- FNAB is the criterion standard in the diagnostic workup of adult thyroid nodules. Several studies report efficacy in the pediatric population.
- High diagnostic accuracy with experienced pathologists improves the selection of pediatric patients for surgery and is an adjunct to guide further management.
- Ultrasonography can be a useful guide for percutaneous needle biopsy when the lesion is difficult to identify with palpation.
- FNAB is often not practical in children younger than 10 years; therefore, excisional biopsy (surgical removal of nodule or tumor mass) under general anesthesia is recommended in this population.
- Using molecular polymerase chain reaction (PCR) studies on FNAB aspirate is mostly beneficial in the clinical research setting. It can be used in a very small number of patients for diagnostic purposes, but it remains expensive.
Significant Histologic Findings Review
Follicular adenoma is the most common cause of solitary nodules of the thyroid in the pediatric population. Adenomas are solitary, well circumscribed, and well encapsulated and are composed of glandular epithelium. Most are histologically follicular but are occasionally papillary.
- Most thyroid cancers (papillary, follicular, anaplastic) originate from follicular cells. Medullary thyroid cancers (25% hereditary vs 75% sporadic) are of C-cell (calcitonin-producing) origin.
- Thyroid malignancies in children are usually well-differentiated papillary or papillary-follicular subtypes, but all histologic types have been observed.
- Papillary carcinoma lesions, which comprise an estimated 72% of pediatric thyroid cancers, are irregular, solid, or cystic masses that arise from follicular epithelium.
- Microscopically, pediatric thyroid cancer masses or nodules have fronds of epithelium and distinct uniform cells with rare mitoses. Most contain both papillary and follicular components. The cells contain pink, finely granular cytoplasm with large pale nuclei (Orphan Annie eyes) and nuclear grooves.
- Psammoma bodies (rounded calcified deposits) can be found in approximately 50% of the lesions.
- Pediatric Papillary Carcinoma has frequent lymphatic and pulmonary metastases.
- Follicular carcinoma lesions, which comprise 18% of pediatric thyroid cancers, are usually encapsulated and have highly cellular follicles and microfollicles with compact dark-staining nuclei of fairly uniform size, shape, and location. Pathologic diagnosis can be made only when invasion of the capsule, adjacent glands, lymphatics, or blood vessels is seen.
- Pediatric Follicular Carcinoma metastasizes intravascularly to the lungs, brain, and bones. When a portion of the cells in the tumor are found to be oxyphilic (Hürthle cells), it is called a Hürthle cell tumor. These lesions tend to have a less favorable prognosis.
- MTC or Pediatric Medullary Thyroid Cancer arises from the thyroid parafollicular or C cells, which secrete calcitonin and are derived from the neural crest and ultimobranchial body. Hyperplasia of the C cells is thought to represent a precancerous state.
- Histologically, MTC is composed of columns of epithelial cells and dense stroma that typically stain for amyloid and collagen. The nuclei are hyperchromatic, and mitoses are common. The cells have a fusiform shape and may form a whirling pattern. Calcifications are observed in 50% of these lesions.
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