acute appendicitis is considered as the most frequent cause of acute abdomen in young patients with a slight predominance in males . although its clinical diagnosis is simple , 20 - 30% of appendicitis cases are reported to be gangrenous or perforated because of delayed diagnosis , which can lead to increased morbidity and mortality . additionally , up to 10% of patients especially older ones , immunocompromised patients , and pregnant women are diagnosed with atypical presentations such as appendiceal mass which requires long hospital admissions , intravenous antibiotics , and often needs percutaneous drainage . using colonoscopy for the diagnosis and treatment of asymptomatic acute appendicitis and appendiceal abscess are rare . in unusual appendicitis cases , especially in the presence of abdominal comorbidities , colonoscopy is used ; although colonoscopy is not considered as the first line intervention because of complications risk such as bleeding or perforation . furthermore non - invasive tests such as ultrasonography and computed tomography with more sensitivity can be used . we report an atypical case of appendiceal abscess , which was diagnosed during colonoscopy . a 30-year - old man referred for evaluation to our center with epigastric pain from three days prior to his evaluation . the pain was nonspecific and colicky distributed in periumblical region , did not radiate to any site and was unrelated to bowel movements . he had experienced also nausea , anorexia and intermittent vomiting . 
 
 there was a history of marijuana and alcohol usage from several years ago . upon physical examination , he was ill with restlessness . other laboratory values such as hemoglobin , platelets , serum amylase , erythrocyte sedimentation rate , aspartate aminotransferase , alanine aminotransferase , alkaline phosphatase , and electrolytes were normal . 
 
 his workup on admission including ; chest x - ray , abdominal x - ray , and abdominal ultrasonography were reported normal . an upper gastrointestinal endoscopy was performed after four days of admission that was normal . 
 
 within second week after admission , the appendiceal orifice was discovered in the floor of cecum which was draining pus into the lumen ( figure 1 ) . purulent discharge from the appendiceal orifice before ( up ) and after ( down ) pressing by forceps ( arrow ) 
 result of the biopsies of the mucosa at the base of the appendix showed mild nonspecific inflammation with some necrotic materials and staphylococcus organism . the biopsies of the mucosa at terminal ileum , left and right colon demonstrated mild nonspecific inflammation . a second abdominal ultrasonography was performed that showed a fluid collection ( about 70 40 mm ) in favor of appendiceal abscess in right lower quadrant ( figure 2 ) . the patient was scheduled for spiral abdomen - pelvic computed tomographic scan which showed a hypodense well defined collection with air fluid level ( about 70 40 30 mm ) in right lower quadrant . the collection was extended to pelvic cavity associated with inflammation of the surrounding fat in favor of appendiceal abscess ( figure 3 ) . ultrasonography showing a fluid collection in favor of appendiceal abscess   computed tomographic scan showing a hypodense well defined collection with air fluid level associated with inflammation of surrounding fat in favor of appendiceal abscess ( arrow ) . one week after antibiotic therapy a third abdominal ultrasonography was performed that showed a smaller fluid collection ( about 40 15 mm ) around the appendix . three weeks after antibiotic therapy the patient was asymptomatic with normal white blood cell count . on the 5th week after antibiotic therapy , exploratory laparotomy did not show any mass or collection in the appendiceal region and elective appendectomy was performed . after 3 months of follow - up the patient was well without any complaint or physical finding . acute appendicitis is one of the most frequent causes of acute abdomen . despite the use of scores in the radiological evaluation , and laparoscopic advances , in a cohort study of patients with appendiceal abscess or phlegmon due to acute appendicitis concluded that initial conservative treatment should be considered . colonoscopy is reported as a diagnostic and therapeutic approach for delayed or atypical presentations of acute appendicitis . our patient is one of these unusual cases among whom complicated acute appendicitis was incidentally diagnosed by colonoscopy . although the appendiceal orifice is routinely examined during colonoscopy , however there are only few published reports describing acute appendicitis diagnosis in the appendiceal orifice . 
 
 in a review article , khawaja fi recommended that colonoscopy should only be done in selected patients with atypical appendicitis or uncertain diagnosis of appendiceal perforation . benatta ma reported an atypical case of pericecal appendiceal abscess diagnosed and treated at colonoscopy , while initial presentation was without any suggestive symptoms of appendicitis . wade ad et al reported an atypical case of appendicitis in a patient with ulcerative colitis diagnosed during colonoscopy . in this report christoffersen mmw et al reported an atypical case of periappendicular abscess diagnosed and treated at colonoscopy , while the patient was admitted for colonoscopy polyp control without any suggestive symptoms . kawahara y et al reported a case of appendiceal abscess with draining pus from appendiceal into the lumen diagnosed at colonoscopy and ct scan . in this report because of spontaneous drainage of abscess into the lumen , the appendiceal abscess had resolved by the time of surgery . kapral c et al . reported a case of pericecal abscess that treated by drainage at colonoscopy and antibiotic therapy . they intubated the appendix by sphincteroltomy catheter which was placed into the abscess cavity . petro m reported a case of the earliest stage of acute appendicitis in an asymptomatic patient undergoing colonoscopy for evaluation of colorectal cancer . for evaluation of the role of colonoscopy in the diagnosis of atypical appendicitis , a retrospective study in 21 patients performed by chang hs et al . some of acute appendicitis cases are reported to be complicated , due to delayed diagnosis . this unusual case highlights a patient with an appendiceal abscess diagnosed by colonoscopy . because of spontaneous drainage of abscess into the lumen of colon and antibiotic therapy , although the diagnostic and therapeutic role of colonoscopy in these patients is uncertain , however , it s use can be selected in special situations in the future .
although complicated acute appendicitis is occasionally observed in general practice , the diagnosis of appendiceal abscess by colonoscopy is unusual . 
 we report a case of appendiceal abscess with spontaneous drainage into the lumen of colon diagnosed during colonoscopy and resolved by the time of surgery .