See also: [[Chest trauma radiology#Obvious density differences]] ## Chilaiditi sign See [radiopedia - Chilaiditi sign](https://radiopaedia.org/articles/chilaiditi-sign) Chilaiditi described this normal variant in 1911 where the transverse colon is interposed between the right hemidiaphragm and the liver. Its prevalence is thought to be 0.025%. Occasional reports describe patients with Chilaiditi’s syndrome where patients complain of intermittent abdominal pain requiring laparotomy to rule out other causes of peritonism, e.g. perforated ulcer, ruptured appendix. The recognition of the haustrations (indicative of large bowel origin) in the bowel shadows is crucial to the diagnosis of Chilaiditi’s sign. Ddx in context of trauma [[Chest trauma radiology#ruptured diaphragm|diaphragm rupture]] ![[Pasted image 20250427080741.png]] ## Rigler sign [radiopedia - Rigler sign](https://radiopaedia.org/articles/rigler-sign-bowel?lang=us) Double-wall sign of pneumoperitoneum (eg bowel perforation or post surgical). Seen on an abdominal XR when gas is outlining both sides of the bowel (gas within lumen and peritoneum). ![[Pasted image 20250427081124.png]] ## Azygos lobe [radiopedia - Azygos lobe](https://radiopaedia.org/articles/azygos-lobe) The azygous lobe is the commonest CXR normal variant seen in up to 0.4% of individuals. This is an embryologic variation which results in an accessory lobe at the right upper lobe. The fissure is due to the invagination of the azygous vein and the condition is of no clinical significance. ![[Pasted image 20250427081646.png]] ![[Pasted image 20250427081725.png]] ## Mach effect **Mach bands** or the **Mach effect** refers to an optical phenomenon from edge enhancement due to lateral inhibition of the retina, where the edges of darker objects next to lighter objects will appear darker and vice versa, creating a false shadow. Mach effect is source of diagnostic error in radiology: - a dark halo around a dense breast lesion in mammography - apparent [[Pneumomediastinum]] ([pseudopneumomediastinum](https://radiopaedia.org/articles/pseudopneumomediastinum?lang=us) ) - fracture mimic - [pseudopneumothorax](https://radiopaedia.org/articles/skinfold-artifact-1?lang=us) secondary to skin fold Normal CXR with appearance of perceived lucency outlining mediastinum and diaphragm. Is NOT [[Pneumomediastinum]] ; optical illusion ![[Pasted image 20250427082422.png]] ### pseudo-pneumomediastinum vs. true pneumomediastinum See also: [[Pneumomediastinum]], [[Chest trauma radiology#pneumopericardium vs. pneumomediastinum]] **Pneumomediastinum** is the presence of extraluminal gas within the mediastinum. Source may be lungs, trachea, bronchi, oesophagus, or peritoneum. Tension pneumomediastinum is a potentially-fatal form of obstructive shock leading to tamponade requiring urgent decompression with mediastinal drain. Most pneumomediastinum requires no treatment, with the air being gradually absorbed on the following days.  Radiographic features include: - s/c emphysema - [[#Continuous diaphragm sign]] - [[Chest trauma radiology#pneumopericardium vs. pneumomediastinum|pneumopericardium]] - Gas around pulmonary artery - In paeds may have elevated thymus, gas crossing superior mediastinum > [!key points]- Causes of pneumomediastinum > - blunt or penetrating chest trauma > - Oesophageal perforation: (boerhaave syndrome, anorexia with cyclical vomiting or malnutrition emphysema, recent endoscopy, oesophageal cancer) > - Trachealbronchial perforation: (bronchoscopy, tracheostomy, laryngeal fracture) > - vigorous exercise: (childbirth ([Hamman syndrome](https://radiopaedia.org/articles/hamman-syndrome-2?lang=us)), valsalva, weightlifting) > - Cough eg asthma or interstitial lung disease > - [[Diving injuries and Dysbarism#Barotrauma|Barotrauma]] : either diving or ventilator eg ARDS, inhaled substance abuse / [[Solvents|chroming]] > - Infection ([[Cavitary lung lesion]] ) **Pseudo-pneumomediastinum**, is radiographic evidence of pneumomediastinum that does not follow the expected time course of a pneumomediastinum and is not associated with the expected clinical signs and symptoms, such as chest pain, labored breathing, crepitus associated with the cardiac cycle, and subcutaneous emphysema. ### Continuous diaphragm sign Sign of pneumomediastinum or pneumopericardium if lucency is above the diaphragm. Sign of pneumoperitoneum if lucency below diaphragm Pneumomediastinum with continuous diaphragm sign: ![[Pasted image 20250427084043.png]]