Ans. c (Complicated acute pancreatitis) (Ref. Bailey and Love 26th/pg. 998).Left inferior (posterior) intraperitoneal space OR Left subhepatic space/lesser sac: The most common cause of infection here is complicated acute pancreatitis. In practice, a perforated gastric ulcer rarely causes a collection here because the potential space is obliterated by adhesions.ABDOMINAL ABSCESS# There are four peritoneal and three extraperitoneal spaces in which pus may collect.# Three of these spaces are on either side of the body, and one is approximately in the midline.# Left superior (anterior) intraperitoneal ('left subphrenic') = common came of an abscess here is an operation on the stomach, the tail of the pancreas, the spleen or the splenic flexure of the colon.# Right superior (anterior) intraperitoneal ('right subphrenic') = Common causes here are perforating cholecystitis, a perforated duodenal ulcer, a duodenal cap 'blow out' following gastrectomy and appendicitis.# Right inferior (posterior) intraperitoneal ('right subhepatic') lies in Rutherford Morison's pouch. It is the deepest space of the four and the commonest site of a subphrenic abscess which usually arises from appendicitis, cholecystitis, a perforated duodenal ulcer or following upper abdominal surgery.# Extraperitoneal. There are three of these:- Right and left extraperitoneal which are terms given to perinephric abscesses;- Midline extraperitoneal which is another name for the 'bare' area of the liver which may develop an abscess in amoebic hepatitis (commonest cause) or a pyogenic liver abscess.Educational Points:# The pelvis is the commonest site of an intraperitoneal abscess because the vermiform appendix is often pelvic in position and also the Fallopian tubes are frequent sites of infection. A pelvic abscess can also occur as a sequel to any case of diffuse peritonitis and is a common sequel of anastomotic leakage following large bowel and rectal surgery.# The most characteristic symptoms of a pelvic abscess are diarrhea and the passage of mucus in the stools.# It is no exaggeration to say that the passage of mucus, occurring for the first time in a patient who has, or is recovering from, peritonitis, is pathognomonic of pelvic abscess.# Left to nature, a proportion of these abscesses bursts into the rectum, after which the patient nearly always recovers rapidly. Laparotomy is almost never necessary.# Rectal drainage of a pelvic abscess is far preferable to suprapubic drainage (risks peritoneal infection).# Subdiaphragmatic abscess: remember the aphorism, 'pus somewhere, pus nowhere else, pus under diaphragm. 9# A swinging pyrexia is usually present, unless antibiotics or drugs (steroids) have interfered.# Ultrasound or CT scanning is the investigation of choice and permits early detection of subphrenic collections.# Ga67/Indium-111 white cell scanning may occasionally prove helpful when other imaging techniques have failed.