Hürthle cell carcinoma (oncocytic carcinoma) is a malignant thyroid neoplasm arising from oncocytic (oxyphilic) transformation of thyroid follicular cells. It is recognized as an independent entity in the WHO 2022 classification. Although previously considered a variant of follicular carcinoma, it is separately classified due to its distinct molecular profile, treatment response, and prognosis. Its most important clinical feature is low response rate to radioactive iodine (RAI) therapy and high FDG avidity.
Age Range
50-70
Peak Age
60
Gender
Female predominant
Prevalence
Rare
Hürthle cells are thyroid follicular cells that have undergone oncocytic transformation due to excessive accumulation of mitochondria. Because the cytoplasm is packed with mitochondria, cells become large, eosinophilic, and granular in appearance. This mitochondrial density increases cellular metabolic activity, reflected as high glucose metabolism (FDG avidity) on FDG-PET — this is inversely proportional to iodine-concentrating capacity loss (low NIS expression), known as the flip-flop phenomenon. The tumor typically presents as a solid, homogeneous, hypoechoic mass; vascular invasion is critical for diagnosis due to the follicular pattern (capsular and/or vascular invasion). On ultrasound, it appears as a homogeneous hypoechoic solid structure with absence of microcalcifications and prominent halo. Due to dense mitochondria in Hürthle cells, MRI typically shows low-intermediate signal on T2 — paramagnetic effects of mitochondria shorten T2 relaxation. On CT, it typically appears as a well-defined, solid, homogeneously enhancing mass.
The most characteristic imaging finding of Hürthle cell carcinoma is the simultaneous demonstration of cold nodule on radioactive iodine scintigraphy (NIS loss) and high uptake on FDG-PET (dense mitochondria → increased glucose metabolism). This inverse relationship is called the 'flip-flop phenomenon' and is pathognomonic for Hürthle cell neoplasms. Response to RAI therapy is not expected and FDG-PET should be preferred for metastasis screening.
Homogeneous hypoechoic solid thyroid nodule surrounded by a prominent thick incomplete halo. Microcalcifications are typically absent — this feature is an important distinguishing point from papillary carcinoma. The nodule is usually wider-than-tall in shape, but taller-than-wide appearance may occur in large lesions. Smooth or slightly lobulated margins are typical; extrathyroidal extension is seen in advanced disease.
Report Sentence
A __ x __ mm homogeneous hypoechoic solid nodule is seen in the [right/left] thyroid lobe. A prominent thick incomplete halo is present. No microcalcifications are identified. TI-RADS score is assessed as __.
On color Doppler, intranodular vascularity is increased with an irregular (chaotic) pattern. Perinodular vascularity may also be present but the intranodular component is dominant. Reflects high metabolic activity and neovascularization. Low resistive index (RI <0.7) on spectral Doppler is a finding favoring malignancy.
Report Sentence
On Doppler examination, markedly increased intranodular vascularity is seen in the nodule; flow pattern is irregular/chaotic. Perinodular flow is also present. Findings are assessed as suspicious for malignancy.
Cold nodule (no or markedly decreased uptake) on I-123 or I-131 scintigraphy. Hürthle cells cannot concentrate iodine because they lose sodium-iodide symporter (NIS) expression. This characteristic is the reason for low response rate to RAI therapy and is critically important in treatment planning. Surrounding normal thyroid tissue shows normal or increased uptake.
Report Sentence
On I-123/I-131 thyroid scintigraphy, no radiopharmaceutical uptake is seen in the region corresponding to the known nodule in the [right/left] lobe (cold nodule). Findings are consistent with Hürthle cell neoplasm/follicular neoplasm; response to radioactive iodine therapy is not expected.
High FDG uptake on FDG-PET/CT (SUVmax usually >5, often >10). This high metabolic activity reflects the dense mitochondrial accumulation and increased glucose metabolism in Hürthle cells. This inverse relationship with radioactive iodine uptake is called the 'flip-flop phenomenon' — FDG avidity increases in iodine-negative tumors. FDG-PET is more sensitive than RAI scintigraphy for metastasis screening.
Report Sentence
High FDG uptake is seen in the known nodule in the [right/left] thyroid lobe on FDG-PET/CT (SUVmax: __). When evaluated together with cold nodule on radioactive iodine scintigraphy, it demonstrates the flip-flop phenomenon. Findings are consistent with Hürthle cell neoplasm.
On contrast-enhanced CT, a well-defined, solid, homogeneously enhancing mass in the thyroid lobe. It enhances less than surrounding normal thyroid tissue (thyroid normally enhances intensely due to high iodine content). Capsular structure may be prominent. Size is usually >2 cm at diagnosis. In advanced stages, extrathyroidal extension, tracheal deviation, or cervical lymphadenopathy may accompany. Necrosis is generally not observed (unlike anaplastic and poorly differentiated carcinomas).
Report Sentence
On contrast-enhanced CT, a __ x __ mm well-defined, solid, homogeneously enhancing mass is seen in the [right/left] thyroid lobe. It is relatively hypodense compared to surrounding thyroid parenchyma. No necrosis or calcification is identified.
Solid mass showing low to intermediate signal intensity on T2-weighted sequences. It is hypointense relative to normal thyroid tissue. This low T2 signal reflects the paramagnetic effects of dense mitochondrial accumulation in Hürthle cells and may be a differentiating point from other thyroid neoplasms (papillary carcinoma generally shows intermediate to high T2 signal).
Report Sentence
On T2-weighted sequences, the mass in the [right/left] thyroid lobe shows low to intermediate signal intensity. It is hypointense relative to normal thyroid parenchyma, and this finding may be consistent with Hürthle cell neoplasm with dense mitochondrial content.
High signal on DWI and low signal on ADC map (true diffusion restriction). Reflects the high cellularity of Hürthle cell carcinoma. ADC values are typically <1.2 x 10⁻³ mm²/s and may show lower values than benign Hürthle cell nodules (despite overlap).
Report Sentence
Diffusion restriction is seen in the mass in the [right/left] thyroid lobe on DWI (ADC: __ x 10⁻³ mm²/s). Consistent with high cellularity and suspicious for malignancy.
Criteria
Capsular invasion only, no vascular invasion or <4 foci. Good prognosis (>95% 10-year survival). RAI is generally not needed after surgery.
Distinct Features
Well-defined on US, predominantly intact capsule, thick but complete halo. No surrounding tissue invasion on CT/MRI. FDG-PET shows uptake in primary tumor but no distant metastasis or lymphadenopathy. Differentiation from benign Hürthle cell adenoma is possible only on pathological specimen.
Criteria
Extensive vascular invasion (≥4 foci) and/or extrathyroidal extension. Poor prognosis — high risk of distant metastasis (lung, bone). Requires aggressive surgery + adjuvant therapy.
Distinct Features
Irregular margins, incomplete or disrupted capsule, signs of extrathyroidal extension on US. Surrounding structure invasion (trachea, esophagus, recurrent laryngeal nerve proximity) on CT/MRI. Primary tumor + cervical lymphadenopathy + possible distant metastases (lung nodules, bone lesions) on FDG-PET.
Criteria
Capsule intact but vascular invasion present in intracapsular or extracapsular vessels. Intermediate prognosis — risk stratification based on number of invasion foci (<4 foci: low risk, ≥4 foci: high risk).
Distinct Features
Well-defined mass on US and CT/MRI — difficult to differentiate from minimally invasive type on imaging. Vascular invasion is generally not demonstrable radiologically and is recognized only on pathological specimen. Therefore, it is not possible to distinguish minimally invasive and encapsulated angioinvasive types based on imaging findings.
Distinguishing Feature
Hürthle cell adenoma and carcinoma appear virtually identical on US — both are homogeneous hypoechoic solid nodules with thick halo. Distinction is NOT RELIABLE radiologically; capsular/vascular invasion is assessed on pathological specimen. Nodules >4 cm, irregular margins, and significant FDG avidity are clues favoring malignancy.
Distinguishing Feature
Papillary carcinoma typically shows MICROCALCIFICATIONS (psammoma bodies), taller-than-wide shape, and irregular margins. Hürthle cell carcinoma generally lacks microcalcifications, presents as a homogeneous hypoechoic nodule with thick halo and smoother margins. Papillary carcinoma may be iodine-avid (responds to RAI therapy), while Hürthle cell carcinoma is iodine-negative.
Distinguishing Feature
Medullary carcinoma also appears as a hypoechoic solid nodule but may contain coarse calcifications (amyloid + calcium deposition). Elevated calcitonin is pathognomonic in medullary carcinoma; calcitonin is normal in Hürthle cell carcinoma. Medullary carcinoma originates from C cells, while Hürthle cell carcinoma originates from follicular cells.
Distinguishing Feature
Follicular carcinoma appears similar to Hürthle cell carcinoma on US but generally has higher T2 signal on MRI (intermediate-high). Dense mitochondrial accumulation in Hürthle cell carcinoma lowers T2 signal. Additionally, follicular carcinoma may be iodine-avid (responsive to RAI therapy), while Hürthle cell carcinoma is iodine-negative.
Urgency
urgentManagement
surgicalBiopsy
NeededFollow-up
specialist-referralTreatment of Hürthle cell carcinoma is total thyroidectomy + central lymph node dissection. Since response to RAI therapy is low (10-30% iodine uptake), FDG-PET should be preferred in adjuvant therapy planning. Lobectomy may be sufficient in minimally invasive type, but definitive diagnosis is made on surgical specimen pathology. FNA is reported as 'Bethesda IV — follicular neoplasm/Hürthle cell neoplasm' and definitive benign-malignant distinction cannot be made cytologically. Prognosis is poor in widely invasive type — high risk of distant metastasis (lung, bone). FDG-PET/CT should be preferred over RAI scintigraphy for metastasis screening. Thyroglobulin is used as a tumor marker in follow-up, but anti-thyroglobulin antibodies are frequently positive in Hürthle cell carcinoma and may affect measurement.
Hurthle cell carcinoma is an aggressive thyroid malignancy. Adjuvant RAI therapy is less effective due to low RAI uptake. Treatment is total thyroidectomy + lymph node dissection. Risk of hematogenous metastasis (bone, lung) is high. FNA reports as Bethesda IV (Hurthle cell neoplasm).