New MRI findings of late delayed radiation injuries in long-term survivors after radiotherapy: punctate enhanced dot, oval, or rod-like lesions

Purpose In long-term survivors of central nervous system (CNS) tumors who have undergone radiotherapy, punctate enhancement within the radiation field is sometimes detected on contrast-enhanced (gadolinium) three-dimensional T1-weighted imaging (CE-3D T1WI). However, the clinical characteristics and significance of this finding remain unclear. The purpose of this study was to clarify the characteristics of this radiological finding. Methods Ninety patients who had received radiotherapy between January 2007 and June 2020 and were still alive 24 months later without recurrence were selected. Patients were classified into punctate enhancement (+) group and punctate enhancement (−) group, and their clinical courses were compared. Imaging examinations were performed using standard procedures, including CE-3D T1WI and gradient echo T2*-weighted imaging (T2*WI). Results Punctate enhancement within the radiation field was observed in 25.7% (19/74 cases). The median onset time of punctate enhanced lesions was 37 months. Lesion size remained stable, but in 21.1% of cases (4/19), enhancement resolved, appearing as low intensity on T2*WI. Significant differences were seen between the punctate enhancement (+) group and the punctate enhancement (−) group in the proportions of pathological diagnosis types (p = 0.001). Also, significant differences were seen between both groups in the proportions of radiotherapy techniques (p = 0.001). Higher radiation doses increased the likelihood of punctate enhancement. Conclusion Punctate enhancement is considered to be one of the late delayed radiation injuries occurring in patients with CNS tumors after high-dose radiotherapy. Some of these lesions showed loss of contrast enhancement and changed to low intensity on T2*WI.