Hashimoto’s thyroiditis and a giraffe pattern on thyroid ultrasound

Issue: May 2015

ByStephanie L. Lee, MD, PhD, ECNU

A 42-year-old woman was referred to the endocrine clinic for multiple growing hypoechoic nodules. Her medical history was significant only for a history of hypothyroidism since her pregnancy in her early 20s. She has been on a stable dose of levothyroxine, with her most recent thyroid-stimulating hormone level at 1.2 mIU/L. She had no history of head and neck radiation. Her family history was significant for hypothyroidism in her sister and mother, but no history of thyroid cancer.

The patient’s primary care provider felt thyroid enlargement 3 years ago. The ultrasound performed at that time at a radiology department of a local community hospital described “numerous” hypoechoic nodules less than 1 cm in maximal size. Repeat ultrasound performed 1 month before referral showed “too numerous to count hypoechoic nodules with an increase in size compared to the prior exam.”

Pseudonodular changes detected

The patient was referred for fine-needle aspiration to exclude cancer. An office ultrasound was performed (Figure 1). Numerous hypoechoic pseudonodules or micronodules with indistinct margins were observed in a “giraffe pattern.” The largest pseudonodule was 1.1 cm in size.

Stephanie L. Lee

Careful sonographic examination did not show discrete nodules, calcifications or abnormal nodes in the bilateral central (level VI) or lateral neck (levels 2-5). The patient was informed that these pseudonodular changes on thyroid ultrasound, or giraffe pattern, is consistent with Hashimoto’s thyroiditis and is not associated with an increased significant risk of malignancy. She did not require biopsy at this time, but should return in 1 year for a repeat ultrasound.

Figure 1. Thyroid ultrasound of Hashimoto’s thyroiditis. Transverse (A) and sagittal (B) images of Hashimoto’s thyroiditis showed multiple hypoechoic micronodules or pseudonodules with ill-defined margins. This pattern is similar to giraffe hide (C). The hypoechoic areas are due to lymphocytic infiltration of the thyroid.

Source: Giraffe photo reprinted with permission from Robert A. Levine, MD, FACE; Other images courtesy of Stephanie L. Lee, MD, PhD, ECNU.

Figure 2. Typical histology of Hashimoto’s thyroiditis. An example of Hashimoto’s thyroiditis histology shows the diffuse and focal lymphocyte deposition (yellow arrow), lymphocyte germinal centers (green arrows) among areas of thyroid follicle destruction (blue arrow) and fibrosis (white arrow).

A benign nodular pattern was originally described by Bonavita as an isoechoic (relatively white) nodule with intervening hypoechoic bands. But, in fact, giraffe hide has an opposite pattern with dark areas separated by lighter-colored bands (Figure 1C). The true giraffe pattern (Figures 1A, B) is demonstrated by this patient with multiple hypoechoic pseudonodules with ill-defined margins due to focal lymphocyte surrounded by more normal areas of thyroid parenchyma and fibrosis (Figure 2).

Figure 3. Thyroid ultrasound with vascular pattern of Hashimoto’s thyroiditis. Hashimoto’s thyroiditis often shows diffusely increased vascular flow with Doppler analysis. Note that increased flow is not within the hypoechoic pseudonodules (yellow arrows), but along the more isoechoic normal thyroid parenchyma.

Sonographic patterns of Hashimoto’s thyroiditis

Hashimoto’s thyroiditis is an autoimmune disease associated with progressive infiltration of the thyroid by T and B lymphocytes resulting in follicle destruction, fibrosis with reduction in thyroid function and hypothyroidism. The activated B lymphocytes secrete anti-thyroid antibodies that can be found either diffusely or in focal deposits throughout the thyroid parenchyma (Figure 2; yellow arrow) or within germinal centers (Figure 2; green arrows). The cytotoxic T cells affect the thyroid follicular cell destruction and hypothyroidism.

There are several sonographic patterns during the process of autoimmune thyroiditis, including hypoechoic parenchyma with a heterogeneous echotexture, hyperechoic septations (fibrous bands) and hypoechoic micronodulation or pseudonodules. The hypoechoic areas with indistinct margins are a result of focal lymphocytic infiltration with the hyperechoic septations caused by fibrosis (Figure 2; white arrow).

Distinguishing nodules

The giraffe pattern is an important vascular pattern to distinguish pseudonodules from real nodules.The hypoechoic areas do not have increased vascular flow. The increased vascular flow by Doppler analysis is in the isoechoic normal thyroid parenchyma, especially along areas of fibrosis (Figure 3). It is important for clinicians to either perform their own thyroid ultrasound or to review the radiology images because radiology reports rarely distinguish real nodules from pseudonodules. Unnecessary thyroid biopsies will be avoided if the benign giraffe pattern of pseudonodules in Hashimoto’s thyroiditis is recognized by the clinician.

Reference:

Bonavita JA, et al. AJR Am J Roentgenol. 2009;doi:10.2214/AJR.08.1820.
Bonavita JA. AJR Am J Roentgenol. 2012;doi:10.2214/AJR.11.7737.
Ceylan I, et al. Quant Imaging Med Surg. 2014;doi:10.3978/j.issn.2223-4292.2014.07.13.

For more information:

Stephanie L. Lee, MD, PhD, ECNU, is an Associate Professor of Medicine and Associate Chief, in the Section of Endocrinology, Diabetes and Nutrition at Boston Medical Center. Lee can be reached at Boston Medical Center, 88 E. Newton St., Endocrinology Evans 201, Boston, MA 02118; email: stephanie.lee@bmc.org.

Disclosure:

Disclosure: Lee reports no relevant financial disclosures.