Magnetic Resonance Imaging Findings of Radiation-induced Changes After Treatment of Malignant Gliomas and Metastases with a Particular Emphasis on Radiation Necrosis

European Neurological Review, 2011;6(2):132-137 DOI: http://doi.org/10.17925/ENR.2011.06.02.132

Abstract:

New contrast-enhancing lesions discovered on routine follow-up brain imaging at or near the site of previously treated primary or metastatic brain tumours represent a clinical and radiological challenge, as radiation necrosis and tumoral recurrence often present at standard magnetic resonance imaging (MRI) with overlapping imaging features. Since the advent of combined therapy, including surgery and/or radiotherapy and chemotherapy, the post-treatment radiological assessment has been made earlier, with a subsequent higher incidence of early radionecrosis and a potential risk of mistaking it for disease progression. Therefore, both clinical and imaging follow-up are essential. This article briefly describes and illustrates the temporal patterns and spectrum of MR findings of radiation-induced brain injury and considers practical aspects of conventional and advanced MR sequences (diffusion-weighted imaging, perfusion MR and MR spectroscopy), with a particular emphasis on the distinction between tumoral recurrence and radiation necrosis.

Acknowledgements: The authors thank Carlos Gutiérrez Pérez for his technical assistance in preparing the photographs for this article.
Keywords: Glioma, neoplasm, metastasis, brain, chemotherapy, radiotherapy, radiation injuries, brain necrosis, neoplasm recurrence, local, magnetic resonance imaging (MRI), magnetic resonance spectroscopy, perfusion MRI, diffusion MRI
Disclosure: The authors have no conflicts of interest to declare.
Received: June 27, 2010 Accepted January 20, 2011
Correspondence: Raquel Cano Alonso, Hospital Universitario Quirón Madrid, Unidad de Diagnóstico por la Imagen, C/ Diego de Velázquez, 1; 28223, Pozuelo de Alarcón, Madrid, Spain. E: rcanoalonso@gmail.com

New contrast-enhancing lesions discovered on routine follow-up brain imaging at or near the site of previously treated primary or metastatic brain tumours represent a challenge for radiologists and oncologists, as radiation-induced injuries may have an appearance that is virtually indistinguishable from that of recurrent disease. With standard magnetic resonance imaging (MRI) modalities, a reliable distinction among tumour recurrence, pseudoprogression and radionecrosis (RN) is not always possible.1–13

Although primary resection is the mainstay of treatment in gliomas and selected cases of metastases, its extent and feasibility are often limited by the location of the tumour near vital or eloquent brain structures. Therefore, tumour sites are often treated in association with radiation therapy (RT), chemotherapy (ChT) or chemoradiotherapy (ChRT).8,14,15 ChT protocols include different dosage schemes of various chemotherapeutic agents.7 RT protocols include whole-brain RT (WBRT) and different schemes of locally administered high doses of radiation (stereotactic RT or radiosurgery), which have resulted in improved outcome but also in a significant incidence of radiation injury to the brain.1 The risk of late effects leading to functional deficits after brain irradiation limits the total dose that can be safely administrated to patients.1,5–7,11,16,17

Nowadays, ChRT with temozolomide (TMZ) is the standard therapy for glioblastoma as it has been shown to improve the survival of newly diagnosed patients.5 In addition, the post-RT radiological assessment is made earlier than in previous eras when RT was given alone.5 The possibility of a higher incidence of early RN and the risk of mistaking it for disease progression remain diagnostic challenges.1,5,18 Histological examination remains the gold standard,1,3 and re-operation via a biopsy or resection to obtain tissue is the treatment or diagnostic procedure of choice.4 However, even biopsy may yield the wrong diagnosis in approximately 10 % of cases and is not always clinically practicable due to a high risk of morbidity.3,4,6,11,15,17 Therefore, the distinction between recurrent tumour and treatment-related lesions is made on the combination of clinical course, brain biopsy and imaging over a lengthy follow-up interval, not the specific imaging itself, which may lead to delays in starting treatment.7–9,15,16

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Keywords: Glioma, neoplasm, metastasis, brain, chemotherapy, radiotherapy, radiation injuries, brain necrosis, neoplasm recurrence, local, magnetic resonance imaging (MRI), magnetic resonance spectroscopy, perfusion MRI, diffusion MRI