Alveolar echinococcosis with bulky peritoneal spread - a rare but important diagnosis in gynaecological practice

Authors


Correspondence: Dr B. Abendstein, Universitätsklinik für Frauenheilkunde, Anichstraße 35, A-6020 Innsbruck, Austria.

Case report

A 40 year old woman presented to the outpatient department of our clinic with abdominal distension and a weight gain of 5 kg in the previous three months. Her health was otherwise normal. While she found vaginal examination too uncomfortable to tolerate, a rectal examination was performed which revealed numerous small nodules in the recto-vaginal pouch. Laboratory investigation showed normal CA125 levels, but abdominal ultrasound and computed tomography scan raised the suspicion of a large mass in the lower abdomen, large round lesions in the liver and spleen, and a thickened gastric wall. The small volume of ascites was detected by ultrasound examination but not by computed tomography. Gastroscopy and colonoscopy did not show any pathology, and mammography and a chest X-ray were normal.

A diagnostic laparoscopy was performed, which revealed multiple smooth, white peritoneal nodules covering the uterus and bladder (Fig. 1a). Thick masses in the greater omentum obscured the ovaries. Both the greater omentum and the parietal peritoneum showed thick tumour deposits. Similar findings were seen on the surface of the liver (Fig. 1b), the lesser omentum and the spleen. Representative biopsies were taken. Histological examination showed the features of disseminated peritoneal echinococcosis as well as multiple irregular cystic cavities lined with characteristic laminated membranes and filled with amorphous material (Fig. 2). This diagnosis was confirmed by species-specific western blots revealing an infection with Echinococcus multilocularis.

Figure 1.

(a) Laparoscopic view of the lower abdomen. 1: alveolar cystic masses attached to the ventral wall of the uterus. 2: bulky partly confluent cystic tumour mass in the distal part of the lower large omentum. The ovaries cannot be seen. (b) Laparoscopic view of the upper abdomen. Alveolar cystic lesions covering parts of the liver, the greater omentum and the falciform ligament.

Figure 2.

Alveolar hydatid cyst. Peritoneal tissue is infiltrated by irregular laminated membranes (arrow) that have no apparent nuclei. The lumen of the cysts contain amorphous material. The adjacent tissue is fibrosed (haematoxylin and eosin).

The woman suffered unexplained post-operative fever for three days. Treatment with albendazole 800 mg per day was started. Three weeks after starting her treatment the woman went back to her normal work and has felt well since then.

Discussion

Alveolar echinococcosis is a zoonosis caused by infection with the larval stage of the roundworm Echinococcus multilocularis, a small tapeworm of canine animals, which enjoys an extensive geographic distribution in the Northern Hemisphere. The infection rate of foxes reaches 55% in endemic areas1. No accurate data are available on the infection rate of E. multilocularis in humans. Seroepidemiological studies show the prevalence to be 0.1 per 1000 to 0.5 per 1000 in endemic areas2,3. Although Austria is not an endemic region, greater movement of populations around Europe could well result in this disease being seen more often in nonendemic countries.

The life cycle of Echinococcus alveolaris involves the fox as final host and mice as intermediate hosts. Domestic dogs and rarely cats may also serve as definitive hosts. In this cycle, humans are infected orally via the intake of eggs. After ingestion, the egg of E. multilocularis releases the embryo (the oncosphere) into the small intestine. The embryo then enters a capillary and is carried to the liver, where it localises to develop the larval stage of the disease. The primary lesion is always found in the liver. Thereafter, the disease spreads by direct extension, lymphatic or haematogenous metastasis, or by peritoneal seeding. In humans the disease clinically does not appear as a cyst but as a firm, white or yellowish, solid cancer-like mass. Histological examination typically reveals numerous microcysts, 1 mm to 3 mm in diameter, embedded in a dense stroma of fibrous tissue. The microcysts are lined by characteristic laminated membranes, vary greatly in size and only rarely contain protoscolices. As the mass enlarges, dense scar tissue causes central, avascular necrosis, and a sterile abscess often develops within the lesion4.

Clinical manifestation frequently occur up to 15 years after ingestion of the eggs of E. multilocularis. The symptoms are not specific and are usually caused by adhesions or local infiltration. The main symptoms are abdominal pain and jaundice.

Because of its cancer-like appearance diagnosis is sometimes very difficult, especially in regions which are not endemic and have little experience with this rare disease. Errors in diagnosis by the surgeon and the pathologist are common5. In this case we were completely misled by the clinical examination and the results of computed tomography, both of which showed evidence of peritoneal carcinomatosis. Tumour markers were negative, however, and this discrepancy led to laparoscopy, which showed the typical findings of peritoneal carcinomatosis, although the surface of the nodules was much smoother than in a typical case of carcinoma. It was also unusual that there was no bleeding when biopsies were taken. The biopsy would have caused some spillage of Echinococcus, which could explain her fever in the post-operative period.

We believe this case is very instructive for gynaecological oncologists. A diagnosis of peritoneal carcinomatosis is quite common in clinical practice. Metastasis of gynaecological malignancies to the liver or spleen is rare, but when such metastases occur CA125 is usually elevated. During the past 13 years at our institution all these cases (n= 14) except one had elevated tumour markers (median CA125 = 1430 U/mL). The coincidence of appearances in the abdomen suggesting cancer, especially with a mass in the liver, without evidence of a primary tumour in the gastrointestinal or genital tracts, and with normal levels of tumour markers, should suggest echinococcosis. Serologic tests should include a specific enzyme-linked immunosorbent assay and western blots. The specific E. multilocularis antigen should be used when testing patients for alveolar echinococcosis1.

In untreated infections mortality reaches 80%4, which makes this disease the most dangerous human parasitosis in Central Europe.

New treatments could ameliorate the prognosis of echinococcosis to a great degree. The 10-year mortality rate has reduced from 94% in the 1960s to 10–16% in recent studies6. The first step in the management of echinococcosis must be the assessment of resectability, for surgical resection of a confined lesion, usually in the liver, offers the only proven curative treatment; only 30% of patients, however, are suitable for resection5. The aim of surgery is the complete removal of all lesions. In patients with inoperable masses, as in our case, chemotherapy with mebendazole or albendazole is recommended6. The therapeutic dose and duration of therapy have not been fully established. Albendazole is preferred over mebendazole because it provides much higher serum levels of the drug and effective treatment may therefore be attained in a much shorter time4,7. Unresectable lesions should probably be treated with a long term chemotherapy8,10, as there is a good chance of improvement with calcification of the alveolar lesions. There is strong evidence that therapy should not be interrupted. Computed tomography and serological surveillance are the best methods of monitoring treatment and detecting recurrences4,11.

Alveolar echinococcosis should be considered in women with negative tumour markers, no ascites, and signs suggesting advanced peritoneal carcinomatosis, especially if radiological signs of calcification are present, or if white or yellow cystic tumour nodules with a smooth surface are observed during laparoscopy or laparotomy.

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