Tuesday, May 14, 2019


Q: A pneumothorax (PTX) can be best identified on which position of chest X-ray? (select one) 

A) upright 
B) supine 
C) lateral decubitus

Answer: C

In a lateral decubitus view, most pleural air accumulates in the non-dependent lateral location. This is the most sensitive way of demonstrating PTX as even 5 mL of pleural air can be visible.

The second most sensitive is an upright position as it requires only 50 mL of air to demonstrate the PTX, and the least sensitive is the supine position which requires 500 mL of air to demonstrate PTX.



 1. Carr JJ, Reed JC, Choplin RH, et al. Plain and computed radiography for detecting experimentally induced pneumothorax in cadavers: implications for detection in patients. Radiology 1992; 183:193.

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