Left perineal fat stranding and subcutaneous gas. Large gas and fluid collection within the posterior aspect of the left perineum with extension into the left ischioanal fossa. The collection is perianal in location, lying immediately left posterolateral to the anal canal with small locules of gas between the collection and posterior (6 o'clock) wall of the anal canal. Left laterally fat stranding extends into the subcutaneous tissues of the gluteal region. Fat stranding gas tracks into the anterior aspect of the left perineum. There is no inferior extension into the upper thighs. No supralevator extension.