Cytology-Radiology Correlation Series: Thyroid cytopathology

Abstract

Thyroid ultrasound is typically the first step in the workup of thyroid nodules. Ultrasonographic features of thyroid nodules can be used to evaluate their risk of malignancy using risk stratification systems to determine whether a nodule is suspicious enough to warrant a more invasive fine-needle aspiration (FNA) for further evaluation. For this review, the authors described and compared two major risk stratification systems, the American Thyroid Association classification system and the American College of Radiology Thyroid Imaging Reporting and Data System, and explored corresponding ultrasound and cytology findings in the thyroid for commonly encountered entities in cytopathology practice.

Keywords: cytology; cytopathology; radiology; risk; thyroid; ultrasound.

FIGURE 1

Longitudinal ultrasound view of a spongiform nodule (arrows). These benign nodules have mixed cystic and solid spaces that mimic the appearance of a cut sponge, which is a characteristic benign appearance.

FIGURE 2

(A–C) Three transverse ultrasound images from the same patient showing multiple benign nodules (arrows) of follicular nodular disease. Benign nodules like these often demonstrate mixed cystic/solid composition and isoechoic echogenicity.

FIGURE 3

Hypocellular smear comprised predominantly of colloid, suggestive of a colloid or cystic nodule (Bethesda System for Reporting Thyroid Cytopathology [BSRTC] category II; Papanicolaou [Pap] stain).

FIGURE 4

Follicular cells with stretched out cytoplasm suggestive of cyst‐lining type changes. Cystic changes are further reinforced by the background of colloid and macrophages. There is nuclear elongation, enlargement, and some irregularities, which, in the context of these cyst lining changes, are acceptable. These findings are suggestive of a cystic nodule (BSRTC category II; DiffQuik [DQ] stain).

FIGURE 5

Smear with a macrofollicle fragment in a background of abundant, watery colloid. The follicular cells have some cytoplasmic elongation suggestive of cyst‐lining type changes. These findings are suggestive of a colloid or cystic nodule (BSRTC category II; Pap stain).

FIGURE 6

Smear with bland follicular fragments and macrophages in a background of blood. Some benign fine‐needle aspiration samples lack abundant colloid, and specimens may be contaminated by blood. These findings would be consistent with follicular nodular disease (BSRTC category II; Pap stain).

FIGURE 7

Two ultrasound images from the same patient with Hashimoto thyroiditis. (A) Longitudinal image showing that the entire gland (marginated by ultrasound calipers) is heterogeneous, hypoechoic, and has a lobulated contour. (B) Transverse image showing a well circumscribed, hyperechoic nodule that is a classic benign white knight nodule.

FIGURE 8

Chronic lymphocytic thyroiditis in a patient with Hashimoto thyroiditis; follicular epithelium with oncocytic change is observed in a background of polymorphous lymphoid elements. Lymphoglandular bodies and focal crush artifact are seen (DQ staining).

FIGURE 9

Two ultrasound images from the same patient with Graves disease. (A) Longitudinal grayscale image shows heterogeneous parenchyma (marginated by ultrasound calipers), reflecting sequela of inflammation. (B) Color doppler image shows marked hypervascularity, in keeping with active inflammation and thyroiditis.

FIGURE 10

Flame cells with abundant cytoplasm and magenta material along the edges of the cells. This finding is characteristic of untreated Graves disease, although it is nonspecific and also can be seen in functioning hot nodules in patients without Graves disease (DQ staining).

FIGURE 11

Transverse ultrasound images in four different patients highlighting the nonspecific appearance across the spectrum of follicular lesions. (A) Solid, mildly hypoechoic nodule was follicular adenoma. (B) Solid, hypoechoic nodule (arrow) was oncocytic adenoma. (C) Solid, isoechoic nodule was noninvasive follicular thyroid neoplasm with papillary‐like nuclear features. (D) Solid, isoechoic nodule with macrocalcifications was follicular carcinoma.

FIGURE 12

Hypercellular slide without colloid or background macrophages comprised of predominantly microfollicles, consistent with a follicular neoplasm (BSRTC category IV; DQ stain).

FIGURE 13

Papillary thyroid cancer in two different patients. (A) Longitudinal ultrasound image shows a solid nodule (large arrow) with several punctate, echogenic foci (small arrows), signifying microcalcifications. (B) Primarily solid nodule (large arrow) with small peripheral cystic spaces, which can be seen in papillary thyroid cancer. Punctate echogenic foci (small arrows) are seen again.

FIGURE 14

Hypercellular smear composed of follicular cells arranged in papillae in a background of blood and multinucleated giant cells, consistent with papillary thyroid carcinoma (BSRTC category VI; Pap stain).

FIGURE 15

Smear with follicular cells arranged in true papillae with fibrovascular cores, consistent with papillary thyroid cancer (BSRTC category VI; Pap stain).

FIGURE 16

Smear that has follicular cells with nuclear overlap, pale chromatin, and intranuclear cytoplasmic inclusions, consistent with papillary thyroid cancer (BSRTC category VI; Pap stain).

FIGURE 17

Smear that has follicular cells with nuclear overlap, pale chromatin, nuclear grooves, and intranuclear cytoplasmic inclusions, consistent with papillary thyroid cancer (BSRTC category VI; Pap stain).

FIGURE 18

Multifocal medullary thyroid cancer. Longitudinal ultrasound images of two nodules in (A) the isthmus and (B) the left lobe. The isthmus nodule (marginated by ultrasound calipers) is solid and mildly hypoechoic, whereas the left‐sided nodule (also denoted by calipers) is hypoechoic with punctate echogenic foci. Despite their differing appearance, both were proven to reflect medullary cancers at surgery.

FIGURE 19

Medullary thyroid carcinoma showing loosely cohesive, plasmacytoid cells with spindling. Chromatin is fine with inconspicuous nucleoli (Pap stain).

FIGURE 20

Medullary thyroid carcinoma demonstrating plasmacytoid cells, some with binucleation (DQ stain).

FIGURE 21

(A, B) Anaplastic thyroid cancer. Transverse and longitudinal ultrasound images show a hypoechoic and solid nodule (bracketed by ultrasound calipers). The nodule is bulging anteriorly in the transverse image (arrow), and appears to extend out of the thyroid capsule in the longitudinal image (arrow). Extrathyroidal extension is a rare feature on ultrasound and suggests a higher likelihood of malignancy.

FIGURE 22

Anaplastic carcinoma with pleomorphic cells in a background of necrosis (DQ stain).

FIGURE 23

Anaplastic carcinoma with highly atypical cohesive cells showing apoptosis and mitotic activity in a background of necrosis (Pap stain).