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A man in his early 20s presented with an 8-month history of unilateral nasal obstruction, hyposmia and thick nasal discharge, unresponsive to topical therapy. Preoperative CT demonstrated a smooth polypoidal mass occupying the left nasal cavity and extending into the postnasal space, most consistent with a choanal polyp of presumed maxillary origin. Endoscopic sinus surgery revealed a pedicle at the sphenoid ostium, with an otherwise clear sphenoid sinus, confirming a sphenochoanal polyp. This was unusual because preoperative CT showed only minimal mucosal change in the sphenoid sinus, a finding that typically argues against a sphenochoanal origin. The lesion was excised endoscopically at its site of attachment. Histopathology showed inflammatory nasal polyp tissue without granulomata, vasculitis or atypia. This case illustrates a diagnostic pitfall in which sphenochoanal polyps may mimic antrochoanal polyps on imaging; intraoperative identification of the true sinus of origin is essential to guide appropriate surgery and minimise recurrence.