Assessment of the bone framework and its deformations
For a comprehensive analysis of radiographs, it is necessary to understand the radiographic anatomy of the bones and variants of their deformations.
Sternum (sternum) is reliably visualized only in the lateral projection. On a plain chest radiograph, it is practically indistinguishable, though the edges of its manubrium can create shadows that are falsely interpreted as mediastinal widening. CT is the gold standard for evaluating the parasternal zone as it eliminates tissue superimposition.
Two main sternal deformations are distinguished:
- Pectus excavatum (pectus excavatum / funnel chest): depression of the sternum with approximation to the spine. It may be associated with Marfan syndrome (Marfan syndrome) and atrial septal defects (ASD). On a plain radiograph, it manifests as displacement of the heart to the left, straightening of its left contour, and bulging of the pulmonary artery. A density appears in the right cardiophrenic angle, mimicking middle lobe pathology. The anterior rib segments are steeply inclined downward, and the thoracic spine is excessively clearly visible through the heart.
- Pectus carinatum (pectus carinatum / pigeon chest): the reverse process, characterized by protrusion (can be either congenital or acquired).
Clavicles (clavicles) allow assessing the correctness of patient positioning. On a standard radiograph, only the acromioclavicular joint is well visualized. In rheumatoid arthritis, erosions may be detected within it, while in rickets or hyperparathyroidism, blurring of the contours can be seen. CT or MRI is required to study the medial ends.
Scapula (scapula) is subject to specific changes. Paralysis of the long thoracic nerve results in an asymmetric "winged scapula" (scapula winging). Congenital high elevation and rotation of the scapula is termed Sprengel deformity (Sprengel deformity). In a third of such cases, an accessory omovertebral bone or fibrous band is discovered, and the anomaly itself is frequently associated with Klippel-Feil syndrome (Klippel-Feil syndrome) and spina bifida.
Chest wall and bone tumors
A critical stage in diagnostic radiology is the differentiation of chest wall tumors from intrathoracic neoplasms. A tumor originating from the chest wall projects into the pleura, forming obtuse angles (obtuse angles) and a tapering margin with it. Intrathoracic tumors, conversely, form acute angles (acute angles) with the pleura.
The pattern of bone involvement helps determine the nature of the lesion:
- Benign: cause erosion, separation, and remodeling of bone tissue in the form of a scalloped defect. The cortical layer remains intact. These patients are most often asymptomatic.
- Malignant and inflammatory: lead to overt bone destruction and are frequently accompanied by pain.
Among bone-destructive tumors in adults, metastases (breast, lung, renal cancer), multiple myeloma, lymphoma, or sarcoma are most common. In children, Ewing sarcoma (Ewing sarcoma) and neuroblastoma must be ruled out first.
Malignant lesions actively take up intravenous contrast, whereas benign lesions predominantly displace vessels (MIP reconstructions are used to evaluate feeding vessels).
Special conditions:
- Pancoast tumor (Pancoast tumour): multislice CT (MSCT / MDCT) with 3D reconstruction is optimal for assessing invasion into the rib cortex, brachial plexus (plexus brachialis), and superior aperture vessels.
- Inferior rib notching (Inferior Rib Notching): a specific sign caused by the pressure of dilated collateral vessels (e.g., in aortic coarctation).
Soft-tissue neoplasms
Mesenchymal wall tumors include hemangiomas, lymphangiomas (cystic hygromas), neurofibromas, but the most frequent benign tumor is lipoma.
- Lipomas (Lipomas): on CT, they appear as homogeneous, well-defined lesions with low density (-90 to -150 HU). On MRI, they exhibit high signal on T1-weighted images, intermediate signal on T2-weighted images, and low signal in fat suppression mode. Important: the appearance of a soft-tissue component within a fatty lesion is highly suspicious for malignant liposarcoma.
- Neurilemmomas / schwannomas (Neurilemmomas): on CT, they are isodense to the spinal cord and show intense contrast enhancement. In a paraspinal location, they frequently acquire a characteristic "dumbbell" shape (dumbbell appearance), growing through the intervertebral foramen.
Briefly: answers to topical questions
Which anatomical structures of the superior thoracic aperture are affected by a Pancoast tumor?
A Pancoast tumor affects neural, vascular, and osseous structures of the superior thoracic aperture. The pathological process involves:
- Brachial plexus (plexus brachialis) — direct tumor invasion occurs.
- Cervical sympathetic trunk — its compression leads to the development of Horner syndrome.
- Vascular structures — displacement and encasement of the left subclavian artery (a. subclavia sinistra).
- Osseous structures — cortical invasion and rib destruction.
The tumor also invades adjacent soft tissues.
In which diseases and conditions does the sign of inferior rib notching occur?
The sign of inferior rib notching occurs in:
- Coarctation of the aorta (coarctation of the aorta) — due to erosion of the inferior rib margins from the pressure of dilated and tortuous intercostal arteries acting as collaterals.
- Neurofibromatosis type I (neurofibromatosis type I).
In aortic coarctation, notches are usually bilateral but asymmetric; they may be shallow or deep and have a sclerotic cortical margin.
The rule of angles: "Obtuse is own, acute is foreign." If a neoplasm forms an obtuse angle with the pleura, it originates from the chest wall tissues (its own). An acute angle indicates an intrathoracic process (foreign to the wall).
Class and exam questions
Why is conventional radiography of low diagnostic value in kyphoscoliosis?
Pronounced spinal deformity significantly distorts the projection of internal organs and leads to shadow superimposition. To reliably rule out thoracic cavity pathology in this case, CT is required.
How to distinguish a regular lipoma from a liposarcoma on CT?
A typical lipoma has a homogeneous structure with fat density (-90...-150 HU) and contains no soft-tissue inclusions. The presence of a soft-tissue component within the fatty mass is the main sign suspicious for liposarcoma.
What does the sign of inferior rib notching mean?
This is a radiologic sign resulting from the erosive pressure of dilated and pulsating intercostal collateral vessels on the inferior margin of the rib. It is characteristic, for example, of aortic coarctation.
What else to study on this topic
- Pancoast tumor: features of vascular structure and nerve plexus invasion
- Ewing sarcoma and neuroblastoma in children: imaging semiotics
- MRI fat-suppression sequences in differential diagnosis
- Omovertebral bone and Klippel-Feil syndrome: comprehensive assessment
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