Antrochoanal polyp

Findings

Noncontrast axial CT image in bone window demonstrating a low density mass opacifying the left maxillary sinus extending to the posterior choana. No bony destruction is present.
Noncontrast coronal CT image in soft tissue window better demonstrating the lesion extending through the middle meatus. Contralateral maxillary antral mucosal thickening is present.


Diagnosis: Antrochoanal polyp


Antralchoanal polyps present as mucoid masses originating at the maxillary antrum extending through a sinus ostium to the choana.
Antralchoanal polyps demonstrate non aggressive features with only peripheral enhancement.
Treatment is complete surgical resection.
Originally described by Killian in 1906, antrochoanal polyps result from edematous hyperplasia of respiratory epithelium that herniates through the maxillary infundibulum or the ostium of the maxillary sinus to the level of the posterior choanal (boundary of the nasal cavity and nasopharynx). They commonly arise from the maxillary antrum, hence antrochoanal; however nasochoanal, sphenochoanal, and ethmochoanal polyps have been reported. They comprise 4-6% of all sinonasal polyps and are frequently associated with bilateral maxillary sinusitis. Younger males with a mean age approximately 10 years, presenting with unilateral nasal obstruction is the typical clinical scenario.

Non-contrast CT imaging will usually reveal a large dumbbell shaped, up to 5-6 cm, mucoid density mass occupying the maxillary sinus, exiting via a widened ostium, and into the nasopharyngeal airway. Rarely will antrochoanal polyps extend deep into the nasopharynx or protrude through a nostril. Peripheral enhancement is frequently seen without central enhancement. MR imaging reveals similar findings with hypointense to variable T1 signal. The lesion is hyperintense on T2WI with only peripheral enhancement.

Differential diagnosis includes intranasal glioma, nasoethmoidal encephalocele, juvenile angiofibroma, inverted papilloma, and esthesioneuroblastoma. Intranasal gliomas usually present at birth or the very young as a soft tissue mass centered at the nasal dorsum. Nasoethmoidal encephaloceles present at birth with a frontal, nasal or medial orbital soft tissue mass contiguous with intracranial brain parenchyma extending through a bony defect. Juvenile angiofibromas present in adolescent males as an intensely enhancing mass originating at the sphenopalatine foramen extending into the posterior nasopharynx. Inverted papillomas are usually found in older males as a locally aggressive mass centered at the middle meatus extending into the maxillary sinus and nasal cavity. Esthesioneuroblastomas present in the second and sixth decades as a solid enhancing mass centered within the superior nasal cavity extending into the cribriform plate. Complete surgical resection is the treatment of choice with mean time to recurrence of 45 months.