Relying too much on upfront radiosurgery: Indolent course misinterpreted as effectiveness of radiosurgery in a case of skull base chondrosarcoma
- Department of Neurosurgery, Postgraduate Institute of Medical Education and Research, Chandigarh, India.
- Department of Pathology, Postgraduate Institute of Medical Education and Research, Chandigarh, India.
Sushant Kumar Sahoo
Department of Neurosurgery, Postgraduate Institute of Medical Education and Research, Chandigarh, India.
DOI:10.25259/SNI_590_2019Copyright: © 2020 Surgical Neurology International This is an open-access article distributed under the terms of the Creative Commons Attribution-Non Commercial-Share Alike 4.0 License, which allows others to remix, tweak, and build upon the work non-commercially, as long as the author is credited and the new creations are licensed under the identical terms.
How to cite this article: Puneet Malik, Sushant Kumar Sahoo, Kirti Gupta, Pravin Salunke. Relying too much on upfront radiosurgery: Indolent course misinterpreted as effectiveness of radiosurgery in a case of skull base chondrosarcoma. 16-May-2020;11:112
How to cite this URL: Puneet Malik, Sushant Kumar Sahoo, Kirti Gupta, Pravin Salunke. Relying too much on upfront radiosurgery: Indolent course misinterpreted as effectiveness of radiosurgery in a case of skull base chondrosarcoma. 16-May-2020;11:112. Available from: https://surgicalneurologyint.com/surgicalint-articles/10028/
Background: Skull base lesions are still considered surgically challenging and primary gamma knife radio surgery (GKRS) is gaining popularity. However the effectiveness of GKRS may be overrated especially in lesions with indolent course.
Case Description: We report a case of chondrosarcoma, mimicking a trigeminal schwannoma treated with upfront radio surgery. Relatively lower dose was administered in view of proximity to the brainstem. The patient was asymptomatic and the size of the lesion remained static for over a decade. This was misinterpreted as effectiveness of GKRS. The lesion grew after a decade necessitating surgery.
Conclusion: With popularity of upfront GKRS, suboptimal but maximal safe radiation dose is usually prescribed for lesions close to critical structures like brainstem. In these cases the long indolent natural course of the pathology, as in the case of chondrosarcoma may be misconstrued as success of radiosurgery. An extended follow up beyond this static period is necessary before concluding its effectiveness.
Keywords: Chondrosarcoma, Gamma knife radiosurgery, Indolent course, Skull base
Skull base chondrosarcomas are slow-growing tumors close to the brainstem and they often present with cranial nerve deficits.[
We have discussed the natural course of chondrosarcoma and 5th nerve schwannoma close to the brainstem. The importance of surgical debulking before radiosurgery has been highlighted. The disadvantages of relying on suboptimal radiation, due to their proximity to brainstem, especially without a tissue diagnosis of such lesions, have been emphasized.
A 50-year-old otherwise healthy lady presented with complains of mild headache and diplopia for 8 weeks duration. On examination, she had the right lateral rectus palsy with diminished right corneal reflex. Radiology showed lesion extending from the cerebellopontine angle to the middle cranial fossa straddling across the petrous apex with its erosion [
Upper row: MRI showing tumor straddling across the petrous apex from middle fossa to the posterior fossa. (a) Tumor is hypointense on T1, (b) hyperintense on T2, and (c) showing contrast enhancement. (d) Note the bony erosion of the petrous apex without any calcification. Lower row: (e-h) serial MR images in the follow-up showing tumor with similar size on volumetric analysis.
The patient was offered surgery. However, she opted for upfront GKRS with presumptive diagnosis of trigeminal schwannoma. As the lesion was close to the brainstem, total dose of 25 Gy was administered. The patient was regularly followed up and showed no symptoms for a decade. Sequential MRI showed no increase in size or change in character of lesion [
She was operated through the right temporal craniotomy and interdural approach (by senior author PS). The tumor was grayish, fleshy with mild vascularity with a plane from the fifth nerve fascicles. Through the expanded Meckel’s cave, the component from posterior fossa was excised. Histopathology confirmed chondrosarcoma Grade II [
(a) Low magnification demonstrating tumor arranged in lobules with a prominent chondromyxoid matrix (H&E ×100); (b) high magnification demonstrating closely packed lacunae containing mononucleate and few binucleate cells with pleomorphic nuclei (H&E ×400); (c) malignant chondrocytes with hyperchromatic nuclei with a prominent chondromyxoid matrix. Occasional mitoses are noted (arrow) (H&E ×400).
Radiosurgery is gaining popularity in treating skull base neoplasm such as schwannomas and chondrosarcomas.[
Because of their common anatomical location around the petrous apex, they may have overlapping clinical features. At times, it is difficult to make accurate diagnosis on the basis of clinical feature and radiology. Upfront GKRS is a viable treatment option for moderate size lesions without significant mass effect. Efficacy of radiosurgery is well documented for skull base chondrosarcomas. The 10-year progression-free survival following radiosurgery is over 70%.[
In the present case, one of our differentials was trigeminal schwannoma. The marginal prescription dose for these tumors is 12–15 Gy.[
This case report exemplifies the variable course of chondrosarcoma. The tumor may remain radiologically static following radiosurgery but may not inactive. The indolent phase of such tumors may be long enough and should not be mistaken as effectiveness of radiosurgery. Adjacent critical neural structures like brainstem may restrain the dose of gamma knife. A relatively high marginal dose of 15 Gy is needed for long-term tumor control.[
Rather than resorting to the suboptimal dose for skull base lesions close to the brainstem, surgical debulking should be considered. This not only establishes the diagnosis but also reduces the tumor volume for an effective radiation dose. The indolent course of the lesion must not be misinterpreted as static disease and effectiveness of GKRS.
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