© The authors, 2025

Introduction

Keratocystoma is an extremely rare, benign salivary gland neoplasm, first reported as a choristoma by Seifert et al. in 1999 [1]. The term “keratocystoma” was later coined by Nagao et al. in 2001 [2]. Most cases have been reported in the parotid gland [3]. Only one previous case affecting the minor salivary glands of the palate has been documented, by Ahuja et al. in 2016 [4,5]. This case report aims to present a second known occurrence of keratocystoma in the palatal minor salivary glands, highlighting its clinical, radiological, and histopathological characteristics.

Case report

A 35-year-old male presented with a painless, slow-growing palatal swelling, progressively increasing in size over the course of one year. He had no notable medical or surgical history. Intraoral examination revealed significant dental caries and residual root fragments.

Clinical evaluation showed a firm, painless, well-defined midline palatal mass measuring approximately 2 × 1.5 cm, with a sessile base and normal overlying mucosa (Fig. 1). Magnetic resonance imaging (MRI) revealed a solid lesion involving both the hard and soft palate, with mild post-contrast enhancement (Fig. 2).

The patient underwent surgical excision of the lesion under local anesthesia. A circumferential incision allowed for complete resection of the mass. A full-thickness mucosal flap was elevated to examine the underlying bone, which showed scalloping of the tumor bed. Curettage and superficial osseous resection were performed. Macroscopically, the excised nodule was well-circumscribed, homogenous, and whitish, measuring 2 cm at its greatest diameter.

Histopathological analysis revealed a nodular lesion composed of multiple cystic spaces lined by non-keratinized squamous epithelium overlying benign salivary gland parenchyma. The cysts contained lamellar keratin and scattered calcifications. The epithelium was regular, with both orthokeratotic and parakeratotic hyperkeratosis, and notably lacked a granular layer. Multinucleated foreign-body type giant cells of Müller type were observed surrounding keratin lamellae (Fig. 3).

These findings confirmed the diagnosis of keratocystoma of the palatal minor salivary glands. The postoperative course was uneventful, with satisfactory healing observed at the 10-day follow-up.

Fig. 1 Intraoral appearance of the palatal lesion.

Fig. 2 MRI demonstrating contrast uptake and osseous scalloping.

Fig. 3 Histological section following hematoxylin and eosin (H&E) staining(DrDerdour).

Discussion

Keratocystoma is a newly characterized, rare benign salivary gland neoplasm. Fewer than 15 cases have been reported in the literature to date [3]. All previously confirmed cases have involved the parotid gland, with a single exception reported by Ahuja et al. in 2016, involving the palatal minor salivary glands in a 34-year-old woman [4].

In the current WHO classification (5th edition, 2022), keratocystoma has been formally recognized as a distinct salivary gland tumor entity [6]. It was previously listed as a differential diagnosis of squamous cell carcinoma of the salivary gland by the WHO working group in 2005(3rd edition, 2005) [7].

Histologically, keratocystomas consist of multiple cystic spaces lined by squamous epithelium without cytologic atypia, necrosis, or invasive features. The absence of a granular cell layer and the presence of keratin lamellae within cystic spaces are distinguishing features. The epithelium is non-malignant, and there is no perineural or vascular invasion. Differential diagnosis includes: Squamous cell carcinoma (primary or metastatic), Mucoepidermoid carcinoma, Necrotizing sialometaplasia, Metaplastic Warthin tumor. The absence of cytologic atypia, necrosis, and invasive behavior supports a benign diagnosis [6].

Immunohistochemical staining typically shows positivity for AE 1/AE 3 and CK 5/6, and negativity for CK8/18, S100, and calponin [8]. Recent genetic studies have identified RUNX2 gene rearrangements in several cases, with an IRF2BP2::RUNX2 fusion found in most of them [9]. This genetic marker has not been found in other salivary gland tumors and may support keratocystoma's classification as a distinct neoplastic entity. Our case is histologically consistent with previously reported features, including keratin-filled cysts lacking a granular layer, but uniquely includes multinucleated Müller-type giant cells.

Conclusion

Keratocystoma is a rare, benign neoplasm of salivary gland origin, now recognized in the WHO 5th edition classification as a distinct tumor entity [6]. While most documented cases have arisen in the parotid gland, this report documents only the second known occurrence in the palatal minor salivary glands, thereby expanding the known anatomic spectrum of this neoplasm. Clinicians and pathologists should include keratocystoma in the differential diagnosis of well-demarcated, cystic palatal lesions, especially those lined by squamous epithelium with keratin accumulation and lacking signs of malignancy. Our case not only reinforces previously described histologic features but also introduces the observation of Müller-type giant cells, potentially enriching the morphologic understanding of keratocystoma. The absence of cytologic atypia and the favorable post-surgical course underscore the tumor's benign behavior. As more cases are reported, molecular testing may further validate RUNX2 rearrangements as a diagnostic hallmark and refine our understanding of its pathogenesis. Future studies should aim to clarify the biological behavior, recurrence rates, and potential genetic underpinnings of keratocystoma, particularly in minor salivary gland sites. Increased awareness and reporting will be essential to ensure accurate diagnosis and optimal patient care in cases of this rare tumor.

Funding

This research did not receive any specific funding.

Conflicts of interest

The authors declare no conflicts of interest in regards to this article.

Data availability statement

The research data is included in the article.

Informed consent

Consent has been obtained to use the patient's clinical photograph.

References

All Figures

	Fig. 1 Intraoral appearance of the palatal lesion.
In the text

	Fig. 2 MRI demonstrating contrast uptake and osseous scalloping.
In the text

	Fig. 3 Histological section following hematoxylin and eosin (H&E) staining(DrDerdour).
In the text