Evolution of radiation-induced brain injury: MR imaging-based study.

PURPOSE

To evaluate the temporal lobes in patients previously treated for nasopharyngeal carcinoma to provide a better understanding of delayed radiation-induced injury in the brain unaffected by the underlying tumor.

MATERIALS AND METHODS

Retrospective analysis of the patient data was approved by the local ethics committee. Informed consent was waived. Magnetic resonance (MR) imaging results in patients with temporal lobe injury (TLI) after receiving radiation for nasopharyngeal carcinoma were analyzed. The appearance and change over time of white matter lesions (WMLs), contrast material-enhanced lesions, and cysts were assessed. The Mann-Whitney U test was used to compare interval time, and the chi(2) and Fisher exact tests were used to compare the pattern of TLI changes.

RESULTS

The study group was 124 patients (95 men, 29 women; mean age, 51.4 years) with 192 injured temporal lobes; 62 of these patients with 103 injured temporal lobes underwent follow-up MR imaging at least once (range, one to five examinations). A total of 332 injured temporal lobes were revealed. WMLs, contrast-enhanced lesions, and cysts were present on 332 (100%), 274 (82.5%), and 42 (12.7%) studies, respectively. All contrast-enhanced lesions more than 2 cm in size showed necrosis, and those 3 cm or greater formed a rim-enhanced necrotic mass. WMLs were the only lesion to occur alone, contrast-enhanced lesions were always accompanied by WMLs, and cysts were always accompanied by WMLs and contrast-enhanced lesions. Detection of cysts was significantly later than detection of WMLs and contrast-enhanced lesions (P <.01). Regression or resolution was found in 27 (28%) of 96 WMLs, 37 (39%) of 94 contrast-enhanced lesions, and one (7%) of 15 cysts.

CONCLUSION

TLI from radiation is not always an irreversible and progressive process but is one that can regress or resolve at MR imaging. In the evolution of radiation injury, WMLs are seen first and are followed by contrast-enhanced lesions, which have an increasing tendency to become necrotic with increasing size. Cysts are the least frequent manifestation and arise in the late stage of TLI.