Reversible protruded lesion regarded as idiopathic appendiceal intussusception

A patient with a reversible protruded lesion regarded as idiopathic appendiceal intussusception was investigated in this study. The patient was a 78-year-old male, who consulted our department as a result of positive occult blood in his stool sample. There was no associated pain, nausea, vomiting, fever, chill or anorexia. He had no prior surgical history. Total colonoscopy detected a sigmoidal polyp and a protruded lesion in the caecum. The protruded lesion (about 12 mm in diameter) covered with normal mucosa was diagnosed as a benign submucosal tumor at that time. The periodic follow-up colonoscopy showed an orifice on top of the protuberance. Further detailed observation revealed that the lesion reduced by itself, and resulted in showing a normal orifice of the appendix; however, afterwards it protruded again. These observations led to the diagnosis of the lesion as type B of Atkinson's classification in appendiceal intussusception. To our knowledge, approximately 200 cases of appendiceal intussusception have been documented in scientific reports worldwide. In Japan, only 10 cases of idiopathic appendiceal intussusception have been described. This case is considered to be important for presenting the initial stage of the complete intussusception of the appendix.