Intestinal ascariasis: CT findings and diagnosis.

To the Editor: Intestinal ascariasis is a disease most commonly diagnosed through stool studies along with traditional imaging studies. Radiographic findings in Ascaris infection have been described in multiple modalities, as well as two descriptions of computed tomography (CT) findings. (1,2) In this letter, we describe an incidental finding on abdominal CT of Ascaris lumbricoides infection.

A 20-year-old Mexican male immigrant presented to the emergency department after being assaulted two nights before admission. The patient complained of right-sided abdominal pain. On review of systems, the patient had experienced fevers and vomiting since the assault. On examination, he was febrile at 39.3[degrees]C (102.7[degrees]F), and his heart rate was 114. Abdominal examination showed diffuse tenderness with mildly positive rebound tenderness, no masses, and normoactive bowel sounds. The remainder of the physical examination was within normal limits.

Due to the patient's abnormal abdominal examination, a CT of the abdomen was ordered. The patient was found to have tubular structures in the jejunum measuring greater than 10 cm in length and 0.4 cm in width. These structures were suspicious for Ascaris infection. The patient was then given 500 mg of mebendazole orally, observed for 24 hours, and discharged from the hospital.

The roundworm group of helminths includes pinworms, whipworms, roundworms, and hookworms. The ascarid infects approximately one billion people worldwide and is the most common human intestinal parasite. (3) In the United States, approximately 4 million people are infected. (4) Certain areas of the country have large numbers of immigrants from regions where Ascaris infection is endemic, such as Central America and Asia. For this reason, Ascaris infections must remain in the differential diagnosis. One must also be aware that many helminths can survive within a host for ten years or more after the initial infection.

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Infestation occurs through ingestion of eggs. Most patients are asymptomatic; however a very heavy worm burden can produce poorly localized and colicky abdominal pain in adults. In children, volvulus, intussusception, or intestinal obstruction may occur.

The definitive diagnosis of a helminth infection is usually done by finding and identifying ova and parasites in the stool. Treatment of ascariasis usually consists of mebendazole or albendazole.

The CT findings of ascariasis in this case consisted of both cross sections and longitudinal sections of worms within the lumen of the small intestine. Contrary to previously reported CT findings, ours revealed a conspicuous lack of oral contrast within the bowel of the worm. (1,2) The longitudinal sections showed worms of at least ten cm within the patient's intestine, while the axial sections showed 0.4 cm tubular structures with a central lumen not enhanced with contrast.

This incidental finding of A lumbricoides on abdominal CT should remind us that diseases prevalent elsewhere in the world should also be considered in our differential diagnoses of recent immigrants and travelers (Fig. 1, 2).

Andrew Pylant, MD

Jeffrey W. Hinshaw, PA-C

Ralph B. Leonard, MD, PHD

Stacie Zelman, MD

Department of Emergency Medicine Wake Forest University Baptist Medical Center Winston-Salem, NC

References

1. Hommeyer SC, Hamill GS, Johnson JA. CT diagnosis of intestinal ascariasis. AbdImaging 1995;20:315-316.

2. Beita AO, Haller JO, Kantor A. CT Findings in pediatric gastrointestinal ascariasis. Comput Med Imaging Graph 1997; 21: 47-49.

3. Mackay AD, Chiodini PL. Parasitic Infections of the Gastrointestinal Tract. In: Infectious Diseases, 2nd ed. New York, Mosby; 2004, pp 503-516.

4. Cox FE. History of human parasitology. Clin Microbiol Rev 2002;15:595-612.