[1] In the lungs, emphysema involves enlargement of the distal airspaces,[2] and is a major feature of chronic obstructive pulmonary disease (COPD).

Pneumoperitoneum (or peritoneal emphysema) is air or gas in the abdominal cavity, and is most commonly caused by gastrointestinal perforation, often the result of surgery.

[3] A minimum wall thickness of 1 mm has been suggested,[3] but thin-walled pockets may be included in the definition as well.

[10] Pneumarthrosis is extremely rare in conjunction with fluid or pus in a joint, and its presence can therefore practically exclude infection.

In rare cases air may escape from the gland and give rise to subcutaneous emphysema in the face, neck, or mediastinum.