Table of Contents
Definition / general | Diagnosis | Prognostic factors | Case reports | Microscopic (histologic) description | Microscopic (histologic) images | Virtual slides | Cytology description | Cytology images | Positive stains | Molecular / cytogenetics description | Differential diagnosis | Additional referencesCite this page: Islam S. Follicular. PathologyOutlines.com website. https://www.pathologyoutlines.com/topic/thyroidfollicularvariant.html. Accessed January 22nd, 2021.
Definition / general
- 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)
Diagnosis
- 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)
Prognostic factors
- Same prognosis as typical papillary carcinoma (Arch Surg 2003;138:1362, Cancer 2003;97:1181)
Case reports
- 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)
Microscopic (histologic) description
- 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
Microscopic (histologic) images
Contributed by Andrey Bychkov, M.D., Ph.D.
Contributed by Mark R. Wick, M.D.
AFIP images
Images hosted on other servers:
Cytology description
- 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)
Cytology images
Images hosted on other servers:
Positive stains
Molecular / cytogenetics description
- 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)
Differential diagnosis
Additional references