Rapid On-site Evaluation (ROSE) Cytology of Mucoepidermoid Carcinoma and its Diagnostic Pitfalls: a Case Report

Abstract

Fine needle aspiration cytology (FNAC) is a basic tool used for the preoperative diagnosis of superficial parotid swellings. Mucoepidermoid carcinoma accounts for approx. 5–10% of all salivary gland tumors. However, due to its morphologic heterogenicity, this tumor poses diagnostic difficulties in its interpretation. This is a case of a 45-year-old male with a history of recurrent swelling in the left infra-auricular region. Cytology with rapid on-site evaluation revealed a triphasic population of basaloid cells, squamoid cells, and intermediate cells on a mucoid background and reported as low-grade mucoepidermoid carcinoma in recurrence. The presence of a triphasic cellular component (mucous, intermediate, and squamoid cells) may not be seen in all cases of mucoepidermoid carcinoma (MEC) for definitive diagnosis. Clinico-radiological correlation, rapid on-site evaluation (ROSE), and high index of suspicion related to cystic lesions are important for early diagnosis and prompt treatment.

Introduction

Mucoepidermoid carcinoma (MEC) is the most common primary malignant salivary gland neoplasm. It was 1st identified as a pathologic entity in 1945 by Stewart et al. Initially termed as “mixed epidermis and mucous secreting carcinoma,” it was later replaced by “MEC” [1]. This tumor has an extreme morphologic array, and hence, diagnostic interpretation on FNAC of this neoplasm is really challenging as FNAC poses a high false-negative rate [2]. ROSE, along with cytology, can help in the assessment of adequacy and look for the possibility of malignancy [3]. The present case was undertaken to explicate the role of ROSE cytological features of MEC and explore the diagnostic difficulties of MECs.

Case Report

A 45-year-old male patient came to otorhinolaryngology out-patient depratment of our institute, with a history of left post auricular swelling since 2½ years. He had a similar episode of swelling 3 years back for which cytology was done and reported as pleomorphic salivary adenoma, followed by superficial parotidectomy and histopathological examination which was diagnosed as benign lymphoepithelial cyst of parotid gland. There was no history of fever, significant weight loss, and loss of appetite.

His laboratory investigations were within normal limits. Serological markers were also negative. The patient was referred to the cytopathology section for fine needle aspiration cytology evaluation. On examination, the patient had a swelling in the left infra-auricular region, well defined, soft to firm with focal cystic areas. The lesion was located over the site of the previous scar mark and measured 2 × 2 cm (shown in Fig. 1). No local increase in temperature or prominence of vessels was noted. There were no palpable superficial local lymph nodes. Systemic examination of the patient was unremarkable. A high-resolution ultrasonogram done was reported as a mixed parotid tumor (shown in insert Fig. 1).

Fig. 1.

Image from swelling in the left infra-auricular region (circle), well defined, soft to firm with cystic areas, over the site of previous scar mark (arrow), and measured 2 × 2 cm. Inset – USG showing the cystic and solid areas at the site of the lesion

Fine needle aspiration cytology of the swelling in the parotid region was performed using a 24G needle. The aspirated sample was a brownish mucoid-like material. Smears were prepared, and 1% aq. Toluidine blue was used for the rapid on-site evaluation. The ROSE-stained slide revealed adequate cellularity with the presence of abundant mucin and mucinophages along with a few squamoid-looking cells (shown in Fig. 2a–d). A provisional diagnosis of mucoepidermoid carcinoma was made.

Fig. 2.

(a–d) Cytology with ROSE showing the mucinophages with pigment (green arrow), squamoid cells (orange arrow), and small basaloid cells in a background of abundant mucin [Tol blue, ×400, ×1000]

The ROSE-stained slides along with the air-dried slides were returned back for routine Giemsa and Papanicolaou stain. Cytosmears were moderately cellular, comprising numerous pigment-laden foamy histiocytes, few intermediate cells with round to oval nuclei, prominent nucleoli, mild-to-moderate nuclear pleomorphism, and a moderate amount of cytoplasm. There are also seen few basaloid-looking cells, mucinophages, multinucleated giant cells, and occasional mast cells on a sheet-like thick and thin fibrillary dirty mucoid background (shown in Fig. 3a–d). Retrospectively, the patient was checked for the previous FNAC and histopathology slides. A review of the cytology slide had similar features to the current FNAC cytomorphology. Histopathology slide had normal mixed salivary acinar tissue along with cystic areas lined by columnar cells, focal stratification of lining, with foamy cytoplasm, few epidermoid cells, and cystic spaces with mucin (shown in Fig. 4a–d). Histopathology was having features of low-grade mucoepidermoid carcinoma. The patient was advised for surgical excision of the lesion with wide margins. However, due to poor socio-economic condition, he has not undergone any treatment in 3 months of follow-up.

Fig. 3.

(a–d) Cytology showing abundant mucin (green arrow) with mucinophages, squamoid cells, and small basaloid cells (yellow arrow) [PAP, ×400, ×1000]

Fig. 4.

(a–d) Histopathology slides were showing cystic spaces lined by columnar cells with basal nuclei, areas of stratification of the epithelium (red arrow), mild-to-moderate nuclear atypia [H&E, ×400]

Discussion

Salivary gland tumors account for approximately 5% of head and neck neoplasms. Although MEC accounts for 10–15% of all tumors of the salivary gland, it constitutes approximately 30% of all malignant tumors of the salivary gland and among major salivary glands seen mainly (80%) in the parotid gland [4, 5]. Male:female ratio of 1:2, with prevalence during 4th–6th decade of life [4]. Present with a slowly enlarging painless mass for several years, clinically mimicking pleomorphic adenoma. MEC of the salivary gland is believed to arise from pluripotent reserve cells of the excretory ducts that are capable of differentiating into squamous, columnar, and mucous cells [6].

In 1945, Stewart, Foote, and Becker introduced the term mucoepidermoid to define a distinct salivary gland tumor characterized by a mixed pattern of the following two main cell types: epidermoid and mucus-producing cells that were thought to arise from the salivary gland ducts [1]. As a third cell type, the intermediate cell, which is not mucous or fully epidermoid, is also often present; they are thought to be capable of differentiating into mucous or epidermoid cells. Because of this cellular heterogenicity, the histopathological, biological, and clinical behavior of MEC vary [7].

FNAC has a significant role in the evaluation of salivary glands. The false-negative or false-positive cases are most likely due to cystic structures, low cellularity, or dilution due to mucin, blood, and watery material. There has been a variable sensitivity and specificity of FNAC in the accurate diagnosis of salivary lesions [1, 8]. So, it was in our case wherein the first FNAC was having abundant mucin.

MECs are most commonly mistaken on cytology due to a lack of all features (mucous cells, intermediate cells, and squamous cells) which may not be present in low-grade MEC. High-grade MEC diagnosis is usually straightforward with the presence of a large number of highly atypical cells with polyhedral appearance, orangeophilia, mucus-secreting cells, and intermediate cells.

The differential diagnosis for the low-grade MECs includes epidermal inclusion cyst and mucous retention cyst, wherein due to cystic appearance with low cellularity, mucous cells and squamoid cells lacking atypia MEC can often be misdiagnosed [9]. MEC can mimic an abscess on cytology due to cystic areas being pauci-cellular, with scant squamoid or mucous cells and plenty of neutrophils. Repeating the procedure from the solid area can yield cellularity. Chronic sialadenitis can also mimic MEC on cytology with inspissated mucin and squamous metaplasia [9, 10].

In cases of pleomorphic adenoma, the intermediate cells and stromal cells can be interpreted as epithelial and myoepithelial cells, pale chondromyxoid stroma to thick mucin, and mucous cells as histiocytes [11, 12]. Cystic lesions with the presence of leucocytes, bland cytological features, and pauci-cellularity can mimic Warthin’s tumor [13].

Metastatic carcinomas of sebaceous or squamous cell origin may be misdiagnosed as high-grade MEC on cytology due to the presence of squamoid cells with a background of foamy macrophages and giant cells. Clinical history plays an important role in the diagnosis of such cases wherein there might be a primary site in the head and neck region [9, 11].

Histologically, the tumor has been divided based on cystic structures, cellular atypia, and cell type into low, intermediate, and high grade. Low-grade tumors are well circumscribed, with >50% cystic areas and mucus cells; intermediate-grade tumors are relatively more solid and less circumscribed. Whereas the high-grade tumors have one or more of the following features: nuclear atypia, increased mitotic figures, PNI, LVI, Bony invasion, and/or necrosis [1, 8].

The use of fluorescent in-situ hybridisation (FISH) and real-time polymerase chain reaction (RT-PCR) has been attempted in the diagnosis of morphologically ambiguous cases. A translocation of t(11;19) (q21:p13) and resultant MEC translocated 1-mastermind-like gene family (MECT1-MAML2) fusion transcript have been identified in varied range (38–81%) of MEC cases. ^1] In a country like India, the availability and cost of such testing tools has limitation for the general public being able to afford it.

Treatment depends on the location, clinical aspect, and histopathological grade of the tumor. Local resection is preferred for less aggressive low-grade tumors, whereas wide resection is adapted for high-grade tumors. Radiotherapy is used only in selective cases, chemotherapy for local aggressive or metastatic diseases. Prognosis depends on stage, site, grading, and adequacy of surgery; 5-year survival for LGMEC and high-grade MECs are 95% and 50%, respectively [1, 8, 14].

Conclusion

Rapid on-site evaluation (ROSE) with cytology not only facilitates adequacy but also provides an overview of what is going to come in the routine stains ahead/provisional diagnosis and triaging sample for further diagnosis. MECs have diagnostic difficulty in cases of cystic lesions of the salivary gland. Clinico-radiological suspicion supported by adequate cytopathological sampling can help in proper diagnosis and future management.

Abbreviations

FNAC

fine needle aspiration cytology

FISH

fluorescent in-situ hybridisation

MEC

mucoepidermoid carcinoma

LGMEC

low-grade mucoepidermoid carcinoma

ROSE

rapid on-site evaluation

RT-PCR

real-time polymerase chain reaction

Author Contribution

TS carried out concepts and design, literature search, participated in clinical study and manuscript preparation, who will stand as guarantor also. DP carried out data acquisition, data analysis, and clinical study. RS & SKM carried out concepts, design and literature search. All the authors have read and approved the final manuscript.

Data Availability

All the data regarding the findings are available within the manuscript. Further enquiries can be directed to the corresponding author.

Declarations

Ethics Approval

This case report was conducted in accordance with the fundamental principles of the Declaration of Helsinki.

Consent for Publication

Consent to publish was taken from the participant for publication of the details of their medical case and any accompanying images.

Conflict of Interest

The authors declare no competing interests.