Salivary gland carcinomas are uncommon neoplasms that make up only a small fraction of head and neck malignancies, and the parotid gland is by far their most frequent site of origin [1,2]. Population-based and institutional series confirm both the rarity and the marked histological heterogeneity of these tumors, with more than 20 recognized malignant epithelial subtypes and considerable variability in biological behavior [1,2].

Within this already scarce group, oncocytic carcinoma (OC) is one of the rarest entities. It represents approximately 5% of oncocytic salivary gland neoplasms, roughly 0.5% of epithelial salivary gland malignancies, and about 0.18% of all epithelial salivary gland tumors [4,5].

OC is defined as a proliferation of cytomorphologically malignant oncocytes—large epithelial cells with abundant granular eosinophilic cytoplasm reflecting an accumulation of mitochondria—arranged in an adenocarcinomatous, infiltrative architecture [3,5]. The terms oncocytic carcinoma, oncocytic adenocarcinoma, malignant oncocytoma, and malignant oxyphilic adenoma have historically been used interchangeably [3]. Because a purely oncocytic malignancy is difficult to define and molecularly poorly characterized, the entity has remained taxonomically contentious, and its status was revisited in the fifth edition of the World Health Organization (WHO) Classification of Head and Neck Tumours [1]. Regardless of nomenclature, the malignant nature of the lesion is established by histological criteria—cellular pleomorphism, mitotic activity, necrosis—and by infiltrative behavior including perineural, vascular, or lymphatic invasion, destruction of adjacent structures, and regional or distant metastasis [5,8].

The principal clinical challenge posed by OC is that its presentation and imaging features closely mimic those of benign oncocytic lesions such as oncocytoma and Warthin tumor, and even fine-needle aspiration cytology may be misleading [5,12]. As a result, the diagnosis is often made only on definitive histopathology after surgery. We report a case of parotid OC with extensive parapharyngeal involvement and radiologically suspicious cervical lymphadenopathy in a middle-aged diabetic man, and we review the literature on the presentation, diagnosis, and management of this uncommon malignancy.

Case Presentation

Clinical history. A 46-year-old man, known to have type 2 diabetes mellitus controlled with oral antidiabetic agents, presented to our department with a slowly progressive swelling of the left parotid region. The history of the disease dated back approximately 10 months to the appearance of a mass in the left parotid area that had gradually increased in size. There were no overlying inflammatory signs, no local pain, and no facial nerve dysfunction. The patient reported no fever, no weight loss, and no prior history of head and neck irradiation or salivary gland disease. There was no reported tobacco or alcohol dependence.

Physical examination. Inspection of the face and neck showed an asymmetry of the left parotid region, with a visible swelling filling the preauricular and retromandibular areas and effacing the retromandibular groove, without overlying skin discoloration or inflammatory changes (Figure 1). On palpation, the left parotid mass was firm, measuring approximately 2 cm at its palpable superficial component, and mobile relative to both the superficial and the deep planes. Facial nerve function was intact in all branches. There was no palpable cervical lymphadenopathy on either side of the neck. Oropharyngeal examination disclosed a homolateral (left) bulging of the lateral oropharyngeal wall/soft palate region, consistent with deep parapharyngeal extension of the parotid process (Figure 2). The remainder of the otorhinolaryngological and general examination was unremarkable.

Figure 1: Preoperative clinical photograph (left lateral view) showing the swelling of the left parotid region, with fullness of the preauricular and retromandibular areas and effacement of the retromandibular groove, without inflammatory skin changes.

Figure 2: Preoperative intraoral photograph showing homolateral (left) bulging of the oropharyngeal wall and soft palate, reflecting deep parapharyngeal extension of the parotid tumor.

Imaging. Contrast-enhanced cervical CT (spiral, millimetric acquisition with multiplanar reconstruction) demonstrated a lesional process of the left parotid gland, spontaneously hypodense (estimated density around 15 HU), moderately and heterogeneously enhancing after contrast, invading the retro- and prestyloid space and measuring 47 × 32 mm in the axial plane with a craniocaudal extension of approximately 60 mm. A bulky left parapharyngeal adenopathy measuring 31 × 26 mm exerted a mass effect and displaced the left aspect of the naso- and oropharynx. No contralateral cervical adenopathy was identified; a few sub-centimetric nodes with a benign fatty hilum were noted. Bone-window analysis showed no aggressive osseous lesion. The overall CT impression was a suspicious left parotid process of 60 × 47 × 32 mm invading the retro- and prestyloid space, associated with parapharyngeal adenopathy and mass effect on the pharynx (Figure 3).

Figure 3: Contrast-enhanced cervical CT (axial and coronal reconstructions) showing the heterogeneously enhancing left parotid lesion extending into the pre- and retrostyloid parapharyngeal space, with adjacent parapharyngeal adenopathy and mass effect on the pharynx.

The difference in lesion dimensions between CT and MRI was considered in the context of different imaging modalities, acquisition planes, and delineation of the infiltrative component; the MRI measurements included the more extensive infiltrative soft-tissue component.

MRI. Parotid MRI (axial, coronal, and sagittal T1 and T2 sequences; axial T2 STIR; axial diffusion-weighted imaging; and post-gadolinium T1 sequences) confirmed an irregular, ill-defined left parotid tissue process, in mild heterogeneous T2 hyperintensity, mild T1 hypointensity, and mild diffusion hyperintensity with an intermediate apparent diffusion coefficient (ADC), enhancing heterogeneously after gadolinium and measuring 75 × 65 mm with a craniocaudal extension of 66 mm. Medially, the process infiltrated the pre- and retrostyloid space with invasion of parapharyngeal fat and exerted a marked mass effect on the soft palate and on the lateral wall of the nasopharynx and oropharynx, resulting in significant narrowing of the aerodigestive lumen. Laterally, it infiltrated the left jugal subcutaneous fat with a discrete bulging of the cheek. A left level IIA laterocervical lymph node measuring 11 mm in short axis was described. The pharynx and larynx were otherwise normal, the contralateral parotid and both submandibular glands were unremarkable, and the jugulocarotid vascular axes were free. The MRI conclusion was a locally advanced left parotid tissue process whose morphological and dynamic features were suspicious for malignancy, to be correlated with histology (Figure 4).

Figure 4: Parotid MRI. Representative axial T2-weighted images showing an irregular, ill-defined, heterogeneously enhancing left parotid mass infiltrating the parapharyngeal space with mass effect on the soft palate and pharyngeal wall.

Surgical management. After multidisciplinary discussion, the patient underwent parotidectomy with facial nerve identification and preservation, through a modified Blair incision with elevation of a cervicofacial flap. Because of the size of the lesion and its deep parapharyngeal extension, the tumor was delivered in two fragments (piecemeal) rather than as a single specimen. The superficial component was resected first: after dissection of its capsule from the surrounding parenchyma, it was mobilized and removed from the parotid bed, exposing the underlying operative field (Figure 5). The second, deeper component, arising from the deep lobe and extending medially into the pre- and retrostyloid parapharyngeal space, appeared as a lobulated, well-vascularized, purplish mass; it was progressively delivered from the parapharyngeal fat, with control of the adjacent vascular structures with a vessel loop and preservation of the facial nerve branches and of the jugulocarotid axis (Figure 6). Macroscopic examination of the resected specimen showed a lobulated, dark reddish-brown, fleshy mass with an irregular surface (Figure 7). Facial nerve function was assessed postoperatively.

Figure 5: Intraoperative photograph after removal of the first (superficial) tumor fragment, showing the left parotid operative field with the residual deep tumor component still lying in the pre- and retrostyloid space.

Figure 6: Intraoperative photograph showing delivery of the second, deep-lobe tumor fragment from the parapharyngeal space. The lesion appears as a lobulated, well-vascularized, purplish mass; the adjacent vascular structures are controlled with a vessel loop.

Figure 7: Gross surgical specimen after parotidectomy. The tumor was removed in two fragments; a syringe is included for scale. Note the lobulated, hemorrhagic, fleshy cut surface of the oncocytic carcinoma.

Histopathology. Definitive histopathological examination of the resected specimen concluded that the lesion was an oncocytic carcinoma of the parotid gland. The tumor was composed of large polygonal cells with abundant granular eosinophilic cytoplasm and an infiltrative growth pattern, consistent with a malignant oncocytic neoplasm. Immunohistochemistry and, where available, antimitochondrial staining are the recommended ancillary tools to confirm the oncocytic nature of the lesion and to exclude oncocytic mimics [5,11].

Postoperative course and follow-up. The immediate postoperative course was uneventful, with primary wound healing and no salivary fistula. Clinically, the parotid swelling had disappeared, the facial contour was restored, and facial symmetry was preserved at rest (Figure 8). Intraoral examination showed marked regression of the homolateral oropharyngeal bulging, with a symmetric soft palate and lateral pharyngeal wall and restoration of a normal oropharyngeal lumen (Figure 9), confirming effective removal of the deep parapharyngeal component. A follow-up MRI performed after surgery documented ipsilateral (left) cervical lymphadenopathy. In light of the radiologically suspicious for nodal involvement neck and the high-grade nature of the tumor, the patient was scheduled for a radical neck dissection, with adjuvant radiotherapy to be discussed at the multidisciplinary tumor board according to the final pathological findings.

Figure 8: Postoperative clinical photograph (left lateral view) showing disappearance of the parotid swelling, restoration of a normal facial and retromandibular contour, and preserved facial symmetry at rest.

Figure 9: Postoperative intraoral photograph showing regression of the left oropharyngeal bulging, with a symmetric soft palate and lateral pharyngeal wall and a normally patent oropharyngeal lumen.