Imaging Methods
The primary method for initial assessment remains chest radiography.
- In the posteroanterior projection (PA radiograph), the domes appear as upwardly convex, smooth lines. The lateral costophrenic angle forms an acute angle, while the cardiophrenic angle is often indistinct due to the fat pad.
- In the lateral projection (Lateral radiograph), the posterior recesses lie significantly lower than the apex of the dome. The right dome can be traced to the sternum, while the left is anteriorly obscured by the heart.
Ultrasound examination makes it possible to assess excursion (in M- and B-modes) and muscle thickness. The diaphragm itself is poorly visualized on ultrasound without pleural effusion; the visible hyperechoic line is the interface with air in the lungs.
Computed tomography (CT) with multiplanar reconstructions is indispensable in trauma and for the differential diagnosis of complex masses.
Magnetic resonance imaging (MRI) provides high tissue resolution, but assessment is difficult due to artifacts from respiratory motion.
Changes in position and shape
Normally, the right dome is higher than the left in more than 90% of people. The position of the diaphragm depends on body habitus: it is lower in asthenics, and higher in hypersthenics, infants, and the elderly.
Shape changes:
- Flattening — a pathognomonic sign of emphysema.
- Elevation (lowering of the diaphragm) — observed in emphysema and severe asthma attacks.
- Inversion — occurs with tension pneumothorax, large bullae, or massive effusion.
High standing of the dome: Unilateral elevation is most often associated with phrenic nerve palsy, atelectasis, pneumonia, or a subphrenic abscess. Bilateral elevation is characteristic of obesity, pregnancy, ascites, supine position, or diffuse pulmonary fibrosis.
Eventration and paralysis
Eventration (relaxation) is a condition where part of the muscle fibers is replaced by thin connective tissue, but the continuity of the diaphragm is preserved. The congenital form is associated with developmental disorders, while the acquired form is related to atrophy following paralysis. Total eventration is more common on the left, and localized eventration on the right (in the anteromedial region).
Paralysis occurs due to injury of the phrenic nerve (phrenic nerve). The most frequent cause is tumor invasion (bronchogenic carcinoma). Trauma, radiation, or neurological conditions can also be causes. Fluoroscopy or ultrasound is used to diagnose paralysis (revealing paradoxical motion on the "sniff test" and the absence of muscle thickening during inspiration).
Diaphragmatic hernias
Hernias are the displacement of abdominal organs into the thoracic cavity through weak points or defects.
- Bochdalek hernia (Bochdalek defect): located posteriorly, usually on the left. Often contains retroperitoneal fat or part of the kidney. Appears on images as a dome-shaped mass.
- Morgagni hernia (Morgagni hernia): an anterior hernia, more frequently in the right cardiophrenic angle. May contain omentum or bowel, requiring differentiation from a pericardial cyst or fat pad.
- Hiatal hernia (Hiatus hernia): very common in the elderly, visualized as a retrocardiac mass (sometimes with a fluid level).
Briefly: answers to topical questions
Which organs and tissues can herniate into the thoracic cavity in a Bochdalek hernia?
In a Bochdalek hernia, retroperitoneal adipose tissue as well as fragments of internal organs can herniate into the thoracic cavity.
- Retroperitoneal fat — visualized on CT as a fatty mass adjacent to the defect in the posteromedial portion of the diaphragmatic dome.
- Kidney — part of the organ may herniate through the pleuroperitoneal canal.
- Spleen — may also be contained within the hernia sac.
Which radiographic and CT signs indicate a traumatic diaphragmatic rupture?
Specific changes on radiographs and CT images indicate a traumatic diaphragmatic rupture. The radiograph shows opacification of the lower part of the right hemithorax with obliteration of the diaphragmatic contour. CT signs include:
- Absent diaphragm sign (absent diaphragm sign) — disruption of diaphragmatic integrity.
- Dangling diaphragm sign (dangling diaphragm sign) — curling inward of the ruptured edges.
- Dependent viscera sign (dependent viscera sign) — herniation of abdominal viscera abutting the posterior ribs.
- Thick crus sign (thick crus sign) — thickening of the diaphragmatic crus.
- Collar sign (collar sign) — constriction of the stomach or bowel at the hernia defect.
- Hump sign (hump sign) — mushroom-like herniation of the liver compressed by the tear margins.
- Band sign (band sign) — a linear lucency through the liver along the torn edges of the diaphragm.
What anatomical openings exist in the diaphragm and what structures pass through them?
The diaphragm has three main openings and additional slits for the passage of anatomical structures.
- Aortic hiatus (hiatus aorticus) — transmits the aorta (aorta), thoracic duct (ductus thoracicus), and sometimes the azygos and hemiazygos veins.
- Esophageal hiatus (hiatus oesophageus) — transmits the esophagus (oesophagus) and vagus nerves (nn. vagi).
- Caval opening (foramen venae cavae inferioris) — transmits the inferior vena cava (v. cava inferior).
- Additional passages — slits between the muscle bundles of the crura for the greater/lesser splanchnic nerves (nn. splanchnici major/minor), sympathetic trunks, and azygos/hemiazygos veins (v. azygos/hemiazygos).
Class and exam questions
Why is the diaphragmatic muscle tissue not always visible on ultrasound?
Normally, ultrasound is strongly reflected by the air in the basal lung segments. What we see as a bright line is a media-interface artifact, not the muscle itself. The layers of the diaphragm can be clearly distinguished only in the presence of fluid (pleural effusion).
How to differentiate eventration from a hernia?
In eventration, the anatomical continuity of the diaphragm is preserved (it is simply thinned), whereas in a hernia, there is a defect through which organs penetrate into the thoracic cavity. This is best visualized on CT or MRI.
Which method is best suited for assessing diaphragmatic motion?
Fluoroscopy and ultrasound examination. They allow real-time assessment of excursion and detection of paradoxical motion in paralysis.
What else to study on this topic
- Technique of diaphragmatic ultrasound in B- and M-modes
- Differential diagnosis of cardiophrenic angle fat pads
- Symptoms and treatment of phrenic nerve palsy
- Magnification and the rule of dome localization on lateral radiographs
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