Utility of Fine Needle Aspiration in Diagnosis of Intraoral Minor Salivary Gland Tumors.

OBJECTIVE: To evaluate the utility of intraoral fine-needle aspiration cytology (FNAC) in diagnosis of minor salivary gland neoplasms (MSGN) with application of Milan system of reporting salivary gland cytopathology; keeping histopathology as gold standard and to detail the cytological findings of MSGNs.
METHOD: Retrospective study between Jan 2008 and June 2017 (appro × 10 years) on the cytology of the minor salivary gland tumor along with the histopathological correlation. The relevant clinical data was collected from the medical record. RESULT: Sixty-four cases of MSGNs were included in the study. The histodiagnosis of the 41 were available. Twenty-one cases were diagnosed as malignant, while rest 20 cases were reported as benign. The most common tumor diagnosed was pleomorphic adenoma (PA) (50% cases), followed by mucoepidermoid carcinoma (14%) and adenoid cystic carcinoma (12.5%). The most common site of MSGT was found to be hard palate (44%), followed by soft palate (23%), floor of the mouth (12%), lip (11%), buccal mucosa (5%), and tongue (5%) with no gender predilection. Sensitivity of FNAC for detection of malignancy was 81% while specificity 95%. For malignancies, positive predictive value for malignancies was 17/18 (94.4%) and negative predictive value was 19/23 (82.3%). According to Milan system out of 21 cases in category IV B, 4 cases were found malignant (Category VI), while 1/18 case in category VI turned out to be nonneoplastic lesion (Category II).
CONCLUSION: FNAC is imperative in early diagnosis and subsequent management of MSGNs. Copyright:

INTRODUCTION

Salivary gland neoplasms account for 2–6.5% cases of all head and neck malignancies.[1] Minor salivary gland tumors (MSGT) on the other hand are rare, which constitute 15–20% of salivary gland neoplasms. Majority of the MSGT cases occur in palate, oral cavity, and lip; however, their frequency remains variable in different studies.[2] Besides being an uncommon entity, MSGT can present with diverse morphological and architectural patterns. The role of fine-needle aspiration cytology (FNAC) in diagnosis of major salivary gland tumors is well established; however, its utility in diagnosis of MSGT is relatively underexplored.[12345] The present study was conducted to evaluate the role of FNAC in diagnosis of MSGT and to assess its sensitivity and specificity with histopathology as gold standard.

MATERIAL AND METHODS

A retrospective study was conducted between the period of Jan 2008 and June 2017 (approximately 10 years). After taking informed consent from the patients, a total of 310 intraoral FNACs were performed during this period, out of which 64 cases were diagnosed as minor salivary gland epithelial tumors. Cases which were inconclusive on FNAC findings while diagnosed as minor salivary gland tumor on histopathology could not be incorporated in our study due to lack of follow-up data in all of them. As per the institutional practice, after taking the informed consent, FNACs were performed in all intraoral mass lesions followed by excision of the mass. Cases diagnosed as lymphomas, squamous cell carcinomas, soft tissue tumors, or any reactive conditions were excluded from the study. FNAC procedures were carried out by dedicated cyto-pathologists independently or in the presence of clinicians/radiologist using a 21-23 gauge needles. The smears were stained with Giemsa postfixation with methanol and reported by a team of 3 cytopathologists with experience of 5 years, 10 years, and more than 30 years, respectively, in reporting cytology. The study-specific proformas were made and the collected data was reviewed. The histopathological findings of the cases which were surgically excised (excision biopsy available in 41 cases) and sent to our department were reported by dedicated histopathologists. The relevant clinical data and definitive histopathological diagnosis in each case were noted. In the cases where both histopathological and cytological diagnosis varied, their slides were reviewed by concerned histopathologist and cytopathologist, and possible reasons for the discordance were elucidated. Final diagnosis were established based on histopathological findings. Sensitivity and specificity of FNAC were evaluated. Since it was a retrospective study with cases evaluated from record, approval from the ethical committee was not required.

The statistical analysis was done using SPSS software version 12.

RESULTS

A total of 64 cases of minor salivary gland tumors were diagnosed based on cytological findings. The age of the patients varied from 2–85 years, mean age being 38.4 ± 17.7 years. Majority of the cases were in the age group of 31–40 years (25%). The mean age of patient presenting with benign lesions was 34.7 ± 1.6 years and the malignant lesions 42.7 ± 1.9 years. MSGT was found in equal proportion among male and female patients (M: F = 1:1) [Table 1].

Table 1

Cytological types, respective sites, and gender distribution

Tumor	Site of tumor						Gender
	Hard Palate	Soft Palate	Cheek	Lip	Tongue	Floor of mouth	M	F	Total
PA	13	9	1	5	1	3	12	20	32
ACC	4	1	1	0	0	2	3	5	8
MEC	4	2	0	2	1	0	9	0	9
Poly adca	3	1	1	0	0	2	5	2	7
PDCA	2	0	0	0	0	0	1	1	2
EMC	1	0	0	0	1	0	0	2	2
Ca Ex PA	0	1	0	0	0	0	0	1	1
Myoepithelioma	1	1	0	0	0	0	1	1	2
Clear cell ca	0	0	0	0	1	0	1	0	1
Total	28	15	3	7	3	8	32	32	64

Surgical excision was advised in all the cases, however, performed in 41/64 cases. Remaining cases were lost to follow-up. Confirmatory diagnosis were rendered based on histopathological findings of the resected specimens. The most common tumor diagnosed on FNAC was pleomorphic adenoma (PA) constituting 50% cases of all cases (32/64), followed by mucoepidermoid carcinoma (MEC) constituting 14% (9/64) and adenoid cystic carcinoma (ACC) constituting 12.5% (8/64). Polymorphous adenocarcinoma was diagnosed in 11% (7/64) of the cases. Two cases each were diagnosed as epithelial-myoepithilial carcinoma, (EMC), poorly differentiated carcinoma (PDCA), and myoepithelioma, while one case was diagnosed as Carcinoma Ex pleomorphic adenoma (Ca ex PA) and one case as Clear cell carcinoma.

The most common site of occurrence of minor salivary gland tumors (MSGT) was hard palate (44%), followed by soft palate (23%), floor of the mouth (12%), lip (11%), buccal mucosa (5%), and tongue (5%). Cytological types with respective sites have been mentioned in Table 1. Twelve patients presented with pain as primary symptom, out of which 6 cases were diagnosed as MEC, 4 cases as polymorphous adenocacinoma, 1 case as ACC, and 1 case as PA. Except for MEC which was exclusive to males in our study, no tumor type-specific gender predilection was present. Malignancy was more frequent among male population [M: F = 1.7:1]. The mean size of the tumor was 2.8 cm. Overall, six patients presented with regional lymph node metastasis, out of which 3 cases were diagnosed as MEC, 1 case each as Ca ex PA, ACC, and c PDCA. Five patients showed ulceration of the overlying mucosa.

Surgical excision was performed in 41/64 cases. Based on histopathological findings, a total of 21 cases were diagnosed as malignant, while rest 20 cases as benign. True positive cases correctly diagnosed on FNACs were 17, while 19 cases were true negative for malignancy following histopathological confirmation. Furthermore, one case was false positive and 4 cases were false negative for malignancy. Overall concordance, including benign and malignant was 31/41 = 75.6% [Table 2]. The lesions were categorized according to Milan system of classification of salivary gland lesions. Out of 21 cases in category IV B, 4 cases were found malignant (CAT VI), while 1/18 case in category VI turned out to be nonneoplastic lesion (Cat II). Exact type-specific concordance of malignancies, diagnosed correctly on FNACs was 13/18 = 72.2%. Sensitivity of FNAC for detection of malignant cases was 81% and specificity was 95%. For malignancies, positive predictive value for was 17/18 (94.4%) and negative predictive value was 19/23 (82.3%).

Table 2

Cytological-Histopathological correlation

Cytological Diagnosis	No of cases	Total Histopath	Histological Diagnosis
			Consistent	Inconsistent
PA	32	22	18	4
ACC	8	4	4	0
MEC	9	5	3	2
PolymorphousAdenocarcinoma	7	5	2	3
PDCA	2	2	1	1
EMC	2	1	1	0
Ca Ex PA	1	1	1	0
Myoepithelioma	2	1	1	0
Clear cell ca	1	0	0	0
Total	64	41	31	10

Based on cytological and histopathological correlation, it was revealed that for malignancies, EMC was most frequently missed on cytology, twice misinterpreted as PA, once as MEC and adenocarcinoma NOS, respectively (4/5 = 80%). Single case each of Ca ex-PA was underdiagnosed as PA (1/3 = 33.3%), and ACC was misinterpreted as adenocarcinoma NOS (1/5 = 20%).

Findings of some of the discrepant cases are discussed.

Case 1 [Figure 1]: FNAC smears showed the presence of cells with round nucleus, inconspicuous nucleoli, and moderate amount of eosinophilic cytoplasm arranged in three-dimensional groups and sheets with the presence of abundant stromal material diagnosed as PA. Histopathology of the same revealed picture showing sheets of squamoid cells, clear cells, and intermediate cells diagnostic of MEC.

Figure 1

Cytology—cells with round nucleus, inconspicuous nucleoli, and moderate cytoplasm in groups with stromal material like PA (A, B, C: Geimsa stain 400×) Histopathology—squamoid cells, clear cells, and intermediate cells diagnostic of MEC (H and E, 400×)

Case 2 [Figure 2]: Cytology showed classical picture of pleomorphic adenoma, whereas histological sections showed areas of pleomorphism, invasion, and necrosis suggestive of carcinoma Ex-Pleomorphic adenoma.

Figure 2

Ulcerated growth on lip (a) Cytology—oval to spindle nucleus, mod pink cytoplasm present in sheets, mild pleomorphism, metachromatic background classical of PA (b, c: Geimsa stain 400×). Histopathology—areas of necrosis, invasion (d: H and E, 100×)

Case 4 [Figure 3]: FNAC showed a dual population of cells with cells showing the presence of intracytoplasmic mucin along with squamoid cells displaying nuclear pleomorpism suspected to be MEC; however, it turned out to be a benign mucus retention cyst on histopathology.

Figure 3

Cytology—cytoplasmic vacoulations (a: solid arrow; Geimsa stain 400×), squamoid differentiation with nuclear atypia (b: dotted arrow; Geimsa stain 600×; c: Geimsa stain 400×) mucinophages and multinucleated giant cells (d: Geimsa stain 400×) possibly mucoepidermoid carcinoma. Mucus retention cyst on histopathology

DISCUSSION

FNAC is a well-established and reliable technique for diagnosing salivary gland lesions. Primary role of FNAC in salivary gland lesions is to differentiate between benign and malignant lesions so that the extent of surgical excision required can be determined accordingly. Diagnostic efficacy of FNAC is well established in major salivary gland tumors, while only a handful studies have been published describing MSGT.[12345]

The mean age found in our study was higher for patients presenting with malignancy than benign lesions as observed in the previous study as well by Waldron et al.[5] MSGT are more commonly diagnosed in females, with a ratio of 1:1.2 (M: F) to 1:1.9.[134] Most common site of MSGT previously described in various studies was hard palate, a finding consistent with our study.[1345] In the present study, the most common benign tumor was pleomorphic adenoma (50%), while most common malignant tumor was MEC, a finding consistent with previous studies.[3678] However, a few studies found ACC to be the most common malignancy[12459] which can probably explained by different geographical and ethnic characteristics.

Our results are different in contrast to the previous studies by Gupta et al. and Singh et al. which found less sensitivity (71.4% and 77.7%, respectively) and higher specificity (97.8% and 100%, respectively).[1011] Majority of the previously published studies included both major and minor salivary glands, found sensitivity of FNAC ranging from 79% to 97% and specificity from 95% to 100%. However, the single Indian study by Sahai et al. on minor salivary gland found diagnostic accuracy almost similar as our study [Table 3].[121314151617] We found slightly lesser diagnostic accuracy as compared to previous studies.[121314151617] This finding can be attributed to lesser cases of minor salivary glands diagnosed in the previous studies.[121314151617]

Table 3

Studies on utility of FNAC in salivary gland tumors[121314151617]

Study	Year	Total cases	Major SG	Minor SG	Sensitivity	Specificity	Diagnostic accuracy
Sahai et al.[12]	2002	55	0	55	-	-	88.4%
Rajvanshi et al.[13]	2006	172	108	64	-	-	-
Christensen et al.[14]	2010	879	790	89	83	99	93
Rajdeo et al.[15]	2015	100	94	6	96.87	100	96
Rohilla et al.[16]	2017	631	612	19	79.4	98.3	91.4
Kakoty et al.[17]	2017	50	47	3	90.91	96.42	94.87
Present study	2018	64	0	64	81%	95%	87.8%

EMC can show a variety of morphological spectrum and, hence, can be easily confused with myoepithelial cell-rich PA on cytology.[18] Histopathological and IHC confirmation is warranted in suspicious cases. In the present study, though specific diagnosis of EMC was seldom made (1 out of 5 cases), malignancy was correctly pointed out in 3 out of 5 cases. Furthermore, cytological diagnosis of Ca ex PA is extremely challenging and has been acknowledged in the previous studies as well.[19] Diagnosing ACC can be difficult in situation where characteristic hyaline globules and other cytological features are absent. ACC was least frequently missed and only once diagnosed as Adenocarcinoma NOS, both of which are well-documented differential diagnosis on cytology.[20] Pleomorphic adenoma as the name suggests is a known mimicker of various benign, malignant, and reactive conditions. PA is known to show extensive squamous metaplasia in cases which can be confused with MEC requiring histopathology for confirmation.[1112] One case of mucus retention cyst was misinterpreted as MEC on cytology, which has also been documented before in the literature. A study by Edward et al. suggested that low-grade MEC can show extensive cystic changes and needs to be differentiated from cystic lesions such as mucus retention cyst, lymphoepithelial cyst, branchial cyst, and Warthin's tumor.[21] Mucus retention cyst in contrast to MEC generally lacks epithelial component and rather shows muciphages and histiocytes. Furthermore, mucus retention cyst with epithelial component does not show intermediate and epidermoid component. Differentiation between two entities is essential to avoid unnecessary extensive surgery.[22] MSGT are rare tumors seldom defined on cytology. FNAC is safe and least invasive procedure for diagnosis with good sensitivity and specificity for these lesions. Since salivary gland tumors show a variety of morphological spectrum, strict caution is warranted while providing a definitive diagnosis. Epithelial-myoepithelial carcinomas are difficult to diagnose on cytology, and pleomorphic adenoma can mimic a wide variety of minor salivary gland lesions.

Declaration of patient consent

The authors certify that they have obtained all appropriate patient consent forms. In the form the patient(s) has/have given his/her/their consent for his/her/their images and other clinical information to be reported in the journal. The patients understand that their names and initials will not be published and due efforts will be made to conceal their identity, but anonymity cannot be guaranteed.

Financial support and sponsorship

Nil.

Conflicts of interest

There are no conflicts of interest.