Occasionally they may be found in the large bowel (Fig. 10.22D), especially in children, where they may be visualized by barium enema.

If the patient has been fasting for over 12 hours, the Ascaris may ingest barium, in which case its alimentary canal appears as a white thread bisecting the length of its body, which is then visible in "double contrast" against the surrounding barium (Figs. 10.21 and 10.22B).

Fig. 10.21 Multiple ascarids are outlined by barium in their usual location within the jejunum of two separate patients (A and B). The alimentary tracts of several worms contain ingested barium and are seen as white thread-like strings bisecting the length of the ascarids. There is coarsening of the mucosal folds in the vicinity of the worms.

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Fig. 10.22A-D. Ascariasis of the ileum and cecum in four different patients. (A) A lone Ascaris in a loop of proximal ileum in the left lower quadrant. A careful examination of the entire small bowel is essential in evaluating possible parasitic disease since occasionally only one adult worm may be found, as in this case. In the majority of patients, multiple ascarids will be demonstrated. (Courtesy of Dr. Douglas Sheft, San Francisco.) (B) Numerous ascarids are seen within the ileum of an Okinawan. The intestinal tracts of many of the worms are clearly visualized as white thread-like lines bisecting the length of the worms. (C) A large mass of tangled roundworms in the distal ileum and right colon (outlined by barium study) causing partial intestinal obstruction in a child from Nigeria. (D) Multiple ascarids in the cecum and ascending colon of another Nigerian child.