A Case Report of Hydatid Cyst Mimicking Thyroid Mass With Mediastinal Extension and Bony Erosion: A Successful Non-surgical Approach to Treatment.

We report an unusual manifestation of hydatid disease, presenting as a progressively enlarging, painless swelling in the right infraclavicular region. Imaging studies revealed a large necrotic mass extending into the superior mediastinum with the destruction of the adjacent right sternoclavicular joint; this was initially suspected to be thyroidal in origin. However, histopathological examination was consistent with a ruptured hydatid cyst, and Echinococcus serology was positive. Due to anatomical considerations, surgical intervention was not pursued, and the patient was managed with oral anthelmintic therapy, resulting in partial radiological response after 12 weeks of therapy. This case underscores the importance of considering hydatid disease as a differential diagnosis, even with atypical anatomical involvement. It also highlights the potential role of medical management alone as a viable alternative when surgery is not feasible.