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Submucosal nodule in buccal mucosa

Open AccessPublished:February 16, 2016DOI:https://doi.org/10.1016/j.oooo.2016.02.004

      Clinical Presentation

      A 65-year-old woman sought the School of Dentistry of the Federal University of Rio Grande do Sul (Porto Alegre, Brazil) for periodontal treatment. During intraoral examination, a single submucosal and well-circumscribed nodular lesion was observed in the posterior region of the right buccal mucosa. The lesion was covered with clinically normal mucosa, measuring approximately 2.5 cm in diameter (Figure 1). Upon palpation, the lesion was found to be firm and asymptomatic. As the patient was unaware of the existence of the lesion, its time course of development is unknown. The patient reported no systemic diseases in her medical history. The extraoral examination revealed no abnormalities.
      Figure thumbnail gr1
      Fig. 1Intraoral clinical examination. A submucosal nodule in the posterior region of the right buccal mucosa covered by normal mucosa.
      An excisional biopsy was performed. During the surgical procedure, the specimen presented well-defined borders, with no attachment to any of the surrounding structures. For this reason, a complete excision was performed (Figure 2A). The specimen was nodular, with smooth surface and firm consistency (Figure 2B).
      Figure thumbnail gr2
      Fig. 2Surgical procedure. A, Intraoperative aspect of lesion excision in the right buccal mucosa showing a well-circumscribed nodule, with no attachment to any of the surrounding structures. B, Gross examination showing smooth surface, firm consistency, and reddish color.

      Differential Diagnosis

      On the basis of the clinical presentation and location of the lesion, the following differential diagnoses were considered: glandular, mesenchymal, neural, or odontogenic tumors or, less probably, oral manifestation of infectious diseases.
      Among salivary gland tumors, pleomorphic adenoma (PA), basal cell adenoma (BCA), canalicular adenoma (CA), and mucoepidermoid carcinoma (MEC) were considered. PA is the most common salivary gland tumor, accounting for approximately 68% of benign salivary neoplasms. These tumors are more frequent in the third decade of life.
      • Oliveira F.A.
      • Duarte E.C.
      • Taveira C.T.
      • et al.
      Salivary gland tumor: a review of 599 cases in a Brazilian population.
      Clinically, these lesions are usually painless, slow-growing, firm on palpation, measuring 2 to 5 cm in diameter, commonly found in the palate or in the buccal mucosa.
      • Khandekar S.
      • Dive A.
      • Munde P.
      • Wankhede N.D.
      Pleomorphic adenoma of the buccal salivary gland.
      BCA is a rare benign tumor of salivary glands, accounting for 1% to 3% of all glandular neoplasms and usually affects the parotid gland. Intraoral lesions present as a slow-growing solitary, mobile, and asymptomatic mass covered by normal mucosa.
      • Seifert G.
      • Sobin L.H.
      Histological Classification of Tumours: Histological Typing of Salivary Gland Tumors.
      The most affected intraoral sites are the upper lip and the buccal mucosa, and the tumor has a predilection for the female gender.
      • Jones A.V.
      • Craig G.T.
      • Speight P.M.
      • Franklin C.D.
      The range and demographics of salivary gland tumors diagnosed in a UK population.
      The clinical features of PA and BCA are very similar to the case reported herein, underscoring the importance of histopathologic examination for the final diagnosis.
      CA affects women four times more than it affects men, with a mean age of 70 years. It presents as an asymptomatic slow-growing mass measuring approximately 1.2 cm in diameter. These lesions affect more frequently the upper lip, followed by the buccal mucosa. In gross examination, CA shows a mucoid or gelatinous consistency, with cyst degeneration.
      • Thompson L.D.R.
      • Bauer J.L.
      • Chiosea S.
      • et al.
      Canalicular adenoma: a clinicopathologic and immunohistochemical analysis of 67 cases with a review of the literature.
      In the present case, this gross appearance was not observed and, therefore, this diagnosis was considered less probable.
      Among malignant salivary gland tumors, MEC is the most common type, usually presenting as a firm, fixed, and painless swelling frequently observed in the parotid gland. When present intraorally, it is more common in the minor salivary glands located in the palate or in the buccal mucosa. In the oral mucosa, it presents as a superficial submucosal nodule, and it can mimic a mucocele or a vascular lesion because of its blue-red color.
      • Barnes L.
      • Eveson J.W.
      • Reichart P.
      • Sidransky D.
      World Health Organization Classification of Tumours
      Pathology and Genetics of Head and Neck Tumours.
      In the present case, the lesion was covered by normal mucosa and firm of consistency; thus, this diagnosis cannot be discarded.
      The possible diagnosis of mesenchymal neoplasms included lipoma, fibrolipoma, fibrosarcoma, and liposarcoma. Lipoma is a benign neoplasm of adipose tissue. More than 50% of the cases occur in the buccal mucosa and tongue. The intraoral clinical aspect is characterized by a sessile or pedunculated and asymptomatic nodule with a smooth surface, averaging 2 cm in diameter and usually yellowish in color; but deeper lesions may look like normal mucosa.
      • Fregnani E.R.
      • Pires F.R.
      • Falzoni R.
      • Lopes M.A.
      • Vargas P.A.
      Lipomas of the oral cavity: clinical findings, histological classification and proliferative activity of 46 cases.
      During surgical excision, the color and consistency of adipose tissues often justify this suspicion, but this did not occur in the present case. Thus, lipoma was considered less probable; however, only the microstructural examination can confirm the absence of adipose tissues.
      Fibrolipoma is a tumor caused by the proliferation of adipose and fibroblastic tissues within a dense connective tissue. When it occurs in the oral mucosa, it presents as a sessile and asymptomatic nodule 2 cm in diameter, of soft consistency, and located in the buccal mucosa or palate. The highest frequency is observed among men with mean aged 63 years.
      • Manjunatha B.S.
      • Deepak Pateel G.S.
      • Shah V.
      Fibrolipoma—a rare histological oral entity: report of 3 cases and review of literature.
      This lesion was ruled out because of its appearance, since our patient was a woman and the consistency of the tumor was fibrous or dense, rather than soft.
      Fibrosarcoma is a malignant proliferation of fibroblasts, accounting for 3.9% of oral sarcomas, with a major incidence among young adult women, most commonly observed as a growing mass in the mandible.
      • Yamaguchi S.
      • Nagasawa H.
      • Suzuki T.
      • et al.
      Sarcomas of the oral and maxillofacial region: a review of 32 cases in 25 years.
      Liposarcoma is a malignant mesenchymal tumor that usually affects men in their fifth decade. The tongue is usually affected, followed by the buccal mucosa and lips. It manifests as a circumscribed, painless, and slow-growing submucosal mass, with an average size of 3.3 cm.
      • Piperi E.
      • Tosios K.I.
      • Nikitakis N.G.
      • et al.
      Well-differentiated liposarcoma/atypical lipomatous tumor of the oral cavity: report of three cases and review of the literature.
      These characteristics are compatible with the present report.
      Among neural tumors, neurilemmoma and neurofibroma must be considered in the diagnosis. Neurilemmoma is a benign nerve sheath tumor that arises from Schwann cells and presents as a smooth submucosal swelling in the oral cavity. This neoplasia most commonly affects the soft tissues of the mouth, such as the palate, floor of the mouth, lips, and buccal mucosa. The tumor usually averages 2 cm in diameter and can be symptomatic, with pain and paresthesia. Its incidence is greater among young and middle-aged adults. No predilection for gender has been detected.
      • Sanchis J.M.
      • Navarro C.M.
      • Bagán J.V.
      • et al.
      Intraoral schwannomas: presentation of a series of 12 cases.
      Neurofibroma is the most common benign neural tumor of the head and neck. This tumor is believed to be composed of Schwann cells, perineural cells, and varying amounts of mature collagen fibers. Clinically, it manifests as nodular lesions, usually sessile and mobile, with slow and painless growth. The affected intraoral sites are mainly the tongue, oral mucosa, and lips.
      • Salla J.T.
      • Johann A.C.
      • Garcia B.G.
      • Aguiar M.C.
      • Mesquita R.A.
      Retrospective analysis of oral peripheral nerve sheath tumors in Brazilians.
      The clinical characteristics of benign neural tumors resemble those of the reported case.
      Other rare entities may have a similar clinical presentation to the case in question, such as odontogenic tumors—keratocystic odontogenic tumor of the buccal mucosa
      • Kaminagakura E.
      • Almeida J.D.
      • Carvalho Y.R.
      • et al.
      Keratocyst of the buccal mucosa: case report and immunohistochemical comparative study with sporadic intraosseous keratocystic odontogenic tumor.
      and peripheral ameloblastoma.
      • Goda H.
      • Nakashiro K.
      • Ogawa I.
      • Takata T.
      • Hamakawa H.
      Peripheral ameloblastoma with histologically low-grade malignant features of the buccal mucosa: a case report with immunohistochemical study and genetic analysis.
      The peripheral location of these usually intraosseous lesions can be explained by the presence of remaining odontogenic epithelium of the dental lamina or possibly by the embryonic origin of the mucosa.
      • Ide F.
      • Kikuchi K.
      • Miyazaki Y.
      • Mishima K.
      • Saito I.
      • Kusama K.
      Keratocyst of the buccal mucosa: Is it odontogenic?.
      Therefore, these diagnostic hypotheses, albeit rare, should also be taken into account.
      Oral infectious diseases, such as cysticercosis
      • Romero De Leon E.
      • Aguirre A.
      Oral cysticercosis.
      and dirofilariasis
      • Tilakaratne W.M.
      • Pitakotuwage T.N.
      Intra-oral Dirofilaria repens infection: report of seven cases.
      can occur in the oral cavity, more specifically in the buccal mucosa. Cysticercosis is acquired by humans by the ingestion of vegetables, food, or water contaminated by Taenia solium eggs. This tapeworm penetrates the intestinal wall and disseminates through the vascular or lymphatic system. Intraoral involvement is rare, but when present, the tongue, lips, and buccal mucosa are usually affected.
      • Romero De Leon E.
      • Aguirre A.
      Oral cysticercosis.
      Human infection by Dirofilaria presents as lymphatic filariasis, subcutaneous or pulmonary nodules, and eye involvement. Its intraoral manifestation, which is very rare, occurs as submucosal nodules, affecting mainly the buccal mucosa.
      • Tilakaratne W.M.
      • Pitakotuwage T.N.
      Intra-oral Dirofilaria repens infection: report of seven cases.
      Given the potential diagnoses mentioned earlier, it is important to highlight that lesions of different etiologies can have the same clinical features and that the histopathologic analysis is crucial for the final diagnosis, treatment, and management of patients.

      Diagnosis and Management

      The lesion was completely surgically removed. Gross examination revealed a well-circumscribed encapsulated lesion of rounded shape and irregular surface. The lesion showed firm consistency and measured approximately 24 × 17 × 15 mm. The longitudinal section revealed no cavity. The microscopic analysis revealed proliferation of basaloid epithelial cells arranged in islands and sheets. The epithelial islands showed a peripheral palisade of cuboid cells surrounded by hyalinized membranes. In addition, ductlike formation filled with an amorphous basophilic substance was also observed (Figure 3). An important observation is that the lesion was encapsulated by a thin fibrous capsule with areas of tumor infiltration.
      Figure thumbnail gr3
      Fig. 3Hematoxylin-eosin staining. A, Low-power photomicrograph showing well-circumscribed lesion and capsule with tumor infiltration areas, original magnification (×100). A high-resolution version of this slide for use with the Virtual Microscope is available as eSlide: VM02375. B, Photomicrograph demonstrating neoplastic islands of basaloid cells in the connective stroma (original magnification ×200). C, Neoplastic cells arranged in a solid pattern with a palisade of peripheral cells surrounded by hyalinized membrane, characteristic of the membranous subtype (original magnification ×200). A high-resolution version of this slide for use with the Virtual Microscope is available as eSlide: VM02376. D, Islands of basaloid cells with ductlike formation filled with an amorphous basophilic substance, which characterizes the tubular pattern (original magnification ×400). A high-resolution version of this slide for use with the Virtual Microscope is available as eSlide: VM02378.
      An immunohistochemical panel, including cytokeratin (Clone AE1/AE3, DAKO, Dako, Carpinteria, CA), Ki-67 (Clone MIB-1, DAKO), and smooth muscle actin (SMA) (Clone 1 A4, DAKO) antibodies was performed. The immunopathologic characteristics of the lesion indicated an epithelial origin because of the expression of cytokeratin, which was positive for all tumor cells. The presence of myoepithelial cells was confirmed by SMA, which was diffusely positive for neoplastic cells. It was observed that 6.6% of tumor cells were Ki-67 positive (Figure 4). Based on the morphologic, immunohistochemical, and clinical features, the final diagnosis indicated basal cell adenoma. The patient remained under clinical follow-up, and after 1 year, there were no signs or symptoms of tumor recurrence (Figure 5).
      Figure thumbnail gr4
      Fig. 4Immunohistochemical staining. A, Cytokeratin-positive neoplastic cells (SABC method, original magnification ×400). A high-resolution version of this slide for use with the Virtual Microscope is available as eSlide: VM02377. B, Tumor cells stained with smooth muscle actin (SABC method; original magnification ×400). A high-resolution version of this slide for use with the Virtual Microscope is available as eSlide: VM02379. C, Scarce Ki-67-positive neoplastic cells (SABC method; original magnification ×400). A high-resolution version of this slide for use with the Virtual Microscope is available as eSlide: VM02374.
      Figure thumbnail gr5
      Fig. 5Clinical aspect at 1-year follow-up. Posterior region of the buccal mucosa is showing swelling compatible with scar fibrosis.

      Discussion

      BCA is a benign epithelial salivary neoplasm first described by Kleinsasser and Klein in 1967.
      • Kleinsasser O.
      • Klein H.J.
      Basalzelladenome der speicheldrusen.
      The tumor is mainly observed in the parotid gland, and only 2% affects the minor salivary glands. In the past, BCA was categorized as a subgroup of monomorphic adenomas; however, in 1991 the World Health Organization recognized this tumor as an independent entity.
      • Seifert G.
      • Sobin L.H.
      Histological Classification of Tumours: Histological Typing of Salivary Gland Tumors.
      BCA is more frequent in adults and elderly in the seventh decade of life. In minor salivary glands, is commonly found as a firm, solitary, and well-circumscribed nodule, not attached to surrounding tissues,
      • Ochicha O.
      • Malami S.
      • Mohammed A.
      • Atanda A.
      A histopathologic study of salivary gland tumors in Kano, northern Nigeria.
      a description that matches the clinical presentation of the case reported herein.
      Histologically, this benign tumor is composed of basaloid cells with a conspicuous basal cell layer, separated from the stroma by a basement membrane. According to the microscopic features, four patterns of BCA can be observed: solid (sheets or islands with a peripheral palisade of basaloid cells interspersed with a collagenous stroma), trabecular (narrow strands, trabeculae, or cords of basaloid cells separated by a cellular and vascular stroma), tubular (in addition to basaloid cells, it is possible to find ductal structures), and membranous (bands of hyaline material at the periphery of basaloid cells and as intercellular coalescing droplets). BCA can also present cystic cavities, squamous differentiation with whorls or “eddies,” or an unusual cribriform pattern.
      • Seifert G.
      • Sobin L.H.
      Histological Classification of Tumours: Histological Typing of Salivary Gland Tumors.
      The trabecular subtype is the most prevalent histologic pattern.
      • Wilson T.C.
      • Robinson R.A.
      Basal Cell Adenocarcinoma and basal cell adenoma of the salivary glands: a clinicopathological review of seventy tumors with comparison of morphologic features and growth control indices.
      All the different histologic subtypes were observed in the present case; however, there was a predominance of the solid pattern.
      Microscopic differential diagnosis of BCA includes the malignant form of this tumor—basal cell adenocarcinoma (BCAC), which is composed of basaloid epithelial cells, which vary from small dark cells to larger paler-stained cells, arranged in the same histologic types as BCA. To differentiate BCA from BCAC, it is important to consider that BCAC is not encapsulated, exhibits invasive growth into adjacent soft tissue, and is often associated with perineural and/or vascular invasion, in addition to different degrees of cytologic atypia and higher number of mitotic figures.
      • Seifert G.
      • Sobin L.H.
      Histological Classification of Tumours: Histological Typing of Salivary Gland Tumors.
      Another pathology that closely resembles BCA microscopically is adenoid cystic carcinoma (ACC), mainly the solid pattern, composed of sheets of basaloid cells lacking tubular or microcystic spaces filled with hyaline or basaloid material in a stromal component. Unlike the reported case, ACC exhibits pleomorphism with cellular, perineural, and bone invasion. Among benign tumors, it is important to distinguish BCA from PA. In the reported case, PA was ruled out because of the presence of a palisade of basaloid cells. Furthermore, myxochondroid areas, typically present in PA, were not detected.
      • Barnes L.
      • Eveson J.W.
      • Reichart P.
      • Sidransky D.
      World Health Organization Classification of Tumours
      Pathology and Genetics of Head and Neck Tumours.
      The histopathologic analysis of glandular lesions may reveal similar features; therefore, immunohistochemical panels are very useful for the differential diagnosis. According to the literature, BCA mitotic rates, expressed by Ki-67 labeling, are approximately 3.3%.
      • Wilson T.C.
      • Robinson R.A.
      Basal Cell Adenocarcinoma and basal cell adenoma of the salivary glands: a clinicopathological review of seventy tumors with comparison of morphologic features and growth control indices.
      Epithelial tissue markers, such as AE1/AE3 and cytokeratin 19 (CK19), are expressed in ductal luminal cells, mostly in the tubular pattern, whereas the intensity of staining varies in basaloid cells. Carcinoembryonic antigen was also investigated in BCA, and it was negative for basaloid cells, with variable intensity of luminal cell staining. Vimentin, SMA, and S-100 are positive for basaloid cells at the periphery of neoplastic epithelial proliferations and for the stromal component of the tumor.
      • Mărgăritescu C.
      • Mercuţ V.
      • Mogoantă L.
      • et al.
      Salivary gland Basal cell adenomas-immunohistochemical evaluation of four cases and review of the literature.
      These data reaffirm the epithelial or myoepithelial nature of the tumor and also indicate the benign nature of the lesion, given its low proliferative and growth index.
      An important observation is the capsular infiltration of the lesion. Some authors suggest that BCA with capsular invasion can reach a similar size to that of BCAC (3.1 cm × 3.5 cm, respectively), whereas BCAs without capsular invasion are smaller in size (1.9 cm); however, no major microstructural differences are reported.
      • Jung Jung M.
      • Roh J.
      • Choi S.
      • et al.
      Basal cell adenocarcinoma of the salivary gland: a morphological and immunohistochemical comparison with basal cell adenoma with and without capsular invasion.
      The present case demonstrates a BCA with capsular invasion, measuring 2.5 cm, with a predominantly solid pattern. This is consistent with the literature, which shows that the solid and cribriform patterns are the most common subtypes in BCA with capsular invasion. It has been suggested that BCA with capsular invasion may precede a BCAC.
      • Jung Jung M.
      • Roh J.
      • Choi S.
      • et al.
      Basal cell adenocarcinoma of the salivary gland: a morphological and immunohistochemical comparison with basal cell adenoma with and without capsular invasion.
      Considering the infiltrative behavior observed in some BCA cases, management must include proactive observation of the patient, with regular follow-up visits to monitor for possible recurrence of the lesion. The case reported here showed no signs of recurrence after 1 year of follow-up.
      Generally, BCA occurs in major salivary glands, as the parotid, and in these cases, a local excision, rather than enucleation, is indicated. When this neoplasia occurs in minor salivary glands, the treatment consists of enucleation of the lesion, taking care not to disrupt the capsule overlying the tumor, thus minimizing the chance of recurrence.
      • Singh A.D.B.
      • Majumdar S.
      • Ghosh A.K.
      • et al.
      Basal cell adenoma - clinicopathological, immunohistochemical analysis and surgical considerations of a rare salivary gland tumor with review of literature.
      This risk is increased in cases of membranous BCA, which have a recurrence rate of 25%, whereas in other histologic patterns, recurrence is rare, with a rate of 3.8%.
      • Wilson T.C.
      • Robinson R.A.
      Basal Cell Adenocarcinoma and basal cell adenoma of the salivary glands: a clinicopathological review of seventy tumors with comparison of morphologic features and growth control indices.
      Malignant transformation is rare and occurred principally in the membranous type
      • Singh A.D.B.
      • Majumdar S.
      • Ghosh A.K.
      • et al.
      Basal cell adenoma - clinicopathological, immunohistochemical analysis and surgical considerations of a rare salivary gland tumor with review of literature.
      ; therefore, both treatment and follow-up of patients with this subtype of tumor should be more rigorous.
      It is also important to consider that multiple neoplasms of the salivary glands may occur, as well as synchronous salivary tumors and eccrine skin tumors.
      • Pires F.R.
      • Alves F.A.
      • de Almeida O.P.
      • Lopes M.A.
      • Kowalski L.P.
      Synchronous mucoepidermoid carcinoma of tongue and pleomorphic adenoma of submandibular gland.
      • Scheller E.L.
      • Pritchett C.V.
      • Shukla A.
      • Pepper J.P.
      • Marentette L.J.
      • McHugh J.B.
      Synchronous ipsilateral sebaceous lymphadenoma and membranous basal cell adenoma of the parotid.
      BCA has already been reported to occur synchronously with sebaceous lymphadenoma in the parotid gland.
      • Scheller E.L.
      • Pritchett C.V.
      • Shukla A.
      • Pepper J.P.
      • Marentette L.J.
      • McHugh J.B.
      Synchronous ipsilateral sebaceous lymphadenoma and membranous basal cell adenoma of the parotid.
      In the case reported here, no signs of other tumors were identified during treatment or during follow-up.
      The diagnosis of BCA can be established based on histopathologic and clinical characteristics. The importance of communication between surgeon and pathologist must be emphasized, as it provides intraoperative guidance. It is important to reach an accurate diagnosis, not mistaking the lesions for other ones with similar clinical and histopathologic characteristics, but with a completely different prognosis. Moreover, the follow-up of this lesion is extremely important and the patient should be monitored for a long period.

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        Basal Cell Adenocarcinoma and basal cell adenoma of the salivary glands: a clinicopathological review of seventy tumors with comparison of morphologic features and growth control indices.
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