Chronic maxillary atelectasis (CMA) is a rare condition where the maxillary sinus becomes hypoplastic secondary to the blockage of its ostium. Although the term silent sinus syndrome (SSS) has also been coined to show comparable conditions, CMA and SSS lie on a similar clinical spectrum, as their clinical and radiographic findings are almost the same.
Although the pathogenesis is still unclear, it is generally accepted that negative pressure in the maxillary sinus secondary to the maxillary ostium occlusion is the cause of this syndrome. Therefore, patients diagnosed with CMA or SSS generally show obstruction of the maxillary infundibulum on computed tomography (CT). It has never been reported that the open maxillary sinus affected CMA. Furthermore, it is unknown how the open maxillary sinus is related to the development of CMA.
We herein report the case of a 49-year-old woman who initially had normal maxillary sinus and then six years later developed CMA, without any impediment of the maxillary infundibulum. The patient is an exception to the commonly accepted mechanism underlying the pathogenesis of CMA. It suggests the existence of alternative potential causes contributing to CMA in the open maxillary sinus.
This 49-year-old woman first presented with left nasal congestion, rhinorrhoea and cheek pain. CT showed partial opacification of the left maxillary sinus but no signs of inward bowing of the sinus, thickening of the maxillary wall or increased orbital volume [Figure 1a-d]. She was diagnosed with acute rhinosinusitis and treated with intravenous antibiotics (cefazolin 1.0 g twice a day) for six days followed by seven days of oral antibiotics (cefcapene pivoxil 100 mg three times a day) at our hospital. After the treatment, magnetic resonance imaging showed only slight mucous swelling in the left maxillary sinus, and we finished the follow-up [Figure 2a and b]. Six years later, she presented with right nasal congestion, rhinorrhoea and cheek pain. She had no other symptoms on her left nose, including no aesthetic asymmetry or any issues with her visual function. She had never experienced facial trauma or undergone relevant surgery in the past.
We performed CT, which revealed the total opacification of the right maxillary and ethmoid sinuses. We treated the patient with intravenous antibiotics for her acute rhinosinusitis. CT incidentally showed a hypoplastic left maxillary sinus with bony hypertrophy, which is a typical finding for CMA. Interestingly, the ostium of the maxillary sinus was potent [Figure 1h], and the uncinate process was intact without external deviation [Figure 1f]. On an axial image, a new bony septum was found to have formed inside the left maxillary sinus, which resulted in the formation of a small maxillary cyst [Figure 1e]. No significant changes were observed in the orbital volume [Figure 1f-h]. Furthermore, the anterior maxillary wall, which was separated from the newly formed cyst and supposedly free from negative pressure, was retracted [Figure 1g].
Since the patient was free from any symptoms, surgical intervention was not considered. We did not treat the left CMA at all. No progression was confirmed clinically or on CT at the 6-month follow-up.
We encountered a patient who developed CMA without occlusion of the maxillary ostium. CMA is a relatively new concept, with the term first used in 1997. It is generally regarded as an acquired condition. The cause of CMA and SSS is considered to be negative pressure on the maxillary sinus. Therefore, the mechanism underlying CMA in our patient is unexplainable by the commonly accepted theory. We considered the possibility that osteitis contributed to CMA in the open maxillary sinus.
The clinical symptoms of CMA and SSS have been defined, including enophthalmos, hypoglobus, retraction of the eyelid, the sinking of the eye, deepening of the superior sulcus, diplopia, ptosis and facial pressure/pain, but their pathogenesis remains unclear.[2,3] One theory is that hypoventilation of the maxillary sinus due to obstruction of the maxillary ostium causes these syndromes. Hypoventilation results in the absorption of gases into the closed sinus cavity capillaries, which creates negative pressure. This leads to the accumulation of secretion with chronic subclinical inflammation, resulting in the inward bowing of the maxillary sinus walls and subsequent thinning of the maxillary wall. In previously reported CMA cases, the maxillary sinus infundibulum was shown to be obstructed on CT. In addition, they were often associated with conditions likely to cause occlusion of the maxillary infundibulum, such as lateralisation of the uncinate process and middle turbinate, enlargement of the ipsilateral middle meatus and ipsilateral septal deviation to the affected sinus.[2,6]
However, our patient was diagnosed with CMA with an open maxillary ostium six years after being diagnosed with acute rhinosinusitis. CT also showed that the new septum in the maxillary sinus had been formed by proliferative bone, which resulted in the formation of a small maxillary cyst; the maxillary wall surrounding this new cyst then retracted and thickened. This phenomenon may be partly understood by applying the above-mentioned negative pressure theory, and long-standing inflammation can lead to hyperostosis of the maxillary wall.
However, the anterior maxillary wall distant from this new cyst was retracted, and the ostium of the maxillary sinus was intact. An open space causing inward bowing of the maxillary wall has never been reported. This finding is unexplainable by the commonly accepted pathogenesis of CMA and SSS. We speculate that osteitis and negative pressure of the surrounding (yet not directly contacted) cavity caused the phenomenon.
Paranasal sinus osteitis is sometimes associated with chronic rhinosinusitis and corresponds to the thickening of the sinus wall on CT. Previous studies have described the associated histological changes, including the presence of new bone formation, fibrosis, periosteal thickening and increased osteoblastic–osteoclastic activity. These processes are not caused by either bacterial invasion or the infiltration of inflammatory cells. Instead, it represents a series of changes that are associated with bone tissue repair.
Apparent bone hypertrophy was seen in our patient [Figure 1e, g and h]. New bone formation occurred, forming a small cyst inside the maxillary sinus [Figure 1e; arrowhead]. Interestingly, the deformed site [Figure 1g; double arrow] itself was not hypertrophied. We assume that osteitis, which was diagnosed with bony hypertrophy in this case, might have partly influenced the inward retraction of the sinus observed in this patient, although the exact mechanism underlying CMA in our patient is unclear. Further studies are needed to clarify the intimate pathogenesis.
The treatment plan for patients without symptoms is controversial. While undergoing antrostomy might prevent the manifestation of ocular aesthetic symptoms, unoperated patients with no significant progression of ocular signs were seen (follow-up period: 4–63 months). The present patient did not undergo surgical treatment because she had no ocular or aesthetic issues, and the ostium of the maxillary sinus was already open. Although no progression was noted clinically or on CT at the 6-month follow-up, we will need to conduct continuous follow-ups going forward if her condition worsens.
We encountered a 49-year-old woman, in whom the maxillary infundibulum was not occluded despite inward bowing of the maxillary sinus being recognised on CT, a finding compatible with CMA. The pathogenesis of CMA was not explainable by the commonly accepted negative pressure concept. Osteitis with chronic rhinosinusitis might have caused the deformity of the maxillary sinus in this case.
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.
Financial support and sponsorship
This work was supported by JSPS KAKENHI Grant Number JP19K08948.
Conflicts of interest
There are no conflicts of interest.
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