Thursday, April 7, 2011

Diagnosing Pediatric Thyroid Cancer: Imaging Studies

Imaging studies reveal the malignant potential and the extent of disease, and they provide an anatomical roadmap for surgical planning. The following are the imaging studies with the highest yield.

Ultrasonography:  The safest and most widely available imaging technique, is the first-line screening diagnostic test in all pediatric patients with thyroid nodules. In particular, children with a history of radiation exposure should be observed with serial ultrasonography. 
  • Nodules that enlarge even a few millimeters should undergo FNAB.
  • Ultrasonography is useful in differentiating solid nodule or mass from cystic lesions and in revealing nonpalpable lesions. Many investigators consider cystic lesions to be benign lesions that represent hemorrhage into, or degeneration of, an adenomatous nodular goiter.
  • A solid nodule is more likely to be malignant; however, up to 50% of malignant lesions may have a cystic component, and approximately 8% of cystic lesions represent malignancies.
  • Ultrasonography reveals critical information regarding the risk of benign versus malignant disease. Benign features on ultrasound include multiple, solid isoechogenic or nonechogenic lesions and a uniform peripheral halo. Malignant features include a thick irregular halo.
  • Color-Doppler sonography may aid in the diagnosis in patients with hyperfunctioning nodules (hot on scintigraphy and usually benign histologically), indicating an intensive vascular flow within a highly vascularized lesion and no visible flow through the remaining suppressed thyroid gland. Color-Doppler sonography is also valuable in distinguishing a cystic lesion (with no vascular flow) from a solid neoplasm (with intranodular flow).
  • One of the most helpful capabilities of ultrasonography is guidance of percutaneous needle biopsy.

Radionucleotide scan (scintigraphy): Thyroid scintigraphy is most useful in revealing tissue function in thyroglossal duct cysts (eg, ensuring that thyroid tissue in the normal location is functioning) and in diagnosing ectopic thyroid. However, thyroid scintigraphy has not proven worthwhile in distinguishing malignant from benign disease.
  • Classic hot nodules show uptake only in the nodule area of the thyroid and are associated with about a 6% incidence of malignancy. Harach et al (2002) wrote that untreated hot nodules can progress to carcinoma. 
  • Surgical treatment is advisable for all children and adolescents with autonomously functioning thyroid nodules because of the risks of hyperthyroidism and thyroid carcinoma.
  • Cold nodules are usually benign adenomas, although, in children, a larger number of them are carcinomas. Solid lesions that are cold on scintigraphy are malignant in about 30% of children.

  • Total-body radioactive iodine (RAI) scans often reveal pulmonary nodal metastases, which are missed on radiography.

CT Scans
  • Noncontrast CT scans can be helpful in patients with substernal extension, local invasion, or lymph node metastasis. 
  • At initial evaluation, approximately 20% of children have pulmonary metastasis that can be revealed by either chest radiography or CT scan.
  • Children have a much higher incidence of pulmonary involvement (spread to or metastatic thyroid cancer disease) than adults.
  • The CT lung findings, which usually consist of diffuse miliary spots and, less often, infiltrating nodules, are often also best noted with RAI scans.

Author: Mark E Gerber, MD, FACS, FAAP  Clinical Assistant Professor of Otolaryngology, University of Chicago, Pritzker School of Medicine; Section Head, Pediatric Otolaryngology-Head and Neck Surgery, NorthShore University HealthSystem  

Co-Author:  Brian Kip Reilly, MD  Assistant Professor of Otolaryngology and Pediatrics, Department of Otolaryngology, Children's National Medical Center, George Washington University School of Medicine 

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