Thyroid Gland Post Fine Needle Aspiration Biopsy (FNAB)-Related Histologic Changes and Intraoperative Consultation

Post Fine Needle Aspiration Biopsy (FNAB)-Related Morphologic Changes ( Figs. 29-1 through 29-11 )

• FNAB has tremendous utility as first interventional diagnostic procedure relative to a patient with a thyroid mass.

• Diagnostic sensitivity and specificity of FNAB of a thyroid mass is high.

• In many situations, surgical removal is treatment for a thyroid mass lesion irrespective of diagnosis by FNAB.

• FNAB may result in a number of histologic changes in resected thyroid gland that may create diagnostic challenges:

  • Histologic alterations caused by FNAB may lead to an erroneous diagnosis, such as changing interpretation from a benign process to a malignant one.

  • Pathologists must be aware of diversity of changes that may occur induced by FNAB.

• Post-FNAB histologic changes occur in numerous lesions, including adenomatoid nodules, hyperplastic lesions, follicular adenoma and its variants, follicular carcinoma and its variants, and papillary carcinoma and its variants.

• Oncocytic (oxyphilic) cells may be present in a wide variety of thyroid lesions (e.g., adenomatoid nodules, follicular adenoma, follicular carcinoma, papillary carcinoma, others) and are more prone to retrogressive changes secondary to a traumatic event such as FNAB owing to prominence of oxygen-sensitive mitochondria in these cells:

  • Any compromise to oxygen supply of onco­cytic cells may result in retrogressive changes, including:

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      Cyst formation, papillary architecture, hemorrhage, infarction

• Based on type of reaction seen post-FNAB alterations may include acute or chronic type changes:

  • Acute changes usually identified within 3 weeks from FNAB to surgical removal and may include:

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      Hemorrhage with hemosiderin-laden macrophages and granulation tissue:

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        Represent most common findings:

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      Localized follicular destruction

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      Capsular alterations

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      Atypical cytologic features with necrosis and mitoses:

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        Nuclear atypia is reactive or reparative, typically occurs near the needle tract, and includes nuclear enlargement (nucleomegaly), hyperchromasia, prominent nucleoli

  • Chronic changes usually identified more than 3 weeks from FNAB to surgical removal and may include (individually or in combination):

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      Metaplasia:

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        Squamous or oncocytic cells

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        Mucous cell may uncommonly be identified.

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      Infarction

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      Nuclear atypia, including nucleomegaly, hyperchromasia, and prominent nucleoli

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      Cyst formation

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      Papillary architecture

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      Fibrosis

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      Calcifications

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      Hemorrhage (recent and remote in form of hemosiderin-laden macrophages) and/or cholesterol granuloma formation

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      Capsular alterations with pseudoinvasive growth and/or epithelial displacement:

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        May take the form of a needle tract in which there is a linear-appearing “bud” into fibrous capsule

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          Low magnification appearance suggests capsular invasion, but at higher magnification follicular epithelium does not violate capsule.

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          Rather, needle tract composed of dense fibrosis as well as chronic inflammatory cells infiltrate including macrophages and giant cells with or without hemorrhage (recent and remote, latter in form of hemosiderin deposition); cholesterol granuloma formation may be present.

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        Epithelial displacement

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      Vascular alterations, including:

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        Dilated vascular spaces with thrombosis, organization, papillary endothelial hyperplasia (Masson tumor-like reaction), and endothelial cell atypia:

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          May suggest presence of a vascular tumor such as hemangioma or even an angiosarcoma

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          Temporal sequence from the FNAB to surgical removal is an important factor in the interpretation of these findings.

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        Artifactual implantation or “invasion” of tumor cells within endothelial-lined space:

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          In this setting, cells float within vascular lumens and are not adherent to vessel wall and/or have associated fibrin thrombus formation as seen in true vascular invasion.

• Reparative changes may be exuberant, including spindle-shaped cells (fibroblasts) that may simulate a sarcoma and have been referred to as post-FNAB spindle cell nodule.

• Needle tract tumor implantation :

  • Rare occurrence

  • Reported in association with papillary thyroid carcinoma

  • Intervals between FNAB and detection of implantation range from 2 to 131 months

  • Location of carcinoma cells in line of needle insertion include:

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      Subcutis

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      Within strap muscles

  • None of the lesions included lymph node components on pathology.

  • Implanted tumors surgically removed without recurrence at focal sites

Intraoperative Consultation (IOC) (Frozen Section) of the Thyroid Gland ( Figs. 29-12 through 29-20 )

Indications

• Most effective in cases in which fine-needle aspiration biopsy (FNAB) results are suspicious for malignancy (Bethesda V)

• Render a histologic diagnosis.

• Differentiate a benign lesion (e.g., adenomatoid nodule[s], adenoma) from a malignant neoplasm that may require additional surgery (i.e., total or near total thyroidectomy).

• Identification of nonsentinel nodal metastasis:

  • Role of sentinel lymph node sampling not established for thyroid tumors

• Incisional biopsy with intraoperative consultation (IOC) may occur:

  • In patients with unresectable disease (e.g., undifferentiated [anaplastic] carcinoma)

  • To ensure adequacy for diagnosis in certain clinical settings (e.g., unresectable disease) or in relationship to certain tumor types (e.g., hematolymphoid tumors)