Simple Bone Cyst (Simple Bone Cyst, SBC)
Synonyms: juvenile, solitary, or unicameral bone cyst. Classified as a benign tumor-like lesion.
- Localization: The lesion is typically located in the center of the metaphysis and abuts the epiphyseal plate. The proximal humerus or femur are most frequently affected.
- Radiological presentation: The lesion causes thinning of the cortical layer combined with mild bone expansion (mild expansion). A characteristic feature is that as the bone grows, the cyst migrates distally, shifting into the diaphyseal region.
- Complications: It may remain an incidental radiological finding for a long time, but most commonly manifests as a pathological fracture. In the event of a fracture, solid areas and fluid levels may begin to appear within the cystic cavity (fluid-fluid levels).
Aneurysmal Bone Cyst (Aneurysmal Bone Cyst, ABC)
An expansile cystic lesion whose internal content often features hemorrhages. In 30% of cases, it arises as a secondary lesion against the background of preexisting bone tumors.
- Localization: It primarily affects the metaphyses of long tubular bones (tibia, femur, humerus) and flat bones. Involvement of the spine requires special attention: the process is frequently localized in the posterior elements (laminae, processes).
- Radiological presentation: Unlike a simple cyst, it develops eccentrically and does not cross the growth plate. It often has a multilocular (multilocular) structure and causes moderate cortical thinning. In the spine, the lesion appears as a destructive expansile process capable of compressing the spinal canal.
- Diagnostics and treatment: Requires cross-sectional imaging (CT or MRI) and mandatory biopsy. MRI allows for detailed visualization of hemorrhagic fluid levels. Percutaneous fluoroscopically guided sclerotherapy is successfully used as a treatment in certain cases.
General principles of diagnostic imaging
Diagnostics is based on the combined use of imaging modalities:
- Plain radiography: The primary screening method for benign bone tumors. Radiographs may reveal indirect signs of underlying space-occupying processes in the spine (scalloping of the posterior vertebral wall, widening of the intervertebral foramen, torticollis, flattening of the lordosis).
- Computed tomography (CT): Provides a detailed display of bone destruction patterns, calcification, and matrix. Indispensable for guidance during puncture, biopsy, and ablation.
- Magnetic resonance imaging (MRI): The method of choice for soft tissue structures and bone marrow. The use of the STIR sequence (short tau inversion recovery) is mandatory. MRI confirms the presence of specific signs, bone marrow infiltration, and epidural extension.
- Bone scintigraphy: Used primarily when multifocal disease is suspected (e.g., metastases).
Differential diagnosis
A radiological presentation similar to a cyst can be caused by other tumor-like lesions (Tumour-like Lesions), as well as malignant neoplasms and infections:
- Telangiectatic osteosarcoma (Telangiectatic OS): It is critically important to rule it out when an aneurysmal cyst is suspected, as their radiological appearances can be identical.
- Osteofibrous dysplasia: Campana-Campanacci disease. On plain radiographs, it presents as multifocal cortical lesions (a mix of sclerosis and radiolucency zones). An important sign is the absence of cortical destruction and periosteal reaction.
- Fibrous dysplasia of bone: Jaffe-Lichtenstein disease.
- Eosinophilic granuloma: A manifestation of Langerhans cell histiocytosis.
- Hematogenous bone tuberculosis: Can form destructive cavities. CT and MRI are required to identify necrosis of vertebral bodies and sequestra.
For radiological differentiation: Simple cyst — Center of the metaphysis (migrates to the diaphysis). Aneurysmal cyst — Asymmetrically (grows eccentrically), has an Architecture with multiple chambers and fluid-fluid levels.
Class and exam questions
Does an aneurysmal bone cyst cross the physis?
No, a typical aneurysmal cyst develops eccentrically and does not cross the growth plate on radiographs.
Which method is considered primary for a detailed assessment of the cyst's internal contents?
Magnetic resonance imaging (MRI) with the mandatory addition of the STIR sequence. It visualizes the internal architecture and fluid-fluid levels.
What happens to a simple bone cyst as the patient grows?
As the bone matures and elongates, a simple cyst migrates distally, gradually shifting from the metaphyseal zone to the diaphyseal zone.
Which malignant tumor must an aneurysmal cyst be differentiated from?
Primarily with telangiectatic osteosarcoma, which can visually mimic a multilocular cystic structure with hemorrhages.
What else to study on this topic
- Telangiectatic osteosarcoma: radiological patterns and differentiation tactics from cysts
- Fibrous dysplasia of bone (Jaffe-Lichtenstein disease) and osteofibrous dysplasia
- Specifics of using the MRI STIR sequence in the evaluation of bone structures
- Chondromyxoid fibroma: eccentric lesions of the metaphyseal zone
- CT-guided puncture and biopsy of bone neoplasms
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