Teaching Case

A 76-year-old female patient was admitted to the emergency room for a contused lacerated wound in the right frontal side after a fall.
To rule out a facial fracture an unenhanced CT scan was requested.

Unenhanced CT scan excluded facial fractures and showed an asymmetry of the maxillary sinuses because of volume loss of the right maxillary sinus, which was completely opacified with inward retraction of its walls and an increased volume of the right orbit with enophthalmos.
These findings are consistent with a silent sinus syndrome that is suggested in the radiological report.

Silent sinus syndrome (SSS), also known as maxillary atelectasis or imploding antrum, is a rare clinical entity causing a progressive loss of volume of the affected sinus which manifests with painless enophthalmos, hypoglobus, facial asymmetry and most rarely with visual symptoms such diplopia or blurred vision. [1, 2, 3, 4, 5]
Onset is in adulthood (19-82 years) without gender predilection, in childhood it is particularly infrequent [6].
Generally, it affects a single maxillary sinus, and bilateral involvement or localisation to other sinuses is very rare [7, 8]
First described by Montgomery in1964 [9], it was renamed SSS by Soparkar in 1994 [10].
The aetiology of SSS is not yet well understood. The most accepted theory suggests an obstruction of the maxillary ostium that causes a reduction of mucosal drainage and hypoventilation of the sinus. The stagnation of mucus causes an inflammation that impairs the sinus walls and weakens them while hypoventilation causes gas resorption and negative pressure in the sinus leading to inward wall retraction. [1, 2, 3, 5].
This cascade of events can be triggered by several causes: mucus thickening, hypermobility of the infundibular wall, paranasal sinuses mucocele, nasal polyp or iatrogenic trauma.  
Anatomic alterations such as hypoplastic sinus, absence of the uncinate process, septal deviation or lateralised middle turbinate can decrease the width of the nasal cavities causing occlusion of the ostium.
The chronic obstructive mucosal disease was considered an aetiologic factor; although plausible, this hypothesis does not explain the rarity of SSS compared to frequency of obstructive sinus disease.
The diagnosis of SSS can be made clinically relying on its characteristic features of progressive and painless changes of the facial aspect with sunken eye and upper eyelid sulcus deepening but needs to be confirmed with imaging investigations and differentiated from other causes.
Plain radiographs are outdated and no longer used because the characteristic abnormalities such as volume loss of sinus, the thinning and the inward retraction of all or some sinus walls associated with increased orbital volume can be better appreciated on CT and MRI. [11]
Other findings are sinus opacification, maxillary infundibulum occlusion and uncinate process retraction against the inferomedial orbital wall, enlargement of the middle meatus and deviation of the nasal septum. Currently treatment is endoscopic with maxillary antrotomy to restore the sinus ventilation and drainage of mucus and a transconjunctival orbital floor repair. [11, 12]
This can be performed simultaneously or in a second stage to avoid an overcorrection  and the risk of infection or injury to the orbital contents, which is much higher than in other patients.
After surgery, sinus conformation may remain unchanged, improve slightly or revert to normal over time.

Written informed patient consent for publication has been obtained.