Solution: Typhlitis is an acute inflammation of the cecum that occurs in immunosuppressed patients and was originally described in children being treated for AML. Presentation is usually RLQ pain, leukopenia, fever, and occasionally lower GI bleeeding and peritoneal signs. The CT findings seen here are typical of this condition. In a CF patient, the most likely reason for immunosuppression (which has been described in the literature) is chronic steroid treatment for bronchospasm. This is presumably the risk factor in this case. This can usually be treated without surgery, but with perforation may require emergent surgery.