Most pneumothoraces post ultrasounded-guided thoracentesis (which are uncommon in themselves) result from unavoidable stress-related parenchymal-pleural fistulas that result from trapped (unexpandable) lung rather than being procedure related (e.g. direct lung puncture, poor technique). 

Radiographic signs of trapped lung include:

• visceral pleural peel (thickening)
• basilar pneumothorax
• ipsilateral volume loss
• lobar atelectasis

Often treatment of these pneumothoraces with chest tubes is unsuccessful and most will slowly resolve in their own time.