Marginal vacuoles in fine-needle aspirates of follicular thyroid carcinoma

Cytodiagnosis of distant metastases from follicular thyroid carcinoma

INTRODUCTION

Follicular carcinoma of the thyroid is second most common primary malignancy of the thyroid gland after papillary carcinoma and metastasis is uncommonly seen in these patients.

AIMS AND OBJECTIVES

To describe the cytomorphologic features for the accurate diagnosis of distant metastases from follicular carcinoma of thyroid.

MATERIALS AND METHODS

A total of 10 aspirates reported as metastatic follicular carcinoma of thyroid were reviewed for the available clinical and radiological details.

RESULTS

All the patients were females. Six of these patients presented with subcutaneous and soft tissue swellings, one presented with a lung mass, one with right breast swelling, one with lumbar vertebral lesion and one with left iliac bone involvement. The cytology smears revealed tumour cells predominantly arranged in a repetitive microfollicular pattern with some scattered individually and in sheets. The tumour cells were small, had mild nuclear pleomorphism, round nuclei, low nuclear-cytoplasmic ratio, fine chromatin, inconspicuous nucleoli, and scanty to moderate amount of cytoplasm with some showing marginal vacuoles with "fire-flare" appearance. Occasional microfollicles showed scanty eosinophilic colloid in the center.

CONCLUSIONS

Identification and establishment of a correct clinical diagnosis of a distant metastasis from a follicular thyroid carcinoma is a challenging task. We believe that with prior knowledge of characteristic cytologic features, such metastases can be rapidly and accurately diagnosed by fine needle aspiration cytology.

Marginal vacuoles (fire-flare appearance) in fine needle aspiration smears of thyroid lesions: Does it represent diffusing out of thyroid hormones at the base of follicular cells?

Marginal vacuoles (MVs) or fire-flare appearance in May-Grünwald Giemsa stained fine needle aspiration (FNA) smears was initially described as a distinctive feature of thyrotoxic goiter in hyperthyroidism, but was subsequently found in various nontoxic thyroid lesions, both non-neoplastic and neoplastic. Although these MVs have been characterized as dilated endoplasmic reticulum, and manifestation of active pinocytosis/vacuoles containing colloid, their exact nature is not so far resolved. In this connection, FNA smears of 82 hyperplasia cases, consisting of 71 colloid goiters and 11 hyperplastic nodules (HN), and 76 thyroid neoplasms of follicular epithelium origin were reviewed to detect the MVs and grade them on a sliding scale of + (scanty), ++ (moderate), and +++ (abundant). A hypothesis was put forth regarding the nature of MVs based on their cytomorphological features as observed by us and the physiological/pathophysiological mechanisms related to synthesis, storage and secretion of thyroid hormones described in the literature. The frequency of MVs in neoplastic goiters (50.0%) was significantly lower than that in HN (90.9%, P = 0.0196) but higher than that in colloid goiters (29.6%, P = 0.0124). MVs were present in a significantly higher number of follicular neoplasm (FN; 85.7%) than in papillary thyroid carcinoma (44.4%, P = 0.0069) and Hurthle cell neoplasm (25.0%, P = 0.0083). Among the variants of papillary thyroid carcinoma (PTC), follicular variant showed MVs in 94.1% cases, which was higher than those in usual variant (23.5%, P < 0.0001), tall cell variant (16.7%, P = 0.001), and PTC with a significant tall cell component (25.0%, P = 0.001). It was possible to demonstrate pinocytic vesicles on one side (luminal aspect) and MVs on the other side (basal aspect) of follicular cells in colloid goiters. In the aspirates from follicular lesions such as HN, FNs, and follicular variant of PTC, numerous MVs were found to be radiating from the basal aspect of follicular cells in the intact follicles with or without colloid in the central lumen. Since MVs in literature have been linked to thyrotoxicity in Graves' disease and neoplasms with a follicular pattern, our findings suggest that MVs represent the diffusing out of thyroid hormones (T(3) and T(4)) from the basal aspect of follicular cells on their way to interfollicular capillaries.

Aspiration cytopathology of metastatic mucinous papillary thyroid carcinoma

The light microscopic histopathology and cytopathology of papillary thyroid carcinoma (PTC) and its variants is amply depicted in reviews, books, and book chapters. One of the changes in PTC, however, that is infrequently discussed or illustrated in the literature is that of mucinous metaplasia. In the aspiration cytopathology literature, we are aware of only a rare report of PTC exhibiting extensive mucinous metaplasia. We present an example correlating the histopathology and fine needle aspiration cytopathology of a PTC that had metastasized on several separate occasions to cervical lymph nodes, and in the process demonstrated mucinous transformation. Without a prior history of PTC, the aspirate smears and tissue sections could have been mistaken easily for metastatic clear cell carcinoma of non-thyroidal origin. Mucinous metaplasia represents an extremely uncommon, but nonetheless potential, pitfall in the aspiration cytopathology and histopathology of metastatic PTC.