Diffusion-Weighted Imaging Can Help Distinguish Tumors From Radiation Injury In The Follow-Up Of Treated High-Grade Gliomas

One of the more perplexing problems in neuroradiology is the differentiation of recurrent cerebral neoplasm from radiation necrosis.

The challenge is that the presence of an enhancing mass following radiation can be either recurrent cerebral neoplasm or radiation necrosis, and the treatment will change based on the diagnosis.

Methods that have been investigated include perfusion imaging, MR spectroscopy, PET, and SPECT.

A retrospective study postulated that diffusion-weighted imaging may be helpful in distinguishing tumor recurrence from radiation injury.

The Study
Patients who had received radiation treatment for proven high-grade gliomas.

Methodology
MRI scans of patients were reviewed, and 18 patients with abnormal areas of enhancement were identified. Apparent diffusion coefficient (ADC) maps were calculated, as well as mean ADC values of areas of enhancement and ratios of the ADC in these areas compared with contralateral normal white matter. Results were compared with final diagnosis as established histologically or by clear progression of disease.

Results
ADC ratios and mean ADC in the recurrence patients were significantly lower than in the nonrecurrence patients. ADC ratios measured 1.43 +/- 0.11 in recurrence compared with 1.82 +/- 0.07 for nonrecurrence, and mean ADCs measured 1.18 +/- 0.13 x 10-3 mm/s2 compared with 1.40 +/- 0.17. Mean difference of ADC of enhancing areas from areas of normal contralateral tissue was 0.36 +/- 0.11 x 10-3 mm/s2 and 0.63 +/- 0.10 x 10-3 mm/s2 for nonrecurrence. Additional measurements assessed were not helpful in differentiating recurrence from nonrecurrence.

Conclusions
Differentiation of tumor recurrence/progression and radiation effects can be determined on the basis of mean ADC ratios. A ratio >1.62 is indicative of treatment-related necrosis, and lower ratios are indicative of recurrence. Mean difference of ADC values was also useful. Although statistical differences were seen in other measures such as mean ADC values, the results overlapped sufficiently to make them less useful clinically.

Reviewer’s Comments
If future studies confirm this finding, this will be a useful and easy way to differentiate a difficult problem in neuroradiology. Diffusion imaging is a very fast and easily performed sequence that is becoming a part of routine imaging in more and more centers.

The take-home message is this: Radiation necrosis has higher ADC ratios than tumor recurrence.

Author: Yaron Lebovitz, MD

Reference:
Hein PA, Eskey CJ, et al: Diffusion-Weighted Imaging in the Follow-Up of Treated High-Grade Gliomas: Tumor Recurrence Versus Radiation Injury. AJNR; 2004; 25 (February): 201-209