The imploding antrum: An unusual case of nontraumatic painless enophthalmos.

The imploding antrum or silent sinus syndrome is a rare phenomenon that presents with spontaneous painless enophthalmos and hypoglobus. It occurs due to ipsilateral maxillary antral atelectasis secondary to asymptomatic obstructive chronic sinus mucosal disease. Ophthalmologists, otorhinolaryngologists, and radiologists must be aware of this entity. This article illustrates the typical presentation in a 17-year-old male with unilateral ptosis and a deep superior sulcus, and characteristic imaging findings of ipsilateral increased orbital volume and depression of the orbital floor, maxillary sinus opacification and atelectasis with retraction of the posterolateral and medial walls, lateralization of the uncinate process, and obstruction of the ostiomeatal unit. This is probably the first time that the syndrome is being reported in such a young person. The pathogenesis, differential diagnosis, and treatment modalities of this entity are also reviewed.

The imploding antrum (IA) or silent sinus syndrome (SSS) is a rare and unusual phenomenon that presents a diagnostic challenge. It presents with facial asymmetry due to spontaneous painless enophthalmos and hypoglobus and occurs due to ipsilateral maxillary antral atelectasis secondary to asymptomatic obstructive chronic sinus mucosal disease and hypoventilation.[1] Although a PubMed search revealed about 180 documented cases till 2014, this entity probably remains underrecognized. This article illustrates the imaging findings and discusses the pathogenesis, presentation, and treatment modalities of this entity. To the best of our knowledge, this entity is being described for the first time in a 17-year-old patient.

Case Report

A 17-year-old male, a nonsmoker, presented with the sensation of left malar heaviness of 1 month's duration. The sensation was felt intermittently, and there was no pain. There was no history of trauma, chronic rhinosinusitis, or sinonasal surgery. On examination, there was mild ptosis on the left side with a deep superior sulcus. The left globe appeared mildly inferiorly placed (hypoglobus). Enophthalmos of 2.0 mm was confirmed with Hertel ophthalmometer. Mild left-sided malar depression was also noted [Fig. 1]. Radiograph of the paranasal sinuses showed a small left maxillary antrum with depression of the orbital floor. A septal spur toward the right side was noted [Fig. 2]. Nasal endoscopy revealed a roomy left middle meatus with lateral retraction of the middle turbinate. A subsequent computerized tomography (CT) scan revealed an atelectatic left maxillary sinus filled with inspissated mucus. There was inward retraction of the anterior, lateral, and superior antral walls; their thickness was normal. The middle turbinate was lateralized, and the uncinate process was apposed to the inferomedial orbital wall. There was also increase in the left retroantral fat [Figs. 3 and 4]. Based on these clinico-radiological findings, a diagnosis of IA was made. The patient underwent functional endoscopic surgery with antrostomy. As the cosmetic deficit was minimal, no orbital reconstruction was undertaken. At follow-up after 6 months, there was no progression of the disease.

Figure 1

Photograph of the patient showing mild hypoglobus and ptosis on the left side. The left malar eminence also has a flattened contour

Figure 2

Radiograph of the paranasal sinuses (Water's view) reveals a small left maxillary antrum with depression of the anteroinferior orbital floor. A septal spur toward the right side is also noted

Figure 3

(a and b) A panel of axial computerised tomography images (caudocranial) in bone window of the maxillary antra reveals atelectatic left maxillary sinus (*), retracted anterior wall of the antrum (white arrow), widened middle meatus (#), and increased retroantral fat (+)

Figure 4

(a and b) A panel of coronal computerized tomography images (anterior-posterior) in bone window of the orbits and maxillary antra shows the atelectatic left maxillary sinus (*). There is lateralization of the middle turbinate, and the uncinate process is apposed to the inferomedial orbital wall (white arrow)

Discussion

A syndrome of facial asymmetry due to spontaneous painless enophthalmos and hypoglobus, due to asymptomatic chronic maxillary sinus atelectasis was first described by Montgomery.[1] Alluding to the “silent” antral disease, this syndrome was named the SSS by Soparkar et al.[2] To better describe the antral atelectasis, Rose et al. named it the “imploding antrum” syndrome.[3]

Most patients present in the third to fifth decades without any gender predilection. There is no laterality bias; however, some have reported right-sided predisposition. Bilateral disease has also been described.[4] Patients usually present with progressive painless enophthalmos noted over a period of 4–8 months.[35] There is no history of acute or chronic sinus mucosal disease and prior facial trauma. The negative association with smoking is attributable to the fact that smokers with predisposing abnormal sinonasal anatomy present with diffuse mucosal disease early and undergo treatment before developing the syndrome.[35]

Physical examination findings may include upper lid retraction, lid lag, deepened upper lid sulcus, malar depression, facial asymmetry, and diplopia. The degree of enophthalmos and hypoglobus ranges between 2–6 mm (mean: 3.4) and 1–6 mm (mean: 3.2 mm), respectively.[5] Ocular dysmotility (inferior rectus and inferior oblique) is noted only with significant hypoglobus.[35]

CT scan is the best diagnostic method because it best delineates the osseous and anatomic changes needed for its diagnosis and differentiation from other conditions.[6] The imaging findings are characteristic. The opacified antrum is atelectatic with inward bowing of the walls, and consequent increased orbital volume and enlargement of the middle meatus. Generally, all four antral walls are involved. The maxillary roof (orbital floor) is retracted and frequently thinned. The other walls may be thinned, normal, or thickened. The maxillary infundibulum is occluded, and the uncinate process is apposed to the inferomedial aspect of the orbital wall. There is a lateral retraction of the middle turbinate and the middle meatus is widened. The nasal septum is deviated toward the affected side in the majority of the patients.[356] The ipsilateral retroantral fat is also increased.

A hypoplastic antrum with chronic obstructive mucosal disease was initially believed to be the cause of the syndrome.[1] Subsequently, subatmospheric intrasinus pressure was demonstrated in patients with IA.[7] It is now believed that ostiomeatal occlusion with the loss of aeration and gradual resorption of secretions and residual air, and chronic mucosal inflammation with osseous demineralization leads to implosion of the weakened antral walls, a phenomenon akin to middle ear atelectasis due to Eustachian tube dysfunction. An abnormally narrowed nasal cavity due to septal deviation and/or laterally deviated middle turbinate may also predispose to maxillary hypoventilation.[5] In the later stages of the disease, mucosal inflammation might lead to hyperostosis and thickened antral walls.[5] Although plausible, this theory does not explain the rarity of this entity amid the commonality of sinus mucosal disease nor the selective involvement of the maxillary sinus. It is possible that anatomic variations such as Type 2 (hypoplastic or absent uncinate process with an opacified affected sinus) maxillary sinus hypoplasia and hitherto other undefined anomalies may be predisposing factors.[8] Local iatrogenic trauma may also be a predisposing factor in this condition.[9]

The diagnosis of IA can be made clinically, but it should be differentiated from other causes of spontaneous enophthalmos such as Parry–Romberg syndrome (progressive hemifacial atrophy) and linear scleroderma. Osseous metastasis and osteomyelitis of the orbital floor may also cause enophthalmos and hypoglobus.

The treatment has two objectives - to reestablish maxillary antral ventilation and restore orbital architecture. The former is achieved by endoscopically creating a nasoantral window with uncinectomy and antrostomy. Careful identification of structures during surgery is essential to avoid orbital injury in view of altered anatomy and osseous rarefaction. As orbital remodeling after antrostomy with improvement in enophthalmos and hypoglobus has been observed, it might be prudent to delay orbital reconstruction for 2–6 months. Orbital floor repair depends on the degree of enophthalmos and hypoglobus and the consequent cosmetic defect. Some prefer to combine both procedures in view of rarity of complications and to avoid a second hospitalization and surgery.[510]

This case is unique due to its presentation in a teenager. The absence of thin antral walls indicates chronicity and implies commencement of the disease process at an even younger age.

Conclusion

The “imploding antrum” is a rare and unusual entity characterized by spontaneous painless enophthalmos and hypoglobus caused by chronic obstructive maxillary sinus atelectasis. The imaging findings are characteristic and confirmatory.

Declaration of patient consent

The authors certify that they have obtained all appropriate patient consent forms. In the form the patient(s) has/have given his/her/their consent for his/her/their images and other clinical information to be reported in the journal. The patients understand that their names and initials will not be published and due efforts will be made to conceal their identity, but anonymity cannot be guaranteed.

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Conflicts of interest

There are no conflicts of interest.