Maffei & Fiorentini (1976).3. Our data suggest that the simple cell may perform approximately linear spatial summation of inputs to the visual system. However, the output of the simple cell is generally non-linear as reflected in its truncated responses to gratings.

This article reports an unusual case of delayed presentation of a tension faecopneumothorax after traumatic injury to the diaphragm 5 years previously. Three important clinical lessons are highlighted: (a) for suspected tension pneumothorax, if a considerable quantity of serous fluid is drained in addition to air, a communication with the peritoneal cavity should be considered; (b) spontaneous tension pneumothorax is an extremely rare condition and other causes should be kept in mind; and (c) in the presence of a tension pneumothorax and diaphragmatic hernia, the contents of the visceral sac may be completely reduced and the hernia may be masked.A 20-year-old man presented to the accident and emergency department with a 1-week history of severe epigastric pain precipitated by weight lifting. He had become progressively short of breath associated with constipation and fever. He had a history of peptic ulcer disease treated on a proton pump inhibitor as well as a stab to the left upper quadrant 5 years previously, which had been managed conservatively and was uneventful at the time.Examination showed that he was in respiratory distress but haemodynamically stable, with decreased air entry on the left side and vague epigastric discomfort. A plain chest radiograph showed a large left-sided tension pneumothorax with a mediastinal shift to the right.A chest drain was inserted on the left side, resulting in clinical improvement of symptoms. Two observations were made: (a) at the time of insertion a large amount of air was drained, followed by about 500 ml of serous coloured fluid and (b) the chest radiograph showed suspicion of a loop of bowel in the chest with a raised left hemidiaphragm. The patient, however, was clinically improved and stable. After a few hours, frank faeces started draining from the chest drain spontaneously and a computed tomography scan showed a large amount of transverse colon in the left hemithorax with faeces and air, which was trapped in a left-sided diaphragmatic hernia (fig 1).A thoracolaparotomy was carried out and showed a strangulated, perforated loop of transverse colon, which had become entrapped in the diaphragmatic hernia due to the stabbing 5 years previously. The patient had extensive lavage of the left hemithorax, and later developed left-sided empyema, which was drained radiologically. Subsequently, the patient made a good recovery.

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