A new retrospective cohort study from a team of Italian neurosurgeons, neurologists, and neuroradiologists led by Francesco Guerrini of Fondazione IRCCS Policlinico San Matteo in Pavia offers a fresh clue. Published in the Journal of Neuro-Oncology, the research examines whether the shape of a lesion visible on postoperative diffusion-weighted imaging—DWI for short—can tell clinicians which patients are most likely to experience neurological worsening after eloquent-area glioma surgery. The answer, the researchers suggest, is more nuanced than a simple yes or no.

DWI is a magnetic resonance imaging technique that detects regions where water molecules cannot move freely, a hallmark of acute ischemic injury. When brain tissue is deprived of blood flow, cells swell and restrict the diffusion of water, producing a bright signal on DWI scans. For years, neurosurgeons have used postoperative DWI to identify silent strokes or small infarcts that might explain why a patient’s speech slurred or a limb weakened after tumor removal. But the technique has limitations. Bright spots on DWI do not always correspond to clinical deficits, and many patients who worsen neurologically show no obvious ischemic lesion at all.

The Italian team hypothesized that the morphology of these postoperative DWI lesions might matter. They classified lesions into two categories: sector-shaped, which appear as wedge-like areas of restricted diffusion, and rim-shaped, which form thin borders around the surgical cavity. Sector-shaped lesions, the researchers reasoned, might represent true arterial infarcts—blocks of tissue deprived of blood supply—while rim-shaped lesions could reflect a different phenomenon, perhaps related to surgical manipulation of the cortex surrounding the resection cavity rather than a genuine vascular occlusion.

To test this, the investigators analyzed 139 consecutive patients who underwent resection of supratentorial gliomas in eloquent areas, all classified as World Health Organization grade 2 through 4. Each patient received a postoperative MRI within 48 hours of surgery, allowing the team to categorize any DWI lesion by its shape. Neurological status was assessed at discharge and again at a follow-up visit four to six months later, providing both an early and a delayed picture of functional outcome.

The results were striking. DWI lesions appeared in 44 of the 139 patients, or 31.7 percent of the cohort. Of these, 31 were sector-shaped and 13 were rim-shaped. Overall, 59 patients—42.4 percent of the entire group—experienced neurological worsening at discharge. When the researchers looked at DWI positivity alone, without considering lesion shape, they found no significant association with worsening. But when they broke the lesions down by morphology, a clear pattern emerged. Sector-shaped DWI lesions were strongly associated with neurological decline, carrying a positive predictive value of 58.1 percent. In other words, if a patient had a wedge-shaped lesion on their postoperative scan, there was a better-than-even chance they would worsen neurologically. After adjusting for other variables in a multivariable model, sector-shaped lesions remained independently associated with worsening, with an odds ratio of 3.83. The confidence interval, however, was wide—ranging from 1.30 to 11.29—reflecting the modest sample size and suggesting that while the signal is real, its precise magnitude remains uncertain.

Rim-shaped lesions told a different story. These thin borders of restricted diffusion carried a positive predictive value of only 38.5 percent, which was essentially indistinguishable from the 37.9 percent risk of worsening observed in patients whose postoperative DWI was entirely negative. In a direct comparison between the two morphologies, the difference did not reach statistical significance, though the trend favored the idea that sector-shaped lesions are the more clinically meaningful finding. This distinction matters because it suggests that not all bright spots on a postoperative DWI scan are created equal. A rim of restricted diffusion hugging the cavity wall may be a benign epiphenomenon of surgery, while a wedge-shaped lesion in the territory of a perforating artery may signal a true ischemic event with real functional consequences.

Perhaps the most sobering finding of the study is what it reveals about the limits of DWI itself. Sixty-one percent of all neurological worsening in this cohort occurred in patients whose postoperative scans showed no DWI lesion whatsoever. This means that the majority of early postoperative decline after eloquent-area glioma surgery cannot be explained by ischemia visible on DWI. The researchers suggest that non-ischemic mechanisms—such as mechanical manipulation of subcortical pathways, edema, vascular dysregulation, or transient metabolic disruption—may be responsible. This finding aligns with a growing body of literature suggesting that surgically acquired deficits often arise from disruption of white matter tracts rather than from overt stroke, and it underscores the need for imaging modalities or biomarkers that can detect these subtler forms of injury.

The study also identified two additional factors associated with neurological outcome. Awake craniotomy, a technique in which the patient is woken during surgery to perform language or motor tasks, was independently associated with worsening, a finding that may reflect the inherent difficulty of operating in eloquent cortex rather than a flaw in the technique itself. Meanwhile, tumors located in the frontal lobe carried a lower risk of worsening compared with those in other eloquent regions, possibly because frontal language and motor networks possess greater redundancy or because surgical corridors in the frontal lobe are more forgiving. At the four-to-six-month follow-up, only nine patients—6.5 percent of the cohort—still had a deficit, and all of them had IDH-wildtype glioblastoma, the most aggressive and least metabolically favorable glioma subtype. Persistent deficit was also associated with a decrease of at least 50 percent in intraoperative evoked potentials, a neurophysiological monitoring signal that reflects the integrity of motor or sensory pathways during surgery.

These findings carry important implications for the field of neuro-oncology. First, they suggest that radiologists and surgeons should pay close attention to lesion morphology when interpreting postoperative DWI in glioma patients, rather than simply reporting the presence or absence of restricted diffusion. A sector-shaped lesion warrants closer clinical scrutiny, while a rim-shaped lesion may be less alarming than its appearance suggests. Second, the high proportion of worsening without DWI ischemia reinforces the idea that function-guided surgery—whether performed awake or asleep—exerts its effects on the brain through mechanisms that standard MRI cannot fully capture. Third, the association between persistent deficit and IDH-wildtype glioblastoma highlights the biological differences between glioma subtypes and suggests that patients with these aggressive tumors may have less capacity for functional recovery after surgery. Finally, the authors caution that their findings require confirmation in larger, prospective series, given the retrospective design, the modest number of patients with each lesion morphology, and the wide confidence intervals around some of their estimates. Still, the study represents a meaningful step toward a more refined understanding of what happens to the brain during eloquent-area glioma surgery, and it offers clinicians a new lens—quite literally—through which to interpret the postoperative scan.

Subject of Research: Postoperative diffusion-weighted imaging lesion morphology and neurological outcome after eloquent-area glioma surgery

Article Title: Postoperative DWI morphology and neurological worsening after eloquent-area glioma surgery: a retrospective cohort study

Article References: Guerrini, F., D’Agata, F., Musella, V., Vitali, A., Giuri, A., Caporrimo, M. C., Chiapparini, L., & Spena, G. (2026). Postoperative DWI morphology and neurological worsening after eloquent-area glioma surgery: a retrospective cohort study. Journal of Neuro-Oncology, 180(2), Article 23. https://doi.org/10.1007/s11060-026-05837-4

Image Credits: AI Generated

DOI: 10.1007/s11060-026-05837-4

Keywords: glioma surgery, diffusion-weighted imaging, DWI lesion morphology, eloquent cortex, neurological worsening, awake craniotomy, intraoperative neurophysiology, postoperative MRI, IDH-wildtype glioblastoma, surgical outcomes, neuro-oncology, brain tumor

The answer, at least for a substantial share of patients, appears to be yes. Individuals who underwent gross total resection, meaning the surgeon removed all visible tumor, experienced a median progression-free survival of 76 months, compared with just 44 months for those who received only a biopsy. More striking still, when the investigators adjusted their analysis for age, tumor grade, and the use of adjuvant therapy, gross total resection stood out as an independent predictor of prolonged progression-free survival, while subtotal resection did not. In other words, in this cohort, the benefit was concentrated in the patients whose tumors were removed completely, a finding that carries real weight for surgical decision-making.

The study’s scale and molecular rigor distinguish it from much of the earlier literature. Before 2016, oligodendroglioma was diagnosed largely on histology, and older datasets inevitably mixed together tumors with very different biology. The 2021 World Health Organization classification resolved this ambiguity by requiring both IDH mutation and 1p/19q co-deletion for the diagnosis, creating a molecularly homogeneous group of tumors known to be unusually sensitive to chemotherapy and radiotherapy. Because prior studies of resection extent often included mixed glioma populations, some researchers had questioned whether maximal surgery truly mattered in oligodendroglioma, or whether the tumors’ chemosensitivity would render the scalpel’s reach irrelevant. This new cohort, drawn entirely from patients with molecularly confirmed disease, directly addresses that uncertainty.

The clinical portrait that emerges from the data is characteristic of the disease. Most patients, 173 of 267 with recorded presentation, came to medical attention because of seizures, a classic first sign of these tumors. The majority of lesions, 128 of 213, showed no contrast enhancement on imaging, reflecting the tumors’ typically indolent behavior, and nearly two-thirds, 170 of 267, arose in the frontal lobe, a location that influences both surgical accessibility and the risk of functional injury. Two hundred seven patients had grade 2 tumors and 70 had grade 3 disease, allowing the investigators to examine whether the value of resection differed across the grade spectrum.

Surgical practice in the cohort was diverse. Among 249 patients with a documented operation, subtotal resection was the most common procedure, performed in 115 cases, or 46.2 percent, followed by gross total resection in 97 cases, or 39.0 percent, and biopsy in 37 cases, or 14.9 percent. Awake craniotomy, in which the patient is roused during surgery so surgeons can map language and motor function in real time, was used in 25 of 173 applicable cases, or 14.5 percent. This technique, long championed for tumors in eloquent brain regions, allows more aggressive removal while safeguarding speech and movement, and its use in this cohort reflects the growing adoption of functional mapping in glioma surgery.

Safety outcomes were a central concern, because any argument for maximal resection collapses if it comes at the cost of neurological harm. Across the cohort, new permanent neurological deficits occurred in 24 of 254 patients, or 9.4 percent. Critically, the analysis found no observed increase in postoperative deficits among patients who underwent gross total resection compared with those who had less extensive surgery. That combination, a survival-linked procedure that does not appear to add measurable neurological risk in experienced hands, is precisely the profile that surgeons hope for when counseling patients about the aggressiveness of a first operation, which is often the single most consequential treatment decision in the disease’s long natural history.

The subgroup analyses added an important nuance. The progression-free survival advantage of gross total resection over biopsy held up among patients with grade 2 tumors, with a p-value of 0.032, but did not reach statistical significance in the smaller grade 3 subgroup, where the p-value was 0.549. The authors and commentators alike caution against over-reading the grade 3 result, which may reflect limited statistical power in a group of only 70 patients rather than a genuine absence of benefit. Still, the finding underscores that the strongest evidence for maximal safe resection currently lies in the lower-grade tumors, which are often diagnosed in young adults facing decades of life with their disease.

Median follow-up in the study was 57 months, with an interquartile range of 20 to 107 months, a window long enough to capture meaningful differences in progression but one that leaves open questions about overall survival, which the abstract does not report as a primary endpoint in this analysis. Progression-free survival matters enormously in oligodendroglioma because every progression typically triggers further surgery, radiation, or chemotherapy, and each intervention carries cumulative cognitive and neurological costs. Delaying the first progression can therefore translate into years of preserved quality of life, particularly in a disease where patients are often working, parenting, and planning careers at the time of diagnosis.

The study arrives amid a rapidly evolving treatment landscape. Molecular classification has already reshaped glioma care, and targeted drugs such as vorasidenib, which inhibits the mutant IDH enzyme, have shown promise in low-grade gliomas, raising the possibility that systemic therapy may one day reduce reliance on surgery. Yet the Johns Hopkins findings suggest that, for now, the extent of the first resection remains a powerful and modifiable prognostic factor. The results also align with a growing body of international work, including recent RANO resect group analyses, that has sought to define resection thresholds and prognostic classifications for IDH-mutant gliomas, moving the field toward standardized, evidence-based surgical goals.

For patients and clinicians, the practical message is one of careful, individualized planning. The data support pursuing gross total resection when it can be achieved safely, particularly in grade 2 tumors, while confirming that subtotal resection, though common, did not independently outperform biopsy in this cohort once other factors were accounted for. The authors emphasize that their study is retrospective and subject to the inherent limitations of such designs, including selection bias in which patients received which operation. Even so, in a disease where molecular definition has finally allowed clean comparisons, the study offers some of the strongest evidence to date that in oligodendroglioma, what the surgeon removes on day one still matters, and it matters without, in this experience, exacting a price in neurological function.

Subject of Research: Extent of surgical resection and postoperative outcomes in molecularly defined oligodendroglioma

Article Title: Surgical characteristics and postoperative outcomes in a retrospective cohort study of patients with molecularly defined oligodendroglioma

Article References: Kalluri, A. L., Carmichael, A., Rakovec, M., Jiang, K., Parker, M., Weber-Levine, C., Raj, D., Materi, J., Schreck, K. C., Aldecoa, I., Redmond, K. J., Holdhoff, M., Weingart, J., Brem, H., Ye, X., Bettegowda, C., Sánchez, J. J. G., & Rincon-Torroella, J. (2026). Surgical characteristics and postoperative outcomes in a retrospective cohort study of patients with molecularly defined oligodendroglioma. Journal of Neuro-Oncology, 180(1), Article 4. https://doi.org/10.1007/s11060-026-05800-3

Image Credits: AI Generated

DOI: 10.1007/s11060-026-05800-3

Keywords: oligodendroglioma, IDH mutation, 1p/19q co-deletion, extent of resection, gross total resection, progression-free survival, neurosurgery, brain tumor, awake craniotomy, WHO classification, glioma, retrospective cohort study