CASE 14624 Published on 08.06.2017

Improved characterisation of cystic liver echinococcosis by MRI

Section

Abdominal imaging

Case Type

Clinical Cases

Authors

Tonolini Massimo, MD.

"Luigi Sacco" University Hospital,
Radiology Department;
Via G.B. Grassi 74
20157 Milan, Italy; E
mail:mtonolini@sirm.org
Patient

29 years, female

Categories
Area of Interest Liver ; Imaging Technique CT, MR, Ultrasound
Clinical History
Young woman with unremarkable medical history, recently returned to her European native country after a two-years stay in South America. Complained of nausea, vomiting, upper abdominal pain with epigastric tenderness, low-grade fever.
Laboratory abnormalities included increased liver enzymes (aspartate aminotransferase 480 U/l, alanine aminotransferase 400 U/l), serum bilirubin 2.5 mg/dl.
Imaging Findings
Ultrasound (Fig. 1) detected a 7-cm well-demarcated inhomogeneous ovoid lesion in the right liver lobe, with thin regular wall, mostly echogenic at the periphery with central hypo-anechoic portion.
Further investigation with CT (Fig. 2) could not clarify the sonographic finding: the liver mass showed peripherally solid attenuation with lobulated contours, central hypodensity (15-18 Hounsfield Units), without calcifications and contrast enhancement on dynamic study.
Considering the unremarkable acute phase reactants, diagnostic percutaneous biopsy was being considered.
Meanwhile, MRI (Fig. 3) showed some additional features, such as thin regular hypointense wall, peripherally arranged components with low-to-intermediate T2-weighted signal intensity and central fluid-like matrix with serpiginous "canalicular" appearance of alternating signal intensities, which suggested radiologists the possibility of a parasitic aetiology.
Serology and Western blot analysis confirmed cystic echinococcosis (CE): since imaging findings were consistent with inactive stage CE4 according to the WHO classification (Fig. 4), aspiration and therapy were obviated.
Discussion
Cystic echinococcosis (CE) is a characteristic zoonosis caused by Echinococcus granulosus, which is endemic in the Mediterranean region, Middle East, Australia, parts of Africa and South America. Parasites live in the bowel of definitive canine hosts, and their eggs excreted in the faeces become ingested by intermediate hosts, particularly sheep. When humans acquire infestation through dogs, contaminated water or vegetables, larvae cross the jejunal mucosa, enter the portal system and reach the liver which is involved in most (75%) patients, usually in the right lobe. Albeit endemic in rural areas, CHD is nowadays encountered globally due to migrations [1].
The CE structure includes three layers: a) the outer protective pericyst represents the host’s protective response, composed of modified fibroblasts and inflammatory cells; b) the middle acellular laminated membrane; and c) the thin inner germinal layer where scolices (infectious embryonic parasites) are produced. Cysts contain strongly antigenic clear fluid. Since hepatic CE is usually asymptomatic, imaging plays the key role in diagnosis and staging, with ultrasound as the first-line investigation; serological tests have a confirmatory role but common false negative results. Sonographic appearances vary depending on natural history, from purely cystic to solid-appearing pseudotumors. Evolved from the classical Gharbi classification, the WHO Informal Working Group system (Table in Fig. 4) currently represents the standardized staging approach, differentiates active cysts (containing viable protoscolices) from transitional forms (with altered cyst structure either by host response or therapy), and inactive degenerated CE, to choose between watchful waiting, antiparasitic drugs, percutaneous treatment or surgery [2-4].
When ultrasound is limited by patient characteristics, CT is often performed in patients with indeterminate cystic lesions; unfortunately, compared to the sonographic reference standard, CT poorly shows key structural details such as membranes and daughter cysts, therefore cannot correctly classify most CE stages before development of calcifications [5-7].
Conversely, albeit limited in the detection of calcifications, MRI reproduces CE-defining sonographic features with superior contrast resolution compared to CT, without radiation and contrast medium, and is warranted in sonographically and clinically indeterminate cystic lesions where CE can be hypothesized, to obviate aspiration. Heavily T2-weighted sequences easily show the collagen-rich hypointense rim which allows differentiation from nonparasitic cysts, the detached laminated membrane (“water-lily sign”), the peripherally arranged daughter cysts, the T1-hypointense - markedly T2-hyperintense hydatid matrix. As in this patient, CE4 lesions are most difficult to interpret, unless the characteristic subtle “canalicular structure” is appreciated at sonography or MRI as thin serpiginous bands of alternating echogenicity or signal intensities [5-7].
Differential Diagnosis List
WHO-IWGE stage 4 cystic echinococcosis of the liver
Congenital cyst
Amoebiasis
Liver abscess
Cystadenoma
Necrotic tumour or metastasis
Final Diagnosis
WHO-IWGE stage 4 cystic echinococcosis of the liver
Case information
URL: https://eurorad.org/case/14624
DOI: 10.1594/EURORAD/CASE.14624
ISSN: 1563-4086
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