Pancreatic endocrine tumour with cytoplasmic keratin whorls. Is the term "rhabdoid" appropriate?

Abstract

A 50 year old woman presented with acute abdominal pain accompanied by nausea and vomiting and was found to have a mass in the head of the pancreas by imaging. The clinical impression was of a pancreatic carcinoma and a Whipple's procedure was performed. Microscopic examination of the tumour showed it to be a low grade neuroendocrine carcinoma arranged in a tubuloacinar or tubulopapillary pattern, and composed of cells harbouring very prominent intracytoplasmic inclusions. These inclusions varied in appearance from being pale pink and hyaline in quality to more eosinophilic and globular causing displacement of the nucleus. Ultrastructural examination showed typical paranuclear aggregates of intermediate filaments. Inclusions of this type have been described previously as "signet ring like" and "rhabdoid". It was felt that the inclusions more closely resemble the fibrous bodies that are seen in pituitary adenomas. In addition, it is suggested that both signet ring and rhabdoid are not appropriate because they do not reflect histogenesis and are not necessarily reflective of tumour biology. It is suggested that the term "cytokeratin aggresomes" should be used to describe this distinctive phenotype.

Figure 1

The tumour had a dominant tubulopapillary appearance with only focal solid and trabecular foci. Haematoxylin and eosin stain; original magnification, ×100.

Figure 2

The inclusions were present in the luminal aspect of the cytoplasm, causing the cells to appear elongated and tall. Haematoxylin and eosin stain; original magnification, ×400.

Figure 3

Some of the intracytoplasmic inclusions were very pale and weakly eosinophilic. In these cells the inclusions imparted a signet ring appearance to the cells. Haematoxylin and eosin stain; original magnification, ×400.

Figure 4

Cells exhibiting a more “rhabdoid” morphology with deeply eosinophilic cytoplasmic inclusions and a globular morphology. The nucleus is displaced peripherally. Haematoxylin and eosin stain; original magnification, ×400.

Figure 5

CAM 5.2 immunohistochemistry highlights the paranuclear globules of intermediate filaments. CAM 5.2 antibody; original magnification, ×200.

Figure 6

Electron microscopic illustration of a cell containing juxtanuclear whorls or bundles of intermediate filaments with occasional embedded neurosecretory granules. Original magnification, ×12 000.