• Papillary carcinoma composed almost completely of follicles, with classic papillary nuclear features
• First described in 1977 (Am J Surg Pathol 1977;1:123)
• Metastases are usually nodal, not distant, with classic papillary features
• Metastatic tumor to tumor lesions may simulate a thyroid primary (Arch Pathol Lab Med 1999;123:703)

• Suggested to classify encapsulated tumors separately due to their superior prognosis (Cancer 2006;107:1255)
• Recommended to diagnose equivocal cases as well differentiated thyroid tumor of uncertain malignant potential (Int J Surg Pathol 2000;8:181)
• Experts often disagree on diagnosis (Am J Clin Pathol 2008;130:736)

• Same prognosis as typical papillary carcinoma (Arch Surg 2003;138:1362, Cancer 2003;97:1181)

• 22 year old woman with extension to parapharyngeal space (BMC Ear Nose Throat Disord 2006;6:3)
• 46 year old man presenting with pleural effusion (Acta Cytol 2007;51:911)
• 56 year old man with glomeruloid growth pattern (Hum Pathol 2008;39:1540)

• Wide fibrous bands incompletely divide tumor into lobules
• Follicular architecture but papillary cytology
• Usually infiltrative with fibrous trabeculation, psammoma bodies, strongly eosinophilic colloid with scalloping
• Important diagnostic criteria include pseudoinclusions (cytoplasmic invaginations into nucleus), abundant nuclear grooves, ground glass nuclei (Am J Surg Pathol 2004;28:1336); also nuclear clearing, nuclear overlapping and crowding, nuclear enlargement

Follicular epithelial cells have ground glass nuclei and occasional nuclear grooves

Vesicular nuclei and hemorrhage in follicular lumina

Crowded nuclei and scalloped colloid

H&E, HBME1, CK19

H&E, HBME and galectin-3

Contributed by Dr. Mark R. Wick

Images from AFIP:

Wide fibrous bands

Microfollicular and macrofollicular patterns

Macrofollicular formations resemble nodular hyperplasia

Clear cytoplasm

Nuclei are overlapping with empty appearance

Some neoplastic follicles lined by granular acidophilic cells

Clear cell change

Intraluminal colloid

Combined with other tumors:

Follicular pattern of papillary carcinoma at bottom (AFIP)

Various images (AFIP)

Collision tumor with squamous cell carcinoma

Childhood tumor, metastatic to lung

Van Gieson

• Increased cellularity, moderate thin watery colloid with variable eosinophilic colloid
• Cells are in sheets, small acini or syncytial fragments
• Nuclear enlargement, but may lack prominent nuclear features of papillary carcinoma (Am J Clin Pathol 1999;111:216)
• Highly suggestive if syncytial clusters, microfollicular architecture, chromatin clearing and nuclear grooves (Acta Cytol 2006;50:663)
• Ultrafast Papanicolaou stained smears makes clear nuclei more conspicuous (Cancer 2006;108:174)

Cellular aspirates with some microfollicular aggregates, no colloid

Nuclear features are prominent with scrape cytology

Acinar arrangement with intranuclear inclusion

Figure 1

Figure 2

Figure 3

• Low and high molecular weight keratin

• 25-43% have Ras mutations, 3-42% have RET / PTC rearrangements (Am J Clin Pathol 2003;120:71, Hum Pathol 2006;37:824)
• May have PAX8-PPARgamma rearrangement of follicular tumors (J Clin Endocrinol Metab 2006;91:213)
• Only 13% have BRAF mutation (Hum Pathol 2009;40:827)

• Follicular adenoma
• Follicular carcinoma

• Am J Surg Pathol 1983;7:809

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