Basics of MRI semiotics and standard sequences
When a neoplastic process in the spine is suspected, MRI is the alternative-free method of choice. A crucial condition for a high-quality scan is the addition of the STIR (short tau inversion recovery) sequence. The method provides direct visualization of the spinal cord, thecal sac contents, ligaments, and nerve roots.
Comprehensive analysis of tomograms allows for the evaluation of the spread of the lesion: soft tissue invasion, compression of neural structures, epidural growth, and bone marrow infiltration. Using complex clinical cases (such as recurrent medulloblastoma) as an example, basic sequences demonstrate the following patterns:
- T1-weighted image (T1-weighted image): reveals a diffuse heterogeneous signal intensity in the vertebral bone marrow, which is a sign of metastatic bone disease.
- T2-weighted image: allows the detection of poorly demarcated high-intensity areas within the spinal cord itself, indicating proximal intramedullary lesions.
Specific radiological patterns also exist. For example, the presence of fluid-fluid levels is typical for an aneurysmal bone cyst (ABC / Aneurysmal bone cyst), whereas contrast-enhancing rings and arcs are characteristic of cartilaginous tumors.
Administration of contrast enhancement (Gadolinium)
The administration of gadolinium agents is critical for increasing the contrast of pathological foci. Contrast enhancement is performed predominantly in the sagittal and axial planes. Coronal projections combined with a fat suppression sequence are essential for assessing the paraspinal spread of the tumor into soft tissues.
Key objectives of contrast use:
- Clear visualization of solid tumor components that uptake the agent.
- Differential diagnosis of neoplastic cysts (which uptake gadolinium strictly along the borders) from concomitant reactive pseudocysts.
- Evaluation of extradural tumors: the method allows viable tumor tissue to be distinguished from avascular necrotic zones, as well as the identification of epidural extension.
- Confirmation of metastasis: T1WI with Gd-enhanced gadolinium demonstrates diffuse leptomeningeal contrast enhancement and intravertebral enhancement.
Additionally, for screening intradural dissemination of the neoplasm, many authors recommend using the contrast-enhanced 3D-GRE T1 sequence.
Diffusion tensor imaging (DTI) and tractography
DWI and DTI techniques are widely used in brain neuroimaging, but their application at the spinal cord level involves major technical hurdles. These include the small size of the structures (requiring high resolution, which reduces the signal-to-noise ratio), pronounced artifacts from macroscopic motion (respiration, swallowing, physiological CSF pulsation), and local magnetic field heterogeneity. The use of echo-planar sequences further amplifies susceptibility effects.
Nevertheless, DTI tractography (fibre tracking) holds enormous potential for surgical planning as it visualizes the relationship of the tumor to healthy nerve fibers:
- If the lesion merely displaces the tracts (for example, peripheral splaying of fibers is observed in ependymoma), this indicates a well-demarcated nodule. In such cases, a clear resection plane exists, making safe surgical removal possible.
- In diffusely infiltrating processes, such as fibrillary astrocytoma, nerve fibers may be pushed anteriorly by the tumor or directly involved in the process, which changes the treatment strategy.
Role of other diagnostic imaging methods
Despite the leading role of MRI, comprehensive diagnosis often requires a multimodal imaging approach:
- Plain film radiography (Plain film radiography): benign bone tumors may be an incidental finding. Indirect signs of an intramedullary process include torticollis (torticollis), straightening of the cervical lordosis, and scoliosis. Scalloping (scalloping) of the posterior vertebral wall and widening of the intervertebral foramina indicate a slow-growing spinal cord or nerve sheath tumor.
- Computed tomography (CT / CT): ideal for detailed analysis of bone destruction, identifying calcification, and assessing the matrix of primary bone tumors. CT also serves as a navigation method for biopsy and interstitial laser ablation (e.g., for osteoid osteoma).
- Bone scintigraphy (Bone scintigraphy): ordered when multifocal bone lesions are suspected, though the method is limited due to low resolution of surgical anatomy.
- FDG-PET: shows promise for assessing metabolically active components and disease progression. The main limitation is the rarity of spinal tumors, which hinders large prospective studies, as well as the risk of false-positive results due to degenerative changes.
All identified central nervous system neoplasms are classified according to WHO standards. The 2007 classification, developed by a consensus of pathologists and geneticists, is based on the cellular origin of the tumor and includes a grading system for selecting optimal treatment and predicting outcomes.
Briefly: answers to topical questions
Which histological types of primary intramedullary spinal cord tumors are most common in adult patients?
In adult patients, glial tumors are the most common, accounting for about 90% of all cases. The main histological types include:
- Ependymoma (ependymoma) — the most frequent tumor, accounting for 40–60% of cases.
- Astrocytoma (astrocytoma) — ranks second, with 75% of cases being low-grade fibrillary tumors.
- Hemangioblastoma (haemangioblastoma) — is the third most frequent type of primary neoplasm in this location.
According to the WHO classification, by which specific histological criteria is the malignancy grade of CNS tumors assessed?
The grade of malignancy of central nervous system tumors is assessed based on four histological criteria. The following parameters are distinguished:
- Nuclear atypia — the sole criterion defining Grade 2 malignancy.
- Mitoses — their presence along with nuclear atypia indicates Grade 3.
- Endothelial proliferation — an additional sign of the highest grade of malignancy.
- Necrosis — also characteristic of Grade 4, which requires the presence of three or four criteria simultaneously.
For Grade 1, these criteria are completely absent.
What signal intensity changes on T1WI and T2WI are characteristic of metastatic vertebral bone marrow involvement?
For metastatic vertebral bone marrow involvement on sagittal T1WI, a diffuse heterogeneous signal intensity in the bone marrow is described, indicating metastatic disease. Specific bone marrow signal changes on T2WI are not described in the source. T2WI may reveal poorly demarcated areas of high signal intensity in the spinal cord at the Th9–Th10 level, raising suspicion for intramedullary lesions.
Class and exam questions
Why are gadolinium-based contrast agents administered during MRI for spinal tumors?
Contrast enhancement is necessary to differentiate viable tumor tissue from necrotic zones, distinguish neoplastic cysts from reactive pseudocysts, and identify solid components and leptomeningeal metastasis.
Why is it difficult to apply DWI and DTI methods in spinal cord imaging?
The main challenges are related to the small size of anatomical structures, local magnetic field inhomogeneity, and motion artifacts from respiration, swallowing, and physiological cerebrospinal fluid pulsation.
How does tractography (DTI) impact neurosurgical planning?
DTI shows the relationship between the tumor and nerve tracts. If the tumor (e.g., ependymoma) displaces the fibers without infiltrating them, a resection plane is formed, which allows safe removal of the lesion.
What indirect radiological signs may indicate an intramedullary tumor?
These signs include the development of scoliosis, torticollis (torticollis), flattening of the cervical lordosis, as well as local scalloping of the posterior vertebral walls and pathological widening of the intervertebral foramina.
What else to study on this topic
- Specifics of using contrast-enhanced 3D-GRE T1 for detecting intradural dissemination
- Differential diagnosis of aneurysmal bone cysts based on fluid levels on MRI
- World Health Organization (WHO 2007) histological classification of CNS tumors
- Capabilities of CT-guided interstitial laser ablation in osteoid osteomas
- The role of fluorodeoxyglucose PET (FDG-PET) in grading tumor malignancy
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