Today, we are outlining key recommendations from the Congress of Neurological Surgeons (CNS) 2026 guideline update on Treatment of Adults With WHO Grade II Diffuse Glioma. Management of WHO grade II diffuse glioma is a key area in neuro-oncology and involves multiple aspects of care. This update builds on the previous 2015 guideline and incorporates current evidence related to imaging, surgical approaches, pathology, chemotherapy, radiation therapy, and management of recurrence. 

In today’s spotlight, we are focusing on updated recommendations as well as newly formulated recommendations. Refer to the full-text version of the guideline for the most thorough look at the following recommendations.

New and Updated Recommendations in the 2026 CNS Diffuse Glioma Update

Imaging

  • The use of diffusion imaging and dynamic susceptibility contrast, dynamic contrast enhancement, and arterial spin labeling sequences is suggested to differentiate World Health Organization (WHO) grade II diffuse glioma from higher grade gliomas when this is not accomplished by T2-weighted and pregadolinium and postgadolinium contrast-enhanced T1-weighted imaging. 
  • The use of diffusion and perfusion is suggested for obtaining information in genomics, prognosis, and post-treatment monitoring when this information would be of value to the clinician and is not obtained through other methods. 
  • The use of MR spectroscopy is suggested to differentiate WHO grade II diffuse glioma from higher-grade gliomas when this is not accomplished by standard MRI, perfusion, and diffusion techniques and when such information would be of value to the clinician. 
  • If not already evident by MRI studies, the addition of amino acid positron emission tomography (PET) with fluoroethyl-L-tyrosine and dihydroxy-6-fluoro-phenylalanine as a tracer is suggested to help determine if a brain lesion is a low-grade glioma or high-grade glioma. 
  • If the standard clinical prognostic parameters are unclear and novel PET tracers are available, the clinician may consider fluoroethyl-L-tyrosine to assist in determination of prognosis in an individual with grade II diffuse glioma. 
  • Clinicians may use dihydroxy-6-fluoro-phenylalanine PET in addition to MRI if additional information is required for detection of tumor progression. 

Surgery

  • In adults with imaging suggestive of a WHO grade II diffuse gliomas (oligodendrogliomas or astrocytomas), surgical resection is suggested over observation or biopsy to improve overall survival. 
  • In adults with imaging consistent with a WHO grade II diffuse glioma who present with seizure activity, surgical resection of greater than 90% of the lesion, when it can be accomplished safely, is suggested over observation or lesser extent of resection/biopsy to improve seizure control.
  • It is suggested that extent of resection be maximized as is safely possible for isocitrate dehydrogenase (IDH) mutant and isocitrate dehydrogenase wild type WHO grade II diffuse gliomas to improve progression free survival (PFS) and OS. 
  • There is insufficient evidence that greater extent of resection of 1p19q codeleted oligodendrogliomas (WHO grade II diffuse gliomas) improves OS.
  • The use of intraoperative ultrasound is suggested to increase the extent of resection compared with conventional surgery for adults with WHO grade II diffuse glioma. 
  • Intraoperative fluorescent-guided surgery with 5-aminolevulinic acid is not suggested to improve the extent of resection for WHO grade II gliomas. 
  • It is suggested that awake craniotomy and other methods of intraoperative mapping can be used to increase the extent of resection for adults with WHO grade II diffuse glioma. 
  • The use of functional MRI and diffusion tensor imaging–related modalities are suggested to decrease surgical morbidity in adults with WHO grade II diffuse glioma. 

Pathology

  • There is insufficient evidence to recommend alpha-thalassemia/mental retardation X-linked mutation testing as a means of predicting survival or making treatment recommendations. 
  • There is insufficient evidence at this time to suggest that intraoperative optical histological methods offer increased diagnostic accuracy when compared with conventional techniques. 

Chemotherapy

  • It is recommended that chemotherapy (procarbazine) be added to RT in all patients with newly diagnosed high-risk WHO grade II diffuse glioma (patients younger than 40 years unable to get gross total resection and older than 40 years regardless of the degree of resection) to improve their overall survival. 
  • It is recommended that chemotherapy be added to radiation therapy in all patients with newly diagnosed high-risk WHO grade II diffuse glioma to improve overall survival without a decline in neurocognitive function. 
  • It is recommended that chemotherapy (temozolomide) be added to RT in all patients with newly diagnosed high-risk WHO grade II diffuse glioma to improve progression free survival and overall survival. 
  • It is suggested that chemotherapy alone should be considered in patients with newly diagnosed WHO grade II diffuse glioma in cases with 1p/19q codeletion.
  • Neo-adjuvant temozolomide may be used in patients with WHO grade II diffuse gliomas deemed unsafe for resection due to infiltration of eloquent areas or with large contralateral extension as an initial step to improve the extent of resection. 
  • There is insufficient evidence to support a recommendation regarding the ability of chemotherapy provided before surgical resection to improve PFS and OS. 
  • There is insufficient evidence to support a recommendation against the use of temozolomide for WHO grade II diffuse gliomas due to concern over increasing the rate of malignant transformation. 
  • There is insufficient evidence to support a recommendation for or against the use of multiagent chemotherapy to improve progression free survival and overall survival when compared with administration of single-agent chemotherapy in patients with newly diagnosed WHO grade II diffuse glioma. 

Radiation Therapy

  • There is insufficient evidence to provide guidance on the superiority or inferiority of proton radiation effect compared with standard radiation therapy on WHO grade 2 diffuse glioma for overall survival, progression-free survival, local control, complications, neurocognitive preservation, and quality of life. 
  • It is suggested that 1p/19q deletion status be used as a positive prognostic indicator regarding the effect of radiation therapy on progression free survival and overall survival for WHO grade II diffuse gliomas. 

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