Cardiac Hydatidosis Presenting as Complete Atrioventricular Block: Multimodality Imaging Diagnosis Despite Conflicting Serology — A Case Report

Background Cardiac echinococcosis accounts for fewer than 2% of Echinococcus granulosus cases but can cause life-threatening conduction disturbances. Serological sensitivity in cardiac involvement may fall to around 50% and may be even lower in calcified lesions, making multimodal imaging the diagnostic cornerstone. Case Summary A 16-year-old man from Senegal presented shortly after arrival by sea with complete atrioventricular (AV) block and general deterioration. Echocardiography identified a cystic lesion with hyperechoic border and anechoic interior in the basal interventricular septum. Cardiac magnetic resonance (CMR) demonstrated STIR hyperintensity and peripheral late gadolinium enhancement (LGE). Computed tomography (CT) confirmed a 3 × 1.6 cm calcified annular cyst in the septum, a second lesion (1.7 × 1.2 cm) in the atrioventricular pericardial recess, with no other extracardiac locations identified. Serological results were conflicting: E. granulosus serology was negative, while Entamoeba histolytica serology was positive (1:1280), although stool examination was negative, suggesting prior exposure rather than active infection. The calcified cystic morphology supported probable hydatid disease as the primary diagnosis. Antiparasitic treatment was administered and a permanent dual-chamber pacemaker was implanted. Discussion Multimodal imaging must take precedence over serology when results are absent or conflicting. The highly suggestive imaging pattern, calcified annular cyst, STIR hyperintensity, and peripheral LGE, should not be dismissed in the presence of a misleadingly positive Entamoeba titre. With increasing migration from endemic regions to Europe, this diagnostic approach is of growing relevance for cardiologists.