There is a complex well circumscribed proliferation of small back to back glands with oncocytic features and cribiform pattern infiltrating the stroma below the respiratory epithelium. The glands shows oncocytic change and also frequent tubulopapillary pattern. Differential diagnosis of this lesion includes 4 possibilities: Oncocytic Papilloma (Schneiderian), low grade non intestinal type seromucinous adenocarcinoma, seromucinous hamartoma or oncocytoma. The fact that the tumor is below the epithelium favoring the last 3 diagnostic possibilities, not a schneiderian or oncocytic papilloma that is a lesion confined to the epithelium. Low grade non intestinal type adenocarcinoma, seromucinous hamartomas and oncocytomas are proliferations with tendency to local recurrence but almost no metastatic potential. Despite deceptively bland histologic appearance, all these tumors have tendency to recur if incompletely excisised, so re-excision is recommended to avoid a potencial local recurrence in the future.
Sinonasal intestinal type adenocarcinoma (ITAC) is defined by an intestinal phenotype with goblet cells and obvious cytologic atypia, non-intestinal type adenocarcinoma (non-ITAC) is traditionally viewed as a diagnosis of exclusion, with great similarity to sinonasal seromucinous hamartomas (SSH). Most non intestinal seromucinous low grade adenoca show bland monomorphic cuboidal epithelium with no evidence of atypia, pleomorphism or mitosis, looking very similar to seromucinous hamartomas. To exclude Sinonasal intestinal type Adenoca immunohistochemistry can be requested with CK20 and CDX2 (positive) and CK7 (negative). Low grade non intestinal seromucinous type Adenocarcinoma and seromucinous hamartomas are invariably CK7 positive and CK20 negative, CDX2 negative with no evidence of neuroendocrine differentiation (synaptophysin negative). Markers of seromucinous differentiation (S100, DOG1, and SOX10) were essentially absent in ITAC, but present to varying degrees in the majority of non-ITAC (low grade seromucinous) and all SSH. P63 is negative in intestinal and non intestinal type adenocarcinomas and seromucinous hamartomas, indicating abascence of myoepithelial component of these 3 lesions.