A Simple Brain Scan Ratio Predicts Survival in Cancer That Spreads to the Brain’s Linings

Neoplastic meningitis, also known as leptomeningeal metastasis, is one of the most feared complications of advanced cancer. It occurs when tumor cells seed the membranes that envelop the brain and spinal cord, bathing the central nervous system in malignant cells through the cerebrospinal fluid that circulates there. The prognosis has long been grim, and clinicians have struggled to identify which patients might benefit from aggressive treatment and which should be steered toward comfort-focused care. Now, a large real-world study from Mexico City offers compelling evidence that a remarkably simple measurement, taken from routine brain imaging, can help answer that question.

The measurement in question is the Evans index, a ratio that radiologists have used for more than eight decades. First described by William Evans in 1942 as a way to estimate ventricular enlargement on pneumoencephalograms, the index is calculated by dividing the width of the frontal horns of the brain’s lateral ventricles by the maximum internal width of the skull at the same level. A value above 0.3 has traditionally signaled enlarged ventricles, whether from hydrocephalus or cerebral atrophy. What is new, and what the latest research confirms, is that this same ratio carries powerful prognostic information for patients whose cancer has spread to the leptomeninges.

In a study published in the Journal of Neuro-Oncology, researchers at the Instituto Nacional de Cancerología in Mexico City analyzed records from 345 patients with neoplastic meningitis from solid tumors who were seen between January 2010 and December 2024 and had imaging studies available for review. The cohort, one of the largest of its kind reported to date, was dominated by breast cancer, which accounted for 66 percent of cases, followed by lung cancer at 12 percent, genitourinary cancers at 6 percent, and head and neck cancers at 5 percent. This distribution reflects the epidemiology of leptomeningeal disease in the modern era, where breast cancer patients, living longer with better systemic therapies, increasingly face this devastating complication.

The headline finding is stark. Across the entire cohort, median overall survival was 6.9 months, with a 95 percent confidence interval of 5.5 to 8.3 months, underscoring how lethal the condition remains even at a major cancer center. But when the researchers stratified patients by their Evans index, the survival curves separated dramatically. Patients with an index of 0.3 or below had a median survival of 7.36 months, while those whose index exceeded 0.3 survived a median of only 2.99 months, a difference that reached statistical significance with a P value of 0.020. In practical terms, a single ratio measured on a scan that every patient already undergoes more than doubled the expected survival gap.

What makes this finding scientifically credible rather than merely suggestive is the rigor of the statistical adjustment. Enlarged ventricles could simply be a marker of older age, worse neurological status, or more advanced disease, all of which independently shorten survival. To rule out such confounding, the investigators built a multivariable model that accounted for age, sex, primary tumor type, Karnofsky Performance Score, neurological symptoms, activity of extracranial disease, and cerebrospinal fluid levels of both protein and lactic dehydrogenase, a marker of tissue breakdown. Even after all of these adjustments, an Evans index above 0.3 remained independently associated with mortality, carrying a hazard ratio of 1.95 with a 95 percent confidence interval of 1.09 to 3.50 and a P value of 0.024. In other words, patients with enlarged ventricles faced nearly twice the risk of death at any given time compared with those whose ventricles were normal in size.

The biological logic behind this association is plausible. Neoplastic meningitis can impair the resorption of cerebrospinal fluid, leading to a form of communicating hydrocephalus in which the ventricles gradually swell. Ventricular enlargement on imaging may therefore be a visible signature of disrupted fluid dynamics, rising intracranial pressure, and accumulating tumor burden within the nervous system. It may also capture the cumulative damage that cancer inflicts on the brain’s ability to manage its own fluid environment. If so, the Evans index functions less as a generic measure of brain shrinkage and more as a window into the pathophysiology of the disease itself, explaining why it retains predictive power even after accounting for clinical variables.

The study is particularly valuable because it provides what scientists call external validation. The prognostic role of ventricular size in leptomeningeal metastasis had been proposed before, most notably in a large European study published in Neurology in 2024 that examined ventricular size and its dynamics in patients with solid tumors. But prognostic biomarkers in oncology have a notorious history of failing when tested outside the populations in which they were discovered. By independently confirming the association in a distinct cohort, drawn from a different continent and health system, and by demonstrating robustness in a fully adjusted model, the Mexican team has strengthened the case that the Evans index is a genuine and transferable prognostic tool rather than a statistical fluke.

The clinical implications could be substantial. Decisions in neoplastic meningitis are among the most difficult in neuro-oncology. Options range from intrathecal chemotherapy and focal radiation to novel systemic agents that penetrate the blood-brain barrier, yet all carry toxicity, and evidence for survival benefit is limited to selected patient groups. Guidelines from the European Association of Neuro-Oncology and the European Society for Medical Oncology emphasize that prognosis should guide treatment intensity, but the prognostic tools available to date, such as performance status and cerebrospinal fluid markers, are imperfect. A ratio that requires nothing more than calipers on an existing magnetic resonance or computed tomography scan could be integrated into clinical trials as a stratification variable, into prognostic scores alongside existing clinical factors, and into everyday conversations between oncologists and patients about what lies ahead.

There are, of course, caveats. The study was retrospective and conducted at a single institution, which raises the possibility of selection bias, and the data could not be made publicly available because they contain potentially identifiable patient information. The Evans index is also a static measurement, capturing ventricular size at a single moment, whereas some researchers argue that serial changes in ventricular caliber over time may be even more informative. Prospective studies that track the index dynamically, and that test whether it improves decision-making in real time, would be the natural next step. Still, the effect size observed here, nearly a doubling of mortality risk after adjustment, is large enough that few would dismiss it.

For a disease that has resisted decades of therapeutic progress, the emergence of a cheap, universally available prognostic marker is a meaningful advance. The Evans index was never designed for this purpose; it was conceived in an era of air encephalography as a crude gauge of ventricular dilation. That it now appears to forecast survival in patients with cancer invading their central nervous system is a reminder that sometimes the most powerful tools in modern medicine are the simplest ones, hiding in plain sight on scans that clinicians already order every day. For the thousands of patients diagnosed with neoplastic meningitis each year, and for the physicians wrestling with how best to treat them, this humble ratio may soon become part of the standard vocabulary of care.

Subject of Research: Prognostic value of the Evans index, a ventricular size ratio on brain imaging, in patients with neoplastic meningitis from solid tumors

Article Title: Prognostic value of the Evans index in neoplastic meningitis: a real-world cohort study

Article References: González-Vázquez, A., Lorenzana-Mendoza, N. A., Reyes Pérez, J. A., & Cacho-Díaz, B. (2026). Prognostic value of the Evans index in neoplastic meningitis: a real-world cohort study. Journal of Neuro-Oncology, 179(2), Article 71. https://doi.org/10.1007/s11060-026-05780-4

Image Credits: AI Generated

DOI: 10.1007/s11060-026-05780-4

Keywords: neoplastic meningitis, leptomeningeal metastasis, Evans index, prognostic biomarker, brain imaging, hydrocephalus, ventricular enlargement, overall survival, breast cancer, neuro-oncology, cerebrospinal fluid, validation study