8     SA JOURNAL OF RADIOLOGY  •  March 2011  

PICTORIAL INTERLUDE

Images of a case of unilateral choanal atresia diagnosed in a 35-year-
old woman are presented. This is an uncommon diagnosis in an adult 
patient, and a less frequently encountered form of the condition. In 
more than 90% of cases of choanal atresia, the abnormality is partly or 
completely osseous; pure membranous atresia is rare.1 It is unilateral in 
50 - 60% of cases, and more than 75% are associated with syndromes 
and systemic anomalies.

Unilateral choanal atresia may go unrecognised until adulthood, 
as in our patient, when she presented with rhinorrhea and unilateral 
recurrent nasal obstruction.

Failure of perforation of the buccopharyngeal membrane during 
midface development in the developing fetus produces membranous 
choanal atresia.2 The imaging modality of choice for suspected choanal 
anomalies is computed tomography (CT). Image reconstruction with a 
bone algorithm is required to clearly depict partially ossified/unossified 
structures. Careful suctioning prior to the scan may be helpful in some 
patients.
The purpose of CT scanning is to:

•   confirm the diagnosis, determine if it is uni/bilateral, and assess if 
it is bony/membranous or mixed

•   determine if it is a stenosis or atresia, and assess vomer bone width 
and choanal airspace distance in atresia. Normal choanal orifices 
measure >0.37 cm in children <2 years.2

•   exclude other possible sites of obstruction.
CT virtual endoscopy is a post-processing tool that can aid in 

depicting disorders of the airways and may assist in preoperative 
planning. In choanal atresia, the posterior view provides a look at the 
abnormality and surrounding anatomical relationships.3

Membranous choanal atresia is usually treated with endoscopic 
perforation. Osseous atresia may require choanal reconstruction or 
transpalatine resection of the thick vomer.

1.  Valencia MP, Castillo M. Congenital and acquired lesions of the nasal septum: A practical guide for dif-
ferential diagnosis. Radiographics 2008;28:205-223.

2.  Castillo M. Congenital abnormality of the nose: CT and MR findings. AJR 1994;162:1211-1217.
3.  Thomas BP, Strother MK, Donnelly EF, Worrell JA. CT virtual endoscopy in the evaluation of large airway 

disease: Review. AJR 2009;192:S20-230.

Unilateral membranous choanal atresia

Fig. 1. Axial CT image demonstrates thin membrane occluding the right 
choanal lumen. No ossification is seen.

Fig. 2. Posterior nasopharynx CT virtual endoscopic view. Roof of nasopharynx 
above and soft palate below. Right-sided membranous atresia shown.

Aadil Ahmed, MB BCh, FCRad (Diag)
Visser, Erasmus, Vawda and Partners, Port Elizabeth