a 37-year - old woman was referred to our hospital for further evaluation of gallstones that had been found on sonography at a private clinic . contrast enhanced ct imaging was performed for further evaluation of the biliary tract and gallbladder . a ct image demonstrated a strong enhancing ring - like mass that abutted the uterine fundus in the right pelvis ( fig . non - contrast enhanced ct images showed the presence of gallstones in the gallbladder lumen and no stones in the extrahepatic bile duct . after four days , the patient presented to the emergency room with acute right lower abdominal pain . a follow - up ct examination was performed and showed massive high attenuation fluid in the peritoneal cavity that represented hemoperitoneum . the previous strong enhancing ring - like mass in the right pelvis was now seen as a heterogeneous enhancing mass on a follow - up ct image ( fig . the heterogeneous mass abutted the uterine fundus in the right pelvis and a linear hypodense line was noted between the mass and the uterus ( fig . after an emergency laparotomy , right interstitial pregnancy with hemoperitoneum was found and a right cornual resection was performed . ectopic pregnancy is a potentially life - threatening condition as ectopic pregnancy can cause rupture of the organ where implantation has occurred with severe bleeding ( 4 ) . ectopic pregnancy may occur in several sites ; the fallopian tube is the most common site . only 2 - 4% of ectopic pregnancies occur in the interstitial portion of the fallopian tube ( 5 ) . the diagnosis of ectopic pregnancy is based on sonography and the demonstration of pregnancy using a serum beta - human chorionic gonadotropin assay . ectopic pregnancy is considered when there are no normal uterine pregnancy findings on sonography ( 5 ) . as pregnant women should not undergo ct imaging , ct findings of ectopic pregnancy are not well known . however , if pregnancy is not identified during an early pregnancy , ct may be inadvertently used for evaluation of abdominal pain . with the increasing use of ct as an initial diagnostic image modality , radiologists may encounter ectopic pregnancy with the use of ct imaging and it is important to know the ct features of ectopic pregnancy . there have been only three reported cases in the clinical literature where ct revealed ruptured ectopic tubal pregnancies ( 1 - 3 ) . to the best of our knowledge , the dramatically enhancing ring in adnexa with hemoperitoneum has been reported as a ct finding of ruptured tubal pregnancy . pham and lin have suggested that the enhancing ring in adnexa on ct images was correlated with the sonographic " ring of fire " sign of tubal pregnancy ( 3 ) . in this case , a ct finding of unruptured ectopic tubal pregnancy was also a strong enhancing ring - like mass that represented the gestational sac without hemoperitoneum . however , the morphological change of the ct appearance of tubal pregnancy after rupture was observed . after rupture of tubal pregnancy , the previous strong enhancing ring - like mass of unruptured tubal pregnancy was seen as a heterogeneous enhancing mass on a ct image with massive hemoperitoneum . the differential diagnosis of an adnexal mass with peripheral enhancement includes a tubo - ovarian abscess , cystic ovarian neoplasm and a functional ovarian cyst including a corpus luteum cyst . pham and lin ( 3 ) have suggested that peripheral enhancement of an adnexal mass of tubal pregnancy was significantly greater as compared to a tubo - ovarian abscess and a cystic ovarian neoplasm . the location of an adnexal mass may help in the differential diagnosis between ectopic tubal pregnancy and a corpus luteum cyst as a corpus luteum cyst is located on an ovary ( 3 , 6 , 7 ) . the presence of hemoperitoneum does not aid in the differential diagnosis between ruptured tubal pregnancy and a ruptured corpus luteum cyst as both conditions cause hemoperitoneum . we suggest that the size of an adnexal mass is also a clue for the differential diagnosis . an adnexal mass of tubal pregnancy may be smaller as compared to a tubo - ovarian abscess and a cystic ovarian neoplasm . ct findings of interstitial ectopic pregnancy have not been previously reported in the literature . for interstitial pregnancy , the part of the ring - like mass that abuts the uterine fundus might represent the portion of the gestational sac surrounded by the myometrium . the diagnosis of ectopic pregnancy was missed , as we did not consider the possibility of pregnancy on initial ct images before rupture . we learned that ectopic pregnancy should be considered without hemoperitoneum on ct images and prompt further evaluation such as determination of the serum beta - human chorionic gonadotropin level is needed for a correct diagnosis . in summary , we have reported an interstitial pregnancy that appeared as a strong enhancing ring - like mass that abutted the uterine fundus in the pelvis on ct images .
ectopic pregnancy is a potentially life - threatening condition . 
 detection of ectopic pregnancy on ct images is rare . in this case , we describe the ct findings of interstitial pregnancy both before and after rupture . if ct images demonstrate the presence of a strong enhancing ring - like mass in the pelvis , ectopic pregnancy should be considered .