Maxillary sinus can pose diagnostic dilemma radiographically because of its anatomical variation which can mimic a periapical pathosis. This case report deals with one such diagnostic problem, where a maxillary sinus was interpreted in an intraoral periapical radiograph as a periapical cyst. With the advances in imaging techniques, the use of an Ultrasound imaging together with application of Colour Power Doppler helped in revealing the contents of the radiolucent area and come up with an accurate diagnosis. Thus a thorough knowledge about the normal anatomy and its variations and proper diagnostic aids are essential in the diagnosis of periapical pathology.