Ultrasound revealed thyroid cyst with shifting contents
A 63-year-old Asian woman was referred for the evaluation of a partially cystic left thyroid nodule. A thyroid mass was found during a routine annual physical exam. The primary care physician ordered a thyroid ultrasound that revealed a thyroid of normal size with a 3 mm simple cyst in the right lobe and a complex cyst in the left lobe. The left cyst measured 2.3 × 1.2 × 2.1 with an irregular nodular wall (figures 1A and 1B). The nodule did not demonstrate intranodular hypervascularity or microcalcifications. The patient was referred to the endocrine clinic for further evaluation. The patient was unaware of the thyroid nodule and did not have any obstructive signs or symptoms of thyroid dysfunction. She had no history of head and neck radiation. No family members had thyroid disease.
On exam, she had a 2.5 cm firm mass in the left lobe that was nontender and mobile. There was no adenopathy found in the neck. Laboratory testing revealed normal thyroid function with a thyroid-stimulating hormone of 2.42 uU/mL. An ultrasound-guided fine needle aspiration was done in the endocrine clinic of the solid nodular rim of tissue along the margins of the partially cystic nodule. The cytology revealed normal follicular cells in a mixed macro-microfollicular pattern, focal Hürthle cell metaplasia, colloid material and numerous hemosiderin-laden macrophages with a blood background consistent with a benign colloid nodule with hemorrhagic/cystic degeneration.
The patient did well for the next year. She returned for her one-year routine visit complaining of nodule growth and mild tenderness for the last two weeks. She had mild dysphagia with solid food only. Repeat ultrasound showed an interval change in her nodule that revealed an heterogeneous isoechoic nodule (figures 2A and 2B). The change was thought to be due to acute nodule degeneration, and it was decided to wait and watch. She returned in two months saying that her nodule was back to the usual size without tenderness or dysphagia. Ultrasound of the nodule showed a remarkable observation of cystic nodule with apparently solid material in the dependent portion of the nodule with a sharp linear separation between the cyst fluid and the solid portion of the cystic nodule (figure 3).
This was such a remarkable observation that the clinician had the patient sit up and reimaged the thyroid. The contents of the cyst changed so the more isoechoic material remained in the dependent portion of the cyst maintaining the linear demarcation with the hypoechoic fluid. This is an example of an apparent solid and cystic nodule but, in fact, was actually less dense fluid above cellular debris in the dependent portion of the gland.
Cystic nodules within the thyroid may represent cystic degeneration or hemorrhage in a benign adenomatous nodule, a benign follicular adenoma or a thyroid malignancy. Papillary thyroid carcinoma frequently contains some elements of cystic degeneration. Large clinical series suggest that a large cystic nodule with >50% solid material has a higher risk of malignancy. Fine needle aspiration biopsy of partially cystic nodules is more often insufficient than solid nodule. The sufficiency rate improves with ultrasound-guided biopsy when ultrasound is used to direct the needle into the solid portion of the nodule. It has been shown that the best place to biopsy a nodule is just under the capsule, presumably because the central nodule is the most poorly perfused and often degenerating. Even with ultrasound guidance, insufficient fine needle aspiration biopsies occur with partially cystic nodules. This patient illustrates how nodular debris appeared to be solid until a change in positions proved it to be shifting debris.
When evaluating a partially cystic nodule, it is important to remember that debris within the cyst may not be hypoechoic. Use of Doppler to locate tissue within the nodule that has vascular flow will help target the fine needle aspiration biopsy to viable tissue for diagnosis. If in doubt, a simple maneuver of having the patient sit up will prove if more isoechoic tissue within a cystic thyroid nodule is solid or debris.
A. Transverse image of the left thyroid lobe. Doppler analysis (blue box) shows some peripheral vascular blood flow. B. Sagittal image of the left thyroid lobe. A mostly cystic nodule is seen with a central cystic hypoechoic region (green arrow) and irregular mural solid tissue along the nodules margin (blue arrow).
Photos courtesy of: Stephanie L. Lee
A. Transverse image of the left thyroid lobe. Doppler analysis (blue box) shows that the nodule does not have vascular flow. B. Sagittal image of the left thyroid lobe. Patient noted two months of tenderness and increase in size of the nodule. Although the appearance could be consistent with a heterogeneous, mostly solid nodule, the increase in bright echoes posterior to the nodule suggest it is still mostly cystic despite the isoechoic appearance of the nodule.
A. Transverse image of the left thyroid lobe with patient supine. B. Sagittal image of the left thyroid lobe with the patient supine. C. Sagittal images of the left thyroid lobe with the patient upright with the isoechoic contents of the cyst shifting to remain in the dependent portion of the cyst.
Stephanie L. Lee, MD, PhD, is Associate Chief in the Section of Endocrinology, Diabetes and Nutrition and Associate Professor of Medicine at Boston Medical Center.
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