Abstract
Acinic cell carcinoma (ACC) is a rare malignant tumor of the salivary glands that accounts for 6%-10% of all salivary gland malignancies. It has a propensity to considerably recur, metastasize to the lung or cervical lymph nodes. In addition, ACC can potentially be fatal. The parotid gland is where ACC most frequently begins. The purpose of this paper was to describe an unusual case of parotid gland ACC in a 58-year-old Vietnamese adult female. Before surgery, a fine-needle aspiration biopsy revealed the existence of tumor cells with acinar differentiation. Following that, she underwent successful surgery without complications. The existence of ACC was verified by the postoperative final histologic results.
Keywords: Acinic cell carcinoma, Parotid gland, Magnetic resonance imaging
Introduction
About 2%-3% of parotid tumors are primary acinic cell carcinomas (ACC), a rare low-grade epithelial neoplasm of the salivary gland [1]. Women are diagnosed with this cancer more often than males, and it often affects people in their fifth and sixth decades of life. The parotid gland is favorable site of tumor origination [2]. ACC was initially described by Godwin et al. [3] more than 50 years ago and labeled as a “benign adenoma,” [3], but in 1953 it as a malignant tumor [4]. As a result of this tumor's propensity to recur, spread, and even cause mortality, it is no longer appropriate to see it as a tumor with a favorable prognosis. Instead, the WHO has reclassified it as a “malignant carcinoma,” despite its typical low-grade behavior [4]. On ultrasound (US), ACCs cannot be distinguished clearly, and they are frequently mistaken as benign tumors. In this article, we aimed to illustrate a rare case of ACC of parotid gland.
Case presentation
A 58-year-old Vietnamese woman visited our hospital because of a painless lump that had been growing in the right parotid region for a month. Medical profile was normal. During a clinical examination, a superficial, soft, movable mass in the right parotid gland that measured 2.5 cm superior-inferior and 2 cm anterior-posterior in diameter was found. There was no discoloration and the skin in this area was normal. Her facial nerve function is normal. The laboratory test findings fell within expected limits.
Ultrasonography showed a heterogeneous hypoechoic mass (30 mm × 17 mm) with well-defined margin in right parotid gland (Fig. 1). A lesion displayed a heterogeneous echo pattern, with hypoechoic in the superior and hyperechogenic in the inferior. Magnetic resonance imaging identified a mass located in the superficial lobe of the right parotid gland (Fig. 2). Lesion has well-defined, multilobulated margin, located entirely in the parotid gland and has not invaded surrounding structures. The size of the mass was 28 mm × 18 mm, which appeared to have low signal intensity on T1-weighted imaging. This lesion exhibited 2 different parts with signal and enhancement patterns. The upper part, corresponding to the hypoechoic area on US, showed intermediate intensity on T2-weighted imaging, hyperintensity short tau inversion recovery and moderately heterogenous enhancement on contrast-enhanced fat-suppressed T1-weighted imaging. The lower part (white arrowhead), which corresponds to the hyperechoic region on US, appeared low-to-intermediate intensity on T2-weighted imaging and short tau inversion recovery, and minimal enhancement (Fig. 2). There was no diffusion restriction observed in the lesion, on diffusion-weighted imaging and apparent diffusion coefficient mapping (Fig. 3). The MRI revealed no suspicious lymph nodes.
Fig. 1.
Doppler ultrasonography showed a right parotid solid mass in the superficial lobe (arrow) with a well-defined, and multilobulated margin. A tumor displayed a heterogeneous echo pattern, with hypoechoic in the superior and hyperechoic in the inferior.
Fig. 2.
A solid mass located entirely in the right parotid gland, which showed low signal intensity on T1-weighted imaging (arrow, A). This lesion exhibited 2 different parts with signal and enhancement patterns. The upper part (green arrow), corresponding to the hypoechoic area on US, showed intermediate intensity on T2-weighted imaging (B), hyperintensity STIR (C) and moderately heterogenous enhancement on contrast-enhanced fat-suppressed T1-weighted imaging (D). The lower part (white arrowhead), which corresponds to the hyperechoic region on US, appeared low-to-intermediate intensity on T2-weighted imaging (B) and STIR (C), and minimal enhancement (D). US, ultrasound.
Fig. 3.
The lesion exhibited facilitated diffusion and had an ADC value of 1.2 × 10−3 mm2/s (arrow, A-B).
The right parotid mass was then fine needle aspiration at our hospital. We inserted the needle into the hypoechoic area on US, and so that the cytologic results revealed acinar differentiated tumor cells and specific cytoarchitectural patterns, which did not rule out ACC. The patient was finally treated surgically with a right full parotidectomy while the ipsilateral facial nerve was preserved. Results from postoperative histology supported the ACC diagnosis. A tumor appeared as solid clusters of cytoplasmic cells with granules similar to those found in serous acinar cells that were obviously acinus under the microscope (Fig. 4).
Fig. 4.
Histopathological finding revealed the ACC (H&E × 400). It presented as groups of solid cytoplasmic cells containing granules that resembled those found in serous acinar cells, which were clearly acinus (arrow). ACC, acinic cell carcinoma.
Discussion
ACC is an uncommon kind of ductal cell-derived malignant salivary epithelial tumor. It is a low-grade malignancy that most frequently affects the parotid gland, manifests earlier than other salivary gland tumors. This cancer has a feminine preference [1]. ACC is thought to be the second most prevalent epithelial salivary malignancy in children, after mucoepidermoid carcinoma, accounting for roughly 17% of primary salivary gland malignancies, the third most frequent epithelial malignancy of the salivary glands in adults. The National Cancer Data Base Report on cancer of the head and neck found that the parotid gland was the primary site of origin (86.3%) for reported ACCs. Women are typically diagnosed more frequently than males [5]. Family history and prior radiation exposure are 2 potential causes of ACC [4].
Radiologically, on CT, MRI, or US imaging, no recognized imaging features of parotid gland ACCs have been discovered. Due to the ACCs' considerable radiologic similarities to benign tumors, the diagnosis of ACCs using simply imaging investigations is challenging [4], [5], [6], [7]. Tumor size, location, and nature may all be determined with ultrasonography, a quick, noninvasive procedure that is commonly available. Additionally, it is utilized to carry out fine-needle aspiration biopsies that are guided by US. It is possible to use a CT scan to assess the tumor's size, involvement, proximity to the facial nerves and other tissues, and distant metastasis. A CT scan with contrast agent often exhibits a modest enhancement. Low T1 and T2 signals can be seen on certain scans, and ACCs often exhibit nonspecific MRI signal intensity patterns. The signals and the histology are correlated, indicating vascularity, hemosiderin accumulation, fibrosis, and calcification inside the tumor itself [4,7].
Histopathologically, the tumor is well-defined, has a distinct capsule, and exhibits different morphologic development patterns. It may be solid or cystic. Solid, microcystic, follicular, and papillary cystic tumors are the terms used to characterize them [8,9]. They are made up of a variety of cell types, including clear cells, acinic cells, vacuolated cells, intercalated cells, and nonspecific glandular cells. Characteristics include large tumor cell lobules or nests with minimal intervening stroma [8], [9], [10], [11]. Contrary to clinical staging, the histologic grading of ACC is debatable, and histomorphology has not consistently been shown to be a good predictor of behavior [12].
The preferred course of therapy for ACCs is total surgical removal of the tumor via an intraoral or extraoral technique. The tumor's distribution and location are what decide this [13]. In cases of a poor prognosis, positive surgical margins, stage T3 or T4 tumors, high histologic grade, numerous positive lymph node involvement, and vascular or perineural invasion, radiation treatment should be taken into consideration [14].
Conclusions
ACC is a rare salivary gland tumor. It usually appears between the fifth and sixth decades of life. Due to the ACC's significant radiologic similarities to benign tumors, the diagnosis of ACC using simply imaging techniques is challenging. The preferred course of therapy is total surgical excision. Further studies are essential to perform to contrast this tumor from other primary salivary gland malignancies.
Authors’ contributions
Huynh-Thi Do Quyen and Nguyen Minh Duc contributed to write original draft. Nguyen-Hoang Thanh Tu and Nguyen Minh Duc contributed to undergo diagnostic procedure, collect, and interpret the imaging. Huynh-Thi Do Quyen, Nguyen-Hoang Thanh Tu, and Nguyen Minh Duc made substantial contributions to collect patient data and clinical data analysis. All authors have read, revised, and approved the final published version of the manuscript. All authors were responsible for submission of our study for publication.
Statement of ethics
Ethical approval was not necessary for the preparation of this article.
Data availability statement
All data generated or analyzed during this study are included in this article and/or its online supplementary material files. Further enquiries can be directed to the corresponding author.
Patient consent
Written informed consent was obtained from the patient for publication of this case report and any accompanying images.
Footnotes
Competing Interests: The authors have no conflicts of interest to declare.
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Associated Data
This section collects any data citations, data availability statements, or supplementary materials included in this article.
Data Availability Statement
All data generated or analyzed during this study are included in this article and/or its online supplementary material files. Further enquiries can be directed to the corresponding author.