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

purposeIn long-term survivors of central nervous system (CNS) tumors who have undergone radiotherapy, punctate enhancing lesions within the radiation field is sometimes detected on contrast-enhanced 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 finding.

methodsNinety 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 the punctate enhancement–positive group and the punctate enhancement–negative 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).

resultsPunctate enhancing lesion within the radiation field was observed in 25.7% (19/74 cases). The median onset time of punctate enhancing lesion 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–positive group and the punctate enhancement–negative 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 enhancing lesions.

conclusionPunctate enhancing lesions may represent a late delayed radiation-associated imaging finding, occasionally showing loss of enhancement and evolution into low-signal-intensity lesions on T2*WI. Punctate enhancing lesions should not be misinterpreted as recurrent disease in long-term survivors of CNS tumors after radiotherapy.