This patient presented for CT pulmonary angiogram to investigate possible pulmonary embolus. The image above is a good example of paraseptal emphysema. There is also a background of centrilobular emphysema.
Pathological correlation is useful when studying emphysema. Paraseptal emphysema involves the alveolar ducts and sacs at the lung periphery. The emphysematous areas are often surrounded by interlobular septa (hence the name). It may be an incidental finding in young adults, and may be associated with spontaneous pneumothorax.
It may also be seen in older patients with centrilobular emphysema (as in this case). Both centrilobular and paraseptal emphysema may progress to bulla formation. A bulla is defined as being at least 1cm in diameter, and with a wall less than 1mm thick. Bullae are thought to arise by air trapping in emphysematous spaces, causing local expansion.
Reference: Webb WR, Higgins CB. Thoracic Imaging. Lippincott, Williams & Wilkins 2005.
Credit: Dr Laughlin Dawes