Why do nasopharyngeal polyps rim enhance?

VRU 57(2): 130-136

June 09, 2023

Study: The study is an original investigation published in Veterinary Radiology & Ultrasound. It is titled “PATHOLOGIC BASIS FOR RIM ENHANCEMENT OBSERVED IN COMPUTED TOMOGRAPHIC IMAGES OF FELINE NASOPHARYNGEAL POLYPS” and was first published on 13 January 2016. The authors are Christopher R. Lamb, Kendall Sibbing, and Simon L. Priestnall.

Methods: This was an observational and retrospective case series study. Medical records of cats referred to the Queen Mother Hospital for Animals (QMHA) between 2008 and 2014 were reviewed. Inclusion criteria were CT imaging of the head that included the ears, and histologic diagnosis of a nasopharyngeal polyp within the same period of hospitalization.

Results: Records were found of 22 cats that had CT and histologic diagnosis of nasopharyngeal polyp. In noncontrast CT images acquired to examine osseous structures, thickening of the tympanic bulla was observed in all 15 cats with a polyp in the tympanic cavity. In CT images acquired to examine soft tissues, a focal, contrast-enhancing mass lesion compatible with polyp was observed in all 15 (100%) cats.

Conclusions: Positive correlations were found between the grade of inflammation in the core stroma and the precontrast HU of polyps, and between the grade of inflammation in the superficial stroma of polyps and the degree of rim enhancement observed in postcontrast CT images for cats in this sample. Hence it appears that inflammation is the major determinant of contrast medium accumulation in feline nasopharyngeal polyps, and the tendency for inflammation to affect predominantly the superficial stroma explains the frequent observation of a rim in postcontrast CT images.

Example of an inflamed nasopharyngeal polyp in a 14-year-old domestic short haired cat. (A) The polyp (arrowheads) has moderate attenuation (40 HU) in precontrast CT image (at left) and is difficult to distinguish from the surrounding tissues. In postcontrast CT image (at right), the polyp has a relatively marked increase in attenuation of the core (120 HU) and rim (191 HU). The rim appears complete in this image. A slight amount of noncontrast-enhancing material, probably exudate, separates the polyp from adjacent nasopharyngeal mucosa. (B) Corresponding histologic section of the polyp (maximal diameter 10 mm), which was graded as having moderate edema and inflammatory infiltrate in the core stroma and marked inflammatory infiltrate in the peripheral stroma (note deep staining; H&E stain).

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