# Hürthle Cell Lesions of the Thyroid

> Hurthle cell thyroid lesions in NEET-PG Pathology: oncocytic change, Bethesda IV reporting, invasion criteria and WHO 2022 oncocytic carcinoma terms.

- Canonical URL: https://prepelephant.com/topics/neet-pg/pathology/thyroid-hurthle-cell-lesions
- Exam / course: NEET-PG · Subject: Pathology
- Publisher: PrepElephant (https://prepelephant.com) — Prepared and reviewed by the PrepElephant Academic Review Team
- First published: 2026-10-02
- Last updated: 2026-10-02
- How to cite: "Hürthle Cell Lesions of the Thyroid", PrepElephant, https://prepelephant.com/topics/neet-pg/pathology/thyroid-hurthle-cell-lesions

## Direct answer

Hürthle cells — properly oncocytic cells — are thyrocytes stuffed with mitochondria, giving abundant granular eosinophilic cytoplasm, large nuclei and prominent nucleoli. When an aspirate is composed overwhelmingly of them without papillary architecture or a lymphoid background, Bethesda reports "Hürthle cell lesion/neoplasm", falling in category IV with a malignancy risk on the higher side of the follicular-neoplasm band. Malignancy is still decided the follicular way — by capsular or vascular invasion on resection — yielding minimally invasive, encapsulated angioinvasive and widely invasive oncocytic carcinomas. The WHO 2022 thyroid classification retired "Hürthle cell carcinoma" in favour of oncocytic carcinoma of the thyroid, acknowledging that these tumours travel molecularly apart from conventional follicular tumours, with RAS plus mitochondrial-DNA changes, frequent chromosomal gains, and worse clinical behaviour including poor radioiodine avidity.

## What you must remember

- **Oncocyte biology:** mitochondria-packed cytoplasm (hence the granular pink), best confirmed ultrastructurally; in Hashimoto thyroiditis Hürthle cell change is reactive and sits in a lymphocytic background.
- **Bethesda handling:** a monomorphic oncocytic aspirate without papillary features is "Hürthle cell neoplasm", category IV; a mixed oncocytic and lymphoid background suggests Hashimoto or Warthin-like papillary carcinoma instead.
- **Carcinoma criteria:** invasion, not cytology — capsular and/or vascular invasion on the resection specimen defines oncocytic carcinoma; thorough capsular sampling (the entire capsule in suspicious cases) is the practical determinant of minimally invasive disease.
- **WHO 2022 terminology:** oncocytic carcinoma of thyroid replaces Hürthle cell carcinoma; oncocytic tumours are excluded from the NIFTP (noninvasive follicular thyroid neoplasm with papillary-like nuclear features) concept by definition.
- **Molecular profile:** RAS-family mutations are commonest, with EIF1AX, PAX8-PPARG and mitochondrial-DNA complex-I mutations; TERT promoter mutation signals the worst prognosis and is increasingly reported.
- **Radioiodine behaviour:** oncocytic carcinomas concentrate iodine poorly (lower NIS expression) — the exam-ready explanation for their worse response to radioactive iodine than conventional follicular carcinoma.
- **Markers:** TTF-1, PAX8 and thyroglobulin positive; calcitonin and CEA negative — the medullary carcinoma with oncocytic change is the classic mimic resolved by calcitonin.
- **Prognostic drivers:** widely invasive and angioinvasive patterns, older age at presentation, larger size and TERT mutation; the minimally invasive encapsulated tumour without angioinvasion is among the more indolent thyroid carcinomas.

## From aspirate to lobectomy: the decisive margin

A 51-year-old woman has a 3.5 cm solitary solid nodule. FNA shows a monomorphic population of oncocytic cells in sheets and microfollicles — Bethesda IV, Hürthle cell neoplasm. Molecular testing on the aspirate returns a NRAS mutation: compatible with neoplasm, non-committal on invasion. Hemithyroidectomy follows, and the pathologist face-blocks and then entirely embeds the capsule — because the entire question of malignancy lives in that fibrous band.

Blocks show a thick capsule with a mushrooming tumour plug breaching it and, in one vessel at the capsular interface, a tumour thrombus adherent to the wall with fibrin: capsular plus vascular invasion. This is oncocytic carcinoma, encapsulated angioinvasive subtype. Angioinvasion drives completion thyroidectomy and radioiodine administration — with the caveat the tumour may not avidly take it up — plus TSH suppression and lifelong thyroglobulin surveillance. Had the capsule held intact after full embedding, the diagnosis would have been oncocytic adenoma, and surveillance without completion surgery would be defensible. One centimetre of capsule decides; hence the embedding protocol.

## Where students slip

Two slips recur in exams. First, calling Hürthle cells intrinsically malignant: they populate Hashimoto thyroiditis, benign adenomas and papillary carcinoma variants alike — only invasion on resection, or papillary nuclear features in an oncocytic aspirate, moves the needle. Second, the radioiodine question: candidates who answer "follicular and Hürthle carcinomas are treated identically" lose marks; the oncocytic subtype's poor radioiodine response and higher recurrence are exactly why WHO 2022 separated it. A sharp viva differentiator is the oncocytic medullary carcinoma mimic — amyloid and calcitonin staining settle a case that H&E alone can misdirect. Indian practice note: thyroid FNA volumes in Indian laboratories are enormous, and "Hürthle cell neoplasm" reports frequently arrive without molecular add-ons, making capsular-sampling discipline at resection the main quality safeguard.

## Frequently asked questions

### What converts a Hürthle cell tumour into a carcinoma?

Demonstrable capsular or vascular invasion on a fully sampled resection — cytology and aspirate-based testing cannot make the diagnosis.

### What did WHO 2022 rename Hürthle cell carcinoma?

Oncocytic carcinoma of the thyroid, reflecting its distinct molecular profile (RAS, EIF1AX, mitochondrial-DNA mutations) and more aggressive, less iodine-avid behaviour.

### Which Bethesda category covers a monomorphic oncocytic aspirate?

Category IV (follicular neoplasm or suspicious for follicular neoplasm), reported as "Hürthle cell lesion/neoplasm" with a malignancy risk in the 10-30% range.

### Why does oncocytic carcinoma respond poorly to radioiodine?

Reduced expression of the sodium-iodide symporter relative to conventional follicular carcinoma limits iodine uptake, worsening therapeutic response.

### Which mutation predicts the worst prognosis in oncocytic carcinoma?

TERT promoter mutation, associated with recurrence and disease-specific mortality and now routinely reported when tested.