Discussion

In this study, the two surgical procedures for nasolabial cysts, namely the intraoral sublabial approach and the transnasal endoscopic approach, were performed at a similar rate. Local anaesthesia and general anaesthesia showed similar rates too. However, there was a statistically significant recent surgical trend in our hospital to treat nasolabial cysts using a transnasal endoscopic approach under local anaesthesia (p < 0.05).

There are two theories for the pathogenesis of nasolabial cysts, but they have not yet been established.^{Reference Boffano, Gallesio, Campisi and Roccia2,Reference Sheikh, Chin, Fang, Liu, Baredes and Eloy3,Reference Özer, Cabbarzade and Ögretmenoglu5} One theory suggests that nasolabial cysts originate from trapped embryonic nasal respiratory epithelium after the fusion of maxillary medial and lateral nasal processes.^{Reference Boffano, Gallesio, Campisi and Roccia2,Reference Sheikh, Chin, Fang, Liu, Baredes and Eloy3,Reference Özer, Cabbarzade and Ögretmenoglu5,Reference Cohen and Hertzanu8} The other theory posits that nasolabial cysts are remnants of embryonic nasolacrimal duct tissue.^{Reference Boffano, Gallesio, Campisi and Roccia2,Reference Sheikh, Chin, Fang, Liu, Baredes and Eloy3,Reference Özer, Cabbarzade and Ögretmenoglu5}

Nasolabial cysts were predominant in females (91.7 per cent) and presented more frequently on the left side (54.2 per cent), similar to previous reports.^{Reference Sheikh, Chin, Fang, Liu, Baredes and Eloy3,Reference Narain7} Nasolabial cyst occurred bilaterally in only one patient (4.2 per cent); this rate of bilateral occurrence is lower than that reported in other studies (approximately 10 per cent).^{Reference Boffano, Gallesio, Campisi and Roccia2–Reference Yeh, Ko and Wang6} The most common symptom of our patients was a mass in the nasolabial region.^{Reference Yuen, Julian and Samuel1–Reference Narain7} Imaging studies, including ultrasonography, CT and magnetic resonance imaging, are usually necessary for the diagnosis of nasolabial cysts.^{Reference Yuen, Julian and Samuel1–Reference Narain7} For accurate diagnosis and economic reasons, we performed CT scans.

Differential diagnoses of nasolabial cysts include both odontogenic and non-odontogenic lesions, such as a radicular cyst, periapical abscess, odontogenic cyst, schwannoma, minor salivary gland tumour, and dermoid and epidermoid cysts, which can develop in the nasolabial fold.^{Reference Sheikh, Chin, Fang, Liu, Baredes and Eloy3,Reference Narain7}

Surgical removal is the treatment of choice for a nasolabial cyst.^{Reference Yuen, Julian and Samuel1–Reference Narain7} There are two surgical methods for nasolabial cysts: an intraoral sublabial approach and a transnasal endoscopic approach. The intraoral sublabial approach is a classic technique and the most common method used for nasolabial cysts, performed via a sublabial incision.^{Reference Boffano, Gallesio, Campisi and Roccia2,Reference Sheikh, Chin, Fang, Liu, Baredes and Eloy3,Reference Özer, Cabbarzade and Ögretmenoglu5} This approach can lead to good exposure of lesions. However, it is associated with some complications, such as facial swelling, numbness of gingiva and teeth, and risk of nasal floor perforation.^{Reference Yuen, Julian and Samuel1–Reference Narain7}

The transnasal endoscopic approach is a simple and effective procedure.^{Reference Boffano, Gallesio, Campisi and Roccia2,Reference Sheikh, Chin, Fang, Liu, Baredes and Eloy3,Reference Özer, Cabbarzade and Ögretmenoglu5,Reference Su, Chien and Hwang9} This approach can lead to a reduced operative time, lower rates of facial swelling and pain, and a lower overall rate of complications.^{Reference Sheikh, Chin, Fang, Liu, Baredes and Eloy3,Reference Lee, Baek, Byun, Chang, Lee and Kim10} However, a small window on the nasolabial cyst may cause stenosis of the opening and a reoccurrence of the nasolabial cyst, as shown in one of our patients.^{Reference Özer, Cabbarzade and Ögretmenoglu5,Reference Lee, Baek, Byun, Chang, Lee and Kim10}

In this study, the most common post-operative complication was numbness of the upper lip or teeth (n = 9, 36.0 per cent). However, there was no significant difference in post-operative complications between treatment involving an intraoral sublabial approach or a transnasal endoscopic approach (p > 0.05). A previous systemic review showed no difference in complications between the two surgical approaches either.^{Reference Sheikh, Chin, Fang, Liu, Baredes and Eloy3}

Recurrence and malignancy transformation are very rare.^{Reference Sheikh, Chin, Fang, Liu, Baredes and Eloy3,Reference Choi, Cho, Kang, Chae, Lee and Hwang4} We only had one case of recurrence (4.0 per cent), in a patient who underwent a transnasal endoscopic approach. In a systemic review, Sheikh et al. demonstrated no significant difference in recurrence rates between an intraoral sublabial approach and transnasal endoscopic approach performed for nasal cysts.^{Reference Sheikh, Chin, Fang, Liu, Baredes and Eloy3}

In this study, there were no significant differences in post-operative complications, anaesthesia method, or nasolabial cyst size between cases treated with an intraoral sublabial approach or a transnasal endoscopic approach (all p > 0.05). However, recently, the transnasal endoscopic approach under local anaesthesia has been performed more often in our institute (p < 0.05).