Ⅰ. INTRODUCTION

Sialadenoma papilliferum is a rare benign salivary gland tumor that most frequently arises on the palate, although it has occasionally been reported in the parotid gland.^1-4). Also, it can occur in the soft palate, buccal mucosa, upper lip and rarely esophagus, and is characterized by papillary and glandular configurations^1,2). The tumor is most commonly observed in individuals aged 50 to 70 years, with a male predilection1,²⁾. Although sialadenoma papilliferum is generally benign, rare cases of malignant transformation have been reported, such as progression to mucoepidermoid carcinoma, highlighting the importance of thorough histopathological evaluation³⁾. Due to its distinctive histopathological features, Sialadenoma papilliferum must be differentiated from other lesions with papillary structures, including syringocystadenoma papilliferum, squamous papilloma, fibroma, mucocele, verrucous hyperkeratosis, sebaceous cysts, and mucoepidermoid carcinoma^4,5). Accurate diagnosis is crucial to determine appropriate management, which is typically conservative surgical excision1,^2,4).

In this report, we present a rare case of a sialadenoma papilliferum of the hard palate and review the relevant literature.

Ⅱ. CASE REPORT

A 56-year-old man visited the Department of Oral and Maxillofacial Surgery of the Kyungpook National University Dental Hospital, with chief complaints of hard palate pain. He had no specific medical history. The lesion on the hard palate had been present for approximately 10 years, but the pain had increased following extraction of the maxillary left second molar three weeks earlier. Despite healing of the extraction site, the pain persisted, prompting referral for further evaluation.

On clinical examination, the left hard palate was slightly swollen, and a round, papillary-shaped mass was observed (Figure 1A). Panoramic X-ray images taken at the time of the visit showed no significant findings in the hard palate. Provisional diagnosis of a benign salivary gland tumor was made on the same day for the purpose of diagnosing the condition, and a biopsy was performed. The biopsy results confirmed a diagnosis of sialadenoma papilliferum. Enhanced CT demonstrated a 1.5-cm ovoid lesion in the left paramedian hard palate (Figure 1B).

A conservative surgical excision under general anesthesia was planned for complete treatment. The lesion was completely excised with a 5mm clear resection margin including the periosteum (Figure 1C), and a palate splint with tissue adhesive hemostatic agent was applied postoperatively to manage swelling and protect the operate site. Postoperatively, the patient was advised to adhere to precautions, including refraining from smoking, avoiding spicy foods, and not touching the operation site with the tongue.

After surgical removal, the excised specimen was carefully dissected to evaluate its internal structure (Figure 2A). The microscopic histopathological examination of the excised specimen revealed multiple exophytic papillary structures lined by squamous epithelium overlying cystic structures (Figure 2B). The overlying epithelium demonstrated prominent epithelial hyperkeratosis with a well-developed granular layer beneath the keratinized surface (Figure 2C). The underlying cystic structures showed ductal formations lined by epithelial cells, including mucin-producing cells, with mucinous material observed within the cystic spaces (Figure 2D).

The final diagnosis was sialadenoma papilliferum, and no recurrence was observed during the follow-up period (Figure 1D).

Ⅲ. DISCUSSION

Sialadenoma papilliferum is a rare benign salivary gland tumor that has been reported in males between the ages of 50 and 70.^1,2) It typically presents as a painless, exophytic papillary mass and endophytic nodular base.1-6) Although it can arise in the parotid gland, sialadenoma papilliferum is primarily known to occur in the oral cavity, particularly in the hard palate.^6-8) It has also been reported in the soft palate, buccal mucosa, and esophageal region.^9,10)

On clinical examination, the lesion may be misdiagnosed as squamous papilloma, fibroma, mucocele, salivary gland tumor, verrucous keratosis, cystadenoma, cystadenocarcinoma, or papillocarcinoma.^2,3,6) Histologically, the lesion consists of papillary epithelial components resembling squamous papilloma, overlaid by papillary squamous mucosa and adjacent non-encapsulated proliferations of salivary gland ducts.¹³⁾ The ductal structures exhibit numerous papillary infoldings and are lined by a bilayered epithelium composed of a basal layer of flattened to low cuboidal cells and a luminal layer of columnar cells.^11,13) Unlike other papillomatous lesions, no association with human papillomavirus (HPV) has been identified.^1,10) The surrounding connective tissue often reveals varying degrees of chronic inflammatory cell infiltration, predominantly lymphocytes and plasma cells.¹²⁾

Differentiation from other ductal papillomas, particularly intraductal papilloma and inverted ductal papilloma, is of clinical significance.^5,12) Intraductal papilloma typically presents as a small, ill-defined, non-invasive lesion confined to a single duct, characterized by submucosal swelling. It most commonly occurs in the minor salivary glands, particularly in the lip and buccal mucosa.¹²⁾ In contrast, inverted ductal papilloma demonstrates an endophytic, infiltrative growth pattern extending from the surface epithelium into the underlying ductal structures, often presenting clinically as an exophytic lesion with a central papillary projection.^1,4) It most commonly occurs in the lower lip and mandibular vestibule.¹²⁾ Given these distinctions, histopathological analysis is indispensable for accurate diagnosis.

Upon histopathological confirmation of sialadenoma papilliferum, conservative surgical excision is recommended based on radiological and clinical findings.^4,9) Although the recurrence rate is relatively low at approximately 7%, complete excision with a clear resection margin is recommended, as the possibility of cystadenocarcinoma with surface papillomatosis cannot be entirely excluded.^1,3) In this case, complete excision including the periosteum and coverage with a palatal splint led to successful healing without recurrence.

In conclusion, early recognition, biopsy, and radiological evaluation are essential for accurate diagnosis and management of sialadenoma papilliferum. Oral and maxillofacial surgeons should maintain awareness of this rare lesion and differentiate it from more common papillomatous and salivary gland tumors.