The initial stage of alveolar echinococcosis is a diagnostic challenge: a case report

Abstract

Background: Alveolar echinococcosis is a rare, potentially fatal parasitosis with the main manifestation site in the liver. Diagnosis already in the initial stage of the disease is important to prevent further exacerbation and possible secondary complications by early targeted therapy. Identifying alveolar echinococcosis lesions on imaging can be difficult, and making the diagnosis can be an interdisciplinary challenge, even in a specialized center.

Case presentation: In a clinically symptom-free 65-year-old white female patient with type 2 diabetes mellitus, an abdominal ultrasonography performed by a colleague in private practice revealed three small hepatic nodules as incidental findings. Further workup focused primarily on the differential diagnosis of hepatic metastatic malignancy. Therefore, a sonographically guided biopsy of the liver lesions was performed under inpatient conditions. During the control sonography routinely performed after the biopsy to exclude postinterventional hemorrhage, an examiner previously uninvolved in the case noticed the typical sonomorphology of initial alveolar echinococcosis lesions in view of the biopsied nodules. The specimens that had been collected peripherally from the target lesion under the primary assumption of metastases histopathologically showed no signs of malignancy and no other landmark findings. Follow-up staining of the biopsies with regard to the recently suspected diagnosis of alveolar echinococcosis, however, remained without a target result as well. Due to the typical sonomorphology, a further biopsy was performed. During rebiopsy, the target lesion was deliberately biopsied centrally to hit the presumed annular lamellar body localized there in alveolar echinococcosis. On the basis of the samples of the second biopsy, the diagnosis of alveolar echinococcosis in the initial stage could be confirmed histopathologically, and the patient was transferred to adequate therapy.

Conclusion: One of the most important differential diagnoses of hepatic alveolar echinococcosis in the initial stage is liver metastases. Knowledge of the typical sonomorphology is essential to avoid misdiagnosis. In addition, proper localization of specimen collection within an alveolar echinococcosis initial lesion is critical to enable histopathologic diagnosis. Imaging and pathology are directly complementary, and imaging can point the way to the correct histopathologic diagnosis on the basis of lesion morphology. For this, knowledge of the specifics of alveolar echinococcosis in imaging and histomorphology is necessary to integratively combine the findings.

Keywords: Alveolar echinococcosis; Evolution model; Histopathology; Imaging diagnostics; Initial stage.

Fig. 1

“Intermodal evolution model of hepatic AE” according to Graeter et al.. Five stages are distinguished: “Initial stage”, “Progressive stage”, “Advanced stage”, “Transitional stage”, “Regressive stage”. A further criterion for the assessment of AE lesions that is for overview reasons not listed in this general intermodal evolution model but should be considered in addition, is the specific calcification pattern. The calcification pattern can be determined by CT and is accordingly listed in the AEUC as an independent pillar of the CT classification scheme. Figure modified, based on publication [37]

Fig. 2

Initial contrast-enhanced computed tomography of the abdomen in venous phase with the main finding of three small, hypodense round lesions in the right liver lobe in segments VIII (a) and VI (b,c), designated as primary metastatic. The arrows point to the lesions

Fig. 3

Presentation of the biopsied alveolar echinococcosis lesion in liver segment VI in different imaging modalities and in the course of ultrasound-guided biopsies (a-i): contrast-enhanced ultrasound (a); first ultrasound-guided, peripherial biopsy (b); B-mode ultrasound (c); planning the puncture route for the second biopsy using color Doppler imaging (d); second ultrasound-guided, central biopsy (e); computed tomography in venous phase (f); positron emission tomography–computed tomography (g); T1-weighted magnetic resonance imaging post-gadobutrol (h); T2-weighted magnetic resonance imaging (i). The arrows point to the lesion

Fig. 4

Histological and immunohistological (antibody EM2G11) analyses of the liver biopsies (a-d) The first biopsy was acquired from the lesion periphery (a,b). It yielded no evidence for malignancy and it was negative for E. multilocularis. In the hematoxylin–eosin staining, only a lymphocytic infiltrate was observed in the liver tissue at the border of a solid necrosis area (arrowheads (a)). An immunohistochemical staining with the alveolar echinococcosis-specific monoclonal antibody EM2G11 was negative (arrowheads—border of the lesion (b)). The second biopsy was taken as a radial section from the margin to the center of the lesion and showed extensive coagulation necrosis surrounded by vigorous chronic lymphocytic inflammation with few eosinophilic granulocyte content (c,d). The different zones correspond to the schematic lesion structure in Fig. 5. The hematoxylin–eosin staining revealed a fragment of the laminate layer in the central part of the biopsy (arrow (c)). Immunohistochemical staining with the antibody EM2G11 showed labeling of the lamellar structures and confirmed a larval-stage E. multilocularis infection (arrow (d)). Spems were only recorded at a single location in the outer part of the solid necrosis near the lesion boundary at the transition to the inflammation zone (star (d))

Fig. 5

Schematic representation of an alveolar echinococcosis initial lesion. The dashed rectangle corresponds to the area of a radial biopsy. The zones shown schematically can be found in the histological preparation of the second biopsy in Fig. 4c,d