Cytological findings of intrathyroidal epithelial thymoma/carcinoma showing thymus‐like differentiation: A study of eight cases

Abstract

The purpose of this article is to describe the cytologic findings of intrathyroidal epithelial thymoma/carcinoma showing thymus-like differentiation (ITET/CASTLE) in detail and discuss its differential diagnoses. We examined cytologic specimens taken from eight ITET/CASTLE cases, who underwent fine needle aspiration. Cytologic features of ITET/CASTLE include (1) hypercellularity, (2) large cell clusters without papillary or follicular pattern, (3) round or spindle tumor cells with distinct nucleoli and cell border, (4) few keratinized cells and intracytoplasmic lumina (ICL), and (5) lymphocytic background. The differential diagnoses included poorly differentiated carcinoma, metastatic lymphoepithelioma, squamous cell carcinoma, and mucoepidermoid carcinoma. The presence of individual keratinizing cells and ICL and the location of the tumor may be helpful in indicating ITET/CASTLE.

Carcinoma Showing Thymus-Like Differentiation (CASTLE): Cytopathological Features and Differential Diagnosis

“…Overall, our findings are in agreement with prior studies; however, one feature in particular appeared common and consistent: the identification of cellular fragments of basaloid cells in the absence of definitive squamous differentiation (5/8 cases). This finding is in contrast to the study by Hirokawa et al [8], in which squamous differentiation was present in the majority of cases (63%). Although we did not detect architectural molding or neuroendocrine-like chromatin, rosette and/or acinar structures were noted in several cases.…”

“…Our cases correlate with previous studies showing that several cytological features appear to be consistently encountered on FNA specimens and include (1, 2) a mixture of dishesive and clustered/fragmented epithelioid cells with high nuclear/cytoplasmic ratio, nuclei with coarse to vesicular chromatin and (3) distinct (prominent) nucleoli, (4) basaloid features, and (5) lymphocytes in the background, and about half of the reported cases show (6) occasional mitotic figures and (7) squamous differentiation (table 3). Features that appear to be less consistently present within both our series and the reported literature include (8) papillary fragments, (9) neuroendocrine features, and (10) intracytoplasmic lumina or inclusions (table 3) [5,8,20,21,22,23]. Overall, our findings are in agreement with prior studies; however, one feature in particular appeared common and consistent: the identification of cellular fragments of basaloid cells in the absence of definitive squamous differentiation (5/8 cases).…”

“…Fine-needle aspiration (FNA) is currently the method of choice for initial pathological evaluation of thyroid nodules. To date, there have been limited studies on the cytomorphological features of this rare entity with only a single published case series [8]. The overall findings within the literature are nonspecific with respect to identifying discrete cytological features definitive of this entity.…”

“…It most commonly afflicts middle-aged adults (fifth decade of life) and occurs in the lower poles of the thyroid [5,6,7,8]. CASTLE has been shown to have an improved prognosis and favorable clinical outcome compared to the other aggressive entities within its differential diagnosis, including primary or metastatic squamous cell carcinoma as well as undifferentiated carcinoma with squamous differentiation [2,7,9,10,11,12].…”

A Carcinoma Showing Thymus-Like Elements of the Thyroid Arising in Close Association with Solid Cell Nests: Evidence for a Precursor Lesion?

“…In the largest series available, Hirokawa et al (13) described the cytological features of eight cases of CASTLE. They were all diagnosed as ''malignant tumors,'' except for one case in which only the necrotic material was aspirated.…”