Cyst with ‘colloid comets’ in the thyroid not derived from thyroid epithelium

Issue: July 2009

ByStephanie L. Lee, MD, PhD, ECNU

ByLisa Usdan, MD

A 38-year-old male with a history of factor XI deficiency hemophilia with severe acquired circulating anticoagulant to factor IX and psoriasis was referred for an abnormal thyroid gland discovered during a CT scan of the thorax. The scan, performed at an outside hospital during an evaluation of an episode of a self-terminating paroxysmal atrial tachycardia, showed a 1.4 x 1.2 x 1.2 cm nonenhancing nodule in the right thyroid lobe. Thyroid functions were normal with thyroid-stimulating hormone 0.85 uU/mL and free thyroxine 0.81 ng/dL. Biopsy was recommended, but because of his complicated hemophilia, the patient was referred to his hematologist at Boston Medical Center.

Lisa Usdan

Stephanie Lee

An I-123 thyroid scan and uptake was ordered that revealed a rounded photopenic defect in the lateral aspect of the lower half of the right thyroid lobe with a thyroid uptake of 7% at four hours (expected is 5% to 15%) (Figure 1). The patient was referred to our endocrine clinic. The patient had no prior history or family history of thyroid disease. He denied head and neck radiation. He noted a several months-long history of an intermittent sensation of lower neck pressure without dysphagia or change in voice. He denied any symptoms of hypothyroidism or hyperthyroidism. Thyroid ultrasound performed in the endocrine clinic showed a 1.6 x 1.4 x 1.2 cm well-demarcated homogeneous hypoechoic nodule with punctate hyperechoic foci that resembled “colloid comets” and posterior cystic enhancement consistent with a degenerating colloid nodule (Figure 2). Because of his hemophilia with circulating anticoagulant to factor IX, the patient was admitted and treated with fresh frozen plasma before and after an ultrasound-guided fine needle aspiration biopsy with a 25 g needle. The biopsy was “dry” and no fluid was removed. On-site cytology showed abundant superficial squamous epithelial cells and anucleated squamous cells. No follicular thyroid cells or lymphocytes were seen. Thyroid-specific antigens, thyroid transcription factor-1, thyroglobulin and immunostains were negative.

The differential for squamous cell epithelium obtained from a fine needle aspiration biopsy of a thyroid mass includes a thymic remnant, thyroglossal duct remnant, ultimobranchial remnant (third or fourth branchial cleft cyst) and squamous cell tumors. The large number of mature, benign-appearing squamous cells favored an intrathyroidal branchial cleft cyst, which is also called a lymphoepithelial cyst.

Figure 1: I-123 thyroid scintigraphy and uptake
Figure 1. I-123 Thyroid scintigraphy and uptake. Four hours after administration of 0.5 mCi of I-123 anterior, left anterior oblique (LAO) and right anterior oblique (RAO) images of the thyroid were obtained. A rounded cold area is identified (green arrow) in the lateral aspect of the mid-right thyroid lobe.

Photos courtesy of: Stephanie L. Lee

Persistence of branchial cleft remnants generally occur as cysts, sinuses or fistulas lined with squamous epithelium, pseudostratified columnar epithelium and may focally show respiratory-type epithelium with underlying lymphoid tissue beneath the cyst wall. Second branchial cleft cysts are usually found anterior to the sternocleidomastoid muscle and lateral to the internal jugular vein at the level of the carotid bifurcation. Anomalies of the third and fourth branchial clefts are uncommon and occur close to or very rarely within the lateral lobes of the thyroid gland. The formation of branchial cleft cysts in the thyroid has, in many but not all cases, been associated with Hashimoto’s thyroiditis. Pathological examination of these intrathyroidal branchial cleft cysts shows a chronic thyroiditis beneath the epithelium resulting in the name, intrathyroidal lymphoepithelial cysts. The cystic contents may be clear, watery or mucinous fluid but may contain desquamated, granular cellular debris that appears to be pus-like fluid. In our case, no visible fluid was removed during the fine needle aspiration biopsy using a 25 g needle.

The ultrasound appearance of the intrathyroidal branchial cleft cysts may show a typical cyst (thin walled, anechoic with posterior cystic enhancement) or a pseudosolid appearance with a uniformly echogenic mass with suspended debris and echogenic artifacts with reverberations that are similar in appearance to “colloid comets” (Figure 2). The echogenic foci are thought to represent debris composed of cellular debris, cholesterol and keratin. These cysts may be solitary, multiple, simple or loculated on ultrasound exam.

Figure 2 A & B: images of the right thyroid lobe and right thyroid nodule
Figure 2A. Transverse image of the right thyroid lobe. Right lobe of the thyroid located between the trachea and carotid artery contains a well-demarcated, rounded nodule with uniform echogenicity (red arrow) and posterior mass enhancement (white arrow).

Figure 2B. Enlarged view of the right thyroid nodule with Doppler analysis shows minimal peripheral blood flow (red and blue dots) with punctate hyperechoic foci located at the periphery of the nodule (green arrowhead).

These pseudosolid cysts sometimes do not demonstrate posterior enhancement and may be confused with a solid lesion. These pseudosolid cysts can often be deformed by pressure of the ultrasound probe, while a solid nodule will not change shape. Fine needle aspiration biopsy of a thyroid cyst or nodule that contains squamous epithelium or produces thick, pus-like material should raise the consideration for an intrathyroidal lymphoepithelial cyst, which is likely the persistence of the third or fourth branchial cleft remnants. Although these are benign, the current literature describes these lesions only after surgical resection.

There are no reports of the natural history of these intrathyroidal lymphoepithelial cysts. This patient has factor XI hemophilia with acquired circulating anticoagulant to factor IX because of repeated infusions of fresh frozen plasma. Concerns of raising the titers of this anticoagulant from repeated use of fresh frozen plasma has led to the decision with the patient and his hematologist to observe this mass for growth by serial ultrasound exams rather than surgical excision. Surgery will be recommended only if the cyst enlarges, resulting in obstructive symptoms.

Lisa Usdan, MD, is an instructor in the Section of Endocrinology, Diabetes and Nutrition at Boston Medical Center.

Stephanie L. Lee, MD, PhD, is Associate Chief, Section of Endocrinology, Diabetes and Nutrition at Boston Medical Center.

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