General Medical Information

Polyposis

Barbara A. Zeifer

Individual polyps are smoothly rounded or pedunculated soft-tissue masses in the nose and sinus cavities. They can obstruct sinus drainage if they are near the ostium. Diffuse sinonasal polyposis produces more pronounced opacification. The multiple, packed polyps can exert pressure on adjacent bony structures and enlarge the involved cavity. This expansile process is slow and gradual, so the bone has time to remodel around the mass. Expansion and distortion occur, and the intersinus septations with are fairly well preserved, a finding most frequent in the ethmoidal labyrinth. Nasal polyps frequently cause expansion of the superior nasal fossa and sphenoethmoid recess that can be easily identified on coronal CT scans. Polyposis often is associated with accumulation of highly proteinaceous secretions. The polyps are low in density on CT scans, hypointense on T1-weighted MR images, and hyperintense on T2-weighted MR images. The secretions are hyperdense on CT scans, hyperintense on T1-weighted MR images, and hypointense on T2-weighted images.

Antrochoanal polyps have a distinct radiographic appearance. At CT, both the maxillary sinus and the middle meatus are completely opacified by an edematous, hypodense polyp that can extend posteriorly into the nasopharynx. The polyp is hyperintense on T2-weighted MR images. The polyp most frequently extrudes through the lateral nasal wall at the posterior nasal fontanelle behind the posterior attachment of the uncinate plate, where normal lack of bone provides a path of least resistance. There usually is radiographic evidence of a slowly expansile process and a partially intact, lateral nasal wall that has been pushed medially. Less frequent routes to the nasal cavity include the infundibulum and the nasal wall below the neck of the inferior turbinate.