An aftertreatment system and method treats exhaust gasses produced by an internal combustion process or similar process. The system includes an aftertreatment module having at least one sleeve extending between a first end and a second end. One or more aftertreatment bricks may be axially inserted through an opening disposed in the first end of the sleeve. The aftertreatment brick may include an substrate matrix surrounded by a tubular, protective mantle. To prevent the aftertreatment bricks from unintentionally exiting the sleeve, a retention ring is releasably engaged with the first end of the sleeve. The retention ring may include a dimension that is less than a dimension of the opening in the first end so that at least a portion of the retention ring contacts the mantle of the aftertreatment brick.