While this sounds like a slang term, it has nothing to do with other previously provided definitions for keyhole
. It is a medical euphemism for laproscopic surgery done through a very small incision.
The doctor recommended keyhole surgery as it would leave only a very small scar.
Likely an example of the Southern Vowel Shift, making "swang" an allophone of "swing," similar to the allophones "thing" and "thang." Meanings associated with "swang" that are not associated with "swing" may occur when this Southern dialect feature (also common to African-American Vernacular English) is interpreted by speakers of so-called "Standard American English" who only hear it used in specific, limited contexts.
Southern American/AAVE: Swang your Cadillac down the street.
"Standard" American: Swing your Cadillac down the street.