Poorly differentiated thyroid carcinoma (PDTC) is a thyroid malignancy of intermediate aggressiveness, positioned between well-differentiated thyroid carcinomas (papillary and follicular) and anaplastic carcinoma. Diagnosis is made according to the Turin criteria: solid/trabecular/insular growth pattern + mitosis (≥3/10 HPF) or convoluted necrosis or conglomerate nuclear features. It is often diagnosed at an advanced stage and may partially respond to RAI, but prognosis is significantly worse than well-differentiated types.
Age Range
50-70
Peak Age
60
Gender
Female predominant
Prevalence
Rare
Poorly differentiated thyroid carcinoma is an intermediate form arising during the dedifferentiation process of well-differentiated thyroid carcinomas (papillary or follicular). Genetically, BRAF V600E, RAS mutations, TP53, and TERT promoter mutations are frequently co-present — particularly the TERT promoter + BRAF combination indicates aggressive behavior. The dedifferentiation process leads to partial or complete loss of NIS expression, increased cellular proliferation, and suppression of apoptosis. Tumor necrosis results from rapid growth exceeding vascular support capacity — therefore necrotic areas appear as hypodense/hypointense regions on imaging. The solid/insular growth pattern reflects loss of normal follicular architecture and leads to formation of compact cell clusters — resulting in diffusion restriction (high cellularity) and heterogeneous enhancement (necrosis + viable tumor mosaic). PDTC may partially produce thyroglobulin and in some cases may concentrate iodine — this feature is a distinguishing point from anaplastic carcinoma (completely dedifferentiated, no iodine uptake).
The most characteristic imaging finding of PDTC is a large (>4 cm), heterogeneously enhancing thyroid mass containing necrotic areas. The presence of necrosis and frequent extrathyroidal extension distinguishes it from well-differentiated carcinomas, while its ability to partially concentrate iodine and less aggressive invasion pattern compared to anaplastic carcinoma reflects its intermediate position.
Markedly hypoechoic, irregularly marginated, solid or predominantly solid mass. Shows heterogeneous echotexture with internal necrotic/cystic areas. Signs of extrathyroidal extension (capsule disruption, surrounding muscle invasion) are frequently present. Microcalcifications may be found (originating from pre-existing papillary carcinoma component) but are not pathognomonic. Tracheal deviation or compression may be seen with large masses.
Report Sentence
A __ x __ mm markedly hypoechoic, irregularly marginated, heterogeneous solid mass is seen in the [right/left] thyroid lobe. Internal necrotic/cystic areas are present. Signs of extrathyroidal extension [are present/are not identified]. Findings are consistent with aggressive thyroid malignancy.
Markedly increased, chaotic intranodular vascularity on color Doppler. Irregular, tortuous vessels are seen due to neovascularization. Vascularity is decreased or absent in necrotic areas — creating heterogeneous vascular distribution. Peritumoral vascularity is also increased; disrupted vascular pattern is seen in areas of invasion into surrounding structures.
Report Sentence
On Doppler examination, markedly increased chaotic intranodular vascularity is seen in the mass. Vascular voids corresponding to necrotic areas are present. Findings are consistent with aggressive malignant process.
On contrast-enhanced CT, large, heterogeneously enhancing thyroid mass. Solid components enhance prominently, while necrotic areas do not enhance and remain hypodense. Extrathyroidal extension is frequent; invasion of the trachea, esophagus, recurrent laryngeal nerve, and vascular structures (carotid, internal jugular vein) should be evaluated. Cervical lymphadenopathy frequently accompanies — necrotic lymph nodes are findings favoring metastasis.
Report Sentence
On contrast-enhanced CT, a __ x __ mm heterogeneously enhancing mass with necrotic areas is seen in the [right/left] thyroid lobe/bilateral. Extrathyroidal extension with invasion of [trachea/esophagus/vascular structures] [is present/is not identified]. [Number] pathological cervical lymph nodes are identified.
Mass showing heterogeneous signal intensity on T2-weighted sequences. Viable tumor tissue shows intermediate T2 signal, while necrotic/cystic areas show high T2 signal. This heterogeneous pattern reflects the mosaic of solid tumor and necrosis. Extrathyroidal extension appears as intermediate signal tumor tissue extending into surrounding structures on T2.
Report Sentence
On T2-weighted sequences, the thyroid mass shows heterogeneous signal intensity. Hyperintense necrotic/cystic areas are seen among solid components showing intermediate signal.
Markedly high signal on DWI in solid components and low signal on ADC map (true diffusion restriction). ADC values are generally lower than well-differentiated carcinomas (<0.9-1.0 x 10⁻³ mm²/s). Necrotic areas do not show diffusion restriction (high ADC). This diffusion contrast helps differentiate viable tumor from necrosis.
Report Sentence
Marked diffusion restriction is seen in the solid components of the thyroid mass on DWI (ADC: __ x 10⁻³ mm²/s). No diffusion restriction is seen in necrotic areas. Low ADC values are consistent with high-grade malignancy.
High FDG uptake on FDG-PET/CT (SUVmax usually >8-10). Shows higher FDG avidity than well-differentiated carcinomas. Variable iodine uptake is seen compared to RAI scintigraphy — some cases partially concentrate iodine while most are iodine-negative. Lymphadenopathy and distant metastases are also seen as FDG-avid. Necrotic areas do not take up FDG.
Report Sentence
High metabolic activity is seen in the thyroid mass on FDG-PET/CT (SUVmax: __). No FDG uptake is seen in necrotic areas. [Number] FDG-avid cervical lymph nodes and [organ] metastases are identified. High FDG avidity is consistent with poorly differentiated or dedifferentiated thyroid carcinoma.
Criteria
Tumor cells form small round islands (insulae). Most common PDTC subtype. Classic pattern defined by Turin criteria.
Distinct Features
Cannot be specifically differentiated from other subtypes on imaging. Defined pathologically. May appear as a relatively more homogeneous solid mass. Iodine uptake capacity may be higher compared to other subtypes.
Criteria
Tumor cells arrange in trabecular (cord-like) pattern. Often co-exists with insular pattern (mixed pattern).
Distinct Features
Cannot be differentiated from insular variant on imaging. Requires pathological diagnosis. Some studies have reported marginally better prognosis compared to insular variant.
Criteria
Tumor cells grow in solid sheets without forming distinct follicular structures. Generally considered the most aggressive PDTC subtype.
Distinct Features
May appear as a more homogeneous solid mass on imaging (reflecting lack of follicular architecture). Necrosis rate may be higher. FDG avidity may be higher compared to other subtypes. Generally the subtype with lowest iodine uptake.
Distinguishing Feature
Anaplastic carcinoma shows a more aggressive invasion pattern — extensive extrathyroidal extension, tracheal invasion, vascular encasement are more prominent. Calcification is frequent in anaplastic carcinoma (psammomatous or coarse). PDTC is less invasive and may be partially encapsulated. On RAI scintigraphy, anaplastic carcinoma shows NO iodine uptake, while PDTC may partially concentrate iodine.
Distinguishing Feature
Papillary carcinoma usually presents as a smaller, homogeneously enhancing nodule without necrosis. Microcalcifications are very frequent in papillary carcinoma. PDTC is larger, necrotic, and heterogeneous. Papillary carcinoma frequently metastasizes via cervical lymphadenopathy, while PDTC shows both lymphatic and hematogenous spread (distant metastasis more frequent).
Distinguishing Feature
Medullary carcinoma also appears as a hypoechoic solid mass and may contain necrosis; however, coarse calcifications (amyloid deposition) are more frequent in medullary carcinoma. Elevated calcitonin is pathognomonic for medullary carcinoma — calcitonin is normal in PDTC. PDTC may produce thyroglobulin, while medullary carcinoma does not (originates from C cells).
Distinguishing Feature
Thyroid lymphoma usually develops in the background of Hashimoto thyroiditis, appearing as a homogeneously hypodense (CT) or homogeneously hypoechoic (US) mass. Necrosis is less frequent in lymphoma compared to PDTC. Lymphoma spreads by 'encasement' around surrounding tissues, while PDTC shows an invasive destructive pattern. Lymphoma is diagnosed by core biopsy, while FNA can be used for initial evaluation in PDTC.
Urgency
urgentManagement
surgicalBiopsy
NeededFollow-up
specialist-referralPDTC treatment is total thyroidectomy + central and lateral lymph node dissection. Extended surgery is needed if extrathyroidal extension and surrounding structure invasion are present. Response to RAI therapy is variable (30-50% partially concentrate) — if RAI is planned, diagnostic whole-body scintigraphy should be performed. External beam radiotherapy is recommended in locally advanced disease or when residual tumor is present after surgery. Chemotherapy (doxorubicin-based) is used in distant metastatic disease but response rates are low. Tyrosine kinase inhibitors (lenvatinib, sorafenib) are FDA-approved in RAI-refractory cases. Prognosis is worse than well-differentiated carcinomas but better than anaplastic carcinoma — 5-year survival 60-70%, 10-year 40-50%. FDG-PET/CT should be preferred over RAI scintigraphy for follow-up and metastasis assessment.
Poorly differentiated thyroid carcinoma is moderately aggressive with 5-year survival around 60-70%. Treatment is total thyroidectomy + RAI + external radiotherapy. RAI uptake is variable. Distant metastasis (bone, lung) is more common than in differentiated carcinomas. Turin consensus criteria are used for diagnosis.