Head and Neck Imaging

Antrochoanal polyp

polyp originating in the maxillary sinus, protruding in the middle nasal meatus through the ethmoidal infundibulum or an accessory opening in the medial wall of the maxillary sinus; further posterior extension moves the polyp through the choana into the nasopharynx, and a very large lesion may appear as an oropharyngeal mass (Fig.1). Such a polyp usually occurs in isolation and is seen mainly in patients younger than 40 years of age. Unilateral nasal obstruction is the most common symptom. Treatment is complete surgical removal of the polyp; incomplete resection is associated with a relatively high recurrence rate.

A similar polyp may arise from a sphenoid sinus, passing through the sphenoid ostium and herniating through the sphenoethmoidal recess into the choana: this is known as a sphenochoanal polyp.

As these polyps pass through narrow spaces, they are susceptible to vascular compromise: dilatation, stasis and occlusion of the feeder vessels may occur, possibly leading to neovascularization; clinically and radiologically the nasochoanal component may therefore be confused with a vascular neoplasm. Such vascular compromised antrochoanal (or sphenochoanal) polyps are called angiomatous polyps (Fig.2). Complete strangulation with autopolypectomy is a rare event.

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Fig.1

Axial CT images demonstrate maxillary polyp passing through an accessory ostium into the posterior nasal cavity and choana (a). Lower section shows extension of the mass (arrow) into the nasopharyngeal lumen (b).
Antrochoanal polyp, Fig.1 (a)
Antrochoanal polyp, Fig.1 (b)
Antrochoanal polyp, Fig.2 (a)
Antrochoanal polyp, Fig.2 (b)