NQ-011 Answer: (C) Metastatic melanoma

Pathology of the case:  In this cytologic preparation, the cells show a ‘discohesively cohesive’ pattern, and they have elongated and rather homogeneous nuclei with open chromatin and prominent nucleoli. The cytoplasmic membrane is rather soft and not very solid. The “vacuole” (arrow) is, in fact, a pseudonuclear inclusion formed by cytoplasm bulging into the nuclei, and both meningioma and melanoma can have these features. However, the prominent nucleoli are not a common feature of meningioma although atypical meningioma can have prominent nucleoli. The imaging characteristic of an intra-axial tumor is more consistent with a metastatic melanoma. Unlike other tumors, metastatic melanoma can be seen more often in younger patients. A primary lesion on skin can be easily missed due to regression.

Meningioma: The prominent nucleoli in these cells here raise a question of meningioma although atypical meningioma may have large nucleoli. Please note that the pseudonuclear inclusion is a common finding of meningioma.  [Click here to see cytologic smears of meningioma]

Astrocytoma: Astrocytoma cells on smear typically have elongated nuclei reminiscent of a baking potato, sometimes with pointed ends. The nuclei contains coarse chromatin and without distinct nucleoli in most cases. pseudonuclear inclusion is not a common feature of astrocytoma or other glial neoplasms.

Metastatic squamous cell carcinoma: They typically have pleomorphic nuclei. For the keratinizing ones, the cell may appear homogeneously eosinophilic with very dark, hyperchromatic nuclei. Pseudonuclear inclusion is not a common feature.

Metastatic adenocarcinoma: While most metastatic adenocarcinomas have high-grade, pleomorphic nuclei, some are not and the most notable members of metastatic carcinoma that may have low-grade nuclei are clear cell renal cell carcinoma, papillary thyroid carcinoma, and prostatic adenocarcinoma post treatment. The pseudonuclear inclusions, however, should not be mistaken as intracytoplasmic vacuoles leading to a diagnosis of adenocarcinoma. Those vacuoles are in the cytoplasm!