Macrofollicular encapsulated variant of papillary thyroid carcinoma as a potential pitfall in histologic and cytologic diagnosis. A report of three cases.
BACKGROUND
Macrofollicular encapsulated papillary carcinoma (MEPC) is a variant of papillary carcinoma with a favorable clinical course. Its characteristic histologic pattern could be mistaken for that of an adenoma or hyperplastic nodule. Fine needle aspiration of this neoplasm may not show the particular nuclear features of papillary carcinoma, so the cytologic diagnosis may be benign.


METHODS
Three paradigmatic cases of MEPC with different histologic patterns, diagnosed as a follicular neoplasm using fine needle aspiration biopsy (FNAB) are described. Preoperative cytology showed scattered clusters of thyrocytes with prominent nuclear pleomorphism and irregularities and focal oxyphilic changes mixed with colloid and aggregates of typical thyrocytes. The histologic picture exhibits small, neoplastic foci showing a microfollicular structure within an encapsulated neoplasm with a macrofollicular pattern. In microfollicular areas obvious nuclear pseudoinclusions were seldom observed.


CONCLUSIONS
MEPC represents a challenging tumor subtype that infrequently shows the pathognomonic cytologic characteristics of papillary carcinoma, and therefore it is much more difficult to diagnose with a FNAB. Nuclear pleomorphism and irregularity of the nuclear membrane of thyrocytes are clues to this variant, although in some cases a clear-cut preoperative diagnosis cannot be made.
Fadda
Guido
G
Division of Anatomic Pathology and Histology, Catholic University of the Sacred Heart, Largo Francesco Vito, 1 00168, Rome, Italy.
Fiorino
Marilena C
MC
Mulè
Antonino
A
LiVolsi
Virginia A
VA
D000236:Adenoma / Q000473:pathology; D000328:Adult; D001707:Biopsy, Needle; D002291:Carcinoma, Papillary / Q000473:pathology*; D018265:Carcinoma, Papillary, Follicular / Q000473:pathology; D002467:Cell Nucleus / Q000473:pathology; D003937:Diagnosis, Differential; D003951:Diagnostic Errors; D006801:Humans; D013964:Thyroid Neoplasms / Q000473:pathology*; D016606:Thyroid Nodule / Q000473:pathology