The patient was a 43-year-old man who consulted for a palpable lump, painful on pressure in the right preauricular region. Physical examination revealed a poorly defined mass measuring 2 cm in the right parotid area, with no other significant findings. The patient reported no personal or family history of interest, only the aforementioned nodule which, according to the patient, had been present for more than five years. The imaging tests performed, computerised axial tomography and ultrasound, showed a well-defined tumour measuring 2.5 x 2 cm centred in the parotid gland, which did not affect bone or muscle structures, suggestive of a low-grade tumour.

Fine needle aspiration puncture of the lesion was performed, using the routine method of 3 passes with a 23G needle, with the help of the Cameco® (manual aspiration device) after which 2 slides were fixed in alcohol to be stained using the Papanicolaou technique and the rest (6 slides) were air-dried to use the Diff-Quick stain. Examination of the smears shows, against a seroproteinaceous background, abundant large cellularity, with central and occasionally peripheral rounded nuclei, little patent nucleolus and finely granular chromatin. The cytoplasm is very characteristic, being abundant, pale and foamy with vague borders, vacuolated and containing abundant purplish granules. The cells are arranged in more or less compact clusters of large two-dimensional sheets, sometimes adopting an acinar architectural pattern. Along with this predominant cellularity, smaller cells with scant cytoplasm and small, round or oval, central nuclei are also present. The cytological image was therefore consistent with serous-type acinar cell pathology, probably carcinoma, and it was therefore proposed to perform DNA quantification by image cytometry on cytological smears. Given that the smears obtained in the first puncture did not allow an adequate assessment, a second FNA was performed in order to process the material for cytometric determination, for which purpose they were fixed in 99º methyl alcohol and subsequently stained with Gill's progressive haematoxylin.

Using TEXCAN® software and a video camera integrated into the microscope, which captures grey scales, the most relevant biological parameters are determined, including ploidy, S phase, and percentage of cells above 5c (aneuploidy), expressed as a histogram (IMAGE 2), reveals an euploidy of 2.1 with no relevant S-phase activity and no cells above 5c, thus indicating low aggressiveness (histogram type 1) according to Azúa's classification for static cytometry.
With the cytological diagnosis of acinar cell carcinoma and the cytometric prognostic index of low grade, conservative surgery was performed, with excision of the parotid gland without cervical emptying and preserving the facial nerve.
Macroscopically we found a whitish piece, with a polylobulated morphology, weighing 12 grams and measuring 8 x 4 x 3 cm in total. The cut showed a 1.5 cm nodular lesion that did not overflow the surgical resection ends, apparently non-cystyphoid. Multiple parallel sections of the specimen were made and embedded in paraffin and then stained with conventional haematoxylin-eosin. Histopathological examination revealed a solid, well-circumscribed, microcystic neoformation composed mainly of acinar cells that did not overflow the glandular capsule. The multiple cystic spaces of very small size, scattered between the solid sheets are formed by dilated lumina lined by intercalated ductal cells, although acinar cells also occasionally participate. The acinar cells are serous secreting, as demonstrated by PAS (periodic acid Schiff) staining which highlights intracytoplasmic zymogen granules as well as intracystic eosinophilic secretion. The neoplasm respects the resection edges and there is no evidence of vascular or nerve infiltration.

The definitive diagnosis is, therefore, low-grade acinar cell carcinoma, well demarcated, without invasion of the surgical edges.