Antrochoanal polyp

Antrochoanal polyps (ACP) are solitary sinonasal polyps that arise within the maxillary sinus.  They pass through and enlarge the sinus ostium and posterior nasal cavity to the nasopharynx

Similar polyps can arise in the sphenoid sinus extending into the nasopharynx: these are termed sphenochoanal polyps.

Antrochoanal polyps represent only ~5% of sinonasal polyps 3. They are most commonly seen in young adults in 3rd to 5th decades. They are slightly more common in males than females 3.

Clinical presentation is usually with an obstructed nasal passage and/or sinus symptoms. Occasionally, larger masses may prolapse posteriorly enough that they may be visible through the mouth as they hang down from the nasopharynx 5.

Unlike other sinonasal polyps, antrochoanal polyps are usually found in non-atopic patients 3.

The exact aetiology is not known, but it is thought that infection may be a common causative association. Chronic sinusitis is present in ~25% of patients 7 but a causal relationship has not been firmly established.

Pathologically, antrochoanal polyps are identical to other inflammatory polyps. However, unlike other polyps, they usually have a narrow stalk arising from the maxillary sinus 5,7.

Histology

Histologically, the polyp is lined by respiratory epithelium with increased inflammatory infiltrate. Due to the narrow pedicle, vascular compromise with secondary change may be seen.  This may result in haemorrhage, organising haematoma, neovascular changes, and/or papillary endothelial hyperplasia 5,7.

Plain radiograph

Plain films are no longer considered adequate in assessment of sinus pathology. However, they continue to be performed in some cases. Findings include 3:

  • unilateral opacification of the maxillary sinus
  • nasopharyngeal mass is occasionally seen
  • frequently bilateral sinus involvement (23-42%) 3
CT

CT is a preferred method for diagnosis due to the exquisite bony detail of the paranasal sinus anatomy. In general, a non-contrast scan is sufficient.  Typically, antrochoanal polyps have the following features:

  • defined mass with mucin density is seen arising within the maxillary sinus
  • widening of maxillary ostium and extending into the nasopharynx
  • no associated bony destruction but rather smooth enlargement of the sinus

These features are best appreciated on true coronal or coronal reformatted scans. Although pathologically antrochoanal polyps have a narrow pedicle or stalk, this is usually not defined on CT.

Occasionally, antrochoanal polyps may have a higher density (and Hounsfield values) if they are long-standing and/or have an associated fungal infection (see fungal sinusitis) 1. A contrast-enhanced scan is not necessary but may demonstrate peripheral enhancement.

MRI
  • T1: intermediate to low signal
  • T2
    • high homogeneous T2 signal
    • signal may vary if they are chronic and/or if fungal infection is present
  • T1 C+ (Gd): peripheral enhancement is seen on post-contrast images

Classic treatment is intranasal snare polypectomy. However, if the base of the stalk is not excised, the polyp may recur. Ideally, minimally invasive endoscopic surgery is performed: the attachment site of the stalk is identified and it is excised along with a small cuff of adjacent mucosa. Visualisation of the stalk base can be achieved in many cases via a medial meatotomy, or may require creation of an additional window through the inferior meatus 6.

Recurrence rate is low (~7%) if the stalk base is excised 6.

They were first described by Killian in 1906. Killian expressed the opinion that it arose from the maxillary sinus and gained access to the nasal cavity through the accessory ostium, based on a detailed study of 22 cases 8.

General imaging differential considerations include:


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Article Information

rID: 9044
System: Head & Neck
Section: Pathology
Synonyms or Alternate Spellings:
  • Antrochoanal polyp (ACP)

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