Dental implants have gained popularity for the treatment of edentulous sites.1,2 Global demand for dental implants is increasing and is expected to increase substantially in the future. In this respect, long-term edentulism of the posterior maxillary dentition poses complications such as insufficient alveolar width, depth or both. Increased pneumatization of the maxillary sinus, alveolar resorption and/or trauma related defects are among many factors contributing to the alveolar ridge atrophy. To regain the lost alveolus height, corrective surgeries with predictable outcomes such as maxillary sinus floor augmentation also known as sinus lift technique or alternatively sinus augmentation, which can be performed either directly or indirectly, has gained popularity.2-4 Careful patient selection, and prevention as well as effective management of complications are in large part responsible for the predictable results reported.
Pathologies noted in the maxillary sinus, and their effect on the outcome of the sinus augmentation procedure has been debated since the introduction of the surgical procedure in 1977 by Tatum at a series of lectures presented at the Alabama Implants Study Group, in Birmingham Alabama.5 In general, any pathology or condition that may adversely affect healing of the surgical site should be taken into consideration prior to the surgical appointment. Soft tissue densities within the maxillary sinuses are a common manifestation of sinus pathology or abnormality.1 As a result, soft tissue density lesions at the floor of the maxillary sinus must be correctly diagnosed prior to surgical procedures. Sinus findings such as mucous retention pseudo-cysts (MRCs) seen superior to the implant surgical site in the maxillary sinus, has been a point of controversy since Ziccardi and Betts identified them as absolute contraindication for sinus augmentation procedures.6 Recently however, others have advocated them as posing no effect in the outcome of the surgery.2
MRCs are common findings of the paranasal, with high occurrence in the maxillary sinuses.7 They are one of the most common radiographic incidental findings.7 Prevalence in the general population, as seen in panoramic images has been reported as 1 percent to 10 percent.8 MRCs may be bilateral or multiple in number.7
Most maxillary sinus lesions are asymptomatic and often discovered incidentally.4 As such, during treatment-planning phase, diagnosis of MRCs must differentiate them from other sinus pathologies.
Radiographically MRCs present as homogeneous, dome shaped structures with soft tissue densities. These are slow growing lesions, and are in majority of cases self-limiting.9
MRCs are usually asymptomatic and an incidental finding on routine radiographic examinations taken for reasons other than a chief complaint of sinus problems. The prevalence of the MRCs varies with the type of radiograph acquired. In panoramic imaging the prevalence is reported to be 1-10 percent1,4 on computed tomography (CT) scans 12 percent1,4 and on magnetic resonance imaging (MRI) 21 percent.1,4 Information on the prevalence in cone beam computed tomography (CBCT) scans was not available.
In addition to MRCs, maxillary sinuses also exhibit a variety of other diseases and conditions manifesting themselves in increased mucosal thickenings. As a result, pre-surgical radiographic evaluation of the patient and acquired images by trained practitioners is a mandatory step in the treatment planning process. Maxillary sinuses present with several types of diseases, ranging from chronic rhinosinusitis, benign and malignant neoplasms, mucoceles or odontogenic sinuses stemming from periodontal or endodontic pathologies. As such appropriate diagnosis is mandatory prior to any intervention.10,11
Dome shaped soft tissue density opacity in the left maxillary sinus, consistent with MRC. (coronal view)
The etiology of MRCs is poorly understood.12 Today they are generally considered to be a sequela of inflammation or hyperplasia of the sinus mucosa.11 Allergic,8,9 inflammatory,9 trauma9,13 and odontognenic causes such as periapical pathosis from non-vital pulps, periodontal disease, impacted teeth, retained roots, and post-extraction oro-antral fistula have been identified as possible causes.12 Celebi and colleagues believe that MRCs have an inflammatory origin and are caused by accumulation of fluid within the sinus membrane.2 As such MRCs are not considered true cysts because they lack an epithelial lining.14
There is no consensus on the etiology of the MRCs, as such a cursory review of the literature reveals numerous names and classifications to describe this common radiographic finding. Linsay proposed two classifications of secreting and non-secreting cysts of the maxillary sinus.8 McGregor suggested MRCs to be a mesothelial cyst and suggested they occur in the subepithelial connective tissue as an accumulation of tissue fluids resulting from a disturbance in water-balancing mechanism.8 While Ash and Raum coined the term pseudocyst or interstitial cyst,8 Shafer et al preferred the term retention cyst of the maxillary sinus.8 Today we commonly refer to them as moucous retention (pseudo) cyst.
While the etiology is not well understood or agreed upon, there is a greater consensus on the course of action when they are discovered. Due to the high rate of spontaneous regression reported at 16 percent to 41 percent,9,15 periodic clinical and radiographic follow-up is preferred to direct intervention. Since the spontaneous regression rate is high, no treatment other than clinical and radiographic follow-up, even in the presence of MRC size increase is indicated.9,15
FIGURE 1. Dome shaped soft tissue density opacity in the left maxillary sinus, consistent with MRC. (coronal view)
FIGURE 2. Note presence of MRC in the proposed sinus augmentation site. (coronal view)
FIGURE 3. Sagittal view of MRC in the left maxillary sinus.
Interestingly, increases in the size of asymptomatic MRCs is not considered a strong reason to necessitate intervention.9 However when MRCs are accompanied with signs or symptoms such as headaches, intervention may become necessary.1,11 In cases of large size MRCs occupying great volume of the maxillary sinus, or in cases with indistinct diagnosis, further imaging and clinical evaluation prior to surgical intervention, to rule out radiographically similar appearing diseases is recommended. While asymptomatic MRCs are generally monitored without direct intervention, secondarily infected or large MRCs may become symptomatic necessitating intervention prior to sinus augmentation surgery.4
The presence of an intact Schneiderian membrane to tent the graft material between the maxillary sinus floor and the internal volume of the maxillary sinus is integral to the success of the procedure. Any disease or condition that reduces this integrity
will have to be resolved prior to the sinus floor augmentation surgery. The question the authors set out to answer was whether MRCs affect this integrity and reduce the success and predictability of sinus augmentation technique in the same manner as other sinus pathologies do.
MRCs, as reported by Donizeth-Rodrigues, do not violate the integrity of the maxillary sinus walls.9 However, presence of the MRCs reduce the volume of the maxillary sinuses.4 Post-surgical superior displacement of the maxillary sinus mucosal lining is postulated to further reduce the sinus volume. In extreme cases, post-surgical edema and reduction in the volume size, in the presence of obstruction of the ostium opening may cause stasis of fluids, which when contaminated could lead to sinusitis.4 However, the ostium is generally located considerably higher, approximately 25 to 35mm16 above the sinus floor, as such reported prevalence of sinusitis following augmentation in the absence of pathology is low, about 3 percent to 20 percent.4 Mardinger et al posited that these types of sinusitis were caused by mucosal edema, therefore are transient and symptoms cease following appropriate treatment.4
Sinus augmentation procedures are proven to be predictable and successful, and as such have been increasingly gaining popularity among practitioners placing dental implants to increase the height of the alveolus for placement of endosseous implant fixtures. The criteria for patients with MRCs undergoing dental implant surgery are not well established. The presence of MRCs, as suggested by Ziccardi et al has long been considered a contraindication. However, Kara et al, contradicted Ziccardi’s recommendations by suggesting that MRCs need not be removed or treated prior to sinus lift procedure.17 Reported interoperative complications associated with the effects of the MRCs and sinus augmentation procedures are rare.4 As such, recently, it is suggested that the presence of asymptomatic MRCs should not alter the treatment or require additional intervention prior to the surgery. Mardinger and colleagues proposed that the risk of perforation of the schneiderian membrane in the presence of MRCs due to the thick mucosal lining present is rare and as such cyst removal is not indicated.4
Multiple authors have looked at their patient pool and concluded that presence of asymptomatic MRCs do not affect the outcome of the sinus augmentation procedures. As such, presence of mucous retention (pseudo) cysts is not considered a contraindication for sinus augmentation.4
However, patients with large or symptomatic lesions, or where the diagnosis is unclear, require further evaluation.4 Radiographic images of these patients should be reviewed by a clinician with the expertise to recognize and rule out pathologic conditions. When concern or uncertainty persists, oral maxillofacial radiologists may be called upon to analyze the radiographic images. OH
Dr. Mitra Sadrameli, DMD, MS is assistant clinical professor at University of British Columbia and in private practice in Vancouver, BC, Canada. Dr. Mahtab Sadrameli, DMD is in private practice in San Francisco, CA. Dr. Taraneh Maghsoodi-Zahedi, DDS, MS is assistant professor in Periodontics department at University of Texas Health Science Center in San Antonio, in Texas, USA. The authors have no conflict of interest.
Oral Health welcomes this original article.
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