Postoperative maxillary cyst (POMC) was first reported in 1927 by Kubo in Japan [1]. POMC occurs years or decades following Caldwell–Luc operation, orthognathic surgery, or maxillary sinus augmentation and is caused by epithelial residues at the surgical site [2-8]. POMCs can cause swelling or perforation of the maxillary sinus wall as it gradually grows over several years.

Although often asymptomatic, various symptoms such as pain in the teeth and alveolar bone or gingival fistulas may appear with increasing POMC size [9,10]. The lack of awareness of POMCs may lead to misdiagnosis as an odontogenic infection and delayed treatment. The average latency time was 4-22 years [11]. Owing to the long latency time, whether the clinical and radiologic features of POMCs may change over time need to be compared. To the best of our knowledge, no studies have compared POMC features across periods. Therefore, this study aimed to provide dentists with information on clinical and radiographic findings of POMC and evaluate the size and symptom difference in lesions according to the time elapsed from radical maxillary sinus surgery to POMC detection.

This study was conducted on 29 patients diagnosed with POMCs (excluding patients with incomplete electronic medical records) at Chonnam National University Dental Hospital between January 2009 and December 2017. This study was approved by the Institutional Review Committee of Chonnam National University Dental Hospital (IRB no. CNUDH-2019-001).

Patients with a previous history of maxillary sinus surgery and histopathologically confirmed diagnosis of POMCs postoperatively were included. Patients who had no previous history of maxillary sinus surgery, had an incomplete clinical and radiographic evaluation, and had clinical and/ or radiographic evidence of any tumor or pseudocyst in the maxillary sinus were excluded.

The study evaluated age, sex, clinical symptoms, surgical history, and period from radical maxillary sinus surgery to POMC diagnosis using electronic medical records. Radiological characteristics by panoramic radiographs and dental cone-beam computed tomography (CBCT) were also assessed.

Clinical and radiologic findings were investigated according to the elapsed period. The average time of latency for POMCs after the first surgery was 24 (min, 6; max, 40) years. Patients were divided into those who underwent maxillary sinus surgery <24 years ago and those >24 years ago. Four patients were excluded because of missing data on the postoperative period. Twenty-five patients with POMCs were compared using the chi-square test. Statistical analysis was performed using IBM SPSS Statistics for Windows, Version 23.0 (IBM Co.), and p<0.05 was considered statistically significant.

The clinical characteristics of the patients diagnosed with POMCs are summarized according to age, sex, location, symptoms, and period until onset after surgery (Table 1). The study included 13 men and 16 women. The average patient age was 52.75 years, and 12 (41.4%) patients were in their 50s.

The average period from surgery to POMC detection was 24.32 years; however, the period could not be confirmed in four patients. The lesion was present on the right side in 17 (58.6%) patients, left side in 7 (24.1%), and both sides in 2 (6.9%). The main symptoms were buccal pain in 17 (58.6%) patients, swelling in 12 (41.4%), pyorrhea in 5 (17.2%), and dullness and toothache in 2 (6.9%). The lesions were found incidentally in 4 (13.8%) patients without specific clinical symptoms.

The radiologic characteristics were recorded according to the lesion location, shape, and size (Table 2). Moreover, 17 (58.6%) patients had lesions on the right side, 7 (24.1%) had them on the left, and 2 (6.9%) had them on both sides. The lesions were categorized as unilocular and multilocular radiolucencies on panoramic radiographs (Fig. 1, 2). Multilocular radiolucencies were observed in 9 (31.0%) patients.

As regards the lesion size, the most extended lengths measured on the buccal–palatal and mesiodistal (MD) sides on the axial plane of the CBCT were recorded (Table 2, Fig. 3). The buccopalatal (BP) length of the lesion was <15 mm in 8 (27.6%) patients, 15-30 mm in 14 (48.3%), and >30 mm in 7 (24.1%). No lesions had an MD length of <15 mm; moreover, 17 (58.6%) lesions measured 15-30 mm, and 12 (41.4%) measured >30 mm (Tables 2, 3). The extent of the lesion was evaluated using CBCT images, and the relationship with the zygomatic bone, ethmoid bone, orbit, and teeth was observed. Moreover, 8 (27.6%) patients had a zygomatic extension, with no ethmoid or orbital extension; however, 20 (69.0%) had tooth involvement. Secondary cysts (Fig. 4) adjacent to the lesion were found in 4 (13.8%) patients.

The patients were divided into those who underwent maxillary sinus surgery <24 years ago and >24 years ago. The study investigated the relationship between the two groups based on clinical and radiologic findings (Table 3). No statistically significant difference was found between the two groups with respect to symptoms, expansion to the surrounding area, and secondary cyst (p-value>0.05, chi-square test). However, the BP lengths of the cyst on CBCT images were significantly different between the two groups (p<0.05).

POMC, a late complication, occurs after radical maxillary sinus surgery and is caused by residual mucosal epithelium during surgery [12]. Rarely reported in West countries, POMC is more prevalent in Asia, particularly in Japan [12,13]. The higher incidence in Japan could be attributed to the source of infection and facial skeletal growth [13]. Pain and swelling are the main clinical symptoms of POMCs [14]. In this study, various symptoms were identified, such as toothache, abnormal sensation on the face, and pus discharge in the gingiva. POMC is also found incidentally on radiographs in asymptomatic cases.

As the lesion grows, the sinus wall may become thin, expand, and disappear, and the cyst may invade adjacent areas. Rarely, POMCs affect the orbit [9,15]. Previous studies have shown secondary or multiple cysts, which were isolated by bony septation on CT [16,17]. In this study, secondary cysts were more easily identified on CBCT images than on panoramic radiographs. Therefore, CBCT rather than panoramic radiography is needed to evaluate the POMC size, its relationship with adjacent structures, and related secondary cysts. A study [18] also showed that CT was superior to panoramic radiography and Waters views for POMC diagnosis. In addition, POMC boundaries were clearly observed on magnetic resonance imaging [14].

POMC is more common in women than in men [11]. In this study, POMCs developed in 13 men and 16 women, with a higher predilection for women. Medical history revealed that 29 cases had a history of sinus operation for maxillary sinusitis, and one patient had a zygomaticomaxillary complex fracture. Dental CBCT images showed 8 (27.6%) lesions that laterally extended to the zygomatic bone and 20 (69.0%) that inferiorly extended between the roots of teeth. Seven cases (35.0%) involving the root were mistaken for odontogenic lesions, such as apical cysts or apical abscesses, resulting in the persistence of the clinical symptoms during the treatment of the tooth alone and delayed treatment of the posterior maxillary cyst. In this study, the size of POMCs in the axial view showed a more significant difference in BP length than in MD length based on the period (24 years) after maxillary sinus surgery.

POMCs should be differentiated from apical cysts in the posterior region, retention pseudocysts in the maxillary sinus, and chronic maxillary sinusitis [2,13]. The treatment of POMCs includes Caldwell–Luc operation, marsupialization, and endoscopic surgery [14]. In this study, POMC surgery was performed using the Caldwell–Luc procedure. PMCs were found 10-40 years after maxillary sinus surgery. POMC recurrence was related to the presence of multiple cysts and extensions outside the sinus wall [17,19].

This study has some limitations. All presented data were collected retrospectively, and some clinical information may be missing. Systemic clinical information was not compared, and postoperative recurrence rates have not been studied.

In conclusion, POMCs may emerge several years after radical maxillary sinus surgery, with an average detection period of 24.32 years. The cyst size, particularly the BP length observed on CBCT images, appears to be significantly related to the time elapsed since surgery, highlighting the importance of long-term monitoring for potential POMC development. Dentists should be aware of the clinical and radiologic features of POMCs and consider the possibility of POMCs in addition to odontogenic infection in patients with a history of maxillary sinus surgery when pain or swelling occurs in the maxillary teeth.

No potential conflict of interest relevant to this article was reported.

The datasets used in this study are available from the corresponding author upon reasonable request.

None.

Conceptualization: HCK, JSL. Data curation: HCK. Methodology: HCK, SJY, YGI. Project administration: JSL. Visualization: HCK, SJY, YGI. Writing original draft: HCK, JSL. Writing review & editing: JSL.