Practice Guidelines for Fine Needle Aspiration Cytology of the Thyroid
By: Dr. Manon Auger

As standardization and establishment of practice guidelines have always been one of the key CSC mission statements, the CSC Executive has recognized the need for practice guidelines for various non-GYN specimens to complement the existing document entitled “Canadian Society of Cytology guidelines for practice and quality assurance in Cytopathology”. The latter document is a reference for the practice in Cytopathology in Canada; it places, however, greater emphasis on GYN cytology and does not address in depth the particularities of other specific body sites.

It was decided that thyroid and breast would be addressed first. I was involved in gathering data and coordinating the feedback related to fine needle aspirates (FNAs) of the thyroid, and Dr. Moosa Khalil is currently organizing the activities for fine needle aspirates of the breast and will report to the membership in the next few months.

The procedure followed for FNAs of thyroid was as follows: the CSC executive asked a panel of Canadian Cytopathologists and Cytotechnologists (Drs. Y. Bedard, G.K. Nguyen, V. Chen, H. Yazdi, L. Kapusta, M. Auger and Mrs. L. MacDonald) to provide feedback on the existing document titled “Guidelines of the Papanicolaou Society of Cytopathology (PSC) for the examination of fine-needle aspiration specimens from thyroid nodules” (1) .

All the panelists found that the above-mentioned guideline document, albeit not perfect, was excellent, and it was agreed that re-writing a new thyroid guideline document was unnecessary. Therefore, the CSC executive endorsed the “Guidelines of the Papanicolaou Society of Cytopathology for the examination of fine-needle aspiration specimens from thyroid nodules” (1) as the CSC thyroid guideline document at its last CSC Executive meeting on May 18 2002 in Calgary. The following comments related to a few specific issues, derived from the feedback from the Canadian panelists, however, should be taken into consideration when using the above mentioned guideline document:

I. Specimen adequacy
The PSC guidelines do not specify a certain required minimal number of follicular cells to determine specimen adequacy; rather, it emphasizes the importance of assessing the amount of colloid present in the specimen.

Most of the Canadian panelists thought, as reflected in the literature, that follicular cells should be present in a specimen for it to be adequate. However, opinions differ as to a specific number of cells. A laboratory may choose to require a specific cell count as one of its own criteria for adequacy. References for cell requirements include the following:

    Goellner et al JR (2) : 5-6 groups, each with 10 or more cells
    Nguyen GK et al (3) 10 groups, each with 20 or more cells
    Hamburger JI (4): 6 groups on at least 2 of six aspirates
    Kini (5) : 8 groups, on at least 2 slides

II. Cyst contents
Relevant to the above discussion on specimen adequacy, most Canadian panelists were uncomfortable with the PSC statement that “ a cystic lesion that yields numerous macrophages with scant or no follicular cells may be reported as consistent with benign thyroid cyst” (1). Instead, most Canadian panelists preferred to report such cystic lesions (with scant or no follicular epithelium) as “non-diagnostic”, and to describe the findings in the specimen (i.e. macrophages), stating that they are consistent with cyst contents but that the underlying nature of the cyst cannot be determined in view of the absence or scantiness of the follicular epithelium.

III. Follicular neoplasms
All the Canadian panelists disagreed with the PSC (albeit optional) stance to use the diagnostic categories “follicular neoplasm, favour benign” versus “follicular neoplasm, favour malignant”. They all thought it impossible to reliably distinguish between benign versus malignant follicular neoplasm on FNA material, and that the diagnostic category of “follicular neoplasm”, without further qualifier, should be used instead.

IV. Diagnostic reporting: Need for an equivocal/indeterminate category
Some of the Canadian panelists pointed out the need for an equivocal diagnostic category for cases in which the findings were not clearly indicative of a benign or malignant condition (e.g. a few atypical cells in an otherwise hypocellular specimen). Therefore, the following broad diagnostic categories were suggested:
On behalf of the CSC, I would like to thank the Canadian panelists who took the time and care to provide their feedback for these thyroid guidelines.

REFERENCES
  1. The Papanicolaou Society of Cytopathology Task Force on Standards of Practice. Guidelines of the Papanicolaou Society of Cytopathology for the examination of fine-needle aspiration specimens from thyroid nodules. Diagn Cytopathol 1996;15:84-89. (also simultaneously published in Mod Pathol 1996;9:710-715)

  2. Goellner JR, Gharib H, Grant CS, Johnson DA. Fine needle aspiration cytology of the thyroid. Acta Cytol 1987; 31:587.

  3. Nguyen GK, Ginsberg J, Crockford PM. Fine-needle aspiration biopsy cytology of the thyroid. Its value and limitations in the diagnosis and management of solitary thyroid nodules. Pathol Annu 1991; 26:63.

  4. Hamburger H, Husain M. Semiquantitative criteria for fine-needle biopsy diagnosis: reduced false-negative diagnosis. Diagn Cytopathol 1988;4:14.

  5. Kini SR. Guides to clinical aspiration biopsy: Thyroid. Igaku-Shoin, second edition, New York, 1996, 521 p.