Medical management of Echinococcus multilocularis infection mimicking a locally aggressive cavitary tumor with pulmonary metastases in a dog

A two-year-old Labrador retriever living in the French Alps was presented with abdominal distension, lethargy and weight loss but no other specific clinical signs. CT examination revealed a large, cavitary liver mass invading the caudal vena cava, associated with multiple hepatic lesions of similar appearance, lymphadenopathy and pulmonary nodules. The condition was initially mistaken for a malignant neoplasm. However, cytologic and histologic examinations of the largest liver mass were consistent with cestodiasis and PCR testing confirmed infection with Echinococcus multilocularis. Medical treatment with albendazole was initiated. The dog remained clinically well for ten months following the diagnosis, but had to be euthanized because the owners had to return to Great-Britain and the dog could not be legally imported. To the authors’ knowledge, this is the first case report, in which long-term follow-up of Echinococcus sp. infection in a dog, managed medically, is described. This case also shows that medical management may be a viable option in case surgery is not feasible.


INTRODUCTION
Canidae are involved in the life cycle of E. multilocularis mainly as definitive hosts, ingestion of infected intermediate hosts causing intestinal infection. However, there have been occasional case reports de-BSTRACT A two-year-old Labrador retriever living in the French Alps was presented with abdominal distension, lethargy and weight loss but no other specific clinical signs. CT examination revealed a large, cavitary liver mass invading the caudal vena cava, associated with multiple hepatic lesions of similar appearance, lymphadenopathy and pulmonary nodules. The condition was initially mistaken for a malignant neoplasm. However, cytologic and histologic examinations of the largest liver mass were consistent with cestodiasis and PCR testing confirmed infection with Echinococcus multilocularis. Medical treatment with albendazole was initiated. The dog remained clinically well for ten months following the diagnosis, but had to be euthanized because the owners had to return to Great-Britain and the dog could not be legally imported. To the authors' knowledge, this is the first case report, in which long-term follow-up of Echinococcus sp. infection in a dog, managed medically, is described. This case also shows that medical management may be a viable option in case surgery is not feasible.

CASE DESCRIPTION
A two-year-old, female, spayed Labrador retriever was presented with progressive abdominal distension associated with moderate lethargy but no other specific clinical signs. The dog was living in the French Alps but travelled regularly to the United Kingdom. The common vaccinations used in France and Great-Britain had been administered correctly, and the dog was given milbemycin oxime and praziquantel tablets (Milbemax ® , Novartis, Switzerland) every three months as prophylactic treatment against endoparasites. Dosages were adequate for its body weight, according to the manufacturer's recommendations.
Upon clinical examination, the dog was in a poor body condition. A firm, voluminous cranial abdominal mass could be palpated. Complete blood count showed mild neutrophilia with a moderate left shift. Serum biochemistry including liver enzyme activity and bile acid measurement were within normal limits. Ultrasonographic abdominal examination performed by the referring veterinarian (HDI 5000 sonoCT, Philips Healthcare, France) confirmed the presence of a voluminous cranial abdominal mass, suspected to be originating from the liver (Figure 1). The large dimensions of the mass impaired comprehensive and detailed examination of the cranial abdominal region.
Computed tomography was performed at a second veterinary referral clinic (Les Hutins Veterinary Clinic, Saint-Julien-en-Genevois, France), using a 16-slice spiral CT (Brivo CT385, General Electric Healthcare, France). Precontrast helical acquisitions of the abdomen and thorax were first obtained with the lungs inflated (single breath-hold technique); CT angiographic examination of the abdomen was then performed by manually injecting 2 mg/kg iohexol (Omnipaque350 ® , Ge healthcare sas, France) followed by an early postcontrast acquisition, approximately ten seconds postinjection (portal phase). Delayed phase (four minute) postcontrast acquisitions of the thorax (thickness 1.25 mm, kV = 120, mA = 150) and abdomen (thickness 1.25 mm, kV = 120, mA = 160) were finally obtained. The CT images were re-  viewed by a diagnostic imaging resident (JF) and a radiologist (EC).
A voluminous mass (20 cm craniocaudally, 22 cm laterally and 15 cm dorsoventrally) was present in the right cranial abdominal quadrant ( Figure 2). The lesion was cavitary with a hypoattenuating center, unenhanced by the contrast medium (8 HU), and with a thick, heterogeneous tissue density (30 HU) periphery, which was very mildly and diffusely mineralized. This peripheral capsule was poorly enhanced by the contrast medium (30-40 HU). The mass displaced both kidneys caudally and to the left, the stomach laterally to the left, the duodenum ventrally and medially, and the portal vein ventrally and to the left. The mass was continuous with the parenchyma of the right liver and caused deviation of the intrahepatic portal vasculature.
The caudal vena cava was displaced dorsally and to the left. It was severely compressed and partially surrounded by the lesion. Although invasion of the venous wall was difficult to confirm, a focal, commashaped tissue density filling defect extended from the mass into the lumen of the caudal vena cava (Figures  3 and 4). The vein was moderately dilated caudal to the mass and barely visible immediately cranial to it. A hypoattenuating filling defect was also visible in the center of the portal vein lumen on postcontrast examinations. Two smaller cavitary nodules (measuring 3 mm and 7 mm, respectively), bearing the same appearance, were noted in the otherwise normal liver parenchyma. Hepatic, gastric and pancreaticoduodenal lymph nodes were moderately enlarged (8-10 mm). No peritoneal effusion was detected. The other abdominal structures were within normal limits. CT examination of the thorax revealed multiple, 3 to 7 mm-diameter nodules, distributed throughout the lung field, mostly in the periphery of the lobes ( Figure  5). The pleural and mediastinal structures were within normal limits. Mediastinal and sternal lymph nodes were moderately enlarged (10 mm).
These features were consistent with a voluminous, locally aggressive cavitary hepatic mass lesion, with a high suspicion of invasion of the caudal vena cava and secondary thrombosis within the portal vein. Hepatic and pulmonary nodules and lymphadenopathy were identified. Based on these findings, including local aggressiveness and distant nodular lesions, a malignant neoplasm was considered most likely. The differential diagnoses included histiocytic sarcoma, hemangiosarcoma or, considering the young age of the dog, juvenile hepatocellular carcinoma. All these differentials were associated with a poor prognosis.
The owners declined surgical treatment, considering the high risks involved with surgical removal of the mass, vascular implication and also the additional suspected parasitic masses in the liver and lungs. Medical treatment was therefore implemented, based on the daily oral administration of albendazole (Zentel 400 ® , GlaxoSmithKline) 10 mg/kg SID for life. Most of the fluid filling the main hepatic cavitary mass was aspirated in order to decrease abdominal pressure.
Considering the zoonotic risks associated with echinococcosis, a coproscopic examination was performed to ensure that the dog was not excreting any eggs, as this would have represented a significant threat to the owner's health. No Echinococcus sp. eggs were found.
The dog was re-examined eight months after the  initial presentation. She was presenting recurrence of abdominal distension, which, according to the owner, had progressively appeared. However, she was not lethargic and the owner reported that her behavior was normal and that there were no clinical signs. Followup CT examination was performed. The main hepatic cavitary mass had regained a volume similar to that in the initial scan (before complete aspiration of the fluid). The two smaller hepatic cavitary nodules had similar dimensions as previously. Pulmonary nodules were still present and yielded a similar size. Invasion of the caudal vena cava was more prominent and extended into the hepatic veins, to the point that the vena cava was barely visible within and cranial to the mass. Collateral drainage of the caudal portion of the caudal vena cava had developed via the deep circonflex iliac veins and dorsal subcutaneous veins, anastomosing with vertebral veins and the right azygos vein which appeared dilated. The cranial part of the liver still drained into the thoracic part of the caudal vena cava. The fluid inside the largest cavitary hepatic mass was again aspirated in order to decrease abdominal pressure. The medical treatment was continued, as follow-up biochemistry and hemograms were within normal ranges (especially no neutropenia). The dog remained clinically stable for ten months after diagnosis. Unfortunately, she had to be euthanized, as her owners were moving back to Great-Britain, where she could no longer be legally imported. Necropsy was declined by the owners.

DISCUSSION
Echinococcus multilocularis is a small, zoonotic, tapeworm that occurs in central Europe, in much of northern, central and eastern Eurasia and parts of North America (Moro et al., 2009). In North America, some authors have reported an increasing incidence of clinical echinococcosis in recent years (Peregrine et al., 2015). Adult parasites reside within the small intestine of definitive hosts, which primarily include wild canids (foxes, coyotes, wolves) and domestic dogs. Intestinal infection in the definitive hosts is usually asymptomatic. Following the ingestion of eggs by an intermediate host, most commonly arvicolidae but also occasionally other mammals including canids or man, the larval stage of the parasite (oncosphere) hatches, migrates to the liver and develops into alveolar echinococcosis (Oscos-Snowball et al., 2015). This larval stage of the parasite undergoes exogenous budding and behaves like an invasive tumor (Moro et al., 2009).
The dog regularly travelled with her owners between the United Kingdom and France and was as  such regularly given prophylactic medication with milbemycin oxime and praziquantel (Milbemax ® , Novartis, Switzerland). Although it cannot be ascertained where the dog had been infected, no known domestically acquired E. multilocularis infection in the United-Kingdom has been recorded (official U.K. government website, updated March 2019), but the French Alps are an endemic region (Umhang et al., 2017). It is therefore most likely that the dog became infected in France. The milbemycin oxime and praziquantel combination is not effective against the cyst stage forms of Echinococcus spp. and has no persistent activity (according to the summary of product characteristics), which may explain why the dog could develop larval disease.
The dog presented in this case report was a young (two-year-old) adult. Although there have only been very few cases reported in domestic dogs (Geisel et al.,1990;Haller et al., 1998) (Scharf et al., 2004;Heier et al., 2007;Peregrine et al., 2012;Pezelet et al., 2013 ;Gendron et al., 2015;Oscos-Snowball et al., 2015;Caron et al., 2017;Gwada et al., 2018), it seems that the condition mostly affects young adults (with the exception of an eleven-year-old, female Siberian Husky in Slovakia (Antolova et al., 2018). It is unclear whether this is due to immune pathophysiological considerations, behavioral patterns in younger dogs or to other causes. A possible bias may be a lack of further (microscopic) investigations performed in older dogs, in which the diagnosis of metastasized malignancy would have been presumed more easily. In one case report, in which a bitch was diagnosed with alveolar echinococcosis in the postpartum period, the authors suggested that gestation might have led to the progression of the disease (Gwada et al., 2018).
In the dog presented in this report, a large, cavitary hepatic mass was identified along with two additional, smaller nodules, both of which had a similar appearance. In a retrospective study of canine alveolar echinococcosis in eleven dogs by Scharf et al., (2004), all animals presented with a large liver mass on radiographs, 5/11 showing multifocal mineral opacities. CT examination was only performed in one dog in that study and yielded a large cavitary lesion with no contrast enhancement of the wall. This absence of contrast enhancement of the wall could have led the authors to consider a benign (including parasitic) lesion rather than a malignant liver tumor, despite local aggressiveness and distant lesions. The wall was partially mineralized, a feature considered typical of echinococcosis in children (Pohnan et al., 2017). In all the reported cases in the veterinary literature (Geisel et al., 1990;Deplazes et al., 2001;Scharf et al., 2004;Peregrine et al., 2012;Geigy et al., 2013;Gwada et al., 2018;Antolova et al., 2018), the most common ultrasonographic feature was a large cavitary mass within the liver. Color-flow Doppler imaging showed no visible blood flow within the lesion. In one case, a voluminous peritoneal effusion was detected, which was not the case in the dog presented here (Gendron et al., 2015).
Although the present case shares many similarities with previously described alveolar echinococcosis liver lesions in dogs, only one other reported dog presented with metastatic spread to the lungs and signs of local aggressiveness (especially invasion of the caudal vena cava) (Gendron et al., 2015). These tomodensitometric features initially led to an erroneous diagnosis of malignant neoplasia in the present case. It is unclear whether invasion of the vena cava represented granulomatous invasion of the local vasculature draining into the caudal vena cava, possibly with secondary thrombus formation, or whether thrombus formation was due to focal compression, turbulent blood flow or coagulation disorder (coagulation tests were not performed).
Confusion between alveolar echinococcosis disease and neoplasia appears to be a major challenge in human medicine, in which alveolar echinococcosis may not be spontaneously included in the differential diagnoses in geographical areas where the disease is uncommon (Atanasov et al., 2013;Bansal et al., 2018). In a recent case report, hepatic E. multilocularis infection with pulmonary nodules was misdiagnosed as a cholangiocarcinoma with lung metastases in a 38-year-old woman from the Czech Republic living in Germany (Pohnan et al., 2017). The pulmonary nodules were resected and partial hepatectomy was performed. Histopathological examination revealed the presence of parasitic structures, subsequently identified as the larval stage of E. multilocularis in both liver and lungs.
In the only other reported dog with pulmonary metastatic nodules, the presence of the parasite was confirmed at necropsy (Gendron et al., 2015). In the present case, pulmonary nodules, in the absence of necropsy, could not be confirmed as parasitic granulomas. However, the peripheral distribution of those nodules in the pulmonary lung fields in combination with the confirmed hepatic E. multilocularis infection were highly suggestive of parasitic lung lesions.
Surgical treatment is usually recommended to treat liver echinococcosis in humans (Pohnan et al., 2017). In the present case, considering the risks due to the dimensions of the mass, the involvement of the caudal vena cava, and multifocal spread, the owners declined surgery. Medical treatment based on the daily administration of albendazole was therefore opted for, as based on previous recommendations and case reports (Haller et al., 1998;Caron et al., 2017). The most serious adverse effect associated with prolonged albendazole treatment in dogs is reversible bone marrow hypoplasia. This has been described to cause neutropenia (Meyer et al., 1998). However, this was not observed in the present case. The dog was found to be clinically stable after ten months of treatment.
While the metacestode stage in dogs does not theoretically carry an infectious risk for humans (De-plazes et al., 2001;Rinaldi et al., 2014), both owner and dog might have been exposed to E. multilocularis eggs. Furthermore, dogs with alveolar echinococcosis may also harbor adult cestodes in their intestines. Eggs shed in their feces may be immediately infective for humans, who are at risk of developing alveolar echinococcosis (Deplazes et al., 2001). Considering the severity of the disease in humans and the potential therapeutic challenge, echinococcosis should be included in the differential diagnosis of cavitary liver nodules in dogs. Whenever there is a potential doubt as to the possibility of echinococcosis infection, coproscopic examination may be recommended to rule out a potential risk for the owners. In this dog, coproscopic examination was negative. Considering that coproscopic examination does not yield a 100% sensitivity, the dog was given milbemycin oxime and praziquantel tablets (Milbemax ® , Novartis) every three months.

CONCLUSION
To the author's knowledge, this is the first report of canine vesicular Echinococcus sp. lesions medically managed for up to ten months. This shows that medical management may be a viable option when surgery cannot be envisaged, as was the case here due to vascular invasion and pulmonary metastases.
The authors suggest that echinococcosis should be included in the differential diagnosis of cavitary liver masses, even in the presence of lung nodules and local aggressiveness, such as vascular invasion, particularly in young dogs in endemic regions. Cytological and histological examinations are useful to confirm Echinococcus sp. infection and allow differentiation from malignant hepatic tumor. This is of particular importance, considering the potential health risk for the owners.