|Year : 2016 | Volume
| Issue : 1 | Page : 66-70
Oncocytoma of the parotid gland: Dilemma for the cytopathologist
Kafil Akhtar, Shagufta Qadri, Presenjit Sen Ray, Rana Khalid Sherwani
Department of Pathology, Jawaharlal Nehru Medical College, Aligarh Muslim University, Aligarh, Uttar Pradesh, India
|Date of Web Publication||6-May-2016|
Dr. Shagufta Qadri
Department of Pathology, Jawaharlal Nehru Medical College, Aligarh Muslim University, Aligarh - 202 002, Uttar Pradesh
Source of Support: None, Conflict of Interest: None
Oncocytoma is a rare benign tumor of the salivary glands usually seen in elderly patients in the sixth to eighth decade. Microscopically, the hallmark of this lesion is the presence of oncocytes that comprise the entire tumor. These are large polygonal cells which have abundant eosinophilic granular cytoplasm, and from central to eccentric round nucleus. Several reactive as well as neoplastic lesions of salivary glands often have concurrent oncocytic changes. On fine-needle aspiration cytology, all of them have overlapping morphological features, thus making the diagnosis difficult by cytology alone. We report a case of oncocytoma of the right parotid gland in a 32-year-old Indian male. Although the tumor was initially suspected on cytology, confirmation was possible only after histopathological examination. The main purpose of this case report is to discuss the cytological differential diagnosis of oncocytic lesions of salivary glands and simultaneously emphasize the importance of histopathology for arriving at conclusive diagnosis in such cases.
Keywords: Oncocytic cells, oncocytoma, parotid gland, salivary gland
|How to cite this article:|
Akhtar K, Qadri S, Ray PS, Sherwani RK. Oncocytoma of the parotid gland: Dilemma for the cytopathologist. J Orofac Sci 2016;8:66-70
|How to cite this URL:|
Akhtar K, Qadri S, Ray PS, Sherwani RK. Oncocytoma of the parotid gland: Dilemma for the cytopathologist. J Orofac Sci [serial online] 2016 [cited 2019 Dec 14];8:66-70. Available from: http://www.jofs.in/text.asp?2016/8/1/66/181932
| Introduction|| |
Oncocytes are cells that can be seen in various tissues and a variety of conditions ranging from reactive changes to malignancy. Irrespective of the underlying etiology, the common features that define them is their characteristic morphology: Large cells with abundant eosinophilic granular cytoplasm and centrally or eccentrically placed nuclei. Oncocytoma of the salivary glands represents a rare group of benign neoplasms which are composed exclusively of oncocytes. These tumors are usually detected in elderly patients in with no sex predilection. , The report describes a case of this tumor arising in a 32-year-old man who presented with swelling in the right parotid region. An initial fine-needle aspiration (FNA) from the lesion showed characteristic oncocytes. Subsequent histopathological examination confirmed that tumor to be oncocytoma. Through this report, the authors intend to highlight the cytological differential diagnosis of oncocytic lesions of salivary glands and simultaneously emphasize the importance of histopathology for arriving at conclusive diagnosis in such cases.
| Case Report|| |
A 32-year-old Indian male patient reported to the Out-patient Department of Surgery with complaints of swelling below his right ear for 8 months, which showed a gradual increase in size. There was no associated history of pain or paresthesia. The man was nonsmoker, and no history of prior radiation exposure in the head and neck region could be elicited. On local examination, the swelling was 2.5 cm × 2 cm, soft and rubbery in consistency, nontender, and free from the skin as well as deeper structures. No cervical lymphadenopathy was detected.
As an initial diagnostic approach, FNA was done from the lesion using a 26-gauge needle which yielded blood mixed, brownish granular aspirate. Microscopically, smears revealed good cellularity consisting of cells arranged in clusters and lying singly. Individual cells had central as well as eccentric nuclei, prominent nucleoli, and abundant well-defined eosinophilic granular cytoplasm. Occasional clusters of regular acinar cell were also seen. The background contained many red blood cells and few macrophages but was devoid of any lymphocyte or nuclear debris [Figure 1] and [Figure 2]. A cytological diagnosis of an oncocytic lesion with the possibility of an oncocytic neoplasm was given.
|Figure 1: Fine-needle aspirate showing cluster of oncocytic cells with abundant eosinophilic cytoplasm, central to eccentric nuclei, and prominent nucleoli (Papanicolaou stain, ×400)|
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|Figure 2: Oncocytic cells (yellow arrow) in association with smaller acinar epithelial cells (white arrow) as seen on fine-needle aspirate (Papanicolaou stain, ×400)|
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Simultaneously, computed tomography (CT) scan showed a homogeneous hyperdense mass (2.2 cm in diameter) in the superficial lobe of the right parotid gland with enhanced signal and regular contours [Figure 3]. Based on the relevant history examination, FNA, and suggestive CT findings, a provisional diagnosis of benign parotid neoplasm was made. The patient underwent superficial parotidectomy.
|Figure 3: Computed tomography scan showing a homogeneous tumor mass in right parotid gland (red arrow)|
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Cut sections from the resected specimen showed a well-encapsulated solid, brownish tumor. Microscopically, the tumor was composed of a single population of large polyhedral oncocytes arranged in solid sheets, islands, and cords. The cytoplasm was abundant eosinophilic and finely granular. The nuclei were large and located centrally or peripherally and often displayed prominent nucleolus. No lymphoid tissue, lymphocytic infiltrate, necrosis, or nuclear atypia were observed. The histopathological findings were compatible with the diagnosis of oncocytoma.
| Discussion|| |
Salivary gland tumors account for 3% of all head and neck neoplasms,  and approximately 80% of these occur in the parotid gland.  The majority of parotid gland tumors are found to be located in the superficial lobe of the parotid gland; however, 2-4% of parotid tumors originate from the deep lobe. A total of 80-90% of these is benign mixed tumors and the others comprising adenoid cystic, mucoepidermoid, acinic cell carcinomas (ACCs), and lipomas.  Parotid gland oncocytoma is an uncommon, benign salivary neoplasm accounting for <1% of all salivary gland tumors. This tumor is composed of mitochondria-rich epithelial cells called oncocytes.  The clinical behavior of oncocytomas is essentially identical to those of other benign salivary tumors presenting as a solitary slow growing painless mass. They are often firm with multi-lobulated appearance and mobile nature on the clinical examination.  According to the newer World Health Organization classification and histologically, they are classified into three distinct types that have been identified, namely oncocytosis, oncocytoma, and oncocytic carcinoma.  Oncocytic changes of secretory epithelia are thought to be metaplastic, a protective phenomenon against adverse change. Aging is also thought to cause a functional exhaustion of the mitochondrial enzymes and a compensatory mitochondrial hyperplasia to overcome an energy-deficient condition.  Oncocytic lesions of the parotid gland demonstrate a spectrum of changes ranging from oncocytosis to benign oncocytomas and oncocytic carcinomas. There have been reports of the coexistence of these oncocytic entities. This raises the concept of a progression model with a progressive transition between these oncocytic lesions. 
Oncocytes are demonstrable in a host of lesions of salivary glands. All of them display similar morphology on FNA cytology (FNAC) and hence raise the need for the cytopathologist to consider them in the differential diagnosis. Focal oncocytic metaplasia or oncocytosis is not uncommon in salivary glands. The latter is characterized by focal or diffuse collection of hyperplastic oncocytes and is devoid of any capsule or clinically palpable mass. Such cases present with cytological picture identical to oncocytoma and distinction on FNAC alone is not possible; the histopathological examination is mandatory in such disputed cases. ,
In neoplastic lesions of salivary glands, diagnostic challenges arise when oncocytic metaplasia is encountered in tumors such as pleomorphic adenoma, myoepithelioma, basal cell adenoma, mucoepidermoid carcinoma, and polymorphous low-grade adenocarcinoma. However, these oncocytic changes are usually not extensive enough to be confused with an oncocytoma. Second, smears from these lesions often contain accompanying cells or stromal tissue, which indicates the nature of the parent tumor. ,,
Of the above, Warthin's tumor is the closest mimicker of oncocytoma as cystic change and lymphocytic infiltrates seen in the former may often be a component of the latter. Furthermore, Warthin's tumor may show focal areas of oncocytic hyperplasia that may resemble oncocytoma. In oncocytoma, FNAC shows epithelial cells are in sheets and papillary clusters with an attempt at acinus formation, little or no lymphoid cells, and single cells are seen in greater abundance. In contrast, aspirates of Warthin's tumor are composed epithelial cells, mostly oncocytic, in sheets with occasional papillary fragments; single cells are scarce and mixed lymphoid cell population along with a fluid background containing lymphocytes and debris are a relatively constant finding. Clinically, another striking feature is that Warthin's tumor has a strong association with cigarette smoking while oncocytoma is preceded by radiation exposure. ,,,
Mucoepidermoid carcinomas usually have squamous, intermediate, and mucin-secreting cells but can sometimes show cells with oncocytic changes. On FNAC, a dirty necrotic background is helpful in distinguishing it from oncocytoma which is devoid of this feature. ,, The role of phosphotungstic acid hematoxylin (PTAH) stain in distinguishing these two tumors has already been discussed. Rarely, ACC with cytological features of abundant, granular vacuolated cytoplasm, eccentric nuclei, and acinar arrangement appear oncocytic on May-Grunwald-Giemsa stain and may thus be confused with oncocytoma. However, the cells of ACC often show mild anisokaryosis, vacuolated cytoplasm, and many naked nuclei in the background which are unlikely with oncocytoma. ,
Differentiating oncocytoma from oncocytic carcinoma can be difficult on cytology as the former can appear cytologically malignant looking while the later can look deceptively monomorphic for which the term "oncocytic neoplasm" is preferred on cytology smears. In such doubtful cases, histologic examination of the resected specimen, histochemical staining, and immunohistochemistry (IHC) (wherever required) provides the accurate diagnosis. ,,
The word "oncocyte" is derived from the Greek word "onkousthai" meaning "increase in bulk."  In relation to cellular morphology, this term was first used by Hurthle, a German pathologist, in 1894; however, the term "oncytoma" was later coined by Hamperl in 1931. , Oncocytes are epithelial cells which appear polyhedral with abundant granular eosinophilic cytoplasm, and a central or eccentric nucleus. These cells are large, often two or more times the size of normal acinar epithelial cells. Ultrastructurally, their cytoplasms are filled with numerous mitochondria of various sizes along with a paucity of other cellular organalles. ,
Oncocytes can be seen in normal salivary glands as a part of reactive or metaplastic change. However, as these cells are capable of undergoing mitosis, a neoplastic transformation is possible.  Capone et al. observed the coexistence of the entire spectrum of these oncocytic entities within the same lesions, thus raising the concept of a progression model with a gradual transition from reactive to neoplastic changes. 
The World Health Organization has defined oncocytoma of salivary glands as a "benign tumor composed exclusively of large epithelial cells with characteristic bright eosinophilic granular cytoplasm."  They are rare representing not more than 1% of all salivary gland tumors. Affected patients are usually elderly in the sixth to eighth decade with a mean age of presentation at 58 years; no sex predilection has been observed in these tumors. , Although the parotid gland is affected more commonly (84%), oncocytoma has also been reported in submandibular gland and minor salivary glands.  The clinical presentation is similar to that seen in other benign parotid tumors, that is, slowly enlarging, nontender mass usually without any regional lymphadenopathy, and signs of neurodeficit. 
FNA smears from oncocytoma shows sheets of cohesive polygonal cells with abundant granular cytoplasm and uniform round central nuclei, bland chromatin with inconspicuous eccentric nucleoli. The background is relatively clean without any necrosis, lymphoid cells, or debris. Histologically, the additional features that support the diagnosis are complete encapsulation. ,, Furthermore, the cells of oncocytoma stain focally positive with PTAH, especially in the cells with clear cytoplasm. This feature is useful to distinguish from the clear cells of mucoepidermoid carcinoma which are PTAH negative. ,
In salivary gland masses, FNAC remains one of the first-line investigations. Various studies in literature have reported a diagnostic accuracy of 86-98% for cytological diagnosis of salivary gland neoplasms. The sensitivity has ranged from 62% to 97.6%, and specificity from 94.3% to 100%. , However, as lesions of salivary glands are notorious for having overlapping morphological features, diagnosis by cytology alone often becomes difficult, and the insufficient or nondiagnostic rate is up to 29%.  In such cases, histopathological examination is of paramount importance. ,
Since open biopsy is generally not a viable alternative as it has many of the disadvantages of general anesthesia, wide excision, possible nerve damage, and bleeding. Hence, core needle biopsies fit the bill by providing the best quality and quantity of tissue with the fewest patient complications. However due to remarkable intra-tumoral variability, the morphology on a core biopsy may be nonrepresentative. This problem can be overcome by taking multiple ultrasonography or CT-guided core needle biopsies  from different representative tumor areas, thus increasing its accuracy almost equal to excisional biopsy. Furthermore, IHC can be more easily performed on core needle biopsy material as compared to FNA biopsy. Therefore, this technique can be viewed as complimentary and could be employed sequentially in selected cases.
Surgical management with superficial or total parotidectomy remains the mainstay of therapy in oncocytomas. Given the benign nature and slow growth rate of the tumor, there is no role of chemotherapy and/or radiation therapy. The tumor has an excellent prognosis although recurrences have been reported to be 20% and are attributed to incomplete surgical resection. ,,
| Conclusions|| |
- Oncocytoma is a rare benign tumor of salivary glands which is exclusively composed of "oncocytes," i.e., large polyhedral cells with abundant granular eosinophilic cytoplasm and central to eccentric nucleus.
- Several reactive as well as neoplastic lesions of salivary glands often show focal oncocytic changes.
- On FNA, these lesions can be confused with oncocytoma as the cellular features show considerable overlap, thus posing a diagnostic challenge.
- A complete history, radiological findings, and above all histopathological examination are mandatory to differentiate this neoplasm from its mimickers.
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