A 25-year-old, 6-months’ pregnant woman presented with hypothyroidism and a thyroid nodule. She had a prior fine-needle aspiration (FNA) of a right-sided nodule with benign results, but on follow-up ultrasound, the nodule had enlarged (Figure 1 A, B).
Fatigue, constipation, dry skin and neck lump during pregnancy
Enlarging solitary mixed solid and cystic nodule in the right thyroid lobe
Thyroid nodules are a common clinical problem. Given the typical pregnant patient demographics and frequent physician encounters during pregnancy, it is not surprising that incidental thyroid nodule workups are common during pregnancy. The radiologist should be prepared to be part of the workup of thyroid nodules and their subsequent management. Although many thyroid nodules are benign, thyroid cancer is common.1 Approximately 10% of thyroid cancers that occur during the child-bearing period are diagnosed during pregnancy or in the first year after birth.2
According to the American Thyroid Association (ATA), the optimal diagnostic approach for a thyroid nodule detected during pregnancy is comprehensive history, physical examination, serum thyroid-stimulating hormone (TSH) and thyroid ultrasound. FNA is indicated according to the level of suspicion defined by ultrasonographic features. Calcitonin measurement may be performed in pregnant women with a family history of medullary thyroid carcinoma, MEN 2 or a known RET gene mutation. Radionuclide scintigraphy or radioiodine uptake determination is contraindicated during pregnancy.3
The American College of Radiology (ACR) Thyroid Imaging Reporting and Data System (TI-RADS) committee has proposed ultrasound-based risk stratification systems to identify nodules that warrant biopsy or sonographic follow-up. Other societies, such as the ATA, have taken a slightly different, pattern-oriented approach, but with the same intent. Although the ACR TI-RADS recommendations provide guidance, radiologists and referring physicians are obligated to use clinical judgment in every case. The decision to perform FNA should also account for the referring physician’s preference and the patient’s risk factors for thyroid cancer, anxiety, comorbidities, life expectancy, and other relevant considerations.4
Although the workup and decision to biopsy is no different between pregnant and nonpregnant patients, the management for a patient diagnosed with malignancy is different. The management is largely based on the histopathology, and whether the malignancy is considered well-differentiated. It is crucial that a multidisciplinary approach be taken involving pathology, radiology (nuclear medicine), obstetrics/gynecology, endocrinology, anesthesiology, and surgery when providing a patient with accurate information and guiding management. The 2017 ATA clinical guidelines aid management of thyroid cancer in pregnancy.3
For patients diagnosed with differentiated (papillary and follicular) thyroid cancer, there are options about whether to begin treatment during pregnancy vs after delivery. If surgery is considered while the patient is pregnant, timing is critical. Surgery could be safely performed during the second trimester or delayed until delivery without worsening prognosis. Thyroidectomy performed during the first trimester carries a risk of teratogenicity or may increase the risk of miscarriage.3 In the third trimester, there is a high risk of premature labor and potential hypotension due to vena cava compression by the uterus in the supine position, which may cause fetal hypoperfusion.3
In contrast to well-differentiated thyroid cancer, delaying surgery until delivery can adversely affect the outcome in pregnant women with newly diagnosed medullary carcinoma or anaplastic cancer. After clinical assessment, surgery should be strongly considered.3
The need for radioactive iodine (RAI) therapy depends on the cell type and risk but must wait until after pregnancy. RAI should only be administered if a woman has a negative pregnancy test 72 hours before treatment is given. RAI is also significantly concentrated in lactating breast tissue. Therefore, RAI should not be given to breastfeeding women. Breastfeeding should stop at least 6 to 8 weeks prior to radioiodine therapy to reduce radioiodine uptake by breast tissue.5
At 6 months’ postsurgery, a neck ultrasound should be performed and serum thyroglobulin should be monitored closely during the first year after thyroid surgery. Additional neck ultrasound and other imaging modalities such as diagnostic radioiodine whole-body scan, MRI, CT and F-18 fluorodeoxyglucose (FDG) PET/CT are tailored according to the patient’s risk of recurrence.5
Overall prognosis and survival rates in patients diagnosed with thyroid cancer during pregnancy are not significantly different from that in nonpregnant women with similar disease.1
Papillary carcinoma is the most common type of thyroid cancer and frequently has lymph node involvement at presentation. It is more common in women with a peak incidence in the third and fourth decades.6 On ultrasound, papillary carcinoma usually appears as a single, solid hypoechoic nodule with cystic component and ill-defined margins. The nodule can contain microcalcifications (psammoma bodies) in the form of punctate echogenic foci without posterior acoustic shadowing. On color Doppler, there is increased internal vascularity. Lymph node metastasis tends to cavitate.6
Follicular carcinoma represents 2% to 5% of thyroid cancers. It can occur in a pre-existing microfollicular or macrofollicular adenoma. Lymph node metastasis in follicular carcinoma is rare. However, hematogenous spread is more common at presentation.6 On ultrasound, it is typically a homogenously hypoechoic nodule without cystic change. Color Doppler shows extensive internal flow with or without a peripheral ring.6 The definitive diagnosis of follicular carcinoma is made by thyroidectomy.
Medullary carcinoma accounts for about 5% of thyroid malignancy. It occurs sporadically and in a familial form as a component of multiple endocrine neoplasia type II syndrome.6 It is characterized by production of calcitonin. On ultrasound, it is a hypoechoic nodule with coarse shadowing calcifications. Involved lymph nodes also contain calcifications.6
Anaplastic carcinoma is a highly aggressive thyroid cancer with peak incidence in the sixth to seventh decades. It carries the worst prognosis.6 Patients usually present late with obstructive symptoms such as dyspnea, dysphagia, and laryngeal nerve palsy. On ultrasound, it appears as an ill-defined infiltrative mass demonstrating necrosis and dense amorphous calcifications with internal flow on color Doppler. The involved nodes are hypoechoic and necrotic. Extracapsular spread with infiltration of the trachea, esophagus, and perithyroid soft tissues is common.6
Papillary thyroid carcinoma
Thyroid nodules occur often in young women and can be discovered during pregnancy. The decision to biopsy is no different than in a nonpregnant woman. However, if thyroid cancer is diagnosed during pregnancy, surgery can be delayed to after delivery for papillary and follicular carcinoma. Delaying surgery for poorly differentiated thyroid cancer may adversely affect prognosis. Radioactive iodine is contraindicated during pregnancy and lactation. The management of thyroid cancer in pregnancy is complicated and requires a solid multidisciplinary team approach, which may need referral to a larger medical center with experience and resources to handle such cases.
Neamaalla S, Kalboush E, Solis M. Suspicious Thyroid Nodule in Pregnancy. J Am Osteopath Coll Radiol. 2019;8(2):34-36.