Characteristics and imaging of primary tumours
Primary malignant tumour of the diaphragm (Primary Malignant Tumour of the Diaphragm) presents a serious diagnostic challenge. On radiological images, it has a number of specific features.
When performing a standard chest X-ray (CXR) in the posteroanterior projection, the pathology often appears as a small focal bulge of the diaphragmatic contour. This sign is almost always combined with a small pleural effusion.
For detailed evaluation, cross-sectional methods are used—computed tomography (CT) and magnetic resonance imaging (MRI). On tomograms, a primary malignant tumour is visualised as an irregular mass. A characteristic structural feature is the presence of a central necrosis zone. Multiplanar reconstructions clearly demonstrate that the mass has a continuous anatomical connection with the diaphragmatic dome (for example, the right dome—hemidiaphragm). Despite these findings, the radiologist should always bear in mind that secondary tumour extension from the lungs or abdominal cavity is statistically observed much more frequently.
General principles of diaphragmatic imaging
Since the normal thickness of the diaphragm is only 2–3 mm, choosing the right imaging modality is critical. Each method has its own strict indications and physical limitations:
- Radiography (CXR): The thin muscular structure becomes visible only when adjacent air is present. This can be aerated lung tissue from above or free gas in the peritoneal cavity (in pneumoperitoneum) from below.
- Ultrasound: The diaphragm is well visualised if there is an acoustic window in the form of an effusion, ascites, or pleural thickening. An important nuance: in the absence of pathological fluids in the pleural cavity, the physician sees a thick hyperechoic line on the screen. This is not the diaphragm itself, but the highly reflective boundary (interface) between dense abdominal structures and lung air.
- Computed tomography (CT): Volumetric CT with multiplanar reconstructions in coronal and sagittal projections is the gold standard for assessing diaphragmatic integrity, especially when traumatic ruptures and hernias are suspected.
- Magnetic resonance imaging (MRI): It possesses unsurpassed soft tissue contrast resolution, which is ideal for evaluating tumour structure. However, artefacts from the continuous motion of the diaphragm during respiration can significantly degrade image quality and complicate diagnosis.
Differential diagnosis: hernias, trauma, and paresis
Tumour bulging must be differentiated from other common alterations in the configuration and function of the diaphragm.
- Movement disorders and paralysis: Tumour invasion can lead to phrenic nerve paresis (phrenic nerve paresis). Other causes of paresis include trauma, radiation therapy, and neurological diseases (poliomyelitis, cervical spondylosis, herpes zoster). Fluoroscopy (fluoroscopy) or ultrasound are best suited for assessing dome excursion. To identify paradoxical motion of the paralysed dome, the patient is asked to perform a sharp sniff through the nose (sniff test).
- Diaphragmatic hernias (Diaphragmatic hernia):
- Congenital hernias: usually located in the lateral parts and are large in size.
- Bochdalek hernia (*Bochdalek hernia):* most common, typical location is left and posterior.
- Morgagni hernia (*Morgagni hernia):* a rarer pathology, located right and anterior.
- Hiatal hernias (*Hiatal hernias):* an extremely common phenomenon, the probability of detecting them steadily increases with the patient's age.
- Traumatic injuries (Diaphragmatic trauma): As a rule, they are combined with severe thoracic or abdominal trauma. They require immediate surgical intervention, and CT with multiplanar reconstructions is optimal for their precise localisation.
Briefly: answers to topical questions
What technical methods can be used to minimise respiratory artefacts during MRI of the diaphragm?
To reduce respiratory artefacts in MRI, data acquisition time-reduction sequences, respiratory gating, and motion-insensitive sequences are used:
- Single-shot techniques (single-shot techniques) — HASTE and FASE sequences, allowing k-space to be filled within a single breath-hold.
- 3D gradient echo sequences (GRE), such as VIBE, are fast enough to acquire images within a single breath-hold.
- Radial sequences PROPELLER, BLADE, MultiVane, RADAR, and JET, which distribute motion artefacts in radial directions.
- Respiratory gating (respiratory gating).
By what pathways, other than direct invasion, do malignant tumours metastasise to the diaphragm?
In addition to direct invasion, diaphragmatic involvement may be associated with peritoneal dissemination of the tumour. In ovarian cancer, peritoneal tumour deposits can localise around the right hemidiaphragm; on CT, they appear as peritoneal implants.
Class and exam questions
What is the difficulty of ultrasound diagnosis of the diaphragm in a healthy person?
In the absence of pathologies (effusion or ascites), the ultrasound beam is strongly reflected by lung air. As a result, the physician sees a thick hyperechoic line (the interface) that obscures the thin diaphragmatic muscle itself.
What is the sniff test and why is it needed?
This is a test in which the patient is asked to take a sharp sniff through the nose under ultrasound or fluoroscopic guidance. It helps to clearly visualise paradoxical dome motion in paralysis or phrenic nerve paresis.
How to distinguish a primary malignant tumour on CT?
A primary tumour often appears as an irregular mass continuously connected to the diaphragmatic dome, with a central zone of necrosis. However, it should be remembered that secondary invasion is much more common.
What else to study on this topic
- CT signs of blunt diaphragmatic trauma, including the dangling diaphragm sign.
- Pathogenesis and imaging evaluation of various pleural effusions and parietal pleural changes in empyema.
- Pleural pseudotumours, asbestosis, and malignant mesothelioma.
- Application of PET/CT (with 18F-FDG) for tumour staging and assessment of metabolic response to chemotherapy.
- Use of diffusion-weighted MRI to differentiate malignant from benign lesions.
- Interventional radiology capabilities in diseases of the pleura and diaphragmatic dome.
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