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Original Report |
1
Department of Radiology, University of Pennsylvania Medical Center, 3400
Spruce St., Philadelphia, PA 19104.
2
Prsent Address: Department of Medical Imaging, The Hospital for Sick Children,
555 University Ave., Toronto, Ontario M5G 1x8 Canada.
3
Department of Pathology, University of Pennsylvania Medical Center,
Philadelphia, PA 19104.
4
Department of Medicine, University of Pennsylvania Medical Center,
Philadelphia, PA 19104.
Received June 12, 2000;
accepted after revision August 7, 2000.
Address correspondence to J.E. Langer.
Abstract
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CONCLUSION. In a patient population undergoing sonography for palpable nodular disease without known thyroiditis, focal nodules of thyroiditis had a wide variety of appearances. They most commonly appeared as solid hyperechoic nodules with ill-defined margins. However, the echogenicity was variable, and calcification and cystic-appearing regions were also noted. The vascularity of these nodules as assessed with color Doppler and power Doppler sonography also varied widely. Biopsy of these lesions is still necessary because there are no sonographic features that can reliably diagnose these lesions as thyroiditis and differentiate them from other lesions.
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Each nodule was assessed for its predominant echogenicity (hypo-, iso-, or hyperechoic relative to adjacent parenchyma, or mixed if no one echogenicity was predominant), regularity or irregularity of its border, presence and characteristics of calcifications, presence or absence of a surrounding halo, and echotexture (entirely solid, containing small cystic regions [estimated <25%], mixed cystic and solid [25-50%], or predominantly cystic [>50%]). The greatest anteroposterior and craniocaudad dimensions as seen on the longitudinal image and the greatest width on the transverse image of each nodule were recorded. The overall echogenicity of the gland was recorded as hypo-, iso-, or hyperechoic compared with adjacent neck musculature. The background appearance of the gland was recorded as homogeneous if uniform in appearance or heterogeneous if micronodules or areas of hypoechogenicity were observed.
Color Doppler sonography and power Doppler sonography using a pulse repetition frequency of 1500 Hz, medium level wall filter, and color gain of 80% were performed on 14 nodules. The examiner estimated the amount of color pixels within the nodule using quartiles of 0-25%, 26-50%, 51-75%, and 76-100% of the nodule written in color pixels. Additionally, the color Doppler and power Doppler flow patterns of each nodule were evaluated for whether most color pixels were in the central aspect of the nodule, at the periphery, or equally distributed between the central and peripheral aspects. Sonographically guided fine-needle aspiration was performed on all nodules that measured more than 10 mm in two dimensions with the exception of one case in which a 4 x 6 x 8 mm nodule was biopsied because it occurred as a solitary nodule in a patient at high risk for thyroid carcinoma. Fine-needle aspiration was performed using a 25-gauge needle attached to a 10-mL syringe. Two to four samples were obtained from each nodule and were reviewed on site by cytopathologists to confirm adequacy.
The diagnosis of lymphocytic thyroiditis was made when the fine-needle aspiration smears satisfied the following criteria: the smears were cellular and showed a mixture of follicular cells and Hürthle cells in a background of small mature lymphocytes; the colloid was scant and mainly consisted of thick eosinophilic colloid; the follicular and Hürthle cells were present as follicular groups, monolayer sheets, and scattered cells; the lymphocytes were present in aggregates and were also scattered among the follicular and Hürthle cells groups; and the follicular cells focally displayed nuclear atypia with nuclear enlargement and clearing but without nuclear grooves or inclusions.
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Eight nodules occurred in the right lobe, 11 in the left, and two in the isthmus. The mean nodule size ranged from 6.0 to 28.3 mm (median, 12.9 mm). The predominant echogenicity of the nodules that proved to be thyroiditis was hyperechoic relative to parenchyma in 10 nodules (47.6%) (Fig. 2), hypoechoic in five (23.8%) (Fig. 1), isoechoic in three (14.3%), and of mixed echogenicity in two (9.5%). The echogenicity of the nodules could not be assessed because of calcifications in one nodule (4.8%).
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Eighteen (85.7%) of the nodules were completely solid, one (4.8%) contained minute cystic-appearing regions, and two (9.5%) were mixed cystic and solid in appearance (Fig. 3). The margins of the nodule were irregular in 17 nodules (80.9%) and regular in four (19%). A partial surrounding halo was noted in seven nodules (33.3%) (Fig. 4) and was absent in 14 (66.7%).
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Calcifications were noted in five nodules (23.8%). In two nodules the calcification (measuring 4 and 8 mm) was solitary and was associated with distal acoustic shadowing (Fig. 5). In the other three nodules, the calcifications numbered between two and five foci, were approximately 1-2 mm in size, and were not associated with distal acoustic shadowing (Fig. 4). The overall echogenicity of the gland was greater than that of neck strap muscles in 15 (75%) of 20 patients (Figs. 4 and 5) and equal to that of neck strap muscles in five patients (25%). The background echotexture of the gland was homogeneous in three patients (15%) and heterogeneous with geographic hypoechoic regions or micronodules in 17 (85%).
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Color Doppler sonography was performed on 14 of the 21 nodules. Color pixels were present in 0-25% of the lesion in seven nodules, in 26-50% in four nodules, and in 76-100% in three nodules. In nine nodules the color pixels were distributed equally between the periphery and the center of the nodule, and in five they were more numerous at the periphery.
Power Doppler sonography was performed in 14 of the 21 nodules. Color pixels were present in 0-25% of the lesion in five nodules, in 26-50% in six nodules, and in 76-100% in six nodules. In six nodules, the color pixels were distributed equally between the periphery and the center of the nodule, and in eight they were more numerous at the periphery.
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Although lymphocytic thyroiditis was originally described as the presence of a firm, diffusely enlarged gland, a large number of patients with lymphocytic thyroiditis have nodular enlargement of their thyroids and are often referred for fine-needle aspiration [3, 6, 8]. In up to 60% of these patients, biopsy of the focal palpable nodule will yield changes consistent with lymphocytic thyroiditis without evidence of malignancy [1, 6,7,8].
We retrospectively reviewed the sonographic appearance of focal nodules that on fine-needle aspiration were shown to be lymphocytic thyroiditis in unselected patients undergoing sonographically guided fine-needle aspiration for the evaluation of palpable nodular thyroid disease. These nodules constituted 5.3% of all nodules biopsied, an incidence similar to the incidence found in other large series [10, 11]. Most patients in our series were euthyroid and had a thyroid gland of normal echogenicity (increased relative to strap muscles) with a micronodular pattern [3,4,5,6]. The normal echogenicity likely reflects a less severe degree of lymphocytic infiltrate and fibrosis in our patient population than in patients with a hypoechoic gland [6].
Other researches have described the sonographic appearance of focal nodules that proved to be thyroiditis in patients with known lymphocytic thyroiditis [7]. These socalled pseudotumors constituted 36% of the nodules detected on sonography and were typically hypoechoic with ill-defined margins, an appearance that was indistinguishable from thyroid lymphoma and papillary carcinoma. Similarly, most areas of focal thyroiditis in our series appeared to be ill-defined solid nodules without a surrounding halo. However, despite the fact that most (75%) of our patients had preserved echogenicity of the gland, the most common appearance of the thyroiditis nodules in our series was hyperechoic (47.7%), an appearance causing less concern for malignancy [10, 11] (Fig. 2). Additionally, partial cystic change was noted in three nodules (Fig. 3) and calcifications in five (Fig. 4). Calcifications have previously been noted in focal thyroiditis [10], but their appearance was not specifically described.
The vascularity of diffuse lymphocytic thyroiditis has been described as variable [12]. To our knowledge, the vascularity of focal thyroiditis has not previously been reported. We assessed 14 nodules with both color and power Doppler sonography. As with other nodules of both benign and malignant histology, the vascularity of focal thyroiditis is markedly variable, without a distinguishing pattern [12]. The amount of vascularity seemed unrelated to size; the three nodules with the greatest flow measured 11.7, 10.7, and 14 mm in mean diameter. On power Doppler sonography, the findings were identical to the findings of color Doppler sonography in 12 nodules, but power Doppler sonography noted more vascularity in two nodules. The pattern of flow was also variable. Color Doppler sonography showed a pattern of equal flow between the periphery and the center of the lesion in nine lesions, whereas power Doppler sonography showed a peripheral predominance of flow in nine nodules. Because power Doppler sonography is the more sensitive technique for slow flow or low-velocity flow, it is likely that power Doppler sonography was more sensitive to slow and peripheral flow in these lesions.
In conclusion, focal thyroiditis is well known pathologically. Lymphocytic thyroiditis may affect the thyroid gland diffusely or focally. The focal form, which may represent a milder or earlier presentation of the disease, may present with focal nodules that prove to be lymphocytic thyroiditis on fine-needle aspiration. In a patient population undergoing sonography for palpable nodular disease without known thyroiditis, these lesions most commonly appeared as a hyperechoic nodule with ill-defined margins. Calcification and cystic change may be present in the nodule. Biopsy of these lesions is still necessary because there are no sonographic features that can reliably diagnose them as thyroiditis and differentiate them from other lesions.
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