A scanty thyroid FNA with focal nuclear grooves: adequacy, Bethesda category and next step
A 38-year-old schoolteacher is referred with a 1.8 cm solid, hypoechoic nodule in the right thyroid lobe, TI-RADS 4, no cervical lymphadenopathy and a normal TSH. Ultrasound-guided FNA produces one air-dried and one alcohol-fixed slide. The pathologist counts two clusters of 12–15 follicular cells on one slide and one cluster on the other, with rare nuclear grooves and one possible pseudoinclusion. There is no colloid and no macrophages. The cytotechnologist's screening note reads 'suspicious'. The endocrinologist wants a definitive answer before surgery because the patient wants to avoid a two-stage procedure before her exams. The laboratory follows the Bethesda System and its adequacy policy requires at least six groups of ten well-visualised follicular cells on one slide or across slides; the sample was not examined on-site. A cell block was not prepared.
1. Assign a Bethesda category and justify it, addressing the cytotechnologist's 'suspicious' note.
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The correct category is Bethesda I, unsatisfactory/nondiagnostic. Adequacy requires at least six groups of ten well-visualised follicular cells; this sample contains roughly three groups in total, one slide with only two clusters, and no colloid or macrophages to indicate a satisfactory aspirate.
The rare grooves and one possible pseudoinclusion cannot be evaluated reliably in such a scanty sample. Grooves occur in benign adenomatoid nodules and Hashimoto thyroiditis, and a single 'pseudoinclusion' may be a mimic. The cytotechnologist's 'suspicious' note reflects a legitimate concern but must not determine the category: screening notes should be descriptive, and the pathologist's category must follow the adequacy criteria. Calling this AUS/FLUS would be worse than unsatisfactory, because it implies the atypia was assessable and may push the patient toward surgery on inadequate material.
Report as unsatisfactory with a comment that focal nuclear features were seen but cannot be interpreted, and recommend repeat FNA with rapid on-site evaluation. Communicate directly with the endocrinologist so that the clinical team understands that the sample, not the nodule, is the problem.
2. What is the next step, and would you send molecular testing on this sample?
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Next step: repeat ultrasound-guided FNA with rapid on-site evaluation, using a 25–27 G needle and several passes, preparing both air-dried and alcohol-fixed slides plus a cell block. On-site assessment allows the aspirator to stop only when adequate material is visible, which is the single most effective way to avoid a second unsatisfactory result.
Molecular testing on the current sample is not appropriate. Commercially available thyroid classifiers (ThyroSeq, Afirma GSC) require adequate cellularity of a validated specimen type; a sample with three groups yields an invalid or indeterminate result, wastes money and delays care. The same applies to BRAF V600E testing, which is uninterpretable when tumour cells are sparse.
After the repeat: a benign result leads to ultrasound follow-up; a suspicious or malignant result leads to surgery; a second AUS/FLUS result opens the choice of a molecular classifier or diagnostic lobectomy. Discuss with the patient that a one-stage operation is possible but depends on obtaining a diagnostic sample, not on her examination schedule. If she declines repeat FNA, diagnostic lobectomy with intraoperative frozen section is a defensible alternative, but she should understand the trade-off.
3. The repeat FNA again shows AUS/FLUS. How do you resolve the case, and what quality issues does the original screening note raise?
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Two adequate AUS/FLUS results in a 1.8 cm TI-RADS 4 nodule carry a malignancy risk of roughly 10–30%. Reasonable options are a validated molecular classifier or diagnostic lobectomy; both are accepted, and the choice should reflect access, cost and patient preference. A negative classifier supports surveillance, but it does not reduce the risk to zero, so follow-up ultrasound is still required. A positive classifier or a suspicious repeat would justify surgery. If lobectomy is performed, request serial sections and a synoptic report so that cyto-histological correlation is possible.
Quality issues: the screening note 'suspicious' should never function as a category. It creates anchoring bias and, if the pathologist had followed it, this inadequate sample could have been labelled AUS and the patient might have undergone surgery on insufficient material. Audit the laboratory's unsatisfactory and AUS rates against benchmarks (AUS is generally kept below about 10% of aspirates), review adequacy documentation, and provide feedback and re-training on adequacy criteria. Record the case in the cyto-histological correlation file, and if surgery follows, compare the final histology with both cytology reports.