Diagnostic imaging of intracranial tumors

Computed tomography (CT)

Computed tomography remains the method of choice for urgent conditions in patients with acute neurological deterioration. Its main advantage is high scanning speed and wide availability, enabling the rapid detection of life-threatening mass effect (mass effect), acute obstructive hydrocephalus, or recent hemorrhage.

On unenhanced (non-contrast) scans, clinically significant tumors are often visualized due to the displacement of brain structures and areas of altered X-ray density. Decreased tissue density (hypodensity) typically corresponds to areas of necrosis or vasogenic edema. Meanwhile, certain neoplasms, such as lymphomas, may appear isodense (blending with the surrounding parenchyma) or even hyperdense.

Quantitative density assessment using the Hounsfield scale helps detect fresh blood or areas of calcification within the tumor structure. Viewing the scans in the bone window (bone-window) is a mandatory step in CT analysis. This allows the detection of benign hyperostosis or bone destruction, which indicates aggressive growth and narrows the differential diagnosis. Contrast administration in CT rarely provides essential information for tumor characterization itself and does not determine surgical tactics if MRI is readily available.

Magnetic resonance imaging (MRI)

MRI is the undisputed leader in neuro-oncology due to its superb anatomical detail and unmatched soft-tissue contrast, which is essential for resection planning. The standard clinical protocol invariably includes T1- and T2-weighted images (T1, T2 weighted), FLAIR, diffusion-weighted imaging (DWI), as well as T1-weighted images before and after intravenous gadolinium contrast administration.

The MR signal characteristics depend on cellular density, the presence of cystic components, calcifications, or blood breakdown products. The FLAIR sequence clearly highlights intra-axial lesions against the normal parenchyma; however, this signal is nonspecific and sometimes provides poorer differentiation between the cortex and white matter compared to conventional T2.

For detecting intratumoral hemorrhages and mineralization zones, magnetic susceptibility-weighted sequences (T2 or *SWI) are optimal. On these images, blood and calcifications appear hypointense**. A hyperintense signal on T1 may result from fat accumulation, hemorrhage, atypical calcification, or the presence of melanin (e.g., in melanoma metastases). When technical resources permit, 3D acquisitions are used, which significantly improve the visibility of small lesions and allow volumetric measurements of the tumor.

Contrast Enhancement and Tumor Characteristics

Gadolinium contrast enhancement provides vital information about the blood-brain barrier, but the enhancement pattern is often nonspecific. Nevertheless, contrast is critically important for postoperative follow-up (detecting recurrence) and ruling out infectious processes. The post-contrast FLAIR sequence is ideal for detecting subtle leptomeningeal disease (involvement of the meninges). In complex cases, visualization can be enhanced by using a double or triple dose of gadolinium or high-relaxivity contrast agents.

Many intracranial neoplasms are prone to hemorrhage or calcification, serving as important diagnostic markers:

• Frequently calcified: oligodendrogliomas (up to 90%), meningiomas, ependymomas, craniopharyngiomas, teratomas, chordomas, central neurocytomas, and choroid plexus tumors.
• Frequently associated with hemorrhage: glioblastomas (WHO grade IV gliomas), oligodendrogliomas, as well as metastases from lung cancer, breast cancer, and melanoma.

Advanced Perfusion Imaging Techniques

Many primary brain tumors and metastases are characterized by increased vascularization due to intensive neoangiogenesis. Perfusion-weighted MRI (PWI) makes it possible to evaluate these pathophysiological processes and distinguish, for example, glioblastoma from a slow-growing glioma.

1. DSC (Dynamic Susceptibility Contrast MRI). The most extensively studied method. It utilizes the paramagnetic properties of a gadolinium bolus, which induces a transient signal drop on T2*-weighted images (acquired every second). It measures cerebral blood volume (CBV). The main limitation of the method is contrast leakage through a disrupted blood-brain barrier, leading to falsely underestimated CBV. This is resolved by administering a pre-bolus (preload) and calculating the relative parameter (rCBV). The method is sensitive to artifacts from blood products and postoperative changes.
2. DCE (Dynamic Contrast-Enhanced MRI). Evaluates the increase in signal intensity on T1-weighted images over approximately 5 minutes. Using complex mathematical models, the transfer coefficient $K^{trans}$ is calculated, reflecting endothelial permeability and blood flow. The method is technically more complex to process, but offers better spatial resolution and is free from magnetic susceptibility artifacts.
3. ASL (Arterial Spin Labeling). Requires no contrast agent injection. It uses the patient's own magnetically labeled blood as an endogenous tracer to evaluate perfusion, making the method entirely non-invasive.

Briefly: answers to topical questions

Class and exam questions

What else to study on this topic

• Classification of Intra-axial and Extra-axial Tumors
• The Role of Magnetic Resonance Spectroscopy (MRS) in Evaluating Neoplasm Metabolism
• Preoperative CT/MR Angiography and Endovascular Tumor Embolization
• Integration of Intraoperative MRI into Neurosurgical Navigation Systems

Other topics in the Neuroimaging section

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