Pleomorphic adenoma with extensive oncocytic change in the parotid gland: a case report and review

Introduction

Salivary gland tumors are rare neoplasms, occurring in approximately 2–3% of head and neck tumors, with most being benign and malignant cases occurring relatively infrequently (1). Among these, pleomorphic adenoma (PA) is the most common benign tumor, while mucoepidermoid carcinoma is the most prevalent malignant tumor (1,2). Diagnosis of salivary gland tumors typically involves computed tomography (CT) and magnetic resonance imaging (MRI), as well as fine needle aspiration (FNA) to determine the histological characteristics of the tumor (3,4). However, PAs can rarely undergo histological transformation due to oncocytic metaplasia. We report a case of PA with extensive oncocytic change in an adult male patient. We present this article in accordance with the CARE reporting checklist (available at https://gs.amegroups.com/article/view/10.21037/gs-2025-232/rc).

Case presentation

A 55-year-old male with no underlying medical conditions presented with a mass on his left cheek. Physical examination revealed a painless mass below the left earlobe. The patient reported no tingling sensation or paresthesia, and the mass had been slowly growing for two years. CT and MRI scans showed a benign-looking, lobulated, enhancing soft tissue lesion measuring approximately 2.6 cm in the left parotid gland, with no cervical lymph node enlargement observed (Figure 1). Initially, an FNA biopsy was performed by the radiology department, which demonstrated cohesive groups of oncocytic cells, characterized by abundant granular eosinophilic cytoplasm and centrally located nuclei, intermixed with typical myoepithelial elements, consistent with PA with extensive oncocytic change without margin involvement (Figure 2).

Figure 1 CT and MRI show a 2.6 cm-sized, well-defined parotid gland tumor. (A) CT scan showing a 2.6 cm ill-defined mass in the left parotid gland (red arrow indicates tumor margin). (B) T1-weighted MRI displaying the lesion involving both superficial and deep lobes (red arrow points to tumor boundary). CT, computed tomography; MRI, magnetic resonance imaging.

Figure 2 Histopathology of oncocytic pleomorphic adenoma. (A) Histologic image of the tumor shows polygonal oncocytic cells with abundant granular eosinophilic cytoplasm (HE stain, ×2.5). (B) Histologic image of the tumor shows polygonal oncocytic cells with abundant granular eosinophilic cytoplasm (HE stain, ×100). (C) Immunohistochemical staining for Ki-67 (×100). (D) Immunohistochemical staining for p63 (×100). (E) Immunohistochemical staining for S100 (×100). (F) Immunohistochemical staining for SOX10 (×100). HE, hematoxylin-eosin.

We planned a total parotidectomy under general anesthesia. A modified Blair incision was made on the left cheek, and dissection was performed beneath the Superficial Musculoaponeurotic System (SMAS) level to identify the parotid fascia and the buccal, zygomatic, frontal, and marginal mandibular branches of the facial nerve. The parotid gland was exposed, and en bloc excision of the parotid tissue, including the mass, was performed with preservation of facial nerve branches.

An artificial dermal matrix was applied to augment soft tissue depression and separate the parotid and skin flap. The tumor was oval-shaped, measuring 3.0×2.4×2.2 cm, and the total excised specimen size was 6.2×4.9×2.4 cm (23.5 grams) (Figure 3).

Figure 3 Clinical photograph of the excised mass. (A) Clinical photograph showing the state after excision. (B) Clinical photograph of the excised tumor specimen.

Postoperatively, weakness of the buccal branch was observed for 15 days but gradually recovered. Salivary function also recovered to normal without any complications. At 12 months of postoperative follow-up, the patient had completely recovered with no complications in facial animation and salivary functions. All procedures performed in this study were in accordance with the ethical standards of the institutional and/or national research committee(s) and with the Declaration of Helsinki and its subsequent amendments. Written informed consent was obtained from the patient for publication of this case report and accompanying images. A copy of the written consent is available for review by the editorial office of this journal.

Discussions

While PA is the most common benign salivary gland tumor, cases with extensive oncocytic change are extremely rare, with oncocytic metaplasia primarily observed in elderly patients (4,5).

Cases like ours, showing clear pathological findings and clinical course in a relatively young man in his 50s, are uncommon (6). The PA with extensive oncocytic change is characterized by accumulation of granular eosinophils in the cytoplasm and distinctive mitochondria-rich cytoplasm, but this can be difficult to differentiate from Warthin’s tumor, oncocytoma, or other malignant tumors (5,6).

In this case, preoperative diagnosis was possible based on CT/MRI imaging and FNA biopsy pathology results. However, the final confirmation was ultimately made through histological examination and immunohistochemical staining of the tumor (5,7-9).

This highlights the need for a careful multidisciplinary approach to the PA with extensive oncocytic change. After much deliberation in treating this patient, we performed a total parotidectomy with the patient’s consent, considering the extensive oncocytic change pattern of the PA (10-12).

A summary of previously reported PA cases with extensive oncocytic change is provided in Table 1 to highlight the rarity and clinical characteristics of this variant. This table compiles key demographic data, tumor size, treatment approaches, and outcomes from recent literature alongside the present case. Most cases involved older patients with tumors primarily located in the parotid gland, all managed surgically with favorable short-term outcomes.

Our case, involving a relatively younger patient and deep lobe involvement, broadens the clinical spectrum of this uncommon entity.

Given the diagnostic challenges posed by oncocytic features, which often mimic other benign and malignant salivary gland tumors, a thorough multidisciplinary evaluation incorporating imaging, histopathology, and immunohistochemistry is essential. Considering the potential for malignant transformation reported in some cases, long-term surveillance with clinical and radiologic follow-up is strongly recommended.

We chose total parotidectomy for two reasons. First, the tumor size of 3.0 cm was large relative to the parotid gland, with a high possibility of deep lobe involvement. Secondly, we aimed to secure margins to prevent recurrence.

In planning this surgery, we optimized functional outcomes through facial nerve preservation. The temporary weakness of the buccal branch post-surgery was presumed to be due to minor damage during nerve dissection and recovered naturally. The use of an artificial dermal matrix was effective in preventing post-surgical soft tissue depression, which also contributed to improving aesthetic results.

The PA with extensive oncocytic change generally maintains a typical epithelial-mesenchymal mixed structure, but clusters of oncocytic cells are observed without cellular atypia (6,7).

In this case, we secured negative resection margins, and subsequent immunohistochemical examination was advantageous in determining the tumor type. While the recurrence rate of PA is generally 1–5%, data on the long-term prognosis of the oncocytic subtype is currently limited, necessitating a multidisciplinary approach and long-term observation (2,6).

Recent studies suggest that PA with oncocytic change may show hamartomatous growth tendencies, consistent with the tumor’s slowly progressing clinical course (6). The growth rate of the mass over two years in this case clearly demonstrates this characteristic.

When establishing diagnostic and treatment strategies for PA with such rare histological variations, performing ultrasound-guided FNA biopsy first can be crucial, as the accuracy of this biopsy can be extremely important (14).

Subsequently, a comprehensive multidisciplinary approach through collaboration between radiology, pathology, and head and neck plastic surgery departments is necessary. Functional surgery that maximally preserves facial nerves while incorporating reconstructive surgery when needed is essential.

As this is a single case report, further verification through large-scale cohort studies is required. Future research elucidating the molecular biological mechanisms of oncocytic metaplasia will be important, potentially enabling prediction of PA’s atypical variations and development of targeted therapies.

This case highlights a rare PA with extensive oncocytic change in the parotid gland. The diagnosis required a comprehensive approach combining clinical, radiological, and cytopathological findings. Successful management was achieved through total parotidectomy with facial nerve preservation, resulting in complete recovery of facial and salivary functions.

Based on our experience with this case, we propose a potential framework for management suggestions for PA with the rare histological variant of oncocytic change. First, a combination of imaging studies such as CT and MRI, together with ultrasound-guided FNA cytology (FNAC), is essential for accurate diagnosis. Unlike conventional PA, PA with oncocytic change demonstrates distinct radiological features on CT and MRI. Specifically, the PA with extensive oncocytic change often presents with irregular borders and areas of necrosis due to capsular disruption, resulting in heterogeneous signal intensity and non-uniform contrast enhancement. On positron emission tomography (PET)-CT, a SUV_max ≥4.0 should raise a strong suspicion for malignancy. When lesions are categorized as “salivary gland neoplasm of uncertain malignant potential” according to the Milan system, diagnostic sensitivity is significantly improved (10). In particular, when oncocytic change is suspected, immunohistochemical staining (including SOX10, S100, and p63) should be performed to reliably distinguish these tumors from malignant neoplasms (6,13).

Surgical management should be tailored according to tumor size and location. For lesions ≤2.5 cm confined to the superficial lobe, superficial parotidectomy is recommended. For tumors ≥3.0 cm, those involving the deep lobe, or cases with multifocal disease, as in our case, total parotidectomy should be performed. Intraoperative facial nerve monitoring is crucial to maximize nerve preservation, and the use of artificial dermal matrix for reconstruction can minimize postoperative cosmetic and physiological complications in cases with significant tissue defects (15).

In cases of PA with oncocytic change, we recommend MRI surveillance during the first two years, followed by clinical follow-up for up to 10 years, in order to facilitate early detection of microscopic recurrence and timely additional treatment (5,15). Oncocytic metaplasia is associated with a higher likelihood of accumulating HER2 or TP53 mutations even in the absence of cytological atypia, which increases the risk of malignant transformation (16,17). If any warning signs of malignant transformation are observed, such as rapid growth or new neurological symptoms, PET-CT and molecular genetic testing should be promptly performed (18). However, we acknowledge that these guidelines may have limitations, and further prospective multicenter trials are warranted to validate our recommendations. Our proposed approach aims to achieve an optimal balance between oncological safety and functional outcomes in PAs with rare histological variants. In the future, the development of personalized treatment strategies based on tumor microenvironment analysis may provide even more evidence-based recommendations.

Conclusions

This case highlights the diagnostic challenges presented by PA with extensive oncocytic change and emphasizes the importance of a multidisciplinary approach. The findings support the role of comprehensive imaging and cytopathologic assessment in differentiating oncocytic variants from malignant neoplasms. However, this case is limited by the single-case nature of the report and the lack of long-term molecular follow-up. Future studies involving larger patient cohorts and molecular profiling are needed to clarify oncocytic transformation mechanisms and inform evidence-based management strategies.

Acknowledgments

None.

Footnote

Reporting Checklist: The authors have completed the CARE reporting checklist. Available at https://gs.amegroups.com/article/view/10.21037/gs-2025-232/rc

Peer Review File: Available at https://gs.amegroups.com/article/view/10.21037/gs-2025-232/prf

Funding: None.

Conflicts of Interest: All authors have completed the ICMJE uniform disclosure form (available at https://gs.amegroups.com/article/view/10.21037/gs-2025-232/coif). The authors have no conflicts of interest to declare.

Ethical Statement: The authors are accountable for all aspects of the work in ensuring that questions related to the accuracy or integrity of any part of the work are appropriately investigated and resolved. All procedures performed in this study were in accordance with the ethical standards of the institutional and/or national research committee(s) and with the Declaration of Helsinki and its subsequent amendments. Written informed consent was obtained from the patient for publication of this case report and accompanying images. A copy of the written consent is available for review by the editorial office of this journal.

Open Access Statement: This is an Open Access article distributed in accordance with the Creative Commons Attribution-NonCommercial-NoDerivs 4.0 International License (CC BY-NC-ND 4.0), which permits the non-commercial replication and distribution of the article with the strict proviso that no changes or edits are made and the original work is properly cited (including links to both the formal publication through the relevant DOI and the license). See: https://creativecommons.org/licenses/by-nc-nd/4.0/.

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