The Diagnostic Value of Fine Needle Aspiration Biopsy in Parotid Tumors

Abstract

The aim of this study was to investigate the diagnostic accuracy rates of the patients who underwent an operation for parotid mass, by comparing their fine needle aspiration biopsy (FNAB) cytology results with the final pathology. A total of 136 patient files of those who applied to Otorhinolaryngology clinic due to parotid mass and underwent parotidectomy procedure between 2010 and 2020 at a tertiary center were scanned retrospectively. Database on patient age, gender, preoperative FNAB results, and final surgical histopathology results was created. The mean age of the patients was 48.26 ± 17.37 Superficial parotidectomy was performed to 108 (79.4%) and total parotidectomy to 28 (20.6%) of the patients. The sensitivity of FNAB was found as 85.2%, specificity as 96.2%, positive predictive value as 85.2%, negative predictive value as 96.2% and accuracy as 94.0%. It is found that FNAB has the high specificity and high negative predictive value with high diagnostic accuracy on detecting preoperative malignancy in parotid gland. We think that FNAB is a significant, necessary and safe method in the diagnosis of parotid lesions in preoperative sense.

Introduction

Major salivary gland tumors are rare and constitute approximately 2–3% of all head and neck tumors [1]. Salivary gland tumors exhibit varying distribution based on localization [2]. While the parotid accounts for 70–85% of these, approximately 10–15% are found in the sub mandibular gland and 5–10% in the minor salivary glands [1]. Most parotid lesions (80–85%) show benign patterns [1, 3]. FNAB (fine needle aspiration biopsy) has been proven to be a safe, cost-effective, rapid and accurate diagnostic method that is widely used preoperatively to assess parotid gland lesions and to aid general treatment [4]. It helps to determine accurate preoperative diagnosis, the need for surgical operation, and which therapeutic approach to adopt, including whether to preserve vital structures such as the facial nerve in case of malignancy [4, 5]. FNAB has been used to differentiate non-neoplastic lesions from neoplasms and benign neoplasms from malignant neoplasms [6–8]. However, despite numerous studies, its role is still widely discussed in the diagnosis of benign and malignant salivary gland disease [9, 10]. While FNAB has high specificity in malignant parotid tumors, its relatively low sensitivity false negative and false positive results decrease the trust of some surgeons [11, 12]. Therefore, a surgical procedure is planned regardless of the result [13]. Additionally, aspiration technique, specimen adequacy and experience of the cytopathologist are among variables that play a role in the outcome [4, 14, 15]. However, histopathological examination after surgical excision is accepted as the gold standard for detecting parotid tumors [15].

In this study, we aimed to reveal the diagnostic accuracy rates of the FNAB cytology of patients operated for parotid mass in our clinic by comparing them with the final pathology.

Materials and Methods

Study Design

A total of 143 patient files of those who applied to Otorhinolaryngology clinic of a tertiary center due to parotid mass and underwent parotidectomy between 2010 and 2020 were scanned retrospectively and included in the study. Database was created for patient age, gender, preoperative FNAB results, and final surgical histopathology results. Approval was received from the Ethics Committee of the Faculty of Medicine of Dicle University (21.01.2016-No:33).

A total of 136 patients with available preoperative FNAB results were included in the study. Patients with unavailable FNAB results were excluded from the study. In addition, the results except those analyzed by experienced pathologists at the university hospital were excluded from the analysis given that preoperative FNAB was performed in an external institution.

Preoperative FNAB results were compared with final surgical pathology. The sensitivity, specificity and positive and negative predictive values and accuracy of FNAB were analyzed. True negative (TN), true positive (TP), false negative (FN) and false positive (FP) ratios were calculated. True positives were defined as cases reported as malignancy on FNAB and final surgical pathologic data confirmed a malignant lesion. True negatives were defined as benign FNAB and benign neoplasms. Those who were benign on FNAB and malignant on final histopathology were defined as false negative. Those who were malignant on FNAB and benign on final histopathology were defined as false positive.

Fine Needle Aspiration Technique

All FNABs were performed by interventional radiologists under ultrasound guidance using 20–22 gauge needle and 5–10 cc injectors without local anesthesia. Multiple aspirations were performed from different points for each mass without removing the injector from its initial location. 3–4 slides were prepared for each cytology. Air-dried smears were stained with May Grünwald Giemsa (MGG) and fixed with alcohol. They were stained with Papanicolaou (PAP) dye and hematoxylin–eosin (H&E). The FNAB results were reported as benign, malignant and non-diagnostic. And the final histopathological diagnosis was grouped as benign and malignant. Surgical specimens were assessed by the same pathologist in our hospital.

Statistical Analysis

The Statistical Package for the Social Sciences (SPSS) version 16 for Windows (SPSS Inc., Chicago, IL, USA) was used to analyse the data. Descriptive analyses were performed on the properties of variables in statistical evaluations. The categorical data were expressed as numbers and percentages, while the numerical data were expressed as mean and standard deviation (Mean ± SD). a = True positive patients, b = False positive patients, c = False negative patients, d = True negative patientssensitivity: a/(a + c) × 100, specificity: d/(b + d) × 100, positive predictive value: a/(a + b) × 100.

Values were calculated as: negative predictive value: d/(d + c) × 100, DOR: (a/c)/(b/d).

Results

A total of 136 patients, 73 (53.7%) male and 63 (46.3%) female, were included in the study. The mean age of the patients was 48.26 ± 17.37 (min = 14, max = 83) years. 108 (79.4%) of the patients underwent superficial parotidectomy while 28 (20.6%) underwent total parotidectomy.

Postsurgical histopathology revealed 108 (79.4%) benign and 28 (20.6%) malignant tumors. Accordingly, 65 patients had pleomorphic adenoma (47.8%), and 35 patients had Whartin's tumors (25.7%) (Table 1). One patient with Whartin's tumor had bilateral TM. The most common malignant tumors were identified as mucoepidermoid carcinoma (6.6%) with 9 patients and scc metastases (5.1%) with 8 patients. As a surgical procedure, 108 patients (79.4%) underwent superficial parotidectomy, while 28 patients (20.6%) underwent total parotidectomy.

Table 1.

Final histopathological diagnosis

	Number	%
Benign tumors
Pleomorphic adenoma	65	47.8
Whartin's tumor	35	25.7
Basal cell adenoma	2	1.5
Myoepithelioma	2	1.5
Monomorphic adenoma	1	0.7
Lymphadenoma	1	0.7
Oncocytoma	1	0.7
Lipoma	1	0.7
Malignant tumors
Mucoepidermoid Carcinoma	9	6.6
Squamous cell carcinoma	7	5.1
Adenoid cystic carcinoma	6	4.4
Acinic cell carcinoma	2	1.5
Ductal adenocarcinoma	1	0.7
Metastatic basal cell carcinoma	1	0.7
Metastatic malignant melanoma	1	0.7
Malignant mixed tumor	1	0.7

A total of 136 adequate specimens were compared in terms of their FNAB and final histopathological results. According to the FNAB results, 106 (77.9%) of the cases were benign, 27 (19.9%) were malignant and 3 (2.2%) were non-diagnostic. 1 of 3 non-diagnostic patients was found to have Pleomorphic adenoma, 1 Whartin's tumor and 1 mucoepidermoid carcinoma.

The sensitivity of FNAB was found as 85.2%, specificity as 96.2%, positive predictive value as 85.2%, negative predictive value as 96.2% and accuracy as 94.0% (Table 2).

Table 2.

Sensitivitiy and specifity ratio

	%
Sensitivity	85.2
Specificity	96.2
Positive predictive value	85.2
Negative predictive value	96.2
Accuracy	94.0

Four false negatives were detected. Of these, 2 were mucoepidermoid carcinoma, 1 was ductal adenocarcinoma, and 1 was acinic cell carcinoma. Again, a false positive diagnosis was made in 4 of the cases. 2 of them were pleomorphic adenoma while 2 were Whartin's tumor (Table 3).

Table 3.

Distribution of final histopathology of false negative and false positives

	Number
False negative
Low-grade mucoepidermoid carcinoma	2
Ductal adenocarcinoma	1
Acinic cell carcinoma	1
False positive
Pleomorphic adenoma	2
Whartin's Tm	2

Discussion

FNAB is a minimally invasive, well-tolerated, relatively painless and inexpensive diagnostic procedure with few complications in diagnosing parotid masses [15]. Common complications include bleeding, facial paralysis, acute parotitis and risk of tumor seeding [9, 16].

The usefulness of FNAB is still discussed in parotid masses, given the current literature [4, 10, 17]. The biggest reason for controversy on FNAB is the low sensitivity compared to specificity [4, 6, 16]. That is associated with the technique used, insufficient specimen collection and parotid masses other than pleomorphic adenoma being extremely rare and quite heterogeneous [18–20]. It can also be influenced by the skills and experience of clinicians who take and study the sample [21]. In our study, FNABs were performed by experienced radiologists under ultrasound guidance and interpreted by experienced pathologists. The current study revealed no complications related to the procedure during or after FNAB on parotid masses.

The high sensitivity of FNAB indicates the rate of accuracy in detecting malignant lesions while high specificity indicates that it can accurately determine benign lesions [17, 22]. High sensitivity and specificity rates also indicate high performance of diagnostic tests. C. carrie Liu et al. carried out a review and meta-analysis where they included 5647 patients from a total 63 studies, and analyzed the specificity, sensitivity, and post-test probability of FNAB of the parotid gland. They reported that FNAB had a sensitivity of 78% (74–82%) and a specificity of 98% (97–98%) in detecting benign and malignant lesions of the parotid gland. They also achieved a 96% diagnostic accuracy rate. Evaluating the results, they stated that FNAB had higher specificity than specificity in differentiating benign-malignant parotid lesions and that FNAB of the parotid gland had moderate sensitivity and high specificity in differentiating malignant from benign disease. They also stated that patients with a negative FNAB might still have a probability of malignancy so they recommended physicians to take the pretest probability of malignancy in their patient populations into account when interpreting parotid FNAB results [4].

Orly Yariv et al. retrospectively analyzed the relationship between parotid FNAB results and final pathology in 98 patients between 2007 and 2018 retrospectively. In the study, they reported 70% sensitivity, 93% specificity, 84% positive predictive value, 89% negative predictive value and 91% accuracy rate. They reported that FNAB is a safe tool for salivary gland lesions and can be useful in many aspects such as preoperative decision-making and surgical planning. However, they also stated that it should only be used as a complementary example as there may be false negative results [23].

Eytan et al. retrospectively reviewed the utility of preoperative FNAB of parotid lesions in 477 patients. They found sensitivity as 82.4%, specificity 90.4%, positive predictive value 80.8%, negative predictive value 91.3% and overall accuracy 87.8%. They stated that preoperative FNAB had high specificity for the detection of malignant disease in parotid lesions and it resulted in a change in the surgical plan in 85 (18.9%) cases. They also proposed that preoperative FNAB was a valuable adjunct in the preoperative evaluation of parotid lesions [14].

In our study, we found 85.2% sensitivity and 96.2% specificity for diagnosing malignant masses. Consistent with previous studies, we also found that sensitivity was lower compared to specificity [8–10], which indicates that the accuracy of a positive result for malignancy is around 86% in FNAB, proving it to be a safe tool to use in planning treatment. In addition, we found negative predictive value as 96.2% in our study, which indicates high confidence regarding the accuracy of a negative result on FNAB. This may help the surgeon to provide a more accurate treatment protocol to the patient.

Among false negatives, there was 1 adeno carcinoma, 2 low-grade mucoepidermoid carcinoma and 1 acinic cell carcinoma. Among false positives, there were 2 pleomorphic adenoma and 2 Whartin's tumors. Low-grade mucoepidermoid carcinoma, Warthin's tumor, acinic cell carcinoma, metastatic squamous cell carcinoma, benign non-neoplastic lesions and pleomorphic adenoma may exhibit cystic changes with abundant mucinous material and insufficient cellularity. And that increases the possibility of misinterpretation at the time of diagnosis. Of all salivary gland tumors, mucoepidermoid carcinoma is accepted to be the most difficult to diagnose on FNAB [6]. It is difficult to diagnose low-grade mucoepidermoid carcinoma due to its excessive morphological heterogeneity [24].These can be misdiagnosed as Warthin's tumor or mucous retention cyst [20, 25, 26]. Additionally, false negatives in acinic cell carcinoma may be due to the vagueness of specific morphological features of malignancy, such as necrosis, cellular pleomorphism and high mitotic activity [6]. The clinical decision should be considered valid given that the results of FNAB contradict other findings. It is important to be aware that false-negative and false-positive results can lead to false diagnosis of malignant lesions. In addition, clinical, physical examination and radiological imaging methods should also be examined in detail in patients with negative FNAB [15]. Malignancy may be still in question even with a negative result. This indicates that the surgeon should consider the clinical history and imaging methods when interpreting the patient.

FNAB is considered a very practical, minimally invasive procedure with a relatively low risk of complications in parotid tumorsDespite a limited amount of inaccuracy, it has a considerable high diagnostic value in distinguishing benign and malignant diseases. Although FNAB cytology bears difficulty in determining the histopathology of the malignant lesion, accurate diagnosis of malignancy in the first plan is more important for the surgeon and delays in determining the type of the malignant mass until the final histopathology is of less significance. However, low sensitivity of FNAB bears some disadvantages, such as the surgeon's inability to overlook the option of surgery due to low sensitivity even if it is a benign pathology.

Conclusion

FNAB of the parotid lesions was found to have high specificity and high negative predictive value with high diagnostic accuracy in detecting preoperative malignancy. We are of the opinion that FNAB is a significant, necessary and safe method in the diagnosis of parotid lesions preoperatively. We think that the data in the FNAB cytology of the parotid is of significant help for the surgeon to create a treatment scheme.

Funding

This study was not funded by any financial support.

Compliance with ethical standards

Conflict of interest

The authors decalre that they have no conflict of interest.