CASE REPOI~T Sphenochoanal polyp: radiological diagnosis MWPak* FRCS(Ed) J Kew# FFRad, (D) SA Abstract * Division of Otorhinolaryngology, Depal1ment of Surgery, # Depal1ment of Diagnostic Radiology and Organ Imaging, Prince ofWa/es Hosp/ta/, Chinese University of Hong Kong A sphenochoanal polyp is seen as an isolated soft tissue density mass that arises from the sphenoid sinus and extends to the choana on computed tomograph ic scans. Distinction from its more cornrnon counterpart, antrochoanal polyp vvbich arises from the maxillary sinus, is essential prior to surgery. A case is presented to i II ustrate that CT scan of paranasal sinus plays an important role in the identification of the sinus of origin. Case report A 47-year-old male presented to Prince of Wales Hospital with a one year history of right sided progressive nasal obstruction following an episode of upper respiratory tract infection. The obstruction was worse on forced expi- ration and more noticeable during 7 SAJOURNAL OF RADIOLOGY. May 1998 swimming. Nasal endoscopy revealed a right sided solitary polypoid mass with a slender pedicle extending from the sphenoethmoidal recess to the choana. An unenhanced CT scan of paranasal sinuses (5 x 5 mm coronal scans) was performed on a GE 8800 scanner (Milwaukee, USA). A soft tis- sue polyp extending from the right sphenoid sinus/sphenoethmoidal recess to the right choana was demonstrated. Chronic right sphenoid sinusitis with reactive sclerosis was seen. Inside the sphenoid sinus there was a convex up- per margin to the soft tissue which in- dicated the presence of either a mucous retention cyst or a polyp. The other paranasal sinuseswere clear (Figures 1-4). The clinical and radiological findings indicated a sphenochoanal polyp. The patient was admitted for excision un- der general anaesthesia. Under endo- scopic control, the anterior wall of the sphenoid sinus was opened and the polyp, together with its sphenoidal com- ponent, was removed. No recurrence was noted two years after surgery. Discussion A choanal polyp results from pro- lapsed mucosa of an isolated paranasal sinus and accounts for 3-6% of nasal polyps.P Characteristically, it passes through the enlarged sinus ostium and protrudes into the choana leading to unilateral nasal obstruction, rhinorrhea and sinusitis. Choanal polyps from sphenoid si- nus are rare but share the characteristic similarity with the more common coun- terparts which arise from the maxillary sinus. They are invariablyunilateral in dis- tribution and common in males between the second and fourth decades.'? Contrary to conventional nasal polyps, choanal polyps are believed to be topageB (rom page 7 Figure 1: Coronal CT scan showing normal maxillary and ethmoid sinuses. No nasal polyposis IS eVident and the osteomeatal units are patent. Figure 2: Coronal CT scan through the posterior maxillary sinuses which are clear. A soft tissue opacity with a convex upper margin is seen in the sphenoid sinus (arrowhead). There is soft tissue in the sphenoethmoldal recess representing the stalk of the polyp (arrow). determine. If the sphenoid sinus is the only opaque sinus, a choanal polyp is prob- ably sphenochoanal, even if the connection cannot be demon- strated. If both the maxillary antrum and the sphenoid sinus are opaque, continuity be- tween the polyp and the correct sinus of ori- gin is important to document. In the case of an antrochoanal polyp, the polyp can be followed passing between the mid- dle turbinate and the lateral wall of the nasal cavity. With a sphenochoanal polyp, the polyp is between the nasal septum and middle turbinate. The dif- ferential diagnosis of a soft tissue mass in the sphenoethmoidal recess/choana could include nasal polyp with sphenoid sinusitis, nasopharyngeal carcinoma and lymphoma. As simple avulsion of the intranasal portion alone is associated with recur- rence of at least 20% within two years, the polyp should be resected together with the pedicle and its intrasphenoidal portion. 1·3 To decrease the morbidity associated with external approaches to the sphenoid sinus, endoscopic removal of the polyp together with sphenoidotomy remains the treatment of choice. References Figure 4: Coronal CT scan showing the polyp in the right choana. polyp may arise from the blocked aci- nous mucous gland and present as an extension of a mucocele.' However, more evidence has suggested that the polyp is an extension of an asympto- matic intramural cyst from within a si- nus through its natural ostium.' The sinus of origin can be identified clinically and radiologically. With a 4 mm, zero degree nasal endoscope, the sphenochoanal polyp is readily recog- nized as a solitary polypoid mass extend- ing posteriorly from the recess between septum and middle turbinate to the choana. Further identification of a long pedicle protruding through the sphenoid ostium in the sphenoethmoidal recess is essential to confirm the di- agnosis. Apart from endos- copy, CT scans of paranasal sinus is indispensable to the evaluation of an isolated na- sal polyp of unknown ori- gin. The radiological find- ings of sphenochoanal pol- yps are characteristic. The CT appearance of the polyp is of a hypoattenuated mass arising from an isolated opaque sphenoid sinus without evidence of bony erosion. The natural ostium of the sphenoid sinus is usually enlarged.ê? Occasionally, the sinus of origin may be difficult to Figure ~: The polyp (arrow) Is seen in the right nasopharynx. The right sphenoid SinUS IS opaque and there Is associated reactive osteitis. of inflammatory or infectious rather than allergic nature. 1·3 The origin of the polyps is contro- versial. Mills has suggested that the a SA JOURNAL OF RADIOLOGY. May 1998 1. Heck WE, Hallberg 0, Williams HL. Antrochoanal polyp. 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