Comparison of imaging modalities (C6 level example)
To assess bone lesions such as giant cell tumor (giant cell tumour) and secondary aneurysmal bone cyst (secondary aneurysmal bone cyst), staged diagnostic imaging is used. Let us examine the classic picture using a lesion of the sixth cervical vertebra (C6) as an example.
On plain film radiography (plain film radiography), signs of the lesion include:
- Absence of the C6 spinous process (spinous process), which is destroyed by the pathological process.
- Replacement of the normal bone tissue of the spinous process with a volumetric soft-tissue mass (soft-tissue mass).
- Presence of minor calcifications.
- Visualization of remnants of the cortical bone layer (remnants of cortical bone).
For a more detailed picture, the use of MSCT (MDCT) and MRI (MRI) is mandatory. These methods allow a reliable and complete assessment of the spread of the pathological process. Tomography clearly demonstrates involvement of:
- The vertebral body (vertebral body).
- The pedicles (pedicles).
- The posterior elements (posterior elements).
- The spinal canal (spinal canal).
Specific MRI signs of the cyst
Magnetic resonance imaging plays a key role in differential diagnosis due to its high soft-tissue contrast.
A specific and most important visual marker is the presence of fluid levels (fluid-fluid levels). This phenomenon is clearly visualized on T2-weighted images (T2 weighted images). The detection of fluid levels is considered a pathognomonic sign (hallmark) that directly indicates the formation of an aneurysmal bone cyst within the lesion.
CT-controlled biopsy and paravertebral extension
For spinal tumors with significant paravertebral extension, morphological verification is required to establish a definitive diagnosis.
MRI semiotics of complex cases: Specialized scanning protocols are used to assess the soft-tissue component and its margins:
- Sagittal contrast-enhanced T1-weighted sequence (sagittal contrast-enhanced T1).
- Axial fat-suppressed T2-weighted sequence (axial fat-suppressed T2, also known as STIR — short tau inversion recovery).
Tomograms may demonstrate the spread of the tumor mass into the paravertebral soft tissues and the anterior epidural space (anterior epidural space). With this growth pattern, a typical «curtain sign» ('curtain sign') is often identified.
Procedure execution: Percutaneous biopsy (percutaneous biopsy) is performed to obtain a tissue sample. The target for tissue sampling is the large paravertebral tumor component. The procedure is performed under strict CT navigation guidance, with the patient in the prone position (prone position) during the manipulation.
In some clinical cases, initially suspected to be a giant cell tumor based on the radiological picture, the pathomorphological report (pathology) following such a biopsy may reveal another pathology, for example, low-grade chondrosarcoma (low-grade chondrosarcoma).
Briefly: answers to topical questions
What conditions must be differentiated from giant cell tumor of bone?
Giant cell tumor of bone is differentiated from a number of neoplastic and tumor-like lesions.
Main differential diagnoses:
- Lytic osteosarcoma (lytic osteosarcoma).
- In elderly patients:
- Undifferentiated pleomorphic sarcoma (undifferentiated pleomorphic sarcoma).
- Plasmacytoma (plasmacytoma).
- Subarticular lytic metastases (subarticular lytic metastasis), primarily metastases from primary renal cell carcinoma.
- Benign fibrous histiocytoma (benign fibrous histiocytoma) may radiologically resemble a giant cell tumor, but differs by having a well-defined sclerotic margin.
When the jaws are involved, the differential diagnosis includes benign jaw tumors: osteoid osteoma, osteochondroma, ossifying fibroma, ameloblastic fibroma, ameloblastoma, cementoblastoma, etc.; tumor-like lesions, including fibrous dysplasia; malignant tumors, primarily osteogenic sarcoma; and in cases of suppuration, acute or exacerbated chronic osteomyelitis.
In which parts of the skeleton is a giant cell tumor most frequently localized?
Giant cell tumors can affect various parts of the skeleton.
Source-confirmed localizations:
- Jaws — a favored localization in the jaws is the premolar region; another source indicates that the mandibular premolar region is more frequently affected.
- Long tubular bones — jaw involvement may be combined with involvement of the femur, tibia, and radius.
- The given examples describe lesions of the femoral head and neck and the proximal tibia.
In rare cases, the tumor can be extraskeletal. Multifocal metachronous giant cell tumor occurs in less than 1% of cases, frequently affects the hands and feet, and is associated with hyperparathyroidism.
What is the histological picture of giant cell tumor of bone?
The histological picture of giant cell tumor of bone is characterized by the presence of osteoclast-like multinucleated giant cells.
The cellular composition includes two main cell types:
- Osteoblast-like cells — predominate; these are slightly elongated small cells with oval nuclei.
- Osteoclast-like cells — multinucleated giant cells.
Remembering the MRI cyst marker is easy: water (fluid) in the cyst settles, forming "layers". Therefore, fluid-fluid levels on T2 are the main key to diagnosing an aneurysmal bone cyst.
Class and exam questions
What can plain radiography detect in this pathology?
Radiographs may show bone destruction (e.g., absence of the spinous process), the appearance of a soft-tissue mass, cortical remnants, and minor calcifications.
Why use MSCT and MRI if the tumor is visible on X-ray?
Only tomographic methods (MSCT and MRI) allow a reliable assessment of the complete extent of the process and involvement of the spinal canal, vertebral body, pedicles, and posterior elements.
Which MRI sign is pathognomonic for an aneurysmal bone cyst?
A pathognomonic sign (hallmark) is the presence of fluid-fluid levels on T2-weighted images.
How is a biopsy performed in cases of prominent paraspinal spread?
A percutaneous biopsy of the paravertebral component is performed under CT guidance, with the patient positioned prone.
What else to study on this topic
- Technique for performing CT-guided percutaneous biopsy of spinal tumors
- The «curtain sign» ('curtain sign'): physical essence and clinical significance
- Differential diagnosis between giant cell tumor and low-grade chondrosarcoma
- MRI modalities: advantages of contrast-enhanced T1 and T2 STIR in soft tissue visualization
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