At least in kids... A Johns Hopkins study published in May 2015 suggests that tonsil size does NOT appear to correlate with obstructive sleep apnea (OSA) severity and degree of response to T&A surgery. Regardless of the tonsil size even if they are small, improvement in obstructive sleep apnea (OSA) occurs based on pre- and post-operative sleep studies.
These findings seem counter-intuitive since one would think that the larger the tonsils, the more severe the OSA and the greater the response after the tonsils are removed. However, this retrospective chart review suggests otherwise. It would seem that T&A helps with OSA regardless of the tonsil size (even if they are "small").
It should be noted that a number of other studies have also noted that tonsil size does NOT correlate with OSA severity.
Given the poor correlation between tonsil size and OSA, it perhaps is no great surprise that tonsil size wouldn't necessarily correlate with how well a child will respond to surgery either.
The take-home message is that if a child has OSA, tonsil removal should still be seriously considered even if they are "small" on exam.
Please note that these findings can not be applied to adults with OSA.
Systematic review of pediatric tonsil size and polysomnogram-measured obstructive sleep apnea severity. Otolaryngol Head Neck Surg. 2011;144:844-850.
Influence of tonsillar size on OSA improvement in children undergoing adenotonsillectomy. Otolaryngol Head Neck Surg. 2015; 153:281-285.