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Cytopathology of insular carcinoma of the thyroid
1Department of Pathology, Memorial Sloan-Kettering Cancer Center, New York, New York 10021, USA.
Insights
Insular carcinoma of the thyroid (ICT) diagnosis can be suggested by fine-needle aspiration (FNA) cytology. Key features include high cellularity, scanty colloid, and a predominance of single cells with mild nuclear atypia.
Area of Science:
- Cytopathology
- Thyroid Neoplasms
- Surgical Pathology
Background:
- Insular carcinoma of the thyroid (ICT) is rare, with limited published cytology reports since its initial description in 1984.
- This study describes the cytologic features of six histologically confirmed ICT cases.
Purpose of the Study:
- To describe the cytologic features of insular carcinoma of the thyroid (ICT).
- To propose diagnostic criteria for ICT in FNA samples.
- To differentiate ICT from other thyroid neoplasms, particularly follicular neoplasms.
Main Methods:
- Analysis of six cases with tissue-proven ICT.
- Four cases involved thyroid fine-needle aspiration (FNA).
- Two cases were FNAs of metastatic lesions.
Main Results:
- Cytologic smears showed high cellularity and scanty colloid.
- Predominance of single cells with round, monomorphic nuclei and finely granular chromatin.
- Features like microfollicles, papillae, necrosis, and mitosis were rare; nuclear grooves and inclusions were rare.
Conclusions:
- ICT shares cytologic overlap with follicular neoplasms, necessitating careful evaluation.
- Distinguishing features favoring ICT include a predominance of single cells, few microfollicles, and minimal nuclear atypia.
- ICT should be considered in the differential diagnosis of thyroid fine-needle aspiration specimens, especially those suspicious for follicular neoplasm.
Background:
Insular carcinoma of the thyroid (ICT) first was reported in 1984. To the authors' knowledge, few cytology reports have been published since that time. The authors describe the cytologic features of six tissue-proven ICTs and propose criteria that suggest its diagnosis.
Methods:
Four cases were thyroid fine-needle aspiration (FNA) samples. Two cases were FNAs of metastases. All cases were found to be classic ICT on examination of primary or metastatic surgical specimens.
Results:
Three cases originally were diagnosed as carcinoma, including two FNAs of metastatic sites and one thyroid FNA. Two additional thyroid FNAs were diagnosed as suspicious for malignancy, favor follicular neoplasm. One case was termed a neoplasm, favor follicular type. Smears showed high cellularity and scanty colloid. Three cases were found to contain some microfollicles. One case showed a few papillae. Necrosis and mitosis were rare. Cells were round with pale, poorly defined cytoplasm. Nuclei were round and monomorphic with finely granular chromatin, mild hyperchromasia, smooth nuclear membranes, and small nucleoli. Nuclear grooves and inclusions were rare.
Conclusions:
Three cases were diagnosed as suspicious for follicular neoplasm, the main differential diagnosis of ICT. Both tumors exhibited high cellularity and scanty colloid. However, ICT showed a predominance of single cells whereas follicular neoplasms reveal microfollicles with more nuclear atypia. There is cytologic overlap between these two neoplasms. Papillary thyroid carcinoma should be distinguished from ICT easily because the latter usually does not reveal the classic cytologic features associated with the former. ICT should be considered in the differential diagnosis of follicular neoplasms. Features favoring ICT are predominance of single cells, small loose nests of cells with few microfollicles, and little nuclear atypia. Cancer (Cancer Cytopathol)