## 3 Discussion
In the presented case, the differential diagnosis considered a residual cyst because of the clinical history of dental extractions and because of the radiological findings. A residual cyst persists after the lack of or an incomplete excision of the initial, usually radicular, cyst after extraction of the affected tooth [12,21]. Residual cysts account for about 10% of odontogenic cysts, with a prevalence of about 2% [21]. They are usually asymptomatic and discovered incidentally [9]. If they become superinfected, they can cause swelling and pain [12,22]. They can be found in all locations [12,21]. The center of such a cyst corresponds to where the apex of the affected tooth was previously located [12]. The boundaries of a residual cyst are rounded, generally well defined and surrounded by a border of peripheral osteecondensation. If superinfection develops, the borders may become poorly defined [12,22,23]. The content of such a cyst appears homogeneously radiotransparent [12]. Residual cysts can affect adjacent structures in ways similar to NPDCs: they can cause displacement or root resorption of adjacent teeth, and expansion and thinning, or lysis of the cortices [15]. A definitive diagnosis requires histological examination. Histologically, NPDCs are variable lined by squamous, ciliated (respiratory) and cuboidal epithelium. A characteristic feature helping the diagnosis of NPDC is the presence of nerve bundles and arterial vessels in the cyst wall. The treatment of choice for an NPDC is palatine enucleation, even in asymptomatic cases, due to the risk of superinfection and possible complications associated with the removal of a very large cyst [3,7,9]. A biopsy should be done before the enucleation to confirm the diagnosis. In the present case, the patient refused the biopsy, preferring the enucleation straight away and the agreed that according to the diagnosis, additional surgery would be necessary. Some authors advocate prior marsupialization for large cysts to reduce the risk of the formation of a naso-antral communication or devitalization of the central incisors [3,9]. The main postoperative complication is paresthesia in the anterior palatine region caused by attorgenic damage to the nasopalatine nerve. It is observed in less than 10% of cases [3,8]. It is generally agreed that NPDCs have a low recurrence rate; reports of recurrence range from 0% to 11% [24]. In this case, the cyst manifested itself clinically in the form of a vestibular lump, which caused discomfort and prevented the patient from wearing his full denture. Radiologically, the cyst was quite aggressive because of its size and its relationship to the surrounding structures it was crossing the maxilla from side to side in the vestibular-palatal plane and extended to the nasal floor. Another peculiarity was that it extended more on the vestibular side, while classically, NPDCs develop mainly on the palatal side. Since the patient had been toothless for years, the differential diagnosis included a residual cyst, even though there were no associated root remnants. We used a slightly modified surgical procedure compared with the classical approach: flaps were raised on both the palatal and vestibular sides instead of the one-sided palatal approach. The specific surgical risk in this case was the accidental creation of naso-antral communication, but the lesion was enucleated without complications. Draft of the manuscript, preparation of images, patient treatment, A.P. ; draft of the manuscript, radiological interpretation preparation of images, V.I. ; conception, drafting and critical review of the manuscript, T.L. All authors have read and agreed to the published version of the manuscript. This research received no external funding. **Institutional Review Board Statement:** The presented study adhered to the Helsinki Declaration of ethical principles by the World Medical Association.