy or vertebral necrosis after spine radiosurgery is very low.
- A 59 year old man presents with high frequency sensorineural hearing loss, near normal speech discrimination (<90% at 40 dB), and an MRI showing a uniformly enhancing 10 mm mass extending into the internal auditory canal. The MOST likely complication of stereotactic radiosurgery of this lesion is :
A. Diplopia
B. Facial numbness
C. Hearing loss
D. Facial weakness
E. Swallowing difficulty
C. Hearing loss
The most likely complication after vestibular schwannoma radiosurgery is hearing loss. As a less invasive alternative to surgical resection, stereotactic radiosurgery has been utilized increasingly over the past 20 years for patients with vestibular schwannomas. Preservation of useful hearing (speech discrimination scores greater than 50%) is possible in approximately 60% of patients after radosurgery. Facial weakness or numbness occurs in less than 3% of patients. Diplopia or swallowing difficulty is rare in large radiosurgical series, the need for later tumor resection has been less than 5%
- A 63 year old man with a history of non small cell lung cancer presents with headaches. An MRI of the brain demonstrates 2 enhancing lesions each measuring 2 cm, with mild vasogenic edema and no mass effect. Which of the following is supported by class 1 evidence regarding stereotactic radiosurgery (SRS) and whole brain radiation therapy (WBRT)?
A. For patients with one to three metastases, SRS alone results in better early outcomes than SRS plus WBRT
B. For patients with one to four metastases, SRS alone is associated with poorer survival than SRS plus WBRT
C. For patients with one to three metastases. WBRT plus SRS boost prolongs survival as compared to WBRT alone.
D. For patients with one brain metastasis. SRS provides improved survival compared to WBRT.
A. For patients with one to three metastases, SRS alone results in better early outcomes than SRS plus WBRT
SRS alone results in better early cognitive outcomes compared to SRS + WBRT for patients with 1-3 metastases. Recent class I evidence reported by Chang et al (2009) demonstrated that early neurocognitive outcomes are signiticantly better in patients with one to three metastases who received SRS only, when compared to SRS plus up-front WBRT. This single institution study specifically examined cognition using the Hopkins Verbal Learning Test; differences in cognition were found between groups at 4 and 6 months. There was a high rate of salvage therapy requirement (87%) in the SRS group, including surgical resection and WBRT.
- A 65-year old female with a growing left intracanalicular 6 mm tumor and progressively worsening yet still serviceable hearing presents with the MRI shown. What is the most appropriate management strategy?
A. Surgical removal via translabyrinthine approach
B. Stereotactic radiosurgery
C. Surgical removal via retrosigmoid approach
D. Reassurance, observation, and follow-up MRI in one year
B. Stereotactic radiosurgery
Stereotactic radiosurgery affords a very low chance of facial neuropathy and a reasonable chance of hearing preservation. Hearing preservation may be more likely in patients for whom a lower dose is delivered to the cochlea. This is usually possible when the tumor is smaller in volume.
Resection via a translabryinthine approach will not preserve the patient’s hearing. Given the patient’s age, radiosurgery is usually preferable to open surgery via a retrosigmoid approach.
- Which of the following cranial nerves is most susceptible to radiation injury after radiosurgery of a cavernous sinus lesion’?
A. Trochlear
B. Abducens.
C. Oculomotor.
D. Trigeminal.
E. Optic.
E. Optic.
Critique
Stereotactic radiosurgery affords a very low chance of facial neuropathy and a reasonable chance of hearing preservation. Hearing preservation may be more likely in patients for whom a lower dose is delivered to the cochlea. This is usually possible when the tumor is smaller in volume.
Resection via a translabryinthine approach will not preserve the patient’s hearing. Given the patient’s age, radiosurgery is usually preferable to open surgery via a retrosigmoid approach.
7. Which of the following cranial nerves is most susceptible to radiation injury after radiosurgery of a cavernous sinus lesion’?
A. Trochlear
B. Abducens.
C. Oculomotor.
D. Trigeminal.
E. Optic.
Answer : E
Critique
The cranial nerve most susceptible to radiation injury after radiosurgery of a cavernous sinus lesion is the optic nerve. Although it appears that cranial nerves will tolerate high doses of radiation (60-70 Gy) when it is delivered in multiple fractions, cranial nerves are more susceptible to injury after radiosurgery. Moreover, different types of cranial nerves appear to have distinct tolerances for radiation. The special somatic sensory nerves (optic, vestibulo-cochlear) are the most susceptible to injury after high-dose, single-fraction radiation (radiosurgeryj. Recent studies have shown that the chance of visual loss is less than two percent when the optic nerves and chiasm receive doses less than 12 Gy. General somatic nerves (oculomotor, trochlear, abducens, hypoglossal) are rarely affected by similar doses. The afferent component of the trigeminal nerve (general somatic afferent) is intermediate in radiation sensitivity. The length of cranial nerve that is irradiated and a prior history of radiation exposure are also important factors related to cranial nerve injury after radiosurgery.
