The diagnosis is made clinically in patients residing in a geographic location where this parasite is endemic, and is supported by serology. Because of the intense inflammatory reaction in the abnormal (human) host, eggs and larvae are destroyed before reaching the bowel lumen and thus no larvae, adults, or eggs are detected in stool samples of patients with abdominal angiostrongyliasis. A specific diagnosis, however, can be made histopathologically following surgery or, less commonly, by endoscopic biopsy, by recognizing the location and morphology of the eggs (dimensions 65 µm by 40 µm), first-stage larvae, and adult nematodes (1 to 2 mm in length) in tissue sections. Angiostrongylus costaricensis is the only human parasite to show eggs, larvae, and adult worms within the bowel wall and is the only human nematode parasite to occur in an intravascular site. Both Stronglyloides stercoralis and Schistosoma spp. must be excluded. Microscopically there is (1) a massive infiltration of eosinophils throughout the intestinal wall, (2) a granulomatous reaction with foreign body giant cells engulfing and destroying the eggs and larvae, and (3) an eosinophilic vasculitis affecting arteries, veins, lymphatics, and capillaries (Graeff-Texeira et al, 1991) (Fig. 13.20A).

The terminal ileum is usually involved to a lesser extent than the colon. On gross examination, the cecum may show patchy hemorrhage and fibropurulent exudate arising from the serosa and pericolic fat (Fig. 13.20B). Bowel wall thickening occurs in both the cecum and terminal ileum, with associated necrosis, an important finding at autopsy. The cecal mucosa may also be ulcerated. Adhesions are often encountered at surgery. Inflammation of the peritoneal surfaces gives support to the theory that larvae migrate freely beyond the mesenteric vessels and bowel wall. Hepatic lesions adjacent to an inflamed Glisson's capsule are likely to be the result of direct penetration of the liver by larvae. There is no effective form of chemotherapy, with surgery the treatment of choice where indicated. In general, the illness is self-limiting, with a mortality estimated at 1 to 2%.

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Fig. 13.20 Angiostrongyliasis costaricensis. (A) Biopsy specimen from the ascending colon of a 14- year-old black American girl with a 10-month history of anorexia, nausea, vomiting, diarrhea, 35 pound weight loss, low-grade fever, and abdominal pain, all of which began 3 months after moving to Ecuador. There is a large multinucleated giant cell in the lamina propria. Scattered eosinophils are present in the mucosa and lamina propria. (H & E, X100). (B) Gross appearance of the small intestine at laparotomy in a 5-year-old adopted Chilean girl hospitalized 8 months after moving to the United States with a 10-day history of fever, vomiting, severe right lower quadrant pain, and jaundice. Stools were negative for ova and parasites. Abdominal ultrasound revealed a complex mass with air-fluid level in the right lower quadrant. At laparotomy there was a 3.5 cm abscess in the right lower quadrant. About 120 cm of ileum and cecum were severely inflamed, thickened, hemorrhagic, and covered with reactive fibrin. A small perforation was repaired and the abscess drained. After an initial erroneous diagnosis of Crohn's disease, serial serum ELISA titers for Angiostrongylus returned positive at 1:1024 (normal <64). (Courtesy of Dr. C.A. Liacouras et al. and J Pediatr Gastroenterol Nutr, 1993).

There have been few reports describing the imaging findings in this disease. In the largest clinical series of 116 children admitted to a children's hospital in Costa Rica (where the disease occurred predominantly in the 6- to 13-year age group and was twice as frequent in males), radiographic findings were localized to the terminal ileum, appendix, cecum, and ascending colon. Barium examination showed spasticity, edema, filling defects, and ulceration in the cecum, and narrowing of the lumen of the terminal ileum with nodular irregularity of the mucosa (Fig. 13.21). Less often, patchy mucosal thickening and edema were noted in the ascending colon. In a minority of patients, the terminal ileum only was involved, with a normal colon.

Extraintestinal sites of infection are uncommon and include lymph nodes, liver, omentum, and testes. There are no imaging studies with findings demonstrating an extraintestinal location. Recurrent gastrointestinal hemorrhage has been reported and the site identified with technetium pertechnetate-labeled red blood cell scanning. Accumulation of radioactivity was seen in the right lower quadrant and a selective SMA arteriogram showed multiple dilated mesenteric arteries and vasa recta throughout the ascending colon. These findings are nonspecific, with the chief differential diagnosis being angiodysplasia.

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Fig. 13.21 Angiostrongyliasis costaricensis in the 14-year-old girl referred to in Fig. 13.20A. (A) Small bowel series shows severe narrowing of a long segment of distal ileum (arrows). (B) Spot film of the terminal ileum reveals ulcers along its mesenteric aspect and nodularity and rigidity extending into the cecum. The ileocecal valve is thickened and ileocecal spasm was noted fluoroscopically. (Courtesy of Dr. A.C. Liacouras et al. and J Pediatr Gastroenterol Nutr, 1993).