The presence of extensive nuclear grooves is a common finding in PTC, caused by an infolding of the nuclear membrane. Nuclear grooves are present in nearly all cases of PTC, but they may be sparse in up to 25% of cases. They are often parallel to the long axis of the oval nuclei, giving a "coffee bean" appearance (see Figure 9.5). Nuclear grooves alone are nonspecific and can be seen in a variety of neoplastic and non-neoplastic cells, including macrophages and benign follicular cells. However, they become an important diagnostic feature when associated with an oval, enlarged nucleus with fine chromatin. Nuclear grooves are most easily appreciated in ethanol-fixed, Papanicolaou-stained samples. Linear structures are often identified in air-dried Diff-Quik-stained nuclei but are less convincing as true nuclear grooves in this preparation (Figure 9.6).
The presence of nuclear pseudoinclusions is highly suggestive of PTC, particularly in combination with other characteristic nuclear features. Nuclear pseudoinclusions represent finger-like invaginations of cytoplasm into the nucleus. Nuclear pseudoinclusions are found in more than 90% of PTC aspirates, although they may be present in a small number of cells. Although they may be seen in air dried Diff-Quik-stained preparations, they are most convincing when identified in ethanol-fixed Papanicolaou-stained specimens. It is important to use strict criteria to identify a nuclear pseudoinclusion because both air-dried and ethanol-fixed preparations can contain artifacts and nonspecific structures (such as a superimposed red blood cell) that mimic a pseudoinclusion. The nuclear pseudoinclusions of PTC are
large, often occupying 50% or more of the nuclear area, are more optically clear than the surrounding chromatin, share the tinctorial properties of the cytoplasm, are bounded by a distinct membrane, and are surrounded by a thin condensed rim of basophilic chromatinic material (Figure 9.7).
Cytologic Features of Nuclear Pseudoinclusions
• Tinctorial pattern similar to cytoplasm
• More clear than the surrounding chromatin
• Outside rim of condensed chromatin
Was this article helpful?