|Year : 2015 | Volume
| Issue : 2 | Page : 111-114
Giant basal cell adenoma of the parotid gland eroding the ramus of mandible: An unusual presentation
Kiran Khande1, Rajshekhar Halli2, Pushkar Gawande3, Manjula Hebbale4
1 Department of Oral and Maxillofacial Surgery, Y C Memorial Dental College and Hospital, Ahmednagar, Maharashtra, India
2 Department of Oral and Maxillofacial Surgery, Bharati Vidyapeeth University Dental College and Hospital, Pune, Maharashtra, India
3 Department of Oral and Maxillofacial Surgery, Sinhgad Dental College and Hospital, Pune, Maharashtra, India
4 Department of Oral Medicine and Maxillofacial Radiology, Bharati Vidyapeeth University Dental College and Hospital, Pune, Maharashtra, India
|Date of Web Publication||11-Dec-2015|
Department of Oral and Maxillofacial Surgery, Bharati Vidyapeeth University Dental College and Hospital, Pune - 411 040, Maharashtra
Source of Support: None, Conflict of Interest: None
Basal cell adenoma (BCA) is an uncommon benign salivary gland epithelial tumor. BCA accounts for 1-2% of all salivary gland epithelial tumors and more than 80% of BCA's arise in the major salivary glands, mostly the parotid. It is usually firm in consistency, mobile, slow growing mass, and tends to be multiple. Due to the prognostic implications, differential diagnosis with basal cell adenocarcinoma, adenoid cystic carcinoma, and basaloid squamous cell carcinoma is essential. We present a giant BCA of the left parotid gland eroding the ramus of mandible in an elderly female and discuss its diagnostic work-up and surgical management.
Keywords: Basal cell adenoma, monomorphic adenoma, parotid tumor, parotidectomy
|How to cite this article:|
Khande K, Halli R, Gawande P, Hebbale M. Giant basal cell adenoma of the parotid gland eroding the ramus of mandible: An unusual presentation. J Dent Allied Sci 2015;4:111-4
|How to cite this URL:|
Khande K, Halli R, Gawande P, Hebbale M. Giant basal cell adenoma of the parotid gland eroding the ramus of mandible: An unusual presentation. J Dent Allied Sci [serial online] 2015 [cited 2020 Mar 29];4:111-4. Available from: http://www.jdas.in/text.asp?2015/4/2/111/171551
| Introduction|| |
In 1967, Kleinsasser and Klein introduced the term "basal cell adenoma (BCA)" to describe a benign salivary gland tumor comprised of uniformly appearing basaloid cells arranged in solid, trabecular, tubular, and membranous patterns, but lacking the myxoid and chondroid mesenchymal-like component as seen in pleomorphic adenoma. 
BCA of the salivary glands is a rare tumor, recognized as an independent entity in the second edition of the salivary gland tumors classification of the World Health Organization.  It is considered as a low-grade malignant tumor with a high recurrence rate and, in general, good prognosis. The most frequent location is the parotid gland, although the other sites are possible such as the upper lip, buccal mucosa, lower lip, palate, and nasal septum. ,,
BCA should be distinguished from basal cell adenocarcinoma, which is a rare entity that was first defined as a malignant salivary gland tumor in 1991. Most of the tumors appear to be benign clinically and mimic other benign salivary gland tumors.
We present a giant BCA of left parotid gland eroding the ramus of mandible in an elderly female with its diagnostic work-up and surgical management.
| Case Report|| |
A 40-year-old woman reported to us with a complaint of massive swelling over the left half of the face and neck for 2 years. There was a previous attempt of surgical excision of the small tumor 2 years back at other center and the patient had lost all the details including operative notes and histopathological report.
On examination, massive, diffuse, irregular swelling was present over the left parotid and submandibular region measuring about 13 cm × 11 cm in its maximum dimension [Figure 1]. Superiorly, the left ear lobule was typically raised, and inferiorly the swelling was extending 5 cm below and posterior to the ramus of mandible. Anteriorly, the swelling was extending about 2 cm ahead of anterior border of ramus and posteriorly about 3 cm behind the posterior border of the ramus, obliterating the mandibular angle-mastoid region. The patient also had restricted jaw opening.
Two separate scars were noticed, one over the left submandibular region and the other over the left preauricular region. These may be the scars of previously attempted surgery at the other center. Mild left-sided facial nerve affectation was evident. The swelling was lobulated and firm in consistency without fixation to the skin.
With brief history and clinical examination, provisional diagnosis of pleomorphic adenoma of the left parotid gland was evident.
Multiplanar magnetic resonance imaging (MRI) of the neck on Siemen's 1.5 Tesla Magnatom Avanto machine using T1- and T2-weighted fast spin echo and fast STIR sequences, postcontrast study was performed [Figure 2].
|Figure 2: Magnetic resonance imaging scan in axial section; (a) Plain, (b) Contrast, and in coronal section; (c) Plain, (d) Contrast|
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Well-defined lobulated soft tissue mass lesion was seen within the left parotid gland. It appeared heterogeneously hyperintense on T2-weighted and hypointense on T1-weighted images. Approximate size of the lesion measured about 8.5 cm × 4 cm × 8.5 cm (APXRLXSI). On postcontrast study, lesion revealed moderate heterogeneous enhancement. Large cystic nonenhancing component of approximate size of 4 cm × 3 cm was seen within medial portion of the lesion. Medially, lesion was extending into para-pharyngeal space displacing the right base of the tongue toward the right side. Inferiorly, the lesion was extending into the right submandibular space. Laterally, lesion reached up to the subcutaneous plane. The para-pharyngeal, right parotid, and carotid spaces were normal in appearance. The anterior and posterior cervical spaces, pre- and para-spinal spaces showed no abnormality. Laryngeal airways were normal. Both the carotid and jugular vessels were unremarkable. Thyroid gland showed no focal abnormality.
Surgical excision under general anesthesia was planned after obtaining the written consent. An extended rhytidectomy incision was placed as the tumor was extending into the submandibular space [Figure 3]. After initial dissection, the tumor capsule was identified and further exploration of the facial nerve trunk was carried out. The main trunk of the facial nerve was identified and dissection was continued anteriorly to note that the branches were running through the tumor mass, posing impossibility to dissect and save them. Further dissection over the ramus revealed the erosion of the posterior border of the ramus by the tumor mass. Whole tumor mass was dissected through the submandibular space as well and was excised in toto sacrificing the facial nerve branches [Figure 4]a. Sternocleidomastoid muscular flap was raised and was anchored with suturing the masseter muscle over the lateral border of the ramus. This helped in filling up the mandibular angle-mastoid dead space to some extent. Suction drain was secured prior to closure in layers. Postoperative recovery was uneventful.
|Figure 3: Intraoperative photographs: (a) Incision marking, (b) Dissection of the tumor, (c) Erosion of the posterior border of the ramus of mandible, (d) Defect after total excision of the tumor, (e) Sternocleidomastoid muscle flap sutured to masseter, (f) Wound closure in layers|
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|Figure 4: (a) Specimen, (b) Histopathological photomicrograph (H and E, ×10)|
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The histopathological examination of the specimen revealed an encapsulated tumor composed of large-sized basaloid cells with eosinophilic cytoplasm and a round to oval nucleus. These basaloid cells were arranged in the form of islands and cords. The arrangement of tumor cells was producing reticular pattern at places. The tumor showed abundant cystic spaces with scanty connective tissue stroma. Large-sized dilated blood vessels were also noticed and the overall impression was in favor of BCA [Figure 4]b.
On follow-up visit, the left facial nerve affectation was evident [Figure 5] Postsurgical MRI showed complete excision of the tumor [Figure 6]. The patient is on regular follow-up for more than 12 months without any signs of recurrence.
|Figure 5: Postoperative views: (a-c) Affectation of the facial nerve, (d) Wound healing|
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|Figure 6: Postoperative magnetic resonance imaging scan in axial section; (a) Plain, (b) Contrast, and in coronal section; (c) Plain, (d) Contrast|
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| Discussion|| |
Majority of the parotid tumors are benign and pleomorphic adenomas are the most frequent. Monomorphic adenomas are uncommon and can be defined as benign epithelial tumors of the salivary glands that are not pleomorphic adenomas. BCA's are monomorphic adenomas that are subdivided into solid, trabecular, tubular, and membranous subtypes.
BCA is a slow growing, encapsulated tumor that do not exceed 3 cm in diameter. It is a firm, mobile, painless mass usually superficial within the glandular body with a brownish appearance.  It has a less infiltrative growth behavior than that of a pleomorphic adenoma. Most of the BCA's occur in men and in older adults with an average age of 60 years.
In our case, all the above findings were contrast as to the size of the tumor, age, sex of the patient, and infiltrative behavior of the tumor. Our case was a 40-year-old female with the tumor size of about 13 cm × 11 cm and the tumor had eroded the posterior border of the ramus.
Diagnosis should be established by the histological study wherein biopsy is the most accurate method; although some authors advocate fine needle aspiration cytology when physical access to the tumor is available.
In its most common location in the parotid gland, BCA is similar to a pleomorphic adenoma or Warthin's tumor. Its superficial location may make it appear to be a sebaceous cyst of skin or enlarged lymph node, which may be related to lymphoma, HIV-related parotitis, lymphadenopathy, or tuberculous-related lymphadenitis. In addition, a variety of malignant salivary gland tumors may also appear as a similar mass. The surgical approach is determined by the location and extent of the tumor. 
Histopathologically, BCA are well-circumscribed or encapsulated masses whose cut surface is homogenous, but often interrupted by cystic spaces containing brownish material, which may be multifocal. The tumor consists of uniform cells with eosinophilic cytoplasm and oval nuclei. The cells may be arranged in several patterns. In the solid pattern, there are large islands with peripheral cells that may be more hyperchromatic and palisading. Occasionally, the central cells are squamous and form keratin pearls. The stroma is usually scanty. The trabecular/tubular pattern forms cords and ducal structures. The membranous pattern has a jigsaw arrangement of epithelial islands in a multilobulated and often unencapsulated tumor. The islands are surrounded by eosinophilic, periodic acid-Schiff -positive, hyalinized material representing replicated basal lamina. The islands may also contain small intercellular hyaline masses that may coalesce. The pattern strongly resembles that of dermal cylindroma.
In our case, histopathological report revealed an encapsulated tumor composed of large-sized basaloid cells with eosinophilic cytoplasm and a round to oval nucleus. These basaloid cells were arranged in the form of islands and cords. The arrangement of tumor cells was producing a reticular pattern at places. The tumor revealed abundant cystic spaces with scanty connective tissue stroma. Large-sized dilated blood vessels were also noticed. The overall impression was BCA of the parotid gland.
Differential diagnosis must be mostly established with some unfavorable entities such as the basal cell adenocarcinoma, adenoid cystic carcinoma, and basaloid squamous cell carcinoma. In contrast to BCA, an infiltrative growth, more mitotic figures (>4 mitotic count/10 high-power field), and Ki-67-staining of 5% of the cells are observed in basal cell carcinoma.  In the adenoid cystic carcinoma, whirlpool of epithelial cells, dark external cells in a stockade pattern, and a thick basal membrane-like structure are observed. It is also referred parenchymatous and perineural invasion. Moreover, vascularization in the microcystic areas is absent, in contrast to BCA, in which multiple endothelial canals are present. Some authors have suggested morphometry as a useful method in the differential diagnosis of both entities. 
Basaloid squamous cell carcinoma is characterized by the presence of solid cells in a lobular fashion, close to the superficial mucosa, in which cells are small and have scarce cytoplasm with hyperchromatic nuclei without nucleoli. These cells constitute small cystic spaces filled by mucinous material. In this latter entity, both populations of basal cells are not observed, in contrast to BCA. ,,
In relation to the histological diagnosis, immunohistochemical analysis is of great help. The majority of authors advocate for the existence of a unique epithelial cell type in the BCA, although some other authors  have referred the existence of some heterogeneity in cellular populations such as ductal epithelial cells and myoepithelial cells. These data contradict what other authors have suggested, in which the absence of myoepithelial cells has been considered as characteristic of this neoplasm, in contrast to pleomorphic adenoma. 
The intense vimentin and HHF-35 staining of some BCA cells have been reported. It is known that these markers are typical for myoepithelial tumoral cells. In the solid BCA subtype, the majority of cells show positivity for KL-1 and negativity for vimentin and HFF-35, with a scarce participation of myoepithelial cells. According to some authors,  it does not occur in the trabecular and ductal subtypes, in which the presence of intensively S-100 stained cells suggest the presence of a myoepithelial nature. However, although some authors  advocate for the specificity of S-100 in relation to myoepithelial cells, some others  suggest the existence of this marker in the neoplastic cells of BCA, independent of their lineage.
The treatment of BCA is surgical excision by means of superficial parotidectomy or total parotidectomy depending upon the nature, extent, and facial nerve affectation. More extensive excision of the parotid gland tumor, careful macroscopic perioperative examination of the surgical specimen, and histologic evaluation of all the surgical specimens might be necessary for reducing revision operations and surgical complications.  Regular follow-up is mandatory to rule out the possibility of recurrence.
Declaration of patient consent
The authors certify that they have obtained all appropriate patient consent forms. In the form the patient(s) has/have given his/her/their consent for his/her/their images and other clinical information to be reported in the journal. The patients understand that their names and initials will not be published and due efforts will be made to conceal their identity, but anonymity cannot be guaranteed.
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Conflicts of interest
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[Figure 1], [Figure 2], [Figure 3], [Figure 4], [Figure 5], [Figure 6]