Antrochoanal polyps (ACP)

• Unilateral mass arising from maxillary sinus with mucin density
• Extension through widened maxillary ostium into nasopharynx
• Narrow pedicle or stalk base (though often not evident on CT imaging)

• CT shows a well-defined mass with mucin density originating from the maxillary antrum, which is the gold-standard imaging modality due to exquisite bony detail of paranasal sinus anatomy.
• Smooth enlargement and widening of the maxillary sinus ostium (accessory ostium) with extension of the polyp mass into the nasopharynx.
• No associated bony destruction is present; the sinus walls show smooth remodeling rather than erosive changes.
• Coronal CT or coronal reformatted images best demonstrate the characteristic features of antrochoanal polyps and their anatomic relationship to the choana.
• On MRI, T1 signal is intermediate to low, while T2 signal is characteristically high and homogeneous in typical cases.
• MRI with contrast (Gd) demonstrates peripheral enhancement on post-contrast T1 images.
• Long-standing or fungally infected polyps may show higher CT density (increased Hounsfield values) and variable T2 signal intensity on MRI.
• Plain radiographs may show unilateral maxillary sinus opacification and occasionally bilateral involvement (23-42%), but CT is the preferred diagnostic modality.

• Inverted papilloma: typically shows more aggressive imaging features with bony destruction and cerebriform appearance, whereas antrochoanal polyps have smooth sinus enlargement without erosion.
• Juvenile nasopharyngeal angiofibroma (JNA): enhances intensely and shows prominent vascularity with flow voids; antrochoanal polyps show only peripheral enhancement.
• Hypertrophied turbinate: arises from the turbinate bones themselves rather than from the maxillary sinus, and lacks the characteristic stalk.
• Nasoethmoidal encephalocele: shows CSF signal on MRI and defect in the cribriform plate; antrochoanal polyps have mucinous signal.
• Maxillary sinus mucocele: lacks the characteristic stalk from the maxillary sinus and does not extend into the nasopharynx.
• Sinonasal organized hematoma: may mimic antrochoanal polyps but clinical history and variable T1/T2 signal reflecting hemosiderin deposition can help distinguish.

Describe the location, size, and relationship to the maxillary ostium clearly: "A mass arises from the maxillary antrum, widening the maxillary ostium, with extension into the nasopharynx consistent with an antrochoanal polyp; note the origin from the maxillary sinus and ensure the surgical team understands the need for complete stalk excision to minimize recurrence."

• Failure to identify the maxillary sinus origin of the mass—the polyp can appear to be primarily a nasopharyngeal mass on axial images alone; coronal imaging is essential to demonstrate the characteristic origin and stalk.
• Mistaking the polyp for other nasopharyngeal masses such as JNA or inverted papilloma based on location alone; careful attention to imaging signal characteristics and extent of enhancement helps distinguish these entities.
• Underestimating the importance of CT imaging and relying on plain radiographs, which lack the detail needed to confirm sinus origin, characterize the mass, and guide surgical planning.
• Not recognizing that the narrow pedicle/stalk may not be visible on imaging despite being the pathologically defining feature; communicate to surgeons that complete stalk excision is critical even if not clearly delineated on preoperative imaging.