A Retrospective Study on Silent Sinus Syndrome in Cone Beam-Computed Tomography Images—Author Classification Proposal

Abstract

Introduction. Facial asymmetry might have many etiological factors. Most known and recognized factors are related to hemimandibular hyperplasia, elongation, condyle-related pathologies hemifacial microsomia, laterogenia, and others. In some cases, however, facial asymmetry has a different origin within the maxillary sinus (MS) bones. This rare entity as a silent sinus syndrome (SSS) causes secondary midfacial and maxillary asymmetry because of the retraction of the sinus walls. The authors present their own proposal for SSS/CMA (chronic maxillary atelectasia) classification and possible maxillary sinus disease alterations related to the scope of changes in the maxillary sinus walls, asymmetry, opacification, and related features. Material and Methods. The study consisted of 131 CBCT images which were evaluated. The authors focus on fourteen retrospective cone beam-computed tomography studies (CBCT) performed to establish and evaluate sources of facial asymmetry. Results. Neither presented maxillary and facial asymmetry cases correspond to the typical SSS/CMA findings. Asymptomatic maxillary sinusitis co-existing in maxillary asymmetry cases in patients suffering from skeletal malocclusion remains atypical for SSS pure and in-pure cases. The osteomeatal complex (OMC) patency is more common for pure forms. Conclusions. Computed tomography quite easily can identify the source of the problems in the maxillary sinus and identify SSS. Coexistent chronic rhinosinusitis might correspond with another MS pathology, CMA—chronic maxillary atelectasia. The scope and the degree of MS cause midfacial asymmetry; however, the scope of sinus opacification, osteomeatal complex drainage, and occurrence of other symptoms might be more or less present. The OMC patency is more common for pure forms.

1. Introduction

Maxillary sinuses (MSs, the antrum of Highmore) are the largest of the paranasal sinuses (Figure 1). They are paired, located in the body of the maxillary bone, and pyramidally shaped. They are surrounded by several bony walls and have four recesses. The main MS walls are the roof (floor of the orbit) and medial, posterolateral, and anterior walls as well. Its drainage is related to the proper function of the osteomeatal complex (OMC), which arises into the infundibulum and then through the hiatus semilunaris into the middle meatus in the nasal cavity. Each of its bony walls has its separate anatomy and function (for example, the superior wall is the floor of the eye socket). When some pathologies arise, the anatomy and structure of bony walls influence the volume and opacity of the MSs [1,2,3,4,5].

Silent sinus syndrome (SSS) is also called imploding antrum syndrome (with the implosion (retraction) of posterior, anterior, lateral, and medial walls into the lumen of the sinus). This asymptomatic maxillary sinus disease is a rare and clinically interesting pathology, without gender, age, or other factors of predilection. SSS has its major typical radiological and clinical features (

Table 1. Most common and typical clinical and radiological symptoms of silent sinus syndrome—SSS in asymptomatic form. Abbreviations: CT—computed tomography, CBCT—cone beam-computed tomography, SSS—silent sinus syndrome, MS—maxillary sinus.

Typical Clinical Symptoms SSS	Typical Radiological Features in CT/CBCT of SSS
spontaneous unilateral enophthalmos	unilateral MS opacification
hypoglobus	MS volume reduction
facial asymmetry	blockage of the osteomeatal complex
asymptomatic maxillary sinusitis	MS walls deformation
diplopia in severe cases	maxillary sinus asymmetry

and Figure 2). The first report of the disease was reported by Montgomery in 1964; however, further milestones for determining the term SSS are related to a study by Soparkar et al. in 1994. The time of occurrence might vary from 17 to 88 years of age, according to the literature, with some slight predominance to the right maxillary sinus (57%). Very rare reports exist of its occurrence in children, in the frontal sinus, or as bilateral MS SSS [1,2,3,4,5,6,7,8].

SSS is a spontaneous painless progressive unilateral collapse of the maxillary sinus and orbital floor with complete or partial opacification of the collapsed sinus with the absence of trauma, tumors, chronic rhinosinusitis (CRS), and surgery-related factors. SSS’s typical characteristics in some cases might vary because of possible CRS presence, as well as lack of full MS opacification or OMC blockage, along with other modifications of clinical and radiological symptoms reported widely [8,9,10,11,12,13,14,15,16]. Some authors distinguish between SSS and chronic maxillary atelectasis (CMA). The MS wall atelectasis quite often results in painless enophthalmos, hypoglobus, and mid-facial asymmetry; however, sometimes atypical SSS manifestations might be also present [17,18,19]. Severe cases might include diplopia without extraocular eye movement disruption. From the authors’ perspective, the clinically present CRS might be helpful for distinguishing between some visualized CT/CBCT (computed tomography/cone beam-computed tomography) radiological pathologies. For years, SSS was the topic of some studies and investigations, mostly because of the influence on eye socket displacement, facial and maxillary asymmetry, and maxillary sinus volume loss with the coexistence of its decreased ventilation through the osteomeatal complex (OMC) [12,13,14,15].

Since most are asymptomatic, some reports indicate its possible occurrence after trauma within one of the walls of the sinus, damage to the OMC, damage during MS, or surgery. SSS can be more easily diagnosed because of a CT evaluation, rather than MR (magnetic resonance studies); however, some clinical and radiological features might be also atypical or less described [8,9,10,11,12,13,14,15,16,17,18,19,20,21] (

Table 2. The ranges of clinical and radiological atypical and additional features of silent sinus syndrome modified by the presence of symptomatic and asymptomatic sinusitis with or without maxillary sinus opacification. Modified from Albadr (2020) [19], Hura et al. (2020) [20], and Rosso et al. (2022) [21] studies. Abbreviations: CT—computed tomography, CBCT—cone beam-computed tomography, SSS—ailent sinus syndrome, MS-maxillary sinus, CRS—chronic rhinosinusitis.

Additional Clinical Alterations in SSS	Additional Radiological Variations in SSS
disturbed eye movements	unilateral MS hypoventilation
asymmetry of pupillary midline	OMC with or without blockage
mid-face asymmetry	most MS walls retraction
deviated maxillary cant	MS opacification: full volume, not full volume
symptomatic maxillary sinusitis	ipsilateral maxillary sinus retraction
MS pain	collapse with/without inferior bowing of the orbital floor
CRS	osteomeatal complex without obstruction
occurrence of skeletal class II maloclusion	lateralization (lateral deviation) of the uncinate and middle turbinate, and infundibular occlusion
occurrence of skeletal class III maloclusion	enlarged middle meatus
disturbed nasal breathing	obstruction of the natural maxillary ostium
underdeveloped midface	retracted downward orbital floor with possible bone thickening
maxilary hypoplasia	demineralization of the sinus walls
maxillo-mandibular asymmetry	other abnormal intranasal characteristics on the affected side
flattening of the malar eminence	concomitant compensatory augmentation in ipsilateral orbital volume
	deviation of the nasal septum
	expanded retroantral fat pad
	retraction of 1–3 MS walls

and Figure 3).

The following study is an attempt to establish a possible classification of SSS/CMA-related MS diseases based on the authors’ own cases and similar cases related to various MS forms of dentoalveolar and skeletal discrepancies and related ones focused on the CBCT/CT evaluation which might be the most helpful to establish the scope of each MS pathology.

2. Material and Methods

2.1. Characteristic of Study Group

In the presented retrospective study, we analyzed 131 CBCT databases of patients with various forms of dental and skeletal malocclusion which were collected between 2017 and 2022 (Figure 1, Figure 2, Figure 3, Figure 4 and Figure 5). There were 79 (60.3%) women and 52 (39.7%) men with a mean age of 34.1 + 11.7 years old. Among the patients, 12 (9.2%) had mucosal thickening related to poor dental status; 7 (5.3%)—had skeletal malocclusion scheduled for orthognathic surgery. Eight cases (6.1%) had an underwood septa in the maxillary sinus; five (3.8%) had chronic rhinosinusitis (CRS); four (3.1%) had pain in the left temporomandibular joint; seventeen (13.0%) had other symptoms, and seventy-eight (59.5%) patients had no additional pathology symptoms related with the sinuses.

Most of them are related to various dento-maxillo-facial deformities. Of those, only 14 meet the inclusion criteria for the SSS/CMA pathologies (Figure 6). Because some pathologies have all characteristics of SSS/CMA, they were entitled by the authors as pure forms; however, on the other hand those with not fully visible all (or clearly established) radiological/clinical symptoms had been entitled as in-pure types. Ten cases of SSS are divided into pure and in-pure cases equally. Two others because of symptoms of CRS are considered CMA with pure and in-pure origins. Two of them are related to a mixture of features from SSS/CMA; therefore, they will be presented as atypical ones. Complete ranges of clinical and radiological atypical and additional features of silent sinus syndrome are presented in Table 2. The knowledge of the presence of CRS was gained from CBCT database descriptions.

Most cases were investigated and diagnosed with CBCT 20 × 20 FOV (field of view) imaging protocol based on a RayScan S 5471.3 mGy (RayCompany Ltd., Samsung 1-ro, Hwaseong-si, Gyeonggi-do, Republic of Korea). Information of a few cases, consulted based on CT/CBCT from outside of the presented herein setup, was related to the SARS-CoV-2 pandemic. The overall data does not have any influence on the presented herein material.

Radiological inclusion criteria were focused on findings such as various maxilla-mandibular skeletal abnormalities and/or maxillary asymmetry, maxillary sinus walls inward volume reduction (1–4 walls), unilateral MS opacification full/partial, OMC drainage full or obstructed, asymmetry in the floor of the orbit, maxillary wall asymmetry, MS 1–4 wall deformations (atelectasis), and cases not related to trauma/sinus surgery (and no signs of such present).

Additional clinical evaluation inclusion criteria included: CRS symptomatic (CMA) or asymptomatic (SSS), pain or asymptomatic cases, and midfacial asymmetry or maxillary asymmetry/deviated maxillary. Presented criteria were related to the aim of the CBCT referral.

Most known cases are symptomless; however, some world reports might suggest the presence of chronic rhinosinusitis (CRS). When present, a quite different situation might occur and indicate CMA (chronic maxillary atelectasis), a form suggested by Brandt and Wright [17] (Table 2). It is worth noticing that based on some reports such as those reported by Lee et al. (2018), a fully aerated maxillary sinus without any opacification but the presence of other features (enophthalmos, hypoglobus, or maxillary atelectasis) should not exclude the diagnosis of SSS [18]. This situation might indicate that SSS might have a form with a maxillary sinus obstruction, which is typical, and a second one with a clear sinus, with atypical features representing the same disease visualized as MS wall asymmetry and an inward position with an affected sinus volume reduction [15,16,17,18,19]. A recent paper by Hura et al. highlighted the most important factors in SSS/CMA [20]. Combining all of the mentioned above characteristics, the authors want to present their own proposal for the classification of the mentioned SSS/CMA MS pathologies.

2.2. Statistical Analysis

The number and percent of observations were calculated for qualitative variables, and the average and standard deviation (+SD) were calculated as well. Fisher’s exact test was used for analysis of differences between diagnostic criteria for SSS/CMA pathologies. A two-tailed p-value of <0.05 was considered statistically significant. Statistical analyses were performed using STATISTICA 13.3 software (StatSoft Inc., Tulsa, OK, USA).

3. Results

3.1. Demographic and Statistical Data

In the presented CBCT findings in SSS/CMA patients, the following data on gender, age, co-morbidities, and other related factors do not pay a role in the etiology and scope of the mentioned herein MS pathologies. A total of fourteen patients were enrolled in the MS study on SSS/CMA and related sinus findings according to the Brandt and Wright study (

Table 3. Diagnostic differences between SSS and CMA based on Brandt and Wright [17] (2008) diagnostic criteria. Abbreviations: CT—computed tomography, CBCT—cone beam-computed tomography, SSS—silent sinus syndrome, CMA—chronic maxillary atelectasis), CRS—chronic rhinosinusitis.

Diagnostic Criteria for SSS	Diagnostic Criteria for CMA
Enophthalmos and/or hypoglobus	Enophthalmos and/or hypoglobus
Maxillary sinus atelectasis or opacification on CT imaging	Maxillary sinus opacification noted on CT imaging
Absence of radiologic findings of CRS on CT imaging
Clinical CRS not present	CRS present at examination

and

Table 4. Used data to ensure the SSS/CMA occurrence in both pure and in-pure forms. Abbreviations: SSS—silent sinus syndrome; CMA—chronic maxillary atelectasia; MSH—maxillary sinus hypoplasia; CBCT—cone beam-computed tomography; 131—number of evaluated radiographs; MS—maxillary sinus with proper anatomy; forms p—pure; i—in-pure; tso—trauma/surgery or other related.

MS Pathology	MS	SSS	SSS	CMA	CMA	SSS-CMA	tsoSSS	MSH
Forms	Proper Anatomy	Pure/pSSS	In-Pure/iSSS	Pure/pSSS	In-Pure/iSSS
Patients	117	5	5	1	1	1	0	1
CBCT = 131	89.32%	3.82%	3.82%	0.76%	0.76%	0.76%	0%	0.76%

).

3.2. Relationship between CT/CBCT Radiological Features and Final Diagnosis of SSS/CMA Pathologies

The data concerning gender, age, co-morbidities, and other related factors do not play a role in the etiology and scope of the mentioned herein MS pathologies. The results of relationships between CT/CBCT radiological diagnostic criteria and the occurrence of SSS/CMA cases in both pure and in-pure forms in fourteen patients were presented in

Table 5. Relationships between CT/CBCT radiological features and occurrence of SSS/CMA cases in both pure and in-pure forms. Descriptive data were presented as number of positive observations (percent). Fisher’s exact test was used for analysis of data.

	SSS		CMA		SSS-CMA (n = 1)	MSH (n = 1)	p-Value
	Pure /pSSS (n = 5)	In-pure /iSSS (n = 5)	Pure /pCMA (n = 1)	In-Pure /iCMA (n = 1)
MS atelectasis	5 (100.0)	5 (100.0)	1 (100.0)	1 (100.0)	1 (100.0)	1 (100.0)	1.000
Unilateral MS opacification	5 (100.0)	0 (0.0)	1 (100.0)	0 (0.0)	1 (100.0)	0 (0.0)	0.002 *
MS volume reduction	5 (100.0)	5 (100.0)	1 (100.0)	1 (100.0)	1 (100.0)	1 (100.0)	1.000
Blockage of the osteomeatal complex	5 (100.0)	0 (0.0)	1 (100.0)	0 (0.0)	1 (100.0)	0 (0.0)	0.002*
MS walls deformation	5 (100.0)	5 (100.0)	1 (100.0)	1 (100.0)	1 (100.0)	1 (100.0)	1.000
MS asymmetry	3 (60.0)	3 (60.0)	1 (100.0)	0 (0.0)	1 (100.0)	0 (0.0)	0.341
Unilateral MS hypoventilation	5 (100.0)	0 (0.0)	1 (100.0)	0 (0.0)	1 (100.0)	0 (0.0)	0.002 *
Osteomeatal complex (OMC) with or without blockage	4 (80.0)	0 (0.0)	1 (100.0)	0 (0.0)	1 (100.0)	0 (0.0)	0.015 *

SSS: silent sinus syndrome; CMA: chronic maxillary atelectasia; MSH: maxillary sinus hypoplasia *: statistically significant.

. Diagnosis tso-SSS was excluded from analysis because any of the patients were diagnosed as this form of SSS/CMA. The rate of unilateral MS opacification, the blockage of the osteomeatal complex, unilateral MS hypoventilation, and the osteomeatal complex (OMC) with or without blockage were significantly higher in the pure SSS, pure CMA, and SSS-CMA pathologies (p < 0.05 for all). There were no significant differences between the following CT/CBCT radiological features: MS atelectasis, MS volume reduction, MS walls deformation, and MS asymmetry in all forms of MS pathologies.

3.3. Association between Clinical Symptoms and Final Diagnosis of SSS/CMA Pathologies

As demonstrated in

Table 6. Relationships between clinical symptoms and occurrence of SSS/CMA cases in both pure and in-pure forms. Descriptive data were presented as number of positive observations (percent). Fisher’s exact test was used for analysis of data.

	SSS		CMA		SSS-CMA (n = 1)	MSH (n = 1)	p-Value
	Pure /pSSS (n = 5)	In-Pure /iSSS (n = 5)	Pure /pCMA (n = 1)	In-Pure /iCMA (n = 1)
Spontaneous unilateral enophthalmos	5 (100.0)	3 (60.0)	1 (100.0)	1 (100.0)	0 (0.0)	0 (0.0)	0.074
Hypoglobus	0 (0.0)	1 (20.0)	0 (0.0)	0 (0.0)	0 (0.0)	0 (0.0)	0.821
Facial asymmetry	4 (80.0)	4 (80.0)	0 (100.0)	1 (100.0)	0 (0.0)	0 (0.0)	0.143
Asymptomatic maxillary sinusitis	5 (100.0)	5 (100.0)	0 (0.0)	0 (0.0)	1 (100.0)	0 (0.0)	0.012 *
Diplopia in severe cases	0 (0.0)	0 (0.0)	0 (0.0)	0 (0.0)	0 (0.0)	0 (0.0)	1.000
CRS presence	0 (0.0)	0 (0.0)	1 (100.0)	1 (100.0)	0 (0.0)	0 (0.0)	0.043 *
Mid-facial asymmetry	5 (100.0)	3 (60.0)	0 (0.0)	0 (0.0)	0 (0.0)	0 (0.0)	0.029 *
Maxillary asymmetry	5 (100.0)	4 (80.0)	1 (100.0)	1 (100.0)	1 (100.0)	0 (0.0)	0.262
Facial pain/pressure	0 (0.0)	1 (20.0)	1 (100.0)	0 (0.0)	1 (100.0)	0 (0.0)	0.089
Headaches	0 (0.0)	0 (0.0)	1 (100.0)	0 (0.0)	1 (100.0)	0 (0.0)	0.042 *
Nasal obstruction with/without taste and smell variations	0 (0.0)	0 (0.0)	1 (100.0)	1 (100.0)	1 (100.0)	0 (0.0)	0.012 *

SSS: silent sinus syndrome; CMA: chronic maxillary atelectasia; MSH: maxillary sinus hypoplasia; *: statistically significant.

, the prevalence of asymptomatic maxillary sinusitis was significantly higher in the patients diagnosed as SSS (both pSSS and iSSS) or SSS-CMA pathologies (p < 0.012), whereas CRS presence was a characteristic clinical symptom for both forms of CMA (p < 0.043). The reason why the authors know about CRS from a clinical point of view is that the CBCT database was labeled with the main cause for each patient who was sent for a radiographic imaging, the CBCT evaluation.

Based on the current literature findings (Brandt and Wright; Lee et al.; Albadir; Hura et al.; Rosso et al.) [17,18,19,20,21], we analyzed the association between additional clinical symptoms such as mid-facial asymmetry, maxillary asymmetry, facial pain/pressure, headaches, and nasal obstruction with/without taste and smell variations and final diagnosis of SSS/CMA pathologies. The mid-facial asymmetry symptom significantly increased in both forms of SSS (pSSS and iSSS, p < 0.029). A headache symptom was characteristic for pure CMA and SSS-CMA (p < 0.042), and nasal obstruction with/without taste and smell variations was significantly higher in both forms of CMA (pCMA and iCMA) and in SSS-CMA pathologies (p < 0.012).

3.4. Classification Proposal

Based on the following, the authors want to suggest their own classification proposal mostly based on radiological findings, where clinical symptoms play a secondary role in either confirming or neglecting the following MS deformities based on SSS/CMA findings [20,21,22,23,24,25,26,27,28,29,30,31,32,33]. Type 0 MS (Figure 1) is a typical MS, with healthy, clear OMC, full symmetry, and no opacification. The authors’ proposal on SSS/CMA divides them into types and sub-types of classification based on the literature [15,16,17,18,19] and their own observations:

(1)

Type 1 SSS (pure SSS = pSSS) (Figure 2) MS four (4) wall retraction, OMC not patent, opacification present;

(2)

Type 2 in-pure SSS (iSSS) (Figure 3, Figure 4 and Figure 6) related to maxillary deformation (might be related to maxilla-mandibular skeletal class II/III deformities or others), clinically asymptomatic, not related to trauma or surgery, 1–3 MS walls retracted, OMC clear, no opacification, like suggested by Lee et al., the “not so silent sinus” [18];

(3)

Type 3 CMA (pure form of chronic maxillary atelectasis—pCMA) (Figure 7), suggested by Brandt and Wright [17], corresponding to the clinical presentation of CRS, pain, and symptomatic sinus manifestation, complete sinus opacification;

(4)

Type 4 CMA (an in-pure form of chronic maxillary atelectasis—iCMA) (Figure 8), corresponding to the clinical presentation of CRS, pain, and symptomatic sinus manifestation, however lacking a complete sinus opacification; OMC function might not be disturbed, 1–4 MS walls can be retracted;

(5)

Type 5 Mixed form SSS-CMA on both MCs (Figure 9)—present asymmetrically, combines both forms of SSS and CMA in pure or in-pure forms;

(6)

Type 6 atypical SSS or CMA (tsoSSS/tsoCMA—trauma, surgery, or other related SSS/CMA) of post-traumatic occurrence, post-surgical, or other iatrogenic related, such as suggested by Araslanova et al. [30];

(7)

Type 7 MSH = maxillary sinus hypoplasia (Figure 10 and Figure 11)—a very rare, probably somehow atypical case of complete symmetrical MS retraction and atrophy, without CRS. Possible relation to bilateral MSH—bilateral maxillary sinus hypoplasia should be considered and requires further studies [33].

3.5. Final Considerations

Radiological studies on CBCT/CT are the first diagnostic steps in SSS/CMA evaluation within MS. The occurrence of presented radiological features plays the most important role in distinguishing the type of MS pathology. Additional clinical symptoms, while present, may not only differentiate whether the present MS pathology is from active, acute, or chronic disease but also underlines the necessity for any surgical, conservative approach or perhaps only the need to closely monitor the presented disease within the sinus. When SSS/CMA is in a stable form, a variety of surgical procedures can be carried out smoothly, especially SARME (surgically assisted rapid maxillary expansion) in patients suffering from skeletal malocclusion (Figure 12).

3.6. Commentary on the Classification

The authors’ point of view on SSS/CMA establishes a proposal on MS classification related to the changes in wall anatomy and its asymmetry compared to the healthy side. Ophthalmologic symptoms such as hypoglobus and diplopia with enophthalmos are very important; however, the authors want to leave them for severe cases of SSS only; therefore, they are considered as important secondary factors for SSS confirmation. Since many literature reports addressed SSS/CMA in the full scope of symptoms, reports on symptoms that are not clearly visible are also known. Because of the following, the authors performed a recent CBCT evaluation of patients in order to present their own findings along with a proposal of classification, based on the full scope of syndromes (pure in CBCT), and did not fully address the scope of symptoms visible in radiological CBCT evaluation (in-pure). Further studies on SSS/CMA will explore the insights of the ophthalmologic spectrum of this MS-related pathology (Table 5 and Table 6).

4. Discussion

The pathology of SSS is widely discussed and not yet fully clear. Its relationship with the occlusion of the MS ostium resulting in gradual air resorption and the presence of negative pressure within the MS is considered the most possible one. During the time when OMC is closed or impatient, the inward bowing of all four maxillary walls is present gradually in time with various stages of intensity. The progression of MS atelectasis and osteomalacia is not possible to estimate. During time asymmetry, the maxilla-malar area might be present along with the occurrence of enophthalmos. Some other theories are known, including the presence of chronic obstructive sinusitis, inflammatory wall erosion, lateralization of the uncinated process, and others [12,13,14,15,16,17,18,19,20].

A differential diagnosis should include other MS-related pathologies such as paranasal sinuses hypo-/hyperventilation cases, MS hypoplasia (MSH), facial deformities, trauma-related cases, surgically related (orbital decompression) cases, mucocele, chronic rhinosinusitis, cancer-related factors, linear scleroderma, hemifacial microsomia, Parry–Romberg syndrome, and others [8,9,10,11,12,13,14,15,16,17,18,19,20,21].

SSS might have some characteristic radiological and clinical features. Most of the features are found accidentally on routine CT/CBCT evaluation (Table 1). In some situations, as reported by Albadr and other authors, magnetic resonance imaging (MRI) might establish some additional features, such as the presence of an opacified sinus with mixed-signal contents and diminished volume, the prominence of orbital fat, and widening of the retroantral fat pad, along with the extraocular muscle (inferior rectus muscle), which may descend along with the globe downwards [11,12,13,14,15,16,17,18,19]. Based on the following occurrence of enophthalmos, maxillary opacification with maxillary atelectasia are a basic characteristic feature of SSS. The presented symptoms confirm the final diagnosis in the typical asymptomatic idiopathic form [18,19,20,21,22].

SSS in MS is a rare asymptomatic finding. The changes within the MS bony walls and their inward retraction causing asymmetrical sinus volume reduction compared to the opposite healthy side is always present. The opacification, OMC drainage, and sinus floor downward position may have different intensities [15,16,17,18,19,20]. Many other pathologies present in MS do not have this full scope of symptoms as this disease. As presented in the authors’ study, clear SSS/CMA can be also divided into in-pure forms with lesser radiological symptoms present, which should be important form clinical point of view, because this fact would impact any additional procedures which could be done if necessary. The occurrence of CRS might improve that diagnosis and indicate CMA, which is mostly a symptomatic disease. When present, each clinician should be aware of its presence and symptoms which require conservative or surgical approaches to treat it. Then, either a detailed pharmacological or surgical approach such as FESS/ESS should be scheduled. Each treatment should be focused on restoring the proper sinus aeration and controlling any sino-nasal and ophthalmic syndromes. Because each symptom could have a different manifestation rate, an adequate clinical and radiological evaluation is essential. Sinus manifestation itself has a great variety of typical and atypical radiological and clinical symptoms related to MS. Despite the fact that enophthalmos with/without hypoglobus are quite more common than ophthalmologic symptoms, diplopia in severe cases might be also present. A discussion is still ongoing if asymptomatic cases require the same approach as symptomatic cases and if the typical forms (pure) and atypical ones (in-pure) need the same procedures. FESS (functional endoscopic sinus surgery) seems to be a treatment of choice, while the surgical repair of the floor of the orbit is rarely used and is mostly case-related. Before, however, any additional diagnostics and treatment are scheduled, it is necessary to establish the scope of symptoms and the necessity for their treatment [15,16,17,18,19,22,23,24,25,26]. The authors would want to point out also that atypical syndromes such as headaches, impaired nose breathing, and facial asymmetry should never exclude the occurrence of SSS/CMA.

Due to the small number of SSS cases, a lot of discussions are focused on its proper classification, definition, and accurate treatment modalities [13,14,15,16,17]. A recent great PRISMA-compliant systematic review by Rosso et al. highlighted some important issues [21]. According to the review, the main SSS definition consists of both the most common and clinically relevant factors like enophthalmos and maxillary atelectasia. Nevertheless, the presence of sino-nasal diseases, history of facial trauma, and related factors are more commonly present in the inclusion criteria for SSS. Therefore, CMA related to CRS requires not only CT/CBCT evaluation [15,16,17,18,19,20]. Presented by the authors, radiological evaluation is fast and easy for any clinician to perform, because key anatomical and radiological changes in MS can be clearly identified as suggested in Table 1, Table 2 and Table 3. It is important to know that trauma-related cases leading to SSS formation are not fully related to SSS, since they are related to idiopathic, asymptomatic, and spontaneous SSS formation [18,19,20,21]. As presented in the authors’ proposal for classification, all cases were not related to either trauma, surgery, or other factors. A pure form of SSS is not related to CRS, which was suggested by Brandt and Wright and confirmed by a study by Rosse et al. [17,21]. In either asymptomatic atelectasia or MS walls, inward traction causing an asymmetrical reduction in MS volume and shape, the relationship with skeletal malocclusion, the degree of MS opacification, and OMC patency have been more common than the downward position of the orbital floor. A good idea for those major factors, followed by more minor factors such as OMC obstruction and the presence or absence of sino-nasal diseases, with CT evaluation, is still the most effective and accurate diagnostic tool for SSS. In the presented study, the osteomeatal patency and sinus opacification are not so typical radiological symptoms of the presented sinus pathologies; however, their occurrence can lead each clinician to identify possible treatment necessities.

Based on the study by Hura et al., there are a small number of differences between SSS and CMA that may differentiate them [20,21,22,23,24,25,26,27,28]. It seems that in most known cases, the spectrum of symptomatic CRS is a still discussable aspect between both pathologies [20,21,22,23]. The degree of CRS manifestation might vary in each case, and so far it is not yet fully understood [25,26,27,28]. While present, they indicate CMA and not the SSS occurrence. The scope of duration with CRS patients might vary from 6 to 12 or more weeks [20,21,22,23,24,25]. Those symptoms might include decreased nasal breathing, with obstruction or blockage of the nasal cavity, some scope of pain, pressure within the sinus, and disturbing smell with also the presence of atypical compression within the affected sinus, malar, and sometimes ale alveolar process of the maxilla, mimicking a tooth pain [20,21,22,23,24,25,26,27,28,29,30]. Since in the presented study the authors have not focused on the scope of CRS symptoms, but just mostly CT/CBCT data, the next studies therefore need to fully estimate the degree of symptoms and the potential clinical aspect of SSS/CMA.

So far, a limited amount of cases reported some atypical SSS manifestations. A few cases of atypical SSS characteristics for lack of MS opacification and not disturbed OMC drainage might be also found, as reported by Lee et al. [18]. Furthermore, atypical and unexplained sources of enophthalmos, hypoglobus, and maxillary atelectasia might also suggest SSS [16,18]. Most MSs still typically lack proper ventilation and total MS volume opacification [16]. On the other hand, some cases describe posttraumatic SSS formation, which is an uncommon type of SSS, and should be described as atypical cases, related to iatrogenic or other factors, as reported by Araslanova et al. [30]. Perhaps other extra-sinus-related factors, that influence any damage to the MS, might promote the formation of SSS/CMA; however, this hypothesis needs more study. While SSS is an asymptomatic disease, some authors also report a “not so silent sinus syndrome”, related to an incompletely opacified hypoplastic sinus and inward traction of some MS walls [31]. The “not so silent sinus” term suggested by some authors is also confirmed in the authors’ study results. Despite the downward traction of the orbital floor, not each case results in hypoglobus and diplopia; however, enophthalmos might have various intensities [32], because each is strongly individual and might progress in time treatment remains discussable and quite individual. The treatment of SSS depends upon if it is a progressive disease or in the stable asymptomatic phase. In the authors’ material, the ophthalmologic syndromes were rare and not clearly established, so none of the patients required ophthalmologic consultation or any scope of intervention.

The main surgical aspect is focused on restoring proper MS ventilation by the FESS procedure and the middle meatal antrostomy procedure. At first, the OMC patency must be restored and improved, followed by sinus debridement in some cases. Endoscopic uncinectomy and antrostomy are sufficient to restore MS drainage. Some technique alternation is associated with the balloon Seldinger technique to improve MS drainage and decrease sinus-related symptoms if present [12,13,14,15,16,17,18,22,23,24,25,26,27,28,29,30,31,32]. In rare cases of bilateral MS opacification, symptoms present should be individually evaluated [33].

Old methods might indicate the currently rarely used Caldwell–Luc procedure to remove the mucosa from the MS and then establish an additional surgical fistula (antrostomy via the medial nasal wall) under the inferior nasal conchae to improve the MS drainage. Most commonly, a Foley catheter is placed for a few days through the nose towards the MS antrum which is placed to ensure good aeration and drainage. This procedure has various limitations; therefore, it is currently rarely used.

Orbital floor reconstruction can be achieved by titanium mesh or perhaps iliac bone grafting. Improving the globe’s superior position is a very challenging procedure, the same as enophthalmos correction in some cases. The so-called “sunken” eye symptom is related to the inferior displacement of the globe, because of the negative pressure within the MS. Its correction might require not only floor reconstruction but also bone grafting. In some cases, a cosmetic approach towards the inferior orbital rim and zygomatico-malar eminence can be achieved with silicone implants, bone grafting, or orthognathic surgery. Some orbitotomy procedures can also be used. Some reports indicate the repair of the medial orbital with implants. Nevertheless, improving midfacial asymmetry and proper horizontal orbital height is challenging and sometimes requires more surgeries [12,13,14,15,16,17,18,22,23,24,25,26,27,28,29,30].

An additional ophthalmologic intervention might be related to the correction of hypoglobus, diplopia, or other atypical features. Diplopia despite its etiology might require revision surgery in time. Some authors indicate that sinus floor malposition is quite common, and when reconstructing it via neuronavigation surgery, the usage of intraoperative CBCT can improve the outcomes [31,32,33,34,35].

Secondly, when MS has not opacified anymore and is properly aerated, skeletal abnormalities related to maxilla-malar area flattening and maxillary, mid-facial asymmetry correction can be achieved either with grafting procedures or orthognathic surgery alone [12,13,14,15,16,17,18,22,23,24,25,26,27,28,29,30].

Special consideration of SSS in children should be noted. FESS with uncinectomy and middle meatal antrostomy is a treatment of choice. Orbital floor reconstruction should be limited to special cases. The study by Farneti et al. indicates that, in children, MS after treatment tends to re-expand in time and is quite comparable in size compared to the healthy side [36].

SSS is not only a silent sinus syndrome but also might be misunderstood as SSS—sick sinus syndrome, related to a heart condition, slow heart rate, palpitations, dizziness, syncope, fatigue, and other symptoms [37].

Study limitations include a low number of cases, a small amount of MS sinus pathologies closely related to SSS/CMA, requirements for further studies, and the necessity to perform a further retrospective investigation of those pathologies.

5. Conclusions

SSS/CMA requires good CT/CBCT evaluation followed by clinical observations. Most cases are still considered undiagnosed. Based on the following authors’ study, both SSS/CMA might have some degree of atypical and typical both clinical and radiological symptoms. On the other hand, a study on a bigger amount of patients should improve the results, especially the correlation between the enopthalmos and osteomeatal complex functions. Asymptomatic maxillary sinusitis co-existing in maxillary asymmetry cases in patients suffering from skeletal malocclusion remains atypical for SSS pure and in-pure cases. Both presented maxillary and facial asymmetry cases do not correspond to the typical SSS/CMA findings. The OMC patency is more common for pure forms. The occurrence of maxillary asymmetry should be always evaluated in such cases.