Sinochoanal polyp and its variant, the angiomatous polyp: MRI findings.

The angiomatous polyp corresponds to the vascular compromised nasochoanal part of a sinochoanal polyp. We describe the MRI characteristics of such lesions in four patients. All patients had an angiomatous polyp, in three cases as part of an antrochoanal polyp, and in one case as part of a sphenochoanal polyp. The unenhanced MR images depicted the typical appearance of a sinochoanal polyp, hypointense on T1-weighted and hyperintense on T2-weighted images. On gadolinium-enhanced MR images, the sinusal part showed little or no peripheral enhancement; however, the nasochoanal part, corresponding to the angiomatous polyp, showed strong enhancement. An angiomatous polyp mimics a hypervascular mass lesion on enhanced MR studies. The anatomic location and association with a sinusal polyp allows the correct diagnosis.