Pneumatosis
Left lung completely affected by bullae shown in contrast to a normal lung on the right.
Causes	Tobacco smoking,pollutants

Pneumatosis is the abnormal presence of air or other gas withintissues.^[1]

In the lungs,emphysema involves enlargement of the distal airspaces,^[2] and is a major feature ofchronic obstructive pulmonary disease (COPD). Other pneumatoses in the lungs are focal (localized)blebs and bullae,pulmonary cysts and cavities.

Pneumoperitoneum (or peritoneal emphysema) is air or gas in theabdominal cavity, and is most commonly caused bygastrointestinal perforation, often theresult of surgery.

Pneumarthrosis, the presence of air in a joint, is rarely a serious sign.

Alung cyst, orpulmonary cyst, encloses a small volume of air, and has a wall thickness of up to 4 mm.^[3] A minimum wall thickness of 1 mm has been suggested,^[3] but thin-walled pockets may be included in the definition as well.^[4] Pulmonary cysts are not associated with either smoking or emphysema.^[5]

Alung cavity has a wall thickness of more than 4 mm.^[3]

• Pneumothorax, air or gas in thepleural space
• Pneumomediastinum, air or gas in the mediastinum
  • Also called mediastinal emphysema or pneumatosis/emphysema of the mediastinum

• Pneumoperitoneum (or peritoneal emphysema), air or gas in theabdominal cavity. The most common cause is a perforatedabdominal viscus, generally a perforatedpeptic ulcer, although any part of thebowel may perforate from a benign ulcer,tumor orabdominal trauma.
• Pneumatosis intestinalis, air or gas cysts in the bowel wall
• Gastric pneumatosis (or gastric emphysema) is air or gas cysts in thestomach wall^[6]

Pneumarthrosis is the presence of air in ajoint. Its presentation onradiography is aradiolucent cleft often called avacuum phenomenon, orvacuum sign.^[7] Pneumarthrosis is associated withosteoarthritis andspondylosis.^[8]

Pneumarthrosis is a common normal finding in shoulders^[7] as well as insternoclavicular joints.^[9] It is believed to be a cause of the sounds ofjoint cracking.^[8] It is also a common normal post-operative finding at least afterspinal surgery.^[10] Pneumarthrosis is extremely rare in conjunction with fluid or pus in a joint, and its presence can therefore practically exclude infection.^[8]

• 
  X-ray of a hip withhip replacement and pneumarthrosis, in this case aseptic.
• 
  A vacuum sign, or vacuum phenomenon, is a normal finding onshoulder X-rays.

Subcutaneous emphysema is found in the deepest layer of the skin.Emphysematous cystitis is a condition of gas in thebladder wall. On occasion this may give rise to secondary subcutaneous emphysema which has a poor prognosis.^[11]

Pneumoparotitis is the presence of air in theparotid gland caused by raised air pressure in the mouth often as a result of playingwind instruments. In rare cases air may escape from the gland and give rise to subcutaneous emphysema in the face, neck, or mediastinum.^[12][13]

The termpneumatosis has word roots ofpneumat- +-osis, meaning "air problem/injury".

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