
==== Front
Int J Surg Case Rep
Int J Surg Case Rep
International Journal of Surgery Case Reports
2210-2612
Elsevier

S2210-2612(24)00999-4
10.1016/j.ijscr.2024.110218
110218
Case Report
Basal cell adenoma of the deep lobe of the parotid gland misdiagnosed as mucoepidermoid carcinoma - A case report
Hage Neemu neemuhage@gmail.com
a⁎
Balaji R. a
Singh Namit Kant a
Sivakoti Sumitra b
Shrinivas Somalwar B. b
a Department of Otorhinolaryngology and Head and Neck Surgery, All India Institute of Medical Sciences, Bibinagar, Hyderabad, Telangana, India
b Department of Pathology and Laboratory Medicine, All India Institute of Medical Sciences, Bibinagar, Hyderabad, Telangana, India
⁎ Corresponding author at: Department of Otorhinolaryngology and Head and Neck Surgery, All India Institute of Medical Sciences, Bibinagar, Yadadri-Bhuvanagiri District, Hyderabad, Telangana, India. neemuhage@gmail.com
28 8 2024
10 2024
28 8 2024
123 1102181 7 2024
19 8 2024
24 8 2024
© 2024 The Authors. Published by Elsevier Ltd on behalf of IJS Publishing Group Limited.
2024

https://creativecommons.org/licenses/by-nc-nd/4.0/ This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/).
Introduction

Basal cell adenoma is a rare, benign epithelial tumour of the salivary gland, comprising only 1–2 % of all salivary gland tumours. Predominantly found in the parotid gland, basal cell adenoma can also occur in minor salivary glands and are often confused with other benign and malignant salivary gland tumours. A thorough histopathological examination can provide a definitive diagnosis.

Presentation of case

A 65-year-old woman presented with a painless mass in the right infra-auricular region. Imaging revealed a well-defined hypodense lesion in the deep lobe of the right parotid gland, initially suspected as mucoepidermoid carcinoma. Fine needle aspiration was inconclusive, leading to the decision to perform a total conservative parotidectomy. Histopathology confirmed basal cell adenoma, characterized by cystic areas filled with mucoid material and basaloid cells arranged in trabecular and tubular patterns.

Discussion

Basal cell adenoma was classified as a distinct entity by the WHO in 1991. Cytologically, they imitate both benign and malignant salivary as well as non-salivary gland tumours. The histological hallmark of basal cell adenoma involves basaloid cells with small round nuclei showing no atypia, scant pale cytoplasm, and distinct peripheral palisading. Treatment involves surgical removal, with a more radical approach for certain variants such as the membranous type.

Conclusion

This case highlights the clinical, radiological, and histopathological features of basal cell adenoma, emphasizing the importance of accurate diagnosis and appropriate surgical management. Early detection and appropriate treatment are crucial for optimizing patient outcomes in basal cell adenoma management.

Highlights

• Basal Cell Adenoma (BCA) comprises of 1-2% of all salivary tumors and can mimic both benign and malignant tumors.

• It is imperative to differentiate BCA from malignant lesions such as adenocarcinoma or adenoidcystic carcinoma.

• Total parotidectomy is recommended due to risk of recurrence and malignant transformation particularly in membranous type.

• Understanding the histopathological and imaging characteristics is key to optimizing management of BCA.

Keywords

Case report
Parotid neoplasm
Parotid gland
Basal cell adenoma
Salivary gland neoplasm
Abbreviations

BCA Basal Cell Adenoma
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pmc1 Introduction

Basal cell adenoma (BCA) is an uncommon, benign epithelial tumour of the salivary gland, constituting only 1–2 % of all salivary gland tumours. BCAs are characterized by the presence of isomorphic basaloid cells with a prominent basal cell layer and the lack of myxochondroid stromal component [1]. While the majority of cases manifest in the parotid glands, instances of BCAs have been documented in minor salivary gland locations such as the lips, palate, and nasal cavity [2,3]. In the parotid gland, it typically occurs between the 5th to 7th decade of life, appearing as a painless, slow-growing mass, resembling other benign parotid gland tumours. BCAs can affect both the superficial and deep lobes of the parotid gland. On fine needle cytology BCAs may often be confused with other benign and malignant salivary gland tumours such as, adenoid cystic carcinoma, epithelial rich pleomorphic adenoma, basaloid squamous cell carcinoma to name a few. The definitive diagnosis relies on identifying specific features through histopathological analysis. Four primary histological patterns, namely solid, trabecular, tubular, and membranous, can be observed. [2] Treatment primarily involves surgical removal, which varies in extent based on the tumour's location within the gland. Notably, for the membranous type of BCA, total parotidectomy is recommended due to a higher risk of recurrence and rare potential for malignant transformation. [4,5] This article presents a case study of basal cell adenoma located in the deep lobe of the parotid gland, delving into clinical, radiological, and histopathological characteristics, as well as outlining the management approach. This case report has been reported in line with the SCARE criteria and PROCESS criteria. [6,7]

2 Case presentation

A 65-year-old woman presented to the outpatient Otorhinolaryngology clinic with a painless mass in the right infra-auricular region for a duration of four months. On examination there was a 3 × 2 cm firm, non-tender swelling appearing to arise from the right parotid gland. Ultrasonography revealed an anechoic thin-walled cystic lesion in the deep lobe of the right parotid gland. There was no other mass lesions or lymph nodes palpable in the cervicofacial region. Contrast enhanced computed tomography showed a well-defined hypodense lesion arising from both superficial and deep lobes of right parotid gland measuring 19(AP) x 23(TR) x 24(CC) mm with significant enhancement and an area of cystic/necrotic component on its lateral aspect (Fig. 1). The mass was suspected to be mucoepidermoid carcinoma based on radiological features. Fine needle aspiration of the swelling was inconclusive as only hemorrhagic fluid was aspirated, possibly from the cystic component of the lesion. Presurgical routine blood tests, biochemical analysis, chest X-ray were all within normal limits. The patient's Karnofsky performance status score was 90 %, and her ECOG (Eastern Cooperative Oncology Group) performance status score was 0. With a provisional diagnosis of mucoepidermoid carcinoma of the right deep lobe of parotid gland, the patient underwent total conservative parotidectomy. All the branches of the facial nerve were identified and preserved (Fig. 2). Level II lymph nodes were found to be enlarged and were removed for further examination. Histopathology of the specimen revealed a well-circumscribed capsulated lesion with more than 60 % cystic change filled with thick mucoid material. The solid areas showed cuboidal to columnar epithelial cells arranged predominantly in trabecular pattern, tubular pattern and rarely in solid nests. The peripheral cells of the trabeculae and nests showed palisading nuclei. The cells appeared relatively small with small hyperchromatic nuclei. The lesional cells exhibited little pleomorphism, and sparse mitotic activity. Overall, the peripheral basaloid appearance of cuboidal cells with minimal proliferative activity and lack of myxochondroid stroma favoured the diagnosis of basal cell adenoma. There was no infiltration of the capsule and the lymph nodes that were sampled were uninvolved (Fig. 3). Postoperatively the patient had transient paresis of the marginal mandibular nerve which completely recovered within 4 weeks (Fig. 4).Fig. 1 Contrast enhanced computed tomography showing a well-defined hypodense lesion (red arrow) arising from both superficial and deep lobes of right parotid gland with enhancement and an area of cystic/necrotic component on its lateral aspect. (For interpretation of the references to colour in this figure legend, the reader is referred to the web version of this article.)

Fig. 1

Fig. 2 (A) Facial nerve exposed after superficial parotidectomy. (B) Total conservative parotidectomy with all the branches of the facial nerve preserved.

Fig. 2

Fig. 3 (A) The Cut section of the superficial parotidectomy specimen shows a well-circumscribed solid and cystic lesion. (B) Microscopically, the neoplasm is well-capsulated and distinct from normal parotid tissue. (C) The solid portion comprises cuboidal cells in trabeculae, tubules, nests and sheets. (D) The tubular-trabecular pattern of cuboidal cells shows minimal nuclear atypia and variable cellular stroma. (B and C are magnified at 100×, and D is at 400×.)

Fig. 3

Fig. 4 (A) Postoperative transient marginal mandibular nerve paresis (B) Normal facial nerve function on 1 month follow up.

Fig. 4

3 Discussion

Previously known as Monomorphic adenoma, BCA was classified as a distinct entity by the WHO in 1991. BCA comprises of 1–2 % of all salivary tumours. Cytologically, they imitate both benign and malignant salivary as well as non-salivary gland tumours. They are indistinguishable from basal cell adenocarcinoma and only a thorough histopathological examination (HPE) can provide a definitive diagnosis. Other entities that can be confused with BCA include canalicular adenomas, cellular pleomorphic adenoma, solid variant adenoid cystic carcinoma, and basaloid squamous cell carcinoma. There have been reports of 42 cases of cytologically diagnosed BCAs, with a false positive rate of 16.7 %. The histological hallmark of BCA involves basaloid cells with small round nuclei showing no atypia, scant pale cytoplasm, and distinct peripheral palisading. These cells are arranged in various patterns such as trabecular, tubular, solid, and membranous, often with a mixture of two cell populations and typically without noticeable mitotic activity [1].

It is important to differentiate BCA from adenocarcinoma because the former has a recurrence rate of 6.7 % while the latter has a higher rate of 16–50 %. The identification of membranous type of BCA is also crucial due to their higher recurrence rates (24 %) and a chance of malignant transformation (4.3 %), which necessitates a more radical surgical approach than required in other variants of BCAs [2,3].

BCAs rarely exceed 3 cm in diameter according to a study with a large cohort. The largest diameter of the lesion in our patient was 24 mm. While the literature suggests that they are most common in the 5th to 7th decades of life, younger patients have also been affected. BCAs are primarily found in the parotid gland, but they can also occur in other locations such as the upper lip, buccal mucosa, lower lip, palate, and nasal septum [3,4]. Although several reports have established BCAs as more commonly occurring in women, newer studies suggest no gender predilection [5].

In the study by Chen et al., plain computed tomography showed regular masses with uniform or uneven density. Contrast enhanced computed tomography showed most masses with early intense BCA enhancement; some masses appeared enhanced in the venous phase and some masses did not show any enhancement, which may be due to the vascular architecture of the tumour. Imaging of most BCAs of the parotid gland showed a very similar picture resembling benign parotid lesions [3].

Chen et al., categorized BCAs into three types based on their location within the parotid gland. Type I tumours are close to the superficial border of the gland, type II are close to the retromandibular vein (RMV) in the superficial lobe, and type III are located in the deep lobe of the parotid. Among a cohort of 41 cases, type III BCAs were found to be the most common (58.5 %), had the largest diameter (2.33 +/− 2.72 cm), and were more likely to exhibit cystic changes. Overall, types II and III accounted for 82.93 % of cases in their study, indicating that BCAs can occur in both the superficial and deep lobes. However, no significant correlation was found between imaging findings and histopathological characteristics [3].

Treatment typically involves surgical intervention, favoring total parotidectomy over superficial removal due to the potential lack of encapsulation of the tumour, or presence of the membranous variant of BCA. In membranous type of BCA total parotidectomy is preferred due to increased risk of malignant transformation and recurrence Therefore, total conservative parotidectomy is recommended for all cases BCA [5]. Prognosis of basal cell adenomas is good, provided adequate surgical management is offered.

4 Conclusion

BCA formerly known as monomorphic adenoma, represents a distinct entity comprising 1–2 % of salivary tumours. Its histological features, including basaloid cells and distinct peripheral palisading, distinguish it from other mimicking lesions. Accurate diagnosis via histopathological examination is crucial, particularly for the recognition of the membranous type, given its higher recurrence rates and potential for malignant transformation. Imaging modalities aid diagnosis, but histopathological examination remains definitive. Treatment typically involves surgical intervention, favoring total parotidectomy for better outcomes, especially in membranous BCAs. Despite challenges in diagnosis and management, prognosis with adequate surgical intervention is generally favorable. Understanding the histopathological and imaging characteristics is key to optimizing BCA management and patient outcomes.

Consent for publication

Written informed consent was obtained from the patient for publication and any accompanying images. A copy of the written consent is available for review by the Editor-in-Chief of this journal on request.

Ethical approval

Case Reports are exempted from ethical approval in our institution.

Funding

This research did not receive any specific grant from funding agencies in the public, commercial, or not-for-profit sectors.

Author contribution

NH- Conceptualization; Methodology; Writing - Original Draft.

BR- Visualization; Writing - Review & Editing.

NKS- Supervision; Writing - Review & Editing.

SS- Visualization; Resources.

SBS- Resources.

All authors read and approved the final manuscript.

Guarantor

Neemu Hage.

Declaration of competing interest

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

Availability of data and material

Not applicable.

Acknowledgements

None.
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