Ultrasound Diagnostics in Alveolar Echinococcosis: An Update

Abstract

Background: Alveolar echinococcosis (AE) is a rare, potentially fatal zoonosis. In recent years, imaging diagnostics have become increasingly important compared to serologic diagnostics in AE. We will provide an overview of the importance of ultrasound diagnostics in AE in the detection of the disease and its significance in follow-up, as well as the typical sonographic presentation patterns and pitfalls.

Summary: The use of the ultrasound classification developed by us and the use of contrast-enhanced ultrasound (CEUS) helps make the diagnosis faster and better. Without CEUS, the hemangioma-like pattern and the metastasis-like pattern in particular cannot be diagnosed with certainty. The limitations of ultrasound diagnostics on the patient side, in terms of examiner experience and equipment, remain.

Key messages: Ultrasound is an important procedure in the detection and follow-up of AE. Contrast-enhanced sonography is indispensable. Fundamental limitations of ultrasound diagnostics such as examiner experience remain.

Keywords: Alveolar echinococcosis; Contrast-enhanced ultrasound; Review article; Ultrasound; Ultrasound classification.

Fig. 1.

Ultrasound classification of alveolar echinococcosis. a Storm and hail pattern: the typical hailstorm appearance is characterized by indistinct, irregular boundaries, nonhomogeneous pattern and hyperechoic formations. b Pseudocystic pattern: pseudocystic alveolar echinococcosis lesions are primarily characterized by an hyperechoic, irregular, and nonhomogeneous rim that is non-vascularized at power Doppler and color-coded duplex ultrasonography. It may appear to be >10 mm in thickness. There is a hypo- or anechoic, often nonhomogeneous central zone that may contain hyperechoic material. c Ossification pattern: the ossification pattern presents with solitary or grouped, mostly sharply delineated lesions with dorsal acoustic shadow. Very large ossification-type AE lesions represent a rarity. Both uni- and multifocal involvement is possible. d Hemangioma-like pattern: sonomorphologically, the lesions present as a relatively clearly demarcated nonhomogeneous tumor that appears hyperechoic in comparison with the surrounding hepatic parenchyma. Echogenicity ranges from slightly and nonhomogeneously hyperechoic to strongly and homogeneous hyperechoic. e Metastasis-like pattern: mostly hypoechoic, these lesions exhibit as a typical characteristic-compared to typical hepatic metastases (e.g., of colorectal cancer)-the absence of the halo phenomenon. Instead, there is a central, hyperechoic, nonhomogeneous scar.

Fig. 2.

Example of histologically confirmed E. multilocularis liver masses that are not classifiable according to the EMUC ultrasound classification.

Fig. 3.

a True hemangioma in B scan. c, d Typical contrast behavior of a true hemangioma with nodular ring enhancement in the arterial phase (b) complete iris diaphragm phenomenon and markedly more echogenic presentation of the hemangioma compared to the adjacent liver tissue in the late phase after administration of 1.6 mL SonoVue.

Fig. 4.

a Image of a hemangioma-like pattern in alveolar echinococcosis. b In contrast to a true hemangioma, contrast-enhanced ultrasound after administration of 1.6 mL SonoVue shows only rim enhancement in the arterial phase. In the portal venous phase (c) and in the late phase (d), the echinococcus lesion does not absorb any contrast medium and thus shows a typical “black hole sign.”

Fig. 5.

Contrast-enhanced ultrasound of a histologically confirmed metastasis in breast carcinoma of the liver after administration of 1.6 mL SonoVue. a In the B scan, the mass is echogenic with a halo phenomenon. In the arterial phase (b), chaotic contrast uptake and a clear wash-out phenomenon in the portal venous (c) and late phase (d). The lesion is never echogenic in the sense of a “black hole sign” in AE during the entire contrast medium phase, as shown below.

Fig. 6.

Contrast-enhanced ultrasound of a histologically confirmed mass of the metastatic pattern of hepatic AE after administration of 1.6 mL SonoVue. In the B scan (a), the mass cannot be differentiated from a true metastasis. During the entire contrast medium phase, the lesion does not absorb any contrast medium in the arterial, portal venous and late phases in the sense of a “black hole sign” (b–d).

Fig. 7.

A change in pattern was seen exclusively for AE lesions initially classified as hemangioma-like or pseudocystic. A total of 70% (7/10) of AE lesions initially classified as hemangioma-like showed a relevant change in pattern over time, and 85.7% (6/7) of these were secondarily classified as having a hailstorm pattern, with the remainder (1/7; 14.3%) classified as having a pseudocystic pattern. A total of 22.2% (2/9) of AE lesions initially classified as pseudocystic showed a relevant change in pattern over time and were classified as having a hailstorm pattern.