Butterfly Glioblastoma: Morphology, Diagnosis, and Treatment

Butterfly glioblastoma is an aggressive brain tumor that grows across both hemispheres of the brain by infiltrating the corpus callosum, the thick bundle of nerve fibers connecting the left and right sides. On MRI, the resulting mass looks roughly like the wings of a butterfly, which gives the tumor its name. It accounts for fewer than one in ten glioblastoma diagnoses and carries a median survival measured in months, yet recent evidence suggests that active treatment, including surgery in selected cases, can meaningfully extend life compared with biopsy alone.

What Makes a Glioblastoma a “Butterfly”

Any lesion that crosses the midline of the brain through the corpus callosum and shows substantial tumor bulk on both sides can qualify as a butterfly glioblastoma. The corpus callosum is the brain’s largest white-matter tract, and glioblastoma cells exploit these fibers as highways to migrate from one hemisphere to the other. Among patients with newly diagnosed glioblastoma, roughly a quarter show some degree of corpus callosum involvement, but only a subset of those have true bilateral infiltration. In one institutional series of 363 newly diagnosed glioblastoma patients, corpus callosum involvement was found in about 26%, and bilateral infiltration, the hallmark of butterfly morphology, was present in 28% of that group.

The butterfly shape can vary quite a bit. Some tumors are roughly symmetric, with comparable mass in each hemisphere. Others are lopsided, with a dominant bulk on one side and a smaller tongue of tumor extending across the midline. The degree of symmetry and the exact location along the corpus callosum, whether it sits in the front (genu), middle (body), or back (splenium), influence both symptoms and surgical options.

How Patients Typically Present

Because the corpus callosum connects the hemispheres and plays a central role in coordinating complex thought, butterfly glioblastomas tend to cause cognitive and personality changes early, sometimes before headaches or seizures draw attention. Memory problems, slowed thinking, personality shifts, and difficulty with language are common initial complaints. Caregivers of glioblastoma patients consistently report that memory problems, personality and mood changes, and language difficulties are the symptoms that affect daily life the most.² Cognitive impairment in butterfly glioma patients is a well-documented clinical feature, and it can complicate both diagnosis and treatment planning.³

Seizures remain a presenting symptom in a meaningful share of patients, particularly when the tumor involves cortical gray matter near the surface in addition to the deep white-matter structures. Increased intracranial pressure from the tumor’s mass can also cause headaches, nausea, and visual changes. The speed of symptom onset varies; some patients deteriorate over weeks, while others present acutely after a seizure or sudden neurological decline.

Imaging and Diagnosis

MRI is the cornerstone of diagnosis. On standard sequences, the characteristic appearance is a contrast-enhancing mass with irregular borders that spans the midline, often with a central necrotic core and surrounding edema spreading through both hemispheres. Advanced MRI techniques, including diffusion-weighted imaging, perfusion imaging, and spectroscopy, help confirm the tumor grade, identify the most aggressive regions for biopsy targeting, and evaluate for recurrence after treatment.⁴ Because glioblastoma is the most common high-grade tumor to cross the corpus callosum, any lesion showing this butterfly pattern should be considered glioblastoma until proven otherwise.⁵

That said, the butterfly pattern is not exclusively glioblastoma. Primary central nervous system lymphoma is the most important mimic, because it can also involve the corpus callosum and look superficially similar on standard MRI. Distinguishing between the two matters enormously: lymphoma responds to chemotherapy alone and is not treated with surgery, while glioblastoma requires a completely different approach. Specific MRI morphological features and signal-intensity ratios can help separate lymphoma from atypical glioblastoma with high accuracy. One multicenter study found that combining morphological signs with quantitative signal ratios achieved correct classification over 90% of the time.⁶ Other conditions that can occasionally mimic the butterfly appearance include demyelinating disease, toxoplasmosis in immunocompromised patients, and lower-grade gliomas, though these usually have features on imaging that help distinguish them.

Molecular Features

One of the first questions molecular testing answers is whether the tumor’s MGMT promoter is methylated, a marker that predicts better response to the chemotherapy drug temozolomide. In butterfly glioblastoma, the available data suggest that the majority of tumors are MGMT-unmethylated. In one population-based cohort with molecular data available on a small subset, nearly two-thirds of tested butterfly glioblastomas were MGMT-unmethylated, while only about 18% were methylated.⁷ This is a concerning proportion, since unmethylated tumors respond less robustly to temozolomide. None of the tumors tested in that cohort carried BRAF mutations, which are occasionally seen in other brain tumor subtypes and can be targeted with specific drugs.

These molecular findings are drawn from small sample sizes, so they should be interpreted cautiously. Larger studies may eventually reveal whether butterfly glioblastomas have a distinct molecular profile compared to glioblastomas in general, or whether they are simply standard glioblastomas that happen to grow across the midline. For now, the molecular workup follows the same protocol as for any glioblastoma: testing for IDH mutation status, MGMT methylation, and other markers that inform treatment decisions.

The Surgery Question

For decades, butterfly glioblastomas were considered essentially inoperable. The thinking was straightforward: the tumor sits deep in the brain, crosses critical midline structures, and involves both hemispheres, so attempting surgical removal seemed too dangerous to justify. Many patients were offered only a needle biopsy for diagnosis, followed by radiation and chemotherapy. That assumption has been challenged by a growing body of evidence.

Two separate meta-analyses have now compared outcomes in butterfly glioblastoma patients who underwent surgical resection versus those who had biopsy alone. One found that resection was associated with nearly three times the odds of being alive at six months and almost four times the odds at twelve months, compared with biopsy.⁸ The other, pooling seven studies with about 293 patients, found a hazard ratio of 0.39 for death with surgery compared to biopsy, meaning that surgical patients had a substantially lower risk of dying during follow-up. The survival benefit persisted whether the surgeon achieved more or less than 80% tumor removal.⁹

The survival advantage of surgery does come with a trade-off. Resection carries a higher rate of new neurological deficits afterward, roughly double the risk compared with biopsy alone.⁸ These deficits can include weakness, speech problems, and a condition called abulia, characterized by a profound lack of motivation and initiative. Abulia is particularly associated with surgery near the front of the corpus callosum, where critical networks governing motivation and decision-making reside.

Reducing Surgical Complications

One of the more notable surgical advances for anterior butterfly glioblastomas involves refined techniques that spare the brain’s default mode network, a set of connected regions involved in motivation, self-reflection, and planning. A study comparing standard surgical approaches to a modified technique designed to preserve this network found striking differences: with the standard approach, 44% of patients had significant abulia on the first day after surgery, and 28% still had it at six weeks. With the newer technique, those rates dropped to 7% on the first day and zero at six weeks.¹⁰ This kind of work illustrates that surgical outcomes for butterfly glioblastoma are not fixed; they depend heavily on technique and institutional expertise.

Not every butterfly glioblastoma is a good surgical candidate. Tumors centered in the splenium (the back of the corpus callosum) are harder to approach safely, and patients with poor baseline functional status may not recover well enough from surgery to benefit from subsequent radiation and chemotherapy. A performance status score at presentation is one of the strongest predictors of survival in this population, making careful patient selection essential.¹¹

Radiation and Chemotherapy

After surgery or biopsy, the standard adjuvant approach for glioblastoma generally applies: radiation with concurrent temozolomide, followed by additional cycles of temozolomide alone. However, the practical delivery of radiation for butterfly glioblastoma has its own challenges. The bilateral extent of tumor and surrounding edema means the target volume can be very large, putting substantial amounts of normal brain tissue at risk for radiation injury. Research on target delineation has shown that using the postoperative tumor cavity and residual tumor plus a margin, rather than trying to encompass all edema, results in smaller volumes of healthy brain receiving high-dose radiation. This approach may reduce the risk of late neurological decline, which matters especially for patients whose cognition is already compromised by the tumor’s location.¹²

Hypofractionated radiation, in which higher doses are delivered over fewer sessions, has become a common approach for butterfly glioblastoma in particular. In the population-based cohort discussed earlier, hypofractionated radiation with or without temozolomide was the most frequently used treatment strategy, given to about 59% of treated patients.⁷ This likely reflects the older age and lower functional status of many butterfly glioblastoma patients, for whom a shorter course of radiation is more practical and less burdensome.

Temozolomide remains the backbone of chemotherapy. Some researchers have explored alternative dosing schedules. One trial testing an alternating weekly schedule of temozolomide in patients with recurrent glioblastoma found that the regimen was safe and produced a six-month progression-free survival rate of about 44%, compared to roughly 21% in historical controls using the standard schedule.¹³ These dose-intensification strategies remain under investigation and are not standard for butterfly glioblastoma specifically, but they illustrate the ongoing effort to squeeze more benefit out of available drugs.

Laser Ablation as a Minimally Invasive Alternative

For patients who are not candidates for open surgery, laser interstitial thermal therapy (LITT) has emerged as an intriguing option. LITT involves inserting a thin laser fiber through a small hole in the skull, guided by MRI in real time, and heating the tumor tissue to destroy it. Because the approach requires only a small puncture rather than a craniotomy, it avoids many of the risks of open surgery.

A small series specifically studying bilateral LITT for butterfly glioblastoma, meaning laser fibers placed in both hemispheres to treat tumor on each side, found the procedure was safe with no intraoperative or postoperative complications, and showed early signs of improved progression-free survival compared with biopsy alone.¹⁴ An earlier case series confirmed the safety of the bilateral LITT approach and suggested it might improve outcomes for patients who would otherwise be limited to biopsy.¹⁵

LITT is still in its early days for this specific indication. The case numbers are small, and there are no randomized trials comparing it to open surgery or biopsy. It is best understood as a potentially useful tool in the toolkit, particularly for tumors in locations that are dangerous to approach with conventional surgery, or for patients whose overall condition makes a full craniotomy too risky.

Prognosis

Butterfly glioblastoma carries a worse prognosis than glioblastoma in general, which already has a grim median survival. Among patients with corpus callosum involvement, median overall survival was about 9 months, compared with 11 months for glioblastoma patients without corpus callosum involvement.¹ For true butterfly glioblastoma specifically, the median overall survival in a population-based cohort was about 5.5 months, with a 3-year survival rate of just over 9%.⁷ Another study reported a median survival of roughly 8.5 months for butterfly tumors of the corpus callosum, with glioblastoma being the most fatal histology among various tumor types that can form this pattern.¹¹

These numbers underscore the importance of treatment. In the population-based cohort, patients receiving only best supportive care had dramatically worse survival than those receiving multimodal treatment, with an adjusted hazard ratio over five.⁷ Factors associated with poorer outcomes include low functional status at presentation, tumor located in the splenium, and glioblastoma histology. For patients with unilateral corpus callosum involvement who can undergo gross total resection, survival can approach the 11-month mark seen in non-corpus-callosum glioblastoma, suggesting that extent of surgical removal remains an important lever even in this difficult tumor location.¹

Palliative and Supportive Care

Given the short survival times and the prominence of cognitive symptoms, palliative care becomes relevant early in the disease course for many butterfly glioblastoma patients. Seizure management is a particular priority. In home palliative care settings for glioblastoma patients, severe seizures occurred in about 30% of cases and were most often managed with phenobarbital. Symptoms like delirium, agitation, and refractory seizures required midazolam in about 11% of cases to achieve adequate control.¹⁶

For family members, the caregiving burden in glioblastoma is substantial and grows as the disease progresses. The cognitive and personality changes that are especially common in butterfly glioblastoma, because of the corpus callosum’s role in higher-order brain functions, can be among the hardest symptoms for families to manage. Caregivers consistently identify memory problems, personality shifts, and communication difficulties as the symptoms with the greatest daily impact on their own lives.² Early integration of palliative and psychosocial support, not as a replacement for treatment but alongside it, can help both patients and caregivers cope with this trajectory.

Liquid Biopsy and Emerging Monitoring Tools

Tracking a butterfly glioblastoma over time is challenging because repeated MRI scans cannot always distinguish true tumor progression from treatment-related changes such as radiation necrosis or pseudoprogression. Liquid biopsy, the analysis of tumor-derived molecules circulating in body fluids, is an area of active research that could eventually help.

For brain tumors, cerebrospinal fluid currently offers the highest sensitivity for detecting tumor-specific genetic alterations, because tumor DNA shed into the fluid surrounding the brain is more concentrated there than in the bloodstream.¹⁷ Circulating tumor DNA from cerebrospinal fluid can be sequenced to reveal the tumor’s genetic heterogeneity and provide diagnostic and prognostic information.¹⁸ Plasma-based liquid biopsy, which requires only a blood draw, is easier to repeat but currently less sensitive for brain tumors because the blood-brain barrier limits how much tumor DNA reaches the general circulation.

None of these liquid biopsy approaches have entered routine clinical use for glioblastoma yet, but they are particularly appealing for butterfly glioblastoma. Repeat tissue biopsies of a deep bilateral brain tumor are impractical and risky. If validated, liquid biopsy could offer a way to monitor molecular changes over time, detect resistance mutations early, and guide treatment adjustments without requiring another procedure that reaches into the center of the brain.

1
Nature. Prognostic differences and implications on treatment strategies between butterfly glioblastoma and glioblastoma with unilateral corpus callosum infiltration
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Frontiers in Oncology. Differentiation Between Primary Central Nervous System Lymphoma and Atypical Glioblastoma Based on MRI Morphological Feature and Signal Intensity Ratio: A Retrospective Multicenter Study
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8
PubMed. Meta-analysis of overall survival and postoperative neurologic deficits after resection or biopsy of butterfly glioblastoma
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PubMed Central. Surgery vs. Biopsy in the Treatment of Butterfly Glioblastoma: A Systematic Review and Meta-Analysis
10
PubMed Central. A method for safely resecting anterior butterfly gliomas: the surgical anatomy of the default mode network and the relevance of its preservation
11
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PubMed Central. Delineation of radiation therapy target volumes for patients with postoperative glioblastoma: a review
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PubMed Central. Temozolomide treatment outcomes and immunotherapy efficacy in brain tumor
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PubMed. Bilateral Laser Interstitial Thermal Therapy for Butterfly Gliomas Compared With Needle Biopsy: A Preliminary Survival Study
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PubMed. Safety Analysis of Bilateral Laser Interstitial Thermal Therapy for Treatment of Butterfly Glioma
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PubMed Central. Palliative care in patients with glioblastoma: A systematic review
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PubMed Central. ctDNA-Based Liquid Biopsy of Cerebrospinal Fluid in Brain Cancer