Discussion

A nasal vestibular cyst is thought to be a cyst arising from non-odontogenic epithelium with secretory function. Two main theories have been put forward about their pathogenesis. One theory presumes that the cyst originates from entrapped embryonic nasal respiratory epithelium in a facial cleft. Another theory postulates that the cyst may emanate from misplaced epithelium of the nasolacrimal duct.^{Reference Yuen, Julian and Samuel6} The two theories may not be mutually exclusive as both show the cyst originates from respiratory epithelium with secretory function. Therefore, complete removal of the cyst was proposed to avoid the risk of mucus retention and infection induced by the secretory function of residual epithelium.^{Reference Yuen, Julian and Samuel6}

A transoral sublabial approach is usually adopted to remove nasal vestibular cysts. A transnasal endoscopic approach has been more reported recently. In 1999, Su et al. firstly reported the method for transnasal endoscopic marsupialisation of a nasal vestibular cyst. All but 1 of the 16 patients were successfully treated with this technique, considered to be a new, less invasive method.^{Reference Su, Chien and Hwang4}

Many studies comparing the above two approaches were reported recently. One author considered that transnasal endoscopic marsupialisation was an effective treatment for nasal vestibular cysts, associated with less cost and fewer complications than transoral sublabial excision. Meanwhile, they suggested that creating a sufficiently large stoma was crucial to prevent the retention of mucus or recurrence of the disease after marsupialisation. They considered that transoral sublabial excision may be a better choice than transnasal endoscopic marsupialisation in patients with small lesions.^{Reference Chao, Huang, Chang, Chen, Chen and Lee7} However, Li et al. considered that total excision via the sublabial approach was a more reasonable surgery than transnasal endoscopic marsupialisation of the cyst.^{Reference Li, Yang and Wang8} In this study, one recrudescent patient repeatedly suffered from mucus retention and erosion of the nasal vestibule after endoscopic transnasal marsupialisation in another hospital five years prior to the study (Figure 3). The histopathological specimen showed inflammatory granulation tissue with mucous glandular tissue.

In addition to transnasal endoscopic marsupialisation, there are also reports about transnasal endoscopic excision. In a study by Huang et al., transoral sublabial excision was performed in 23 patients with nasal vestibular cysts and transnasal endoscopic excision was performed in 30 patients. After comparing their duration of surgery, hospital stay time, total cost and incidence rate of post-operative lip swelling or numbness, it was concluded that the transnasal endoscopic excision was a simple, less invasive, low-cost and effective surgical procedure for the treatment of nasal vestibular cysts.^{Reference Huang, Li, Yang, Li, Ye and Liu9} In another study, 42 patients with nasal vestibular cysts underwent transnasal endoscopic excision, followed up for six months to five years, and no complications or recurrence were observed.^{Reference Hao, Yan and Tao5} However, in spite of the advantages of the transnasal endoscopic approach, a systematic review showed that transnasal endoscopic marsupialisation (or excision) and the transoral sublabial approach offered no statistically significant difference in post-operative facial or perinasal swelling, pain or overall recurrence rate.^{Reference Sheikh, Chin, Fang, Liu, Baredes and Eloy3}

Findings from literature and clinical practice show that a classical transverse incision via a transoral sublabial approach may lead to higher incidence of post-operative nasal alar and upper lip swelling or numbness and more blood loss, whereas a transnasal endoscopic approach is prone to mucus retention, infection or recurrence due to stoma stenosis.

For a very small cyst, it is difficult to find the cyst in the nasal cavity through a nasal endoscope. Through study and review of anatomy, it was found that the nasal vestibule, nasal alar and upper lip are innervated by the infraorbital nerve, an entirely sensory nerve.^{Reference Hu, Kwak, Koh, Abe, Fontaine and Kim10,Reference Nderitu, Butt and Saidi11} The infraorbital artery, accompanying the infraorbital nerve, is located within the deep medial cheek fat and supplies the lateral nasal and superior labial regions.^{Reference Kim, Lee, Gil, Hu, Tansatit and Kim12} Both the infraorbital nerve and infraorbital artery branches are radially distributed from up to down.^{Reference Hu, Kwak, Koh, Abe, Fontaine and Kim10,Reference Kim, Lee, Gil, Hu, Tansatit and Kim12} According to the distribution characteristics of the infraorbital nerve and infraorbital artery, a modified longitudinal incision via transoral sublabial approach was designed to remove nasal vestibular cysts. Because the longitudinal incision is aligned with the direction of the branches of infraorbital nerve and infraorbital artery, it may avoid injuring infraorbital nerve and artery branches as much as possible, so as to alleviate post-operative nasal alar and upper lip swelling or numbness and reduce blood loss. In this study, 28 patients with a nasal vestibular cyst received a modified longitudinal incision via a transoral sublabial approach. All cysts were completely removed with little intra-operative bleeding and without significant post-operative nasal alar and upper lip numbness. No post-operative haematoma, infection, oronasal fistula and malformation occurred in any of the patients. All patients were followed up for 2 to 57 months without recurrence.