Metatypical Adenoid Cystic Carcinoma: A Variant Showing Prominent Squamous Differentiation With a Predilection for the Sinonasal Tract and Skull Base.

Adenoid cystic carcinoma is a malignant salivary gland neoplasm, commonly involving the major and minor salivary glands. Adenoid cystic carcinoma arising in the skull base region is considerably less common and is characterized by aggressive clinical behavior, perineural invasion, and intracranial extension. Classically, these tumors are composed of ductal and myoepithelial cells, arranged as tubules and cribriform structures, as well as in a solid pattern when higher in grade. The distinctive molecular findings in this tumor are the gene fusions involving the MYB/MYBL1 and NFIB genes. Squamous differentiation, trabecular, and macrocystic growth patterns are exceedingly rare in these tumors and when present can cause significant diagnostic challenges. Squamous differentiation, in particular, is considered by many to be an exclusion criterion for adenoid cystic carcinoma outside of cases with high-grade transformation. In addition, a similar-appearing tumor with squamous differentiation, namely human papillomavirus-related multiphenotypic sinonasal carcinoma, has recently been defined, further complicating this differential diagnosis. Recently, we have come across 3 cases of adenoid cystic carcinomas involving the sinonasal tract and skull base having extensive interconnecting trabecular growth, macrocysts, and squamous differentiation, yet demonstrating the signature fusions involving MYB-NFIB and MYBL1-NFIB by RNA sequencing. In this article, we describe the clinical, histomorphologic, and imaging findings of these cases and propose the appellation "metatypical adenoid cystic carcinoma" for this uncommon variant morphology.

Role of cell block in cytopathologic evaluation of image-guided fine needle aspiration cytology.

CONTEXT: Fine needle aspiration cytology (FNAC) of superficial or deep-seated lesion is an increasingly common practice, eliminating time consuming and costly diagnostic procedures and providing rapid and safe diagnosis. AIMS: To assess utility of cell block preparation method in increasing sensitivity of cytodiagnosis in deep-seated image-guided FNACs. SETTINGS AND DESIGN: This was a hospital-based observational study conducted in the Department of Pathology, over a period of one and a half years. MATERIALS AND METHODS: A total of 46 cases of abdomino-pelvic and intrathoracic masses subjected to guided FNACs were included. Along with conventional smears, cell blocks were prepared by using AAF (95% Ethanol 34 ml + formalin 4 ml + Glacial acetic acid 2 ml) as fixative agent. STATISTICAL ANALYSIS USED: Done using MedCalc Version 12.7.5.0 to find out the sensitivity, specificity, and diagnostic accuracy of conventional smears and cell blocks. RESULTS: The sensitivity, specificity, and diagnostic accuracy of cell blocks in our study was 71.11%, 100%, and 71.73%, respectively. The figures for FNA smears were 62.22%, 100%, and 63.04%, respectively. CONCLUSIONS: Cell block technique by AAF fixative is a simple, inexpensive procedure. Cell block method allows the recovery and processing of minute amounts of cellular material, facilitating better classification of tumor when reviewed along with cytological smears, the ability to obtain many sections for immunostains and other studies to be performed akin to paraffin sections produced in histopathology.