Managing incidental parathyroid adenoma with a normal PTH

Issue: January 2017

ByStephanie L. Lee, MD, PhD, ECNU

A 35-year-old man with a medical history significant for a thoracic aortic aneurysm repair with aortic root replacement had an incidental left thyroid nodule found on a thorax CT scan. The patient had no prior history of thyroid disease or head and neck radiation. He had no family history of thyroid disease or thyroid cancer and no symptoms or signs of thyroid dysfunction or local obstructive symptoms.

At a different academic thyroid center, a 1.2-cm solitary, hypoechoic left thyroid nodule with discontinuous macrocalcification was noted (Figure 1). The report indicated no abnormal nodes or masses in the neck. An ultrasound-guided thyroid biopsy of the nodule showed a papillary thyroid carcinoma. The patient was referred to our center for a second opinion on whether he should have thyroid surgery or undergo watchful waiting.

Laboratory tests, imaging

Local review of his cytology confirmed a Bethesda category VI assignment as diagnostic for papillary thyroid carcinoma. Although his prior ultrasound was read by an expert radiologist at an academic thyroid center, we repeated the ultrasound assessment of the thyroid nodule with a node survey.

Figure 1. Thyroid ultrasound of thyroid nodule. A single heterogeneous hypoechoic nodule (red arrow) was found in the left upper lobe of the thyroid. Discontinuous surface calcification made it difficult to see the margins for invasion or posterior extrathyroidal extension. (A) Transverse. (B) Sagittal. *See Figure 2 Legend.

The nodule was very hypoechoic with indistinct margins and was located in the left upper lobe. There was surrounding normal thyroid parenchyma medial, superior and lateral to the nodule. The discontinuous surface macrocalcification made it impossible to determine whether the margins were infiltrative or inferior posterior extrathyroidal extension.

The node survey revealed a 1.5-cm hypoechoic mass with peripheral vascularity adjacent to the superior lobe of the ipsilateral thyroid lobe adjacent to the superior lobe of the left thyroid (Figure 1B, Figure 2). The differential diagnosis for this mass was either a node with metastatic thyroid cancer or a parathyroid adenoma. Based on this appearance, watchful waiting could not be recommended.

Laboratory testing revealed normal levels for calcium, 10.4 mg/dL; albumin, 4.4 g/dL; intact parathyroid hormone (PTH), 72 pg/mL (normal, 11 pg/mL-90 pg/mL); and 25-hydroxyvitamin D, 29.9 ng/mL.

Figure 2. Thyroid ultrasound of extrathyroidal mass. The calcified thyroid nodule is located in the left upper thyroid lobe (red arrow). A hypoechoic mass was located superior and outside the thyroid capsule of the left upper thyroid lobe (yellow arrow and * in Figure 1B). The mass has vigorous peripheral vascularity with a possible feeding vessel by Doppler. (A) Transverse. (B) Sagittal. (C) Sagittal plus Doppler. CA: carotid artery.

Surgery was planned for a total thyroidectomy with removal of the parathyroidal mass. If the mass was a metastatic node, then a therapeutic central neck dissection would be performed. Intraoperatively, the surgeon identified the extrathyroidal mass as a parathyroid adenoma and not a metastatic lymph node.

After the total thyroidectomy, the operation was concluded without a central neck dissection. Surgical pathology showed a 1.9-cm x 1.5-cm x 1.1-cm classical papillary thyroid carcinoma without capsular or lymphovascular invasion or extrathyroidal extension. No abnormal nodes were found during the surgery. The extrathyroidal mass proved to be a 1.1-cm x 1-cm x 0.4-cm 470-mg parathyroid adenoma. Two weeks after surgery, the patient’s laboratory tests continued to be normal: calcium, 9.6 mg/dL; albumin, 4 g/dL; and intact PTH, 54 pg/mL.

Ultrasound considerations

Studies of large numbers of patients show a prevalence of incidental parathyroid adenoma in 0.5% to 1.2% of these patients found during thyroid ultrasound. When these extrathyroidal masses have been confirmed to be a parathyroid adenoma with an elevated PTH level on a needle aspiration, only one in three patients had biochemical hyperparathyroidism. These extrathyroidal masses are difficult to distinguish between a parathyroid adenoma and a metastatic foci of thyroid cancer. Biochemical testing for hyperparathyroidism is often negative and unrevealing.

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Preoperative fine-needle aspiration for cytology and PTH measurement could be considered if the testing would change the surgical management. After a needle biopsy, the sample can be used for cytology and then needle washed with 1 cc of normal saline and placed in a red-top tube for PTH measurement.

It is important that the preoperative node survey be performed by clinicians who are experienced in head and neck ultrasound. Often examinations do not extend the area of examination sufficiently rostral and caudal to detect metastatic nodes or parathyroid adenomas. It is critical that cine loops of the entire examination of each compartment of the neck are saved for later analysis.

Of note, the outside radiology department examination captured images of the extrathyroidal parathyroid adenoma (see * in Figure 1B), but the mass was not recognized by the radiologist.

References:
Frasoldati A, Valcalvi R. Endocr Pract. 2004;10:261-268.
Ghervan C, et al. Med Ultrason. 2012;14:187-191.
Kwak JY, et al. Thyroid. 2009;19:743-748.

For more information:
Stephanie L. Lee, MD, PhD, ECNU, is an Endocrine Today Editorial Board member. She is associate professor of medicine and director of thyroid health in the section of endocrinology, diabetes and nutrition at Boston Medical Center. She can be reached at Boston Medical Center, 88 E. Newton St., Boston, MA 02118; email: stephanie.lee@bmc.org.

Disclosure: Lee reports no relevant financial disclosures.