Case history: A 35-year-old patient with history of unilateral nasal obstruction.
Figures 1-5 Axial images showing defined mass arising within the right maxillary sinus, widening of right maxillary ostium and mass extending in to middle meatus.
Findings: Defined mass arising within the right maxillary sinus; widening of right maxillary ostium and extending in to middle meatus; no associated bony destruction but rather smooth enlargement of sinus.Postoperative antrochoanal polyp was found at surgery.Discussion: An antrochoanal polyp (ACP) is a solitary polyp that arises within the maxillary sinus but passes through and enlarges the sinus ostium or more commonly an accessory ostium. The nasal cavity is therefore extended posteriorly into the nasopharynx through the posterior chonae. Similar polyps can arise in the sphenoid sinus and extend in to nasopharynx : these are termedsphenochoanal polyps.Epidemiology: Antrochoanal polyps represent only approximately 3 percent to 6 percent of sinonasal polyps. The exact etiology is not known, but it is thought that infection may be a common causative association. Chronic sinusitis is found in approximately 25 percent of patients, but again, a causal relationship has not been firmly established. Unlike other sinonasal polyps, antrochoanal polyps are usually found in non-atopic patients. They are most commonly seen in young adults and in third to fifth decades. They are slightly more common in males compared to females.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. Pathologically, antrochoanal polyps are identical to other inflammatory polyps. However, unlike other polyps, they usually have a narrow stalk that arises from the maxillary sinus. 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 including: haemorrhage, oraganising haematoma, neovascular changes, and papillary endothelial hyperplasia.Radiographic features: Plain films are no longer considered adequate in assessment of sinus pathology. However, they continue to be performed in some cases. Features include
• unilateral opacification of the maxillary sinus
• nasopharyngeal mass is occasionally seen
• frequently bilateral sinus involvement (23 â 42 percent)CT is a preferred method for diagnosis since it is able to give exquisite bony detail of the paranasal sinus anatomy. In general, a non-contrast scan suffices. Although classification system exists, detailed description is usually preferred 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 in to nasopharynx
• no associated bony destruction but rather smooth enlargement of sinusThese features are best appreciated on true coronal or coronal reformat 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 HU values if they are long standing and/or have an associated fungal infection. A contrast scan is not necessary but may demonstrate peripheral enhancement.MRIT1: 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.Treatment and prognosis: Classic treatment is intranasal snare polypectomy. However, if the base of the stalk is not excised, recurrence may occur. Ideally, minimally endoscopic surgery is performed; the attachment site of the stalk is identified and it is existed along with a small cuff of adjacent mucosa. Visualization 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. Recurrence rate if the stalk base is excised is low (about 7 percent).Harpreet Singh, MDJP Scan private diagnostic center, Khanna, Punjab, India