What is the likelihood of gliosis in the brain appearing as non-enhancing with contrast and without midline shift on imaging?

From the Guidelines

Gliosis in the brain is very likely to appear as non-enhancing with contrast and without midline shift on imaging studies. This is because gliosis represents a non-neoplastic proliferation of glial cells in response to brain injury, and typically does not disrupt the blood-brain barrier significantly enough to cause contrast enhancement, as noted in the context of diffuse gliomas which can present with variable contrast enhancement patterns 1. Unlike space-occupying lesions such as tumors or large hemorrhages, gliosis generally does not create enough mass effect to cause midline shift. The imaging characteristics of gliosis are more in line with those of non-contrast-enhancing tumor portions, which can represent a combination of tumor cell invasion with an intact blood–brain barrier and edema, as discussed in the context of diffuse IDH-mutant gliomas of CNS WHO grade 2 which often show little or no contrast-enhancement 1.

Key characteristics of gliosis on imaging include:

• Appearance as an area of T2/FLAIR hyperintensity
• Lack of enhancement on post-contrast T1-weighted images, reflecting its non-disruptive nature with respect to the blood-brain barrier
• Absence of significant mass effect or midline shift, distinguishing it from more aggressive or expansive lesions
• Maintenance of the original volume of the affected tissue rather than expanding beyond it, consistent with scar tissue formation rather than an expanding lesion

These characteristics align with the recommendations for preoperative MRI datasets which should include T2-weighted sequences and contrast-enhanced T1-weighted sequences to aid in distinguishing contrast-enhancing and non-contrast-enhancing tumor portions 1. The use of advanced imaging techniques such as diffusion-weighted imaging, perfusion MRI, and magnetic resonance spectroscopy can also provide insights into the nature of the lesion, though gliosis itself would not typically exhibit the metabolic abnormalities or hyperperfusion seen in more aggressive tumors 1.

From the Research

Gliosis in the Brain

• The likelihood of gliosis in the brain appearing as non-enhancing with contrast and without midline shift on imaging can be related to the presence of gliomas, which are primary brain tumors that can be low-grade or high-grade 2, 3, 4, 5.
• Studies have shown that some high-grade gliomas (HGGs) may not enhance on imaging, leading to a delay in diagnosis and treatment 2, 3.
• Non-enhancing lesions on MRI can be indicative of low-grade gliomas (LGGs), but a significant proportion (27.9%) of non-enhancing lesions can be HGGs, especially in patients older than 60 years 2.
• The appearance of multicentric non-enhancing lesions on MRI can be a poor prognostic feature, with these lesions progressing faster than expected for LGGs and likely representing more advanced lesions than their appearances suggest 5.
• Magnetic resonance perfusion can be used to differentiate low-grade from high-grade gliomas, but the limited available evidence precludes reliable estimation of its performance for identifying grade in untreated solid and non-enhancing LGGs from that of HGGs 6.

Imaging Characteristics

• Non-enhancing lesions on MRI can demonstrate increased T2 signal changes without contrast enhancement, and may be indicative of LGGs or HGGs 2, 3, 4.
• The presence of multicentric non-enhancing lesions on MRI can be a characteristic of glioblastoma, with these lesions progressing to ring-enhancing lesions over time 5.
• Magnetic resonance perfusion-derived rCBV values can be used to differentiate LGGs from HGGs, but the optimal threshold for this differentiation is not well established 6.

Clinical Implications

• The presence of non-enhancing lesions on MRI should prompt further investigation, including biopsy, to determine the grade and type of glioma 2, 3, 4.
• Patients with multicentric non-enhancing lesions on MRI may require closer monitoring and more aggressive treatment, as these lesions can progress rapidly 5.
• The use of magnetic resonance perfusion and other advanced imaging techniques can aid in the diagnosis and treatment of gliomas, but further research is needed to establish their role in clinical practice 6.