The specific linear or curved boundaries between WHO grade II–III insular gliomas and the basal ganglia indicate distinct biological features, survival outcomes, and surgical strategies: evidence from 330 cases

• The boundary shape of insular glioma could provide clinical suggestions. • It indicated different tumor features, survivals and surgical strategies. • The benefits of surgery may vary depending on the boundary shape. WHO grade II–III insular glioma (InG) can displace the basal ganglia, resulting in distinct linear or curved boundary shapes. This study retrospectively explored this morphological distinction and its clinical relevance. MRI and clinical data were collected from Beijing Tiantan Hospital over the past 20 years. The boundary shape on the FLAIR sequence was characterized using the fractal dimension (FD) and curved parameters. Statistical analyses included the χ 2 test, Cox regression, Kaplan–Meier analysis, and correlation analysis. Regression models were constructed using the stepwise Wald method. Model performance was evaluated through internal validation, including bootstrap resampling and 5-fold cross-validation. A total of 330 patients were included. Based on the FD, patients were classified into linear (’L’; 49%) and curved (’C’; 51%) subgroups. Compared with the L subgroup, the C subgroup exhibited more favorable biological features and progression-free survival (PFS) ( p < 0.001). Using routine pathological variables, regression models were constructed to identify crucial factors in different subgroups and perform disease stratification for Statistical explanation. Internal validation supported model stability. With regard to surgical responses, although the rate of gross total resection (GTR) was higher in the L subgroup, the PFS was not increased, whereas that of the C subgroup demonstrated an increase ( p < 0.001). The boundary shape between WHO grade II–III InG and the basal ganglia may reflect differences in biological features, survival outcomes, and surgical responses. Thus, the boundary shape should be considered in clinical practice.