This is a case of Fournier's gangrene showing florid necrotizing fasciitis (infection of the deep soft-tissues) centered on the perineum and external genitalia.

The cause can be either mono or polymicrobial with Streptococcus Pyogenes often being the culprit in the former. Treatment is emergency debridement of the infected & nonviable tissue. 

Garden-variety necrotizing fasciitis can often be difficult clinically to differentiate from severe cellulitis through several scoring systems to aid establish diagnosis. Severe pain in early stages & blister formation over the skin in late stages are often clues for the physician. 

Indeed the surgical team found this diagnosis difficult to accept given the profound lack of pain but note the history of tetraplegia. Sometimes clinical correlation is truly required!