Acinic cell carcinoma with extensive neuroendocrine differentiation: a diagnostic challenge

Abstract

Primary salivary gland carcinoma with neuroendocrine differentiation is of rare occurrence, especially so in the parotid gland. Amongst the various reported primary tumors with neuroendocrine differentiation, acinic cell carcinoma (ACC) one such tumor. A 48 year old lady presented with a gradually increasing right infra-auricular swelling for a period of 1 year which enlarged suddenly in a short period. Contrast Enhanced Computed Tomography (CECT) suggested diagnosis of Pleomorphic Adenoma. Fine Needle Aspiration Cytology (FANC) yielded a cystic fluid suggesting a possibility of Warthin's tumor or Oncocytic lesion. Intraoperative findings were suggestive of a Warthin's tumor. Initial histopathological examination of the tumor was suggestive of neuroendocrine carcinoma. However, extensive sectioning revealed peripheral islands of ACC. Immunoexpression of S-100, Neuron specific Enolase (NSE), Chromogranin A and Synaptophysin confirmed the diagnosis. The possibility of neuroendocrine differentiation in a primary salivary gland tumor should be kept in mind whenever a salivary gland tumor shows only neuroendocrine histology.

Keywords: Acinic cell; Carcinoma; Chromogranin; Neuroendocrine; Parotid; Warthin’s.

Fig. 1

Right infra-auricular, painless swelling 4.5 × 3.5 cms

Fig. 2

CECT scan showing a well defined, homogenously enhancing soft tissue mass, measuring 3.5 × 3 × 2.5 cms, in the superficial lobe of the right parotid gland with displacement of the retromandibular vein

Fig. 3

Cut section showing a well defined nodule (3.3 × 2.9 × 2.2 cms), which is grey white to dark in color with areas of congestion and surrounding thin rim of normal salivary gland

Fig. 4

Tumor cells arranged in organoid and nesting pattern, separated by thin and think hyalanised fibrous septae. Both small and large cell neuroendocrine pattern can be identified. (H&E, 100×)

Fig. 5

a Tumor cells show large round, uniform nuclei with stippled nuclear chromatin. Moderate amount of finely granular and eosinophilic cytoplasm can be seen with well defined cytoplasmic membranes. Mitotic figures both typical and atypical can be seen (H&E, 600×). Inset—Showing atypical mitosis (H&E, 600×). b Small microcystic areas seen amidst tumor cells filled with pale eosinophilic material (H&E, 250×)

Fig. 6

Tumor at the periphery shows cells in clusters and sheets with centrally placed small nuclei and abundant cytoplasm studded with fine basophilic granules suggestive of acinic cell carcinoma (H&E, 250×)

Fig. 7

a Strong cytoplasmic positivity for S-100 (DAB chromogen, 400×). b Strong cytoplasmic positivity for Neuron Specific Enolase (DAB chromogen, 400×). c Strong granular cytoplasmic positivity for Chromogranin A (DAB chromogen, 400×). d Strong cytoplasmic positivity for Synaptophysin (DAB chromogen, 400×)