Intestinal anisakiasis is not only a rare parasitic disease, but is also difficult to diagnose. The symptoms are not specific and are often very severe and abrupt, and the findings of clinical imaging are very remarkable. Therefore, intestinal anisakiasis is often misdiagnosed as acute abdomen or intestinal obstruction and is treated surgically. However, if intestinal anisakiasis could be diagnosed correctly, it is well treated conservatively. We experienced three cases of intestinal anisakiasis, which were diagnosed correctly and treated successfully with conservative therapy. A correct clinical history and imaging interpretation helped us diagnose intestinal anisakiasis correctly and thus treat the patients successfully with conservative therapy.

Anisakiasis is a parasitic disease caused in humans by the accidental ingestion of Anisakis larvae, present in fresh fish and squid. The larvae stick to the gastro-intestinal membrane and cause a set of symptoms, which are called anisakiasis. Depending on the site of the digestive system where the Anisakis larvae are stuck, anisakiasis can be divided into the following three types; gastric, intestinal, and ectopic anisakiasis[1-3]. Most of the cases consist of gastric anisakiasis. According to a series of 15715 cases of anisakiasis reported by Ishikura, gastric anisakiasis accounts for 95.6% of the cases, whereas intestinal and ectopic anisakiasis account for 4.1% and 0.3% of the cases respectively[4].

Patients with perforations or strangulation of the intestine require surgical therapy, but conservative therapy is the basic treatment of anisakiasis. Cases of non-gastric anisakiasis are not only very rare, but are also difficult to diagnose because the small intestine is an inaccessible zone for endoscopy. Thus, the diagnostic procedure required for anisakiasis, which is to detect the whole worm, is not feasible. As a result, patients with intestinal anisakiasis, have been diagnosed with acute abdominal or intestinal obstructions preoperatively, and have undergone unnecessary surgical operations[5-10]. We herein describe three cases of intestinal anisakiasis, which were correctly diagnosed clinically and treated successfully with conservative therapy.

The adult anisakis lives in the intestine of marine mammals, such as whales and dolphins. The eggs that they lay, come out and spread in the ocean when these mammals defecate. L2 larvae hatch out-of the eggs and swim freely in the water. These larvae are ingested by crustaceans in which, they mature into L3 larvae. These crustaceans are eaten by fish and squid, which are finally eaten by humans and marine mammals. For those that are eaten by marine mammals, the larvae molt and mature into the adult worms, which lay eggs and enter into the life cycle again. Larvae eaten by humans cause anisakiasis.

Anisakiasis was first reported by Van Thiel et al[11] Since then, many cases have been reported in different parts of the world. Because of the tradition of eating raw fish (sushi and sashimi) in Japan, the incidence of anisakiasis is higher than that in other countries (2000-3000 cases per year according to the Ministry of Labor, Health, and Social Welfare).

The most common symptom of anisakiasis is severe abdominal pain, for which the patient often requires painkillers, as observed in case 1. Anisakiasis is diagnosed by the detection of the worm sticking to the gut wall. However, as far as intestinal anisakiasis is concerned, diagnosis is difficult because the small intestine is an inaccessible zone for endoscopy, although capsule endoscopy or double balloon endoscopy can be performed in a very few institutions. The only method for diagnosing anisakiasis, other than endoscopy, is immunological examination (e.g., by examining Anisakis-specific IgA, IgG, and IgE). The sensitivity is as high as 70%-80%[12,13], but the results take time (a week) and, therefore are not at all helpful in the clinical field.

Because abdominal pain is severe and abrupt and the findings of clinical imaging are very remarkable, intestinal anisakiasis is often misdiagnosed as acute abdomen or intestinal obstruction and is treated surgically. According to the report by Ishikura et al[14] intestinal anisakiasis was correctly diagnosed postoperatively in only 23% cases, whereas 38% cases were acute appendicitis, 12% were intestinal obstructions and 10% were acute celiopathy. Anisakis larvae survive only for a few days in the intestinal tract of humans. Therefore, the symptoms due to acute inflammation subside within 2-3 wk and are treated well by conservative therapy[15]. However, there have been cases of strangulation or severe long segmental stenosis of the intestine caused by Anisakis, which of course required surgical therapy[10,16]. However, there are cases involving acute abdominal pain that are not intestinal anisakiasis. They should be correctly diagnosed and treated surgically.

Thus, we herein suggest methods to correctly diagnose intestinal anisakiasis and avoid unnecessary surgical intervention.

Collecting correct details of clinical history is the first step required for the correct diagnosis of intestinal anisakiasis. The onset of intestinal anisakiasis varies from 1-7 d after the ingestion of the raw fish and differs from that of gastric anisakiasis, which develops symptoms a few hours after the ingestion of raw fish[1,17]. However, there are cases in which the patients forget the food they ate, and thus, we should be very careful in collecting their clinical history details.

Accurate reading of the findings of the clinical images is the second step that is required for making a correct diagnosis of intestinal anisakiasis. CT shows swelling of a partial segment of the small bowel, dilatation of the intestine with fluid collection on the oral side of the lesion, and collection of ascites, as observed in all three cases experienced[8,10,18]. Ultrasound shows marked local edema of Kerckring’s fold, which is known as the corn sign, dilatation of the oral portion of the small intestine with fluid accumulation, and accumulation of ascites. We did not use ultrasound during the diagnostic procedure in our cases, but integrating the information from different modalities of images would certainly increase the rate of correct diagnosis.