THE INCOMPLETE ring enhancement sign (IRES) on contrast-enhanced 3D T1-weighted gradient-echo MRI (CE 3D T1 GRE) showed potential as a marker of brain radionecrosis after stereotactic radiotherapy, a study found.
Brain radionecrosis is a treatment-related change in brain tissue that can be difficult to distinguish from recurrent metastases on imaging. The researchers assessed whether IRES could help clinicians make this distinction, while also examining associated morphological features.
The retrospective case-control study identified 45 cases of radionecrosis from an institutional database of 1,179 brain metastases treated consecutively with stereotactic radiotherapy between 2015 and 2022.
Researchers reviewed 90 CE 3D T1 GRE examinations in a blinded fashion: 45 from patients with radionecrosis and 45 matched treatment-naïve metastases from the same patients.
Against the treatment-naïve metastases, IRES had mean sensitivity of 97% (95% CI, 87–99) and specificity of 76% (95% CI, 61–88). Interobserver agreement was substantial (κ=0.75). IRES was already present in 50% of MRI examinations where radionecrosis was first suspected.
Fragmentation was seen in 89% of radionecrosis cases compared with 2% of metastases (p<0.001), while satellite lesions occurred in 29% and 2%, respectively (p<0.001). Watershed localisation was present in 83% of supratentorial radionecrosis.
The findings suggested that IRES, together with fragmentation, satellite foci and watershed localisation, could help support the diagnosis of brain radionecrosis.
However, the control group comprised treatment-naïve metastases rather than metastases recurring after radiotherapy. The reported diagnostic accuracy should therefore be interpreted as proof-of-concept rather than evidence that IRES can reliably distinguish radionecrosis from recurrent metastases in clinical practice.
This distinction was important because, in routine clinical settings, the key diagnostic challenge lies in separating radionecrosis from post-radiotherapy tumour recurrence, where both entities can share overlapping imaging features such as contrast enhancement patterns, necrotic change and treatment-related tissue effects, unlike untreated metastases. Further assessment against post-treatment recurrent metastases would be needed to establish the sign’s diagnostic value and determine whether the reported sensitivity and specificity translate to clinical practice..
Reference
de Mendivil AO et al. Imaging MRI biomarkers for diagnosing brain radionecrosis: focus on incomplete ring enhancement sign. Neuroradiology. 2026;DOI:10.1007/s00234-026-04096-4.
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