2. Endoscopic retrograde appendicography (ERA): After cannulation of the appendiceal lumen, decompression of lumen will be achieved by suction using a 5-mL syringe attached to the catheter. A soluble contrast agent (iobitridol) will be then used to fill the appendix while being monitored by fluoroscopy to check the radiographic features of the appendix (including position, length, contour, mobility, intraluminal content and inner diameter of appendiceal lumen).