What are the possible differentials of air/fluid level in this case?
Abscess formation- Enteroenteric fistula or vesicoenteric fistula in inflammatory bowel disease.
Giving transrectal contrast was necessary in this case?
It is not necessary, although it helps in outlining and mapping of the adjacent bowel loops.
Pelvic collection and abscess formation in young adult male, what are the possibilities?
Perforated, complicated appendicitis - Inflammatory bowel diseases as Crohn's.
A calcified lesion is seen within a mass-like appearance in the pelvis likely an appendicolith. An associated air/fluid level can be depicted.
After post-contrast series, it shows multiloculated and marginated enhancement in the right iliac fossa and in the suprapubic regions. Following administration of transrectal contrast in delayed phase, the adjacent large bowel loops can be assessed.