1. X-ray diagnostics of lung and pleural diseases
A classic example of an inflammatory lesion is lobar pneumonia. It most commonly occurs in young patients. On a plain chest radiograph in the anteroposterior projection (e.g., involvement of the upper lobe of the right lung), an intense, homogeneous opacification is visualized. This uniformity indicates the filling of alveoli with inflammatory exudate, which is characteristic of the hepatization stage. A distinctive radiological sign is the clear, smooth, and horizontal lower border of the infiltration. Anatomically, this is explained by the process being strictly limited by the minor (horizontal) interlobar pleura. The remaining parts of the lungs (middle and lower right, as well as the entire left lung) retain normal pneumatization (are clear) and show no enhanced pulmonary pattern.
Another frequent finding is pleural effusion. For accurate topographic diagnosis, the anteroposterior view is necessarily complemented by a lateral projection. Free fluid accumulates under the influence of gravity in the deepest areas—the costodiaphragmatic sinuses. On the lateral view, an intense, homogeneous opacification is determined in the posterobasal regions (in the region of the spine and posterior ribs), the contour of the diaphragmatic dome on the affected side is not differentiated, and the posterior sinus is completely opacified. The upper border of the shadow often has an indistinct, obliquely ascending direction (fluid level).
In the case of interstitial lung diseases, such as pulmonary Langerhans cell histiocytosis (formerly histiocytosis X), the "gold standard" of imaging is high-resolution computed tomography (HRCT). In advanced stages, a pattern of end-stage lung disease ("honeycomb lung") is formed—irreversible structural changes combining diffuse interstitial fibrosis and cystic-bullous transformation, in which normal parenchyma is replaced by giant air bullae. Multiplanar reconstruction (MPR) is used for a complete assessment:
- Coronal section — shows the bilateral nature and height distribution.
- Sagittal section — details the spread from the sternum to the spine.
- Axial section — allows assessment of the thickness of the bullae walls and the condition of the preserved tissue.
Note: sometimes radiographs (e.g., of the lower lobes) are taken from the screen of an image intensifier (IITV), as indicated by the circular shape of the image field.
2. CT semiotics of renal tumor involvement
Computed tomography is used to diagnose retroperitoneal space-occupying lesions. The use of intravenous contrast enhancement is a key factor (evaluated on axial slices).
The healthy (contralateral) kidney is normal in size and shape, with an unexpanded pelvicalyceal system, and intensively and evenly accumulates contrast (appears hyperdense), indicating preserved function and perfusion.
In the presence of a giant tumor (most likely advanced renal cell carcinoma), the affected kidney is significantly enlarged in volume, occupying a large part of the abdominal cavity, and its normal anatomical shape is lost. The pathological mass totally or subtotally replaces the parenchyma. The structure of such a tumor is heterogeneous (non-uniform) due to the uneven distribution of the contrast agent. Inside the tumor tissue, hypodense (dark) areas are clearly distinguishable, corresponding to zones of breakdown, necrosis, or massive hemorrhage.
3. Macroscopic changes in chronic gout
In addition to radiological methods, visual macroscopic tissue assessment is important for diagnosing pathologies. With prolonged hyperuricemia, the disease progresses to a chronic stage (usually several years after the first attack of arthritis urica). In the soft tissues of the fingers (predominantly the big toes/thumbs), tophi form—specific subcutaneous nodules.
These nodules are tissue deposits of uric acid crystals (sodium urate) that deform the finger. Gross examination clearly reveals the contents shining through the thinned and taut skin. Tophi have a characteristic whitish-yellow ("chalky") color.
The condition of the skin also undergoes changes: the coloration is uneven, areas of ischemia (blanching) are visible directly above the deposit, and the surrounding tissues demonstrate mild hyperemia (redness), indicating a local inflammatory reaction. The localization and yellowish color make it possible to visually distinguish gout from rheumatoid nodules or Heberden's and Bouchard's nodes (encountered in osteoarthritis).
Briefly: answers to topical questions
How to differentiate gouty tophi from rheumatoid nodules and Heberden's/Bouchard's nodes?
These formations can be visually differentiated by their color, consistency, and characteristic localization.
- Gouty tophi (tophus) — have a characteristic whitish-yellow ("chalky") color due to the accumulation of uric acid crystals, shine through the thinned skin, and are located in the soft tissues of the fingers (predominantly the thumb/big toe).
- Rheumatoid nodules — subcutaneous formations most commonly localized on extensor surfaces, predominantly in the elbow joint area.
- Heberden's nodes (Heberden's nodes) — located in the area of the distal interphalangeal joints (enlargements of the terminal phalanges).
- Bouchard's nodes (Bouchard's nodes) — hard formations localized at the base of the middle phalanges of the fingers (proximal interphalangeal joints).
How to differentiate exudate from transudate in pleural effusion?
Exudate and transudate in pleural effusion must be differentiated based on the properties of the pleural fluid and the characteristics of fluid accumulation.
| Parameter | Transudate | Exudate |
|---|---|---|
| Nature of the fluid | Non-inflammatory edema fluid | Inflammatory fluid |
| Formation mechanism | Hemodynamic and colloid-osmotic pressure disorder without endothelial damage | Increased vascular permeability due to alteration/inflammation |
| Specific gravity | Lower specific gravity; in classical textbooks — generally below 1.015–1.018 | Higher; indicated as >1.015 for exudate, in classical textbooks — >1.018 |
| Protein | Protein-poor fluid | High protein content; indicated as >2.5% for exudate |
| Rivalta test | Negative | Positive: formation of a "cloud" indicates inflammation |
| Pleural fluid protein / plasma protein | — | Ratio >0.5 indicates exudate |
| Blood cellular elements | Generally absent or solitary | Frequently contains leukocytes and erythrocytes |
| Cellular composition | — | Neutrophils — purulent inflammation; lymphocytes — immune inflammation; erythrocytes — hemothorax, pleural tumors, or trauma; atypical cells — mesothelioma |
| Fluid border | Percussion upper border of dullness closer to a horizontal line | In exudative pleurisy on radiography, opacification with an oblique upper border — Damoiseau's line |
To memorize the X-ray picture of lobar pneumonia: "Lobar means large (an entire lobe is affected), but with a smooth lower border (bounded by the interlobar pleura)."
Class and exam questions
Why is the lower border of opacification in upper lobe lobar pneumonia even?
The inflammatory infiltrate (exudate in the alveoli) spreads within a single lobe and abuts against the minor horizontal interlobar pleura, which creates a clear, smooth horizontal border on the radiograph.
Why is a lateral X-ray view necessary when pleurisy is suspected?
Free fluid in the pleural cavity accumulates under the influence of gravity at the lowest points. On the lateral projection, opacification of the posterior costodiaphragmatic sinus is clearly visible, which may be poorly seen on the anteroposterior view.
What method is considered the gold standard for diagnosing histiocytosis X?
High-resolution computed tomography (HRCT), as it allows detailed visualization of interstitial remodeling, diffuse fibrosis, and cystic-bullous transformation ("honeycomb lung").
What else to study on this topic
- Features of multiplanar reconstruction (MPR) in diagnostic radiology.
- Differential diagnosis of Heberden's nodes, Bouchard's nodes, rheumatoid nodules, and tophi.
- Pathogenesis of necrosis zone formation in malignant renal tumors.
- Stages of lobar pneumonia and their radiological correlates.
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