acinic cell carcinomas ( acc ) are usually low grade , uncommon neoplasms constituting 2.54% of parotid gland tumors .
papillary cystic variant ( pcv ) of acc is a rare tumor , the diagnosis of which is based on histopathological examination .
it is composed of tumor with papillary and cystic growth patterns , with varying proportions of one or more cell types .
it has mostly been reported in younger patients ( 16 - 40 years ) when compared to the classic type that characteristically presents in the fifth decade of life .
although an uncommon tumor , it is important to recognize this variant as it has proved to be universally fatal within 10 years .
we hereby report an unusual case of acc - pcv in a 20-year - old male which was considered a benign parotid mass both cytologically and radiologically .
a 20-year - old male presented to the surgical clinic with a complaint of swelling on the left angle of mandible below the ear lobule since 4 months .
it was 3.5 cm  2 cm in size , firm to hard with limited mobility and nontender .
laboratory investigations revealed hemoglobin 16.2 gm% , total leucocyte count 6,800 cells/l , differential leukocyte count 
neutrophils 74% , lymphocytes 18% , eosinophils 5% , monocytes 3% , platelet count - 1.15 lac/l and blood sugar 120 mg / dl .
contrast - enhanced computed tomography of neck showed a soft tissue nodular lesion isodense to the parotid ( attenuation 40 hu ) of size 2.3 cm  1.6 cm  1.3 cm with mildly enhancing peripheral walls in the left superficial parotid gland .
few spiculated nodules were also seen in the right lung apart from patches of numerous centriacinar nodules .
both lobes of the thyroid were normal in size , shape , attenuation and enhancement .
grossly , the specimen measured approximately 6.5 cm  4.5 cm  3.5 cm with attached flap of skin measuring 3.5 cm  1.5 cm .
cut surface showed a large cyst measuring 2.8 cm  1.5 cm filled with dark brown material [ figure 1 ] .
histopathological examination showed a large well - circumscribed cystic space lined by numerous papillary projections few of them showing thin vascular cores [ figure 2 ] .
many hemosiderin - laden macrophages and areas of hemorrhage are also seen [ figure 3a ] .
these papillae were mostly lined by hobnail cells with round , vesicular nuclei , central nucleoli and eosinophilic to vacuolated cytoplasm [ figure 3b ] .
gross specimen cut surface of which shows a large cyst measuring 2.8 cm 1.5 cm filled with dark brown material numerous papillae lying in cystic cavity ( black arrow ) , fibro collagenous tissue and adjacent normal salivary gland tissue ( white arrow ) ( a ) papillary growth pattern along with hemosiderin within the papillae .
acinic cell carcinoma is an uncommon salivary gland tumor , making up 1% of all salivary gland neoplasms .
they most often arise in the parotid gland , but may occasionally involve the submandibular , minor salivary or seromucinous glands .
it is the least aggressive of salivary gland cancers with low malignant potential , but several recurrences and metastasis have been reported .
few high - grade variants of acc are known such as papillocystic carcinoma or carcinomas with undifferentiated cells in the medullary pattern .
lesions of the  tail  of the parotid gland are difficult to assess clinically and provide a diagnostic dilemma on imaging .
most benign parotid tumors present as slow - growing , painless masses often in the tail of the parotid gland .
defines the  tail  of the parotid gland as inferior 2 cm of the superficial lobe of the gland . in a study by hamilton on 117 parotid tail masses ,
seventeen types of parotid tail masses were identified out of which benign lesions were the most common .
also as it was a slow - growing painless mass present in the parotid tail , clinically it was thought to be a benign parotid mass which was also supported by cytological examination
. accurate localization of these lesions on imaging is essential to assist the clinical diagnosis and to prevent inadequate / incomplete excision and complications , especially damage to the facial nerve .
the diagnosis of pcv of acc usually poses a challenge because of the cytoarchitecture that is different from classic type .
cystic fluid in the case of acc - pcv dilutes the overall cellularity leading to a mistaken diagnosis of benign lesion as was seen in the present case .
histopathologically , acc shows a myriad of architectural patterns : solid , solid - lobular , acinar - microcystic , papillary cystic , tubuloductal , follicular and macrocystic , and dedifferentiated .
the solid and microcystic are the most common subtypes and the pcv accounts for one - fourth of acc .
varying proportions of one or more of five cell types are seen including hobnail , acinar , intercalated , vacuolated , nonspecific glandular and clear cells .
this is due to bulging of the apical portions of lumen lining cells into the lumen presumably after release of secretions .
the clinical picture is not specific , and diagnosis is based on the histopathologic examination .
the mean age of occurrence is in the fifth decade , but the pcv is reported to occur in younger patients compared to the classic type .
the most significant differential diagnosis of acc - pcv is papillary carcinoma of the thyroid .
thyroid ultrasonography , hormonal assays , and immunohistochemistry for thyroglobulin are helpful in differentiating these two lesions .
timely diagnosis and treatment of acc - pcv is essential as it has been found to be universally fatal within 10 years .
although most parotid masses are benign , removal is required for histopathologic confirmation because of the clinical and radiologic overlap .
to conclude , the present case emphasizes the importance of histopathological examination in parotid masses as the imaging features as well as cytology lack the necessary specificity to differentiate benign from malignant masses , especially in a case of papillary cystic acc .
it also highlights the need to consider malignant lesion in the differential diagnosis of parotid tail tumor .
 acinic cell carcinoma ( acc ) is an uncommon low - grade tumor of the salivary glands that constitutes 2.54% of parotid gland tumors . 
 papillary cystic variant ( pcv ) of acc is even rarer and can be diagnosed on histopathological examination only . 
 it is important to diagnose this variant as it carries a poor prognosis when compared with other variants of acc and is known to be universally fatal in 10 years . 
 the present case describes acc - pcv in a 20-year - old male , which presented as a slow growing parotid tail tumor and was misdiagnosed as a benign lesion both cytologically and radiologically . 
 this case emphasizes the importance of histopathological examination in parotid masses as well as the need to consider malignant lesion in the differential diagnosis of a parotid tail tumor . 
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