DOI: 10.1148/rg.243035173
RadioGraphics 2004;24:861-865
© RSNA, 2004
Echinococcal Cyst1
Stefania Proietti, MD,
Amina Abdelmoumene, MD,
Muriel Genevay, MD and
Alban Denys, MD
1 From the Departments of Radiology (S.P., A.A., A.D.) and Pathology (M.G.), Centre Hospitalier Universitaire Vaudois, Lausanne, Switzerland. Received July 28, 2003; revision requested August 28 and received October 8; accepted November 7. Address correspondence to S.P., Department of Radiology, Prof Grenier University Hospital, La Pitié-Salpetrière, 105 boulevard de l’Hôpital, 75013 Paris, France (e-mail: sproietti@hotmail.com).
Index Terms: Echinococcosis, 761.2083 • Liver, cysts, 761.312 • Liver, echinococcosis, 761.2083 • Parasites, 761.2083
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History
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A 42-year-old Portuguese woman had a several months history of abdominal bloating and recent occasional pain in the right upper abdomen. In Portugal, she had lived in a rural area; she had left Portugal several years ago but returned every summer. Her medical history was relevant for 10 years of corticoid therapy for lupus erythematosus.
Physical examination showed upper abdominal tenderness and a palpable mass in the right upper abdomen. Laboratory data showed normal glutamic oxaloacetic transaminase and glutamic pyruvic transaminase activities and slightly elevated alkaline phosphatase levels. Tests for tumor markers were negative. A parasitologic serologic test (enzyme-linked immunosorbent assay) was positive for Echinococcus granulosus (level, 60 U/mL; normal level, <0.9 U/mL).
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Imaging Findings
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A right-sided hepatic mass was seen at ultrasound (US), computed tomography (CT), and magnetic resonance (MR) imaging. US revealed a multilocular anechoic cystic lesion made up of cysts that ranged from 0.2 to 12 mm in diameter. The mass involved a major part of the hepatic parenchyma. Biliary and vascular structures were displaced but not involved.
Abdominal CT performed before and after intravenous administration of contrast material demonstrated a multilocular hypoattenuating mass (16 x 9 x 12 cm) in segments IV, VII, and VIII (Fig 1). Before injection, CT demonstrated thin eggshell calcifications within septa. Segment II and III bile ducts were dilated. After injection, the mass showed slight enhancement of the septa. The left portal vein was displaced. Multiple nodules located in the right subhepatic space appeared to be subserosal because of the mass effect they produced on the adjacent liver parenchyma (Fig 1). No segmental atrophy was observed.
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Figure 1a. (a) Abdominal CT scan obtained before administration of contrast material shows a large multilocular mass in the liver. The mass consists of multiple small hypoattenuating cysts. Thin eggshell calcifications can be seen within the cyst walls (arrows). The bile ducts of segments II and III are dilated. (b) Abdominal CT scan obtained after administration of contrast material shows the mass. Multiple cysts are seen in the right subhepatic space (arrow). They appear to be subserosal because of the mass effect they produce on the adjacent hepatic parenchyma.
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Figure 1b. (a) Abdominal CT scan obtained before administration of contrast material shows a large multilocular mass in the liver. The mass consists of multiple small hypoattenuating cysts. Thin eggshell calcifications can be seen within the cyst walls (arrows). The bile ducts of segments II and III are dilated. (b) Abdominal CT scan obtained after administration of contrast material shows the mass. Multiple cysts are seen in the right subhepatic space (arrow). They appear to be subserosal because of the mass effect they produce on the adjacent hepatic parenchyma.
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MR imaging demonstrated a well-defined, smooth, thin-walled, multilocular cystic mass involving segments IV, VII, and VIII. The cysts appeared hypointense on T1-weighted images (Fig 2a) and markedly hyperintense on T2-weighted images (Fig 2b). Coronal T2-weighted images demonstrated perihepatic and extrahepatic extension under the right hemidiaphragm and along the gastrohepatic ligament, respectively. MR cholangiopancreatography did not demonstrate communication between the cysts and biliary tree but did show compression of the left lobar ducts.
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Figure 2a. (a) Axial T1-weighted MR image shows the mass, which is well defined, smooth, thin walled, multilocular, and cystic and involves segments IV, VII, and VIII. The cysts are hypointense. (b) Axial T2-weighted MR image shows extrahepatic cysts along the gastrohepatic ligament (arrow). The cysts are hyperintense.
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Figure 2b. (a) Axial T1-weighted MR image shows the mass, which is well defined, smooth, thin walled, multilocular, and cystic and involves segments IV, VII, and VIII. The cysts are hypointense. (b) Axial T2-weighted MR image shows extrahepatic cysts along the gastrohepatic ligament (arrow). The cysts are hyperintense.
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These imaging findings were consistent with the following differential diagnosis: alveolar echinococcosis and biliary cystadenocarcinoma.
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Pathologic Evaluation
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A polymerase chain reaction performed on a laparoscopic biopsy specimen revealed the DNA of Echinococcus multilocularis. At laparotomy, multiple cystic lesions were observed on the peritoneal surface, principally in the submesocolic area. In concordance with the radiologic assessment, the hepatic lesion invaded segments IV, VII, and VIII of the liver. Cystic lesions also involved the main portal vein and the hepatic artery.
The right hepatic mass was removed by a central hepatectomy that included segments IV, VII, and VIII. It measured 18 cm in greatest dimension and had an alveolar structure composed of numerous irregular cysts varying from 0.5 to 1.5 cm in diameter (Fig 3). The cyst walls were transparent or yellowish and less than 2 mm thick (Fig 4). The peritoneal cystic lesions demonstrated exactly the same morphology. The peritoneal nodules could not be removed completely. The biliary structures and main portal veins were not involved by the mass.
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Figure 4. Photograph of the bisected mass shows good correlation with the US and CT appearances. The lesion has an alveolar structure composed of numerous irregular cysts. Note the focal calcifications (arrows).
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Histopathologic examination of the hepatic mass showed E multilocularis metacestodes, thus demonstrating alveolar echinococcosis. Histologic examination revealed a three-layer cyst wall, typical of hydatid disease cysts (Figs 5, 6). The inner (germinal) layer possessed nuclei. The second layer (laminated membrane) was eosinophilic, amorphous, and avascular. The third (adventitial) layer was rich in inflammatory cells. Most of the cysts contained numerous protoscolices and daughter cysts (Fig 7). Some of them were calcified, as shown on the CT images. Around these lesions, an abundant granulomatous (foreign body–type) reaction was present in the hepatic parenchyma.
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Figure 5. Photomicrograph (original magnification, x4; hematoxylin-eosin stain) shows the infiltrative border between the lesion and the adjacent hepatic parenchyma (arrow). This appearance is unlike that of lesions due to E granulosus.
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Figure 6. Photomicrograph (original magnification, x10; hematoxylin-eosin stain) shows multiple cysts separated by dense, hyaline, fibrous tissue. Note the laminated membrane in the inner part of the cysts (arrows), which is avascular, refractile, and chitinous.
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Figure 7. Photomicrograph (original magnification, x20; hematoxylin-eosin stain) shows the contents of the cysts. Multiple protoscolices of E multilocularis (arrows) are seen within daughter cysts.
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The radiologic, intraoperative, and histopathologic findings were all consistent with alveolar echinococcosis, despite the presence of numerous protoscolices, an atypical feature for this disease (<10% of cases) (1).
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Discussion
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Hepatic alveolar echinococcosis is a rare parasitic disease caused by E multilocularis that is endemic in central and northern Europe (south Germany, Switzerland, Austria, and eastern France), northern Asia, Japan, China, Turkey, and parts of North America. Its development typically requires a sylvatic cycle involving wild canids as a definitive host (rarely domestic dogs and cats) and various species of rodent as a natural intermediate host. The adult worm lives in the proximal small intestine of the definitive host, especially red foxes. The intermediate host acquires the infection by ingesting wild berries or water soiled by the parasite’s eggs, which are released in the feces of infected foxes. The host’s digestive secretions destroy the egg wall, and the resulting embryo penetrates the host’s intestinal wall and reaches the liver by the portal or lymphatic system, where the larvae will develop indefinitely. An aberrant intermediate host, such as a human, exhibits a slowly progressive life-threatening tumorlike growth in the liver, delaying the diagnosis for several years (2).
According to the natural history, the liver is the most common location (95% of cases), but many other organs may be involved. By secondary hematogenous dissemination, the process may reach any other organ such as the adrenal gland, lung (10%), and brain. The process may also spread contiguously to adjacent organs by direct extension (3).
Although more sporadic than the hydatid form caused by E granulosus, the alveolar form is relevant because of its infiltrating masslike growth (2). The hydatid form appears as a benignlike mass, and the alveolar form appears as a slowly developing malignantlike mass. A cystic component is more common in the hydatid form, which is also called cystic echinococcosis.
The typical macroscopic appearance is an infiltrating mass composed of multiple small cysts (4). The external germinal membrane explains the commonly irregular margins. The mass usually consists of fibrosis and calcifications. The liver parenchyma near the mass is typically atrophic with capsular retraction due to biliary or vascular invasion. In our case, the appearance was actually not characteristic of alveolar echinococcosis, since we did not observe any fibrosis or adjacent liver atrophy. The absence of fibrosis may be explained by the corticoid therapy that the patient had been taking for several years because of lupus erythematosus.
Because the clinical presentation is nonspecific, diagnosis relies predominantly on imaging, serologic, and pathologic findings. Serologic testing for E multilocularis is based on the detection of a specific antibody response by using an enzyme-linked immunosorbent assay with a possible cross-reaction for E granulosus (5). Polymerase chain reaction technology is now widely used because it is more specific and does not involve cross-reactions.
Imaging procedures are essential in diagnosis and evaluation of the extent of the disease. US is the screening method of choice (6). Typical findings include an amorphous, heterogeneous, hyperechoic mass sometimes associated with hypoechoic, irregular, central areas of pseudo–liquid necrosis. The reactional fibrotic tissue appears hyperechoic. Many lesions contain irregular calcifications, which may be nodular or "en plaque." Signs of vascular or biliary invasion may be demonstrated (6).
CT is always performed because it has a high sensitivity (94%). It is an important preoperative tool to determine vascular, biliary, or extrahepatic extension and therefore to determine resectability (4,7). Classically, CT demonstrates an infiltrating tumorlike hepatic mass with irregular margins and a calcified or cystic component. The fibroparasitic component may enhance a little, in contrast to the necrotic areas, which appear hypoattenuating. The cysts are classically rarely identified (4).
In uncertain cases, MR imaging may be performed to confirm the hypothesis and visualize the lesion in different planes. It is the best imaging procedure to demonstrate a cystic component. It helps establish vascular or biliary tree involvement as well as extrahepatic extension. Usually described as an ill-defined partially solid and partially cystic lesion, the appearance of alveolar echinococcosis at MR imaging was recently categorized into five types by Kodama et al (8). Multiple small cysts without a solid component are type 1 (4%), a solid component associated with small cysts is type 2 (40%), a solid component associated with irregular large cysts is type 3 (46%), a solid component with no cysts is type 4 (4%), and a large cyst without a solid component is type 5 (6%). According to this classification, our case would correspond to type 1.
Alveolar echinococcosis is reported to exhibit variable signal intensities on T1- and T2-weighted images and to demonstrate slight enhancement on gadolinium-enhanced images (8,9). The cystic, necrotic, and fibrotic component appears hypointense compared with the liver parenchyma on T1-weighted images. T2-weighted images are useful to detect small cysts and, as in our case, to localize extrahepatic cysts (8,9).
The differential diagnoses on the basis of the imaging findings were biliary cystadenoma and biliary cystadenocarcinoma. These entities are described as well-defined unilocular or multilocular masses associated with nodules or papillary projections. Calcifications may be present in the cyst walls (10). The serologic and pathologic findings led to our diagnosis.
Surgery is the treatment of choice and is combined with parasitostatic chemotherapy involving use of benzimidazole carbamate derivates, such as albendazole and mebendazole. Various types of hepatectomy have been performed; when localization of the liver precludes liver resection, liver transplantation can be proposed (4).
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References
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- Saul SH. Masses of the liver. In: Sternberg SS, eds. Diagnostic surgical pathology. 3rd ed. Philadelphia, Pa: Lippincott Williams & Wilkins, 1999; 1553-1628.
- Eckert J, Conraths FJ, Tackmann K. Echinococcosis: an emerging or re-emerging zoonosis? Int J Parasitol 2000; 30:1283-1294.[CrossRef][Medline]
- Tuzun M, Hekimoglu B. Various locations of cystic and alveolar hydatid disease: CT appearances. J Comput Assist Tomogr 2001; 25:81-87.[CrossRef][Medline]
- Bresson-Hadni S, Vuitton DA, Bartholomot B, et al. A twenty-year history of alveolar echinococcosis: analysis of a series of 117 patients from eastern France. Eur J Gastroenterol Hepatol 2000; 12:327-336.[Medline]
- Ito A. Serologic and molecular diagnosis of zoonotic larval cestode infections. Parasitol Int 2002; 51:221-235.[CrossRef][Medline]
- Macpherson CN, Milner R. Performance characteristics and quality control of community based ultrasound surveys for cystic and alveolar echinococcosis. Acta Trop 2003; 85:203-209.[CrossRef][Medline]
- Reuter S, Nussle K, Kolokythas O, et al. Alveolar liver echinococcosis: a comparative study of three imaging techniques. Infection 2001; 29:119-125.[CrossRef][Medline]
- Kodama Y, Fujita N, Shimizu T, et al. Alveolar echinococcosis: MR findings in the liver. Radiology 2003; 228:172-177.[Abstract/Free Full Text]
- Balci NC, Tunaci A, Semelka RC, et al. Hepatic alveolar echinococcosis: MRI findings. Magn Reson Imaging 2000; 18:537-541.[CrossRef][Medline]
- Buetow PC, Buck JL, Pantongrag-Brown L, et al. Biliary cystadenoma and cystadenocarcinoma: clinical-imaging-pathologic correlations with emphasis on the importance of ovarian stroma. Radiology 1995; 196:805-810.[Abstract/Free Full Text]
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History
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