A Partly Cystic Thyroid Nodule With Four Small Groups
A 38-year-old woman has a 1.2 cm mixed solid-cystic right thyroid nodule with smooth margins and no microcalcifications. Ultrasound-guided FNA yields 2 mL of brown fluid and the aspirator makes four smears plus a cell block. The smears show abundant colloid, numerous hemosiderin-laden macrophages, and four groups of six to eight follicular cells each. A minority of the follicular cells have mildly enlarged, pale nuclei with rare longitudinal grooves; there are no nuclear pseudoinclusions, no powdery chromatin, and no psammoma bodies. The residual solid component was not separately sampled. The patient's mother had a total thyroidectomy for a 'thyroid tumor' in her forties, and the patient asks to skip further testing and go straight to surgery.
1. Assign a Bethesda category and justify it, distinguishing it from the adjacent categories.
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Category: nondiagnostic (Bethesda I). Not AUS/FLUS, not benign.
- Adequacy for a thyroid FNA requires roughly six groups of at least ten well-visualized follicular cells, on at least two slides (or about 60 follicular cells on one slide if only one slide is available). Four groups of six to eight cells falls short.
- Abundant colloid and macrophages do not make a cystic lesion benign. They are expected in cyst fluid and say nothing about the wall or the residual solid component, which was never sampled.
- Why not AUS: the nuclear features offered (mild enlargement, rare grooves) are nonspecific - grooves occur in benign nodules, Hashimoto thyroiditis, and papillary carcinoma. Calling AUS attributes meaning to changes that were never interpretable in the first place, and AUS carries roughly a 10-30% risk of malignancy and triggers repeat or molecular testing anyway. Nondiagnostic more honestly describes the specimen.
- Why not benign: a benign call on a cyst with an unsampled solid component risks a false-negative on exactly the tissue that matters.
- Report should state the limitation and recommend repeat with sampling of the solid component and cyst wall.
2. The patient requests surgery now. Build the argument for repeat FNA, including how you would make the repeat more likely to succeed.
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Repeat FNA is the correct next step; surgery now is not justified on these data.
- The nodule is 1.2 cm with low-risk sonographic features; the only risk factor is a vague family history of a 'thyroid tumor,' which is not equivalent to a documented carcinoma syndrome. Diagnostic lobectomy without a cytologic diagnosis risks overtreatment of a benign cyst and undertreatment if the nodule is not the only focus.
- Interval: repeat in roughly 3-6 months, which allows the cyst to reaccumulate and avoids confusing post-procedure change.
- How to improve yield: aspirate the residual solid component and the wall, not just the fluid; use ultrasound guidance; use rapid on-site evaluation so the aspirator knows within minutes whether adequate follicular groups have been obtained and can make another pass instead of ending the procedure with four small groups.
- If a second attempt is nondiagnostic, the reasonable options are molecular testing on the collected material or diagnostic lobectomy - discuss both, and note that neither is urgent.
- Document the conversation: the patient's preference is respected by offering an accelerated plan, not by abandoning adequacy standards.
3. The repeat aspirate yields six groups of ten to fifteen follicular cells with mild nuclear enlargement and rare grooves, and no other atypia. What is your interpretation and how do you communicate uncertainty?
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Interpretation: AUS/FLUS (Bethesda III), with a comment that the atypia is mild and focal.
The specimen now meets the adequacy threshold, so the question shifts from 'can I interpret this' to 'does this pattern mean anything.' The changes are those of a follicular-pattern lesion with slight nuclear atypia - not the powdery chromatin, pseudoinclusions, and irregular contours that would justify suspicious for malignancy.
Communication points for the report and the clinician:
- AUS is a category of uncertainty, not a diagnosis; state the risk range (roughly 10-30% malignancy) so the clinician can weigh options.
- Acceptable next steps are repeat FNA in about 6-12 months or molecular testing; a benign molecular result supports observation, an abnormal one supports surgery.
- Explicitly note what is not present (no pseudoinclusions, no psammoma bodies, no irregular nuclear contours) so the reader understands the reason for the hedge.
- Flag the sonographic context (1.2 cm, smooth margins) - a small, low-risk nodule tolerates surveillance better than a larger or sonographically suspicious one.