Imaging features of fibrous dysplasia
When evaluating pathology (e.g., at the level of the right 4th rib), two main imaging modalities are used. Classic chest radiography demonstrates thickening of the affected bone structure. There is a local expansion of the rib and a clear increase in its radiodensity.
More detailed information is provided by computed tomography (CT). In this case, fibrous dysplasia is most characteristically featured by a structure described as the ground-glass sign (ground-glass appearance). However, no imaging method replaces a biopsy, the results of which are necessary for accurate confirmation of the diagnosis.
Bilateral pleural effusion: effect of patient positioning
The radiographic appearance of bilateral fluid accumulation (Bilateral Pleural Effusion) changes drastically depending on the patient's position during the examination.
In the upright position (Erect):
- Fluid obscures the contours of the diaphragmatic domes.
- Blunting of the costophrenic angles occurs (costophrenic angles).
- A specific upper border is formed: it has a curvilinear contour that is concave relative to the lung parenchyma.
- The lateral edge of this opacity is always located higher than the medial edge.
In the supine position (Supine):
- The effusion appears completely different and becomes barely perceptible.
- It manifests as a diffuse, indistinct "hazy" opacity (hazy opacity) localized predominantly in the lower lung zones.
- The costophrenic angles remain free of opacification in this projection.
- The preserved vascular pattern (vascular opacities) of the underlying lung tissue is clearly visible through the fluid layer.
Loculated pleural effusion
Loculated fluid (Loculated / Encysted / Encapsulated pleural fluid) has specific features of localization and formation. It can accumulate between the layers of the visceral pleura (directly within the interlobar fissures) or between the parietal and visceral pleura, most often adjacent to the inner surface of the chest wall.
Causes of occurrence:
- The primary cause is the formation of adhesions (adhesions). In such situations, chest radiographs typically reveal other concurrent signs of pleural pathology.
- Transudates are an exception: they can loculate within the interlobar fissures even in the complete absence of adhesion formation.
Differential diagnosis: Fluid collections within the interlobar fissures can visually mimic true masses (mass). In radiology, this phenomenon is known as "pseudotumours" (pseudotumours) or "vanishing tumours" (vanishing tumours). Differentiating them from an actual pleural neoplasm can be extremely difficult.
Encapsulated fluid is characterized by the following radiological criteria:
- Homogeneous (homogeneous) structure.
- Smooth, regular contour when the X-ray beam passes tangentially.
- Poorly circumscribed (poorly circumscribed) margins when assessed in other projections.
Briefly: answers to topical questions
What forms of fibrous dysplasia exist depending on the extent of the process?
Depending on the extent of the pathological process, two main forms of fibrous dysplasia are distinguished.
- Monostotic — characterized by isolated involvement of only a single bone.
- Polyostotic — characterized by the involvement of multiple bones in the pathological process.
The polyostotic form may manifest as multifocal bilateral involvement. In addition, it often acts as a component of specific syndromes. For example, Mazabraud syndrome (Mazabraud syndrome) represents a combination of the polyostotic form with soft tissue myxomas, whereas McCune–Albright syndrome (McCune–Albright syndrome) is a subtype accompanied by pituitary hypersecretion and skin pigmentation.
To remember the contour of fluid in the upright position, imagine a bowl: the fluid "crawls" upward along the lateral chest wall, forming a line concave toward the lung.
Class and exam questions
How does the visibility of the costophrenic angles in effusion change depending on posture?
In the upright position, the costophrenic angles are obscured (opacified) by fluid, whereas in the supine position they remain clear.
What is a "vanishing tumour" on a radiograph?
This is an encapsulated pleural effusion localized in the interlobar fissure, which visually mimics a mass lesion (pseudotumour).
What else to study on this topic
- Histological picture of fibrous dysplasia of bone tissue
- Technique for performing a biopsy of the affected rib
- Differences between transudates and exudates in the formation of an encapsulated effusion
- Causes of pleural adhesions (adhesions)
- Physical principles of the tangential X-ray beam path when assessing contours
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