Indian Journal of Dental Research

: 2012  |  Volume : 23  |  Issue : 2  |  Page : 286--288

Peripheral squamous odontogenic tumor

N Malathi1, T Radhika1, Chelvan H Thamizh1, N Nandakumar2,  
1 Department of Oral and Maxillofacial Pathology, Faculty of Dental Sciences, Sri Ramachandra University and Hospital, Porur, Chennai - 600116, Tamil Nadu, India
2 Department of Oral and Maxillofacial Surgery, Faculty of Dental Sciences, Sri Ramachandra University and Hospital, Porur, Chennai - 600116, Tamil Nadu, India

Correspondence Address:
N Malathi
Department of Oral and Maxillofacial Pathology, Faculty of Dental Sciences, Sri Ramachandra University and Hospital, Porur, Chennai - 600116, Tamil Nadu


A case of peripheral squamous odontogenic tumor is described in a 60-year-old female who presented with a sessile growth in the right posterior mandible. Radiographic examination revealed no evidence of a central lesion in bone. With the characteristic histopathological picture of benign-appearing islands of squamous epithelium scattered randomly against a background of mature fibrous connective tissue, the tumor was diagnosed as peripheral squamous odontogenic tumor (PSOT). The epithelial islands showed peripheral cuboidal or flattened cells, microcyst formation, individual cell keratinization, and keratin pearl formation.

How to cite this article:
Malathi N, Radhika T, Thamizh CH, Nandakumar N. Peripheral squamous odontogenic tumor.Indian J Dent Res 2012;23:286-288

How to cite this URL:
Malathi N, Radhika T, Thamizh CH, Nandakumar N. Peripheral squamous odontogenic tumor. Indian J Dent Res [serial online] 2012 [cited 2020 May 27 ];23:286-288
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Full Text

Squamous odontogenic tumor (SOT) is a rare, benign but locally infiltrative, epithelial odontogenic tumor. The term SOT was first suggested by Pullon et al. in 1975. Earlier, the tumor was reported under a variety of names, including benign epithelial odontogenic tumor; acanthomatous ameloblastoma; acanthomatous ameloblastic fibroma; hyperplasia and squamous metaplasia of residual odontogenic epithelium; and benign odontogenic tumor, unclassified. [1]

 Case Report

A 60-year-old female patient presented with a sessile growth in the right lower jaw of 2 years' duration. History revealed that the lesion had begun as a small growth and gradually increased in size. Intraoral examination revealed a well-defined sessile growth in relation to the lingual gingiva of the mandible [Figure 1], extending from the distal aspect of the mandibular right central incisor up to the mesial aspect of the mandibular right first molar. The growth measured approximately 2 × 1.5 cm in size and had a smooth surface. On palpation, the lesion was firm and non-tender. Radiographic examination [Figure 2] revealed no {Figure 1}{Figure 2}

central lesion. The orthopantomogram showed loss of interdental bone at the site of the lesion. The possibility of a fibroma was considered clinically. The lesion was excised under local anesthesia and placed in 10% neutral buffered formalin for subsequent light microscopic examination.

Microscopic examination revealed peripheral stratified squamous epithelium [Figure 3]. The underlying connective tissue showed islands and broad strands of well-differentiated squamous epithelial cells in a mature connective tissue stroma [Figure 4]. The islands were lined by flat to cuboidal cells [Figure 5] and exhibited vacuolization, microcyst formation [Figure 6], and squamous differentiation with keratin pearl formation. The lesion was diagnosed as peripheral squamous odontogenic tumor.{Figure 3}{Figure 4}{Figure 5}{Figure 6}


Squamous odontogenic tumor is defined as 'a benign but locally infiltrative neoplasm consisting of islands of well-differentiated squamous epithelium in a fibrous stroma. The epithelial islands occasionally show foci of central cystic degeneration' (WHO). [2]

SOT was first described in 1975 by Pullon et al. In 1984, Norris et al. reviewed 26 cases of SOT. A review of 36 cases was done by Philipsen et al. in 1996. [2] Fewer than 50 cases have been reported till date. [3] The most common variant is the intrabony or central type of SOT. A rare peripheral variant has also been described. [2] The first completely extraosseous case was reported by Baden et al. in 1993. [4] Cases of PSOT were also reported by Tamaki et al. (1990), Ikai et al. (2001), and Ide et al. (2005).

The origin of the SOT is uncertain. It is thought to arise from the rests of Malassez in the periodontal ligament or, in the case of peripheral SOT, from the gingival surface epithelium or from remnants of dental lamina. [3]

SOT is a slow-growing neoplasm, presenting with few clinical signs and symptoms, the most common being mobility of teeth adjacent to the tumor, swelling of the gum, and moderate pain. [2] The most common locations for the development of SOT include the anterior maxilla and posterior mandible. The tumor has been found in patients in the age range of 8-74 years and shows a definite peak in the third decade of life. [3] Males and females appear to be equally affected.

Radiography of the central variant shows a well-defined unilocular triangular radiolucency in the alveolar process localized between the roots of teeth. The peripheral variant may cause some saucerization of the underlying bone, which is likely to be a pressure phenomenon rather than the result of true tumor infiltration. [2] Histopathologically, SOT shows islands of bland-appearing squamous epithelium in a mature fibrous connective tissue stroma. The peripheral cells of the epithelial islands do not show the characteristic polarization seen in ameloblastomas. Microcystic vacuolization, individual cell keratinization, and laminated calcified bodies are also seen. The peripheral variants exhibit hyperplasia of the surface epithelium, with formation of irregular rete ridges and 'dropping off' of small sheets and islands into the upper lamina propria. [1]

The differential diagnosis of squamous odontogenic tumor includes acanthomatous and desmoplastic variants of ameloblastoma, well-differentiated squamous cell carcinoma, and SOT-like proliferations that occur in the wall of odontogenic cysts such as dentigerous cyst and apical periodontal cyst. [2] Both desmoplastic and acanthomatous variants of ameloblastoma exhibit squamous differentiation within the tumor islands, but there is demonstrable ameloblastic change of the peripheral cells. The islands and strands of desmoplastic ameloblastoma often are thin and compressed rather than rounded and broad-based as seen in SOT. The squamoid areas in desmoplastic ameloblastoma often exhibit swirls of squamous cells, which are not seen in SOT. The epithelial cells in squamous cell carcinoma exhibit characteristic dysplastic features but this is usually absent in SOTs. SOT-like proliferations represent a reactive proliferation of the cystic lining epithelium or residual odontogenic epithelial cell rests in the connective tissue wall of the cyst. [1]

Immunohistochemical studies of SOT have confirmed the proliferative activity of the odontogenic epithelium, as indicated by heavy staining for keratin 13/16; also, the squamous differentiating cells in the center of the tumor islands have shown a strong positive reaction for involucrin staining. [5] Transmission electron microscopy of tumor cells reveals mature squamous epithelial cells with intercellular edema as is seen in the stratum spinosum of the oral mucosa. [6] Desmosomes are numerous and the cytoplasm contains abundant tonofibril bundles, glycogen granules with scattered mitochondria, and sparse rough endoplasmic reticulum.

Treatment includes enucleation, curettage, and local excision in cases of PSOT. Tumors located in the maxilla require more radical treatment because they show more aggressive biological behavior. [1] Recurrences due to insufficient initial removal have been recorded but are very rare. A case of intraosseous squamous cell carcinoma arising from SOT has been reported, emphasizing the fact that there remains a possibility of malignant transformation of SOT. [7]

The present case adds on to the reported rare peripheral variant of the SOTs.


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