Pathogenesis and clinical presentation
Chordoma is the most common primary bone tumor of the sacrum and mobile spine. It is localized exclusively within the axial skeleton. If the tumor affects the mobile spine, the cervical segment is the favored site.
For a long time, it was believed that the neoplasm originates directly from remnants of the embryonic notochord, which normally regresses into the nucleus pulposus. However, modern studies have proven that chordomas develop from benign notochordal cell tumors (Benign Notochordal Cell Tumours, BNCT). The transformation process includes a transitional phase—"incipient" chordoma—which invades through the cortical layer into soft tissues and requires the same treatment as the classic form.
The tumor is classified as a low-grade malignancy (low-grade). Due to its slow growth, the diagnosis is often made at a stage when the masses reach giant sizes, which critically complicates resection and leads to a high probability of local recurrences. Metastases (to the lungs, skeletal system, skin, or brain) are atypical upon initial presentation (about 5%), but in advanced disease, they are detected in 65% of patients.
CT and MRI semiotics of chordoma
The epicenter of the destructive lesion is located along the midline in the vertebral body, surrounded by a growing soft tissue mass.
- Computed tomography (CT):
An expansive osteolytic lesion with irregular contours is determined. CT brilliantly visualizes the infiltration of the paraspinal and epidural spaces, as well as the presence of characteristic intratumoral calcifications and areas of osteosclerosis.
- Magnetic resonance imaging (MRI):
Serves as the gold standard for analyzing the heterogeneous matrix structure.
- T2-WI: A sharply hyperintense (bright) signal is visualized, which is the most striking sign caused by the abundance of intra- and extracellular mucin. Areas of low signal against this background correspond to hemosiderin deposits.
- T1-WI: The signal is most often isointense or hypointense relative to muscle tissue. High-signal zones indicate fresh hemorrhages or protein accumulations in mucinous compartments.
- Contrast enhancement (gadolinium): Contrast agent uptake is variable. The most specific is peripheral septal enhancement reflecting a network of fibrous strands or chondroid tissue between lobules.
Features of specific localizations
Shape and growth pattern directly depend on the affected segment:
- Mobile spine: The soft tissue component often sprawls along several segments, forming the "collar" sign on sagittal tomograms.
- Cervical spine: The lesion can grow in a "mushroom" or "dumbbell" shape, widening the neural foramen. Sometimes the bone is not destroyed, causing the chordoma to reliably mimic a neurogenic tumor.
- Sacrococcygeal region: A multilobular mass is formed, involving tissues anterior to the sacrum. The structure appears encapsulated, with internal septations. The sacroiliac joints are usually intact. A lobular structure with calcifications and areas of hemorrhage against the background of a bright T2 signal unmistakably points to a chordoma.
Differential diagnosis
It is critically important to distinguish chordoma from its precursor—BNCT. Recognizing the benign tumor prevents unwarranted debilitating surgical interventions.
Key differences of BNCT:
- Absence of a soft tissue component and cortical destruction.
- An isolated sclerotic lesion replacing bone marrow (sometimes up to the formation of the "ivory vertebra" sign on radiographs).
- No contrast enhancement on MRI.
The appearance of an extraosseous component and enhancement on contrast studies are the main indicators of malignant transformation.
Briefly: answers to topical questions
What radiologic signs allow differentiation of sacral chordoma from giant cell tumor of bone?
Sacral chordoma can be distinguished from giant cell tumor by the features of localization, spread, and MRI signal.
| Sign | Chordoma | Giant cell tumor |
|---|---|---|
| Localization | Along the midline | Often crosses the midline |
| Sacroiliac joints | Intact (not involved) | May be involved |
| T2-weighted imaging | Pronounced hyperintense signal | Low or intermediate signal |
| Contrast enhancement | Variable, including septal | Contrast enhancement reflects rich vascularization |
What is the appearance of benign notochordal cell tumors (BNCT) on standard radiography?
On standard radiography, a benign notochordal cell tumor may appear normal or manifest as ill-defined sclerosis of the vertebral body. Rarely, pronounced diffuse sclerosis is determined—the "ivory vertebra" sign.
According to CT data, cortical destruction or bone destruction is absent.
To distinguish an aggressive chordoma from a benign BNCT on MRI, look for two markers: extension beyond the bone (formation of soft tissue masses) and contrast enhancement. BNCT "sits inside and does not enhance."
Class and exam questions
From which structures does a spinal chordoma develop?
It is now proven that chordomas develop from benign notochordal cell tumors (BNCT), gradually passing through the stage of cortical invasion ("incipient chordoma").
Which radiologic sign of chordoma is considered most pathognomonic?
A sharply hyperintense signal on T2-weighted images due to a large amount of mucin, as well as a lobular structure with enhancing septa.
What can a chordoma in the cervical spine be confused with?
With a neurogenic tumor. A chordoma can have a "dumbbell" shape and widen the neural foramen without overt bone destruction, mimicking a neurilemoma.
How often do chordomas produce distant metastases?
At the time of initial diagnosis, metastases are extremely rare (up to 5%), but in late, advanced stages, their frequency reaches 65% (affecting the lungs, bones, skin, and brain).
What else to study on this topic
- Benign notochordal cell tumors (BNCT)
- Giant cell tumors of the spine (GCTs) and sacrum
- Aneurysmal bone cyst: MRI fluid-fluid level sign
- Eosinophilic granuloma and vertebra plana syndrome
- Multiple myeloma and solitary plasmacytoma
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