The authors investigated the clinicopathological characteristics of keratocystoma of the parotid gland. Two cases of parotid gland keratocystoma in the files of Nanjing Stomatological Hospital were analysed. These slowly growing parotid gland tumours occurred in two women aged 29 and 49 years. The cut surface showed multilocular cystic lesions filled with keratin materials. Histologically, there were multi-cystic spaces and solid epithelium islands, containing keratinized lamellae. Without cytological atypia, the lining stratified squamous epithelium showed apparent keratinization through an orthokeratotic or parakeratotic pathway. No skin appendage formation was observed. Both cases immunoreactively stained positively for AE1/AE3 and CK5/6 but negatively for CK8/18, S-100 and Calponin. There was no evidence of recurrence 3 or 4 years after superficial parotidectomy. The data from these two cases and cases previously published suggest that keratocystoma of the parotid gland is a benign cystic neoplasm. Surgical resection is apparently sufficient for cure.
Keratocystoma of the parotid gland is a rare benign tumour. The revised World Health Organization Classification of Salivary Gland Tumours (3rd Edition) only mentions this tumour in the differential diagnosis of squamous cell carcinoma of salivary glands . Until now, only four cases have been reported in the English literature . These cases have involved children and adults (age 8–38 years), three males and one female. After complete excision, there has been no evidence of recurrence. Histologically, the presence of multicytic spaces lined by stratified squamous cells containing keratotic lamellae and focal solid epithelial nests is essential for diagnosing a tumour as a keratocystoma .
The authors have also found two cases of keratocystoma, which are histopathologically similar to the cases described by N agao et al. . Here, they present some clinicopathological and immunohistochemical features of these two cases, and compare them with previous cases. The authors focus on discussing the nature of these two cases in connection with the differential diagnosis.
Materials and methods
The authors retrospectively studied two cases diagnosed in 2006 and 2007, retrieved from the files in the Department of Pathology at their institution between 1974 and 2010. Information about the patient’s age and gender and the location and size of the tumour was obtained from the clinical records.
The biopsy specimens were fixed in 10% buffered formalin, dehydrated through graded concentrations of ethanol, and subsequently embedded in paraffin wax. Serial 4 μm thick sections of the tumour were processed for haematoxylin and eosin (H–E) staining. The two cases were diagnosed according to the 2005 World Health Organization Classification of Salivary Gland Tumors .
The slides were deparaffinized, rehydrated, and boiled in 10 mM citrate buffer (pH 6.0) for 20 min in a pressure cooker. After cooling for 30 min, the slides were incubated overnight at 4 °C with one of the following primary antibodies: AE1/AE3, CK5/6, CK8/18, S-100, Calponin, PCNA, Ki-67 (DAKO, Denmark). The EnVision method (DAKO, Denmark) was used for detection, using diaminobenzidine as the chromogen. Sections were counter-stained with haematoxylin.
Case 1 was a 29-year-old woman who presented with a painless, moveable mass that had disturbed her for 2 years. She had neither systemic nor hereditary diseases in her familial history. The mass was located in the right parotid gland region and was 2.5 cm in diameter with an easily distinguishable boundary. The texture of the tumour was medium. The clinical features were similar to those of a benign lesion. A facial nerve exclusion and subtotal parotidectomy were performed. Four years after surgery, the patient had no evidence of recurrence.
Case 2 was a 49-year-old woman who presented with a painless, right-sided parotid gland nodule that had been growing slowly for 2 months. She was not taking medication at the time of presentation and had no family history of hereditary diseases. The medium swelling was moveable. The mass was well-defined and 2.0 cm in diameter. No malignant manifestations were detected in the clinical appearance. The patient underwent a facial nerve exclusion and subtotal parotidectomy. No tumour recurrence was observed 3 years after the surgery.
Both tumours were confined within the parotid gland parenchyma. They were well-demarcated masses with complete capsules, the multilocular cystic cut surfaces of which were filled with solid grey creamy keratin material. The tumour in case 1 measured 2.5 cm × 2.0 cm × 2.0 cm and that in case 2 measured 2.5 cm × 2.0 cm × 1.5 cm ( Fig. 1 ).
The cystic tumour was seen near the parotid gland tissues ( Fig. 2 A). There were multiple, randomly distributed cystic structures and solid squamous epithelium islands, containing keratinized lamellae ( Fig. 2 B). The cystic space was lined with orthokeratinized or parakeratinized squamous epithelium lacking a granular cell layer. In a few orthokeratinized areas basophilic keratohyaline granules could be distinguished sporadically. Atypia was not observed in the epithelium whilst mitotic figures were occasionally present in the germinal layer. Pin-like protrusions were focally distributed in the outer layer, without skin appendage formation underlying the epithelium. The tumour nests were circumscribed in the collagenous stroma by basement membrane. The stroma was infiltrated by chronic inflammatory cells with foci of foreign-body reaction against keratin material leaked from the ruptured cysts. The sporadic parotid gland ducts were in conjunction with solid squamous cell islands ( Fig. 2 C).
In both cases, the tumour cells immunohistochemically stained positively for AE1/AE3 and CK5/6 ( Fig. 3 A) but negatively for CK8/18 ( Fig. 3 B), S-100 and Calponin. In contrast, nearby parotid gland cells stained positively for CK8/18, S-100 and Calponin. In addition, PCNA ( Fig. 3 C) and Ki-67 were expressed in basal cells of the tumour islands in both cases.