A choanal polyp is defined as an isolated solitary sinus mass or cyst which has passed through the sinus ostium and protruded into the boundaries between the nasal cavity and nasopharynx, the choana.2
These polyps can arise from the maxillary sinus, sphenoid and ethmoid, there being questions in relation to its formation from the frontal sinus. According to Dadas, 4–6% of all nasal polyps are the antrochoanal type. Isolated sphenochoanal polyps are extremely rare. Sphenochonal and ethamochoanal polyps are even more uncommon.1
Only one case of simultaneous antrochoanal polyp and sphenochoanal polyp was reported in the literature.3
Sphenochoanal polyps are difficult to document. They can be present in any age group. To the best of our knowledge the youngest patient reported to have a sphenochoanal polyp was a 3.8-year-old female, and was the only case in which the polyp had completely regressed.6
Most sphenochoanal polyps are not associated with other sinus diseases, although in some cases other sinuses are affected, possibly as a result of blockage by the polyp.7
Sphenochoanal polyp may have a variety of anatomical origins. Although most sphenochoanal polyps arise from the sphenoid ostium, some have been reported to originate in adjacent areas and the sinus. In our case it originated from the sphenoid sinus.3
Choanal polyps have a firmer consistency than nasal polyps owing to their extensive fibroblastic activity. They are believed to arise from an expanding intramural cyst that protrudes through the ostium of the sinus into the nasal cavity. The pathogenesis of the cyst may involve thrombosis of lymphatic vessels following sinus inflammation. Preoperative identification of the sinus from which a choanal polyp arises is important because the site of origin of the polyp in the sinus must be resected in order to minimise recurrence. This consideration may influence the surgical approach.7
In our case the sphenoid sinus was divided into three parts by two septa and the polyp arose from the middle part.
For descriptive purpose, clinicians have divided them into inflammatory and non-inflammatory polyps, with greater prevalence of the former.3
Histopathology is of the utmost importance as, unlike antrochoanal polyps, sphenochoanal polyps have higher chances of exhibiting neoplastic pathology, most often inverted papilloma.1
Downward extension of intracranial pathology must also be considered. CT or MRI serve as invaluable tools for making the differential diagnosis in these cases. Because most choanal polyps are not associated with other sinus diseases, a finding of an opaque sphenoid sinus and a clear maxillary sinus is a likely indicator that the polyp is sphenochoanal, even if its origin cannot be clearly identified. If both the sphenoid and maxillary sinuses are opaque, it is important to identify the continuity of the polyp with its origin at surgery. An antrochoanal polyp originates in the middle meatus; in contrast, a sphenochoanal polyp passes between the nasal septum and the middle turbinate, leaving the middle meatus clear.7
Management of choanal polyps involves complete excision of the polyp including its pedicle and its sight of origin within the sinus. Endoscopic sinus surgery offers excellent views of the sinuses and is associated with lower recurrence rates than simple polypectomy.7
Tosun et al8
reported that almost 50% of sphenochoanal polyps reported in the literature occurred in children. So the most aggressive surgical approach should be avoided. Lopatin suggested that the basic concept of functional endoscopic sinus surgery (FESS) of not manipulating the sinus mucosa (as long as the improvement in drainage and aeration to the PNS tends to restore normal sinus mucosa) is not applicable to choanal polyps. According to Lopatin, removal of damaged mucosa from the sinus during polyp removal by FESS is preferable, since it may be the cause of the recurrence.1
Simple avulsion of the polyp with forceps or snare will result in a 25% rate of recurrence. Gradual debulking of the polyp with a microdebrider facilitates the ability to trace the pedicle to the offending sinus and thus serves not only a therapeutic role, but a diagnostic one as well.2
Operative complications of endoscopic sphenoid surgery are rare but the surgeon must be aware of the close proximity of critical anatomical structures surrounding the sphenoid sinus.3
- We attempt to highlight and alert the clinician that, although antrochoanal polyp is the most common type of choanal polyp, the origin of the polyp from another sinus is possible and should be taken into consideration.
- CT scan is a valuable tool for confirming the diagnosis.
- While performing sphenoid surgery the surrounding critical structures should be kept in mind.