The guideline begins with the fundamentals. Thyroid ultrasound is indicated whenever a patient presents with enlargement or atrophy of the gland, or when cystic, solid-cystic, or solid nodules are suspected, whether solitary or multiple. The technical core of the examination is a high-frequency linear-array probe operating between 9 and 16 megahertz, a range chosen because shorter wavelengths provide the fine spatial resolution needed to resolve the millimeter-scale architecture of the thyroid and its nodules. Patients are positioned supine with the shoulders elevated on a pillow and the head resting on the bed, hyperextending the neck to expose the anterior and lateral compartments. For nodules hidden laterally, the patient is rolled onto the left or right side. Transverse sections of both lobes, with the isthmus aligned horizontally, yield transverse and anteroposterior measurements, while sagittal planes provide the longitudinal diameter; the guideline explicitly notes that measuring the longitudinal diameter of normal thyroid tissue is unnecessary, a small but telling instruction aimed at trimming wasted scan time.

What must appear in the report is specified with equal rigor. The document sets normal reference values: a major axis of 4.0 to 5.5 centimeters, a transverse diameter of 2.0 to 2.5 centimeters, an anteroposterior diameter of 1.0 to 1.5 centimeters, and an isthmus thinner than 0.4 centimeters. Beyond gland size, reports must record each nodule’s lobe or isthmic location, whether it is solitary or multiple, its cystic or solid composition, its echogenicity, morphology, and margins, and the presence of punctate echogenic foci, the tiny bright specks that often correspond to the microcalcifications associated with papillary carcinoma. Cervical lymph nodes must be assessed for enlargement or abnormal architecture, and where color Doppler is available, blood flow within the gland and around nodules should be documented. The guideline adds two clinical pearls: abnormal neck lymph nodes should prompt a search for same-sided thyroid lesions, and cysts above the isthmus deserve evaluation for a thyroglossal duct origin, while lateral neck cysts may instead represent branchial cleft cysts or cystic lymphangiomas.

The heart of the guideline is its refined version of the Thyroid Imaging Reporting and Data System, or TI-RADS, the risk-stratification framework first proposed by a Chilean group in 2009 and since adapted by radiology societies in Korea, China, Europe, and the United States. Rather than endorsing any single existing version, the CACA authors synthesized multiple standards into an improved classification built on six ultrasound features of malignancy: solid composition, marked hypoechogenicity, irregular margins or extrathyroidal extension, a taller-than-wide shape in which the nodule’s height equals or exceeds its width, microcalcifications, and enhanced blood flow signals. The number of malignant features present determines the category, and the category determines management, creating a direct pipeline from pixel patterns to clinical action.

The resulting categories span the full spectrum of risk. Category 0 describes normal ultrasound findings in clinically suspicious patients who need additional testing; Category 1 is a normal thyroid requiring no follow-up. Category 2 covers benign nodules with a malignancy risk of zero percent, where follow-up is optional. Category 3 nodules, probably benign with a single malignant feature and a malignancy probability of five percent or less, warrant repeat imaging in six months or fine-needle aspiration biopsy when clinically indicated. Category 4 is the suspicious middle ground, subdivided by feature count: 4a nodules with two malignant features carry a 6 to 30 percent risk, 4b nodules with three or four features carry 31 to 80 percent, and 4c nodules with five or six features reach 81 to 95 percent. For any Category 4 nodule measuring at least half a centimeter, the guideline recommends biopsy; smaller nodules are followed instead. Category 5, with a malignancy probability above 95 percent, is reserved for lesions accompanied by ultrasound features of definite metastatic cervical lymph nodes and points directly to surgery, while Category 6 denotes biopsy-proven malignancy managed by surgical resection or ablation.

Beyond conventional grayscale imaging, the guideline devotes detailed sections to two advanced techniques. Contrast-enhanced ultrasound (CEUS) involves injecting microbubble contrast agents into a peripheral vein to visualize microvascular perfusion in real time. The protocol is strikingly specific: SonoVue dry powder is reconstituted with 5 milliliters of saline to create a sulfur hexafluoride suspension, injected at 2.4 to 4.8 milliliters per dose through the superficial elbow vein and chased with a saline flush, while Sonazoid is prepared with 2 milliliters of saline and dosed at 0.6 to 0.8 milliliters. A timer starts at injection, the dynamic enhancement of the lesion is recorded as video, and quantitative software can then extract parameters such as arrival time, time to peak, peak intensity, and area under the curve. Qualitative assessment focuses on the lesion margin, shape, enhancement direction, intensity, and uniformity. CEUS is indicated for distinguishing benign from malignant nodules, assessing nodules after biopsy, and evaluating lesions before and after ablation therapy.

Yet the guideline is candid about the limits of contrast imaging. Its primary value lies in determining whether the solid components of complex cystic-solid nodules have a blood supply, which guides puncture targets. Because papillary thyroid carcinomas, the most common thyroid malignancy, often show poor perfusion, CEUS alone cannot reliably separate benign from malignant nodules, a limitation the authors state plainly. Ultrasound elastography, the second advanced technique, faces similar constraints. Elastography applies internal or external mechanical excitation, static or dynamic, and exploits the physics of elastodynamics to map how tissue deforms, thereby inferring stiffness, a property that tends to increase in malignant tissue. Three implementations are described: real-time elastography, shear wave elastography, and acoustic radiation force impulse imaging, assessed qualitatively, semiquantitatively, or quantitatively. But pulsation from the adjacent carotid artery contaminates measurements, and the thyroid’s small size makes it difficult to frame comparable regions of interest, so the guideline judges elastography of limited value for benign-versus-malignant differentiation, positioning it mainly for assessing nodule rigidity and monitoring tissue before and after radiofrequency ablation.

The most operationally detailed section concerns ultrasound-guided fine-needle aspiration biopsy, the procedure that converts imaging suspicion into a cytological diagnosis. For solid hypoechoic nodules larger than one centimeter, biopsy may be considered routinely. For nodules under one centimeter, the guideline enumerates specific triggers: ultrasound signs of malignancy such as suspected papillary, medullary, or undifferentiated carcinoma; malignant-appearing neck lymph nodes; childhood radiation exposure; RET oncogene variants as in multiple endocrine neoplasia type 2 or familial medullary carcinoma; dynamic enlargement or increasing blood flow on follow-up; and a patient’s strong desire for pathological or genetic answers. Contraindications are equally explicit, including severe bleeding tendency, unstable carotid plaques at risk of embolization, uncooperative patients, nodules indistinguishable from follicular tumors on imaging, and lesions smaller than 5 millimeters or in technically inaccessible sites.

The procedural choreography reflects decades of accumulated practice. After reviewing images, confirming coagulation safety, and obtaining informed consent, the operator scans with a high-frequency probe, disinfects the field, and anesthetizes the track with 1 to 2 percent lidocaine. Under real-time guidance, the needle enters from the probe’s lateral edge, kept parallel to the probe’s long axis so the shaft remains visible while avoiding major vessels. Sampling follows one of two methods: the negative pressure technique, in which a 5 milliliter syringe maintains 1 to 2 milliliters of suction through roughly 10 to 20 needle excursions, deliberately targeting calcified or otherwise suspicious areas; or the capillary siphoning method, in which a 21 to 23 gauge needle is moved within the nodule and left briefly to let cells wick into the bore. Specimens are fixed in 95 percent ethanol or liquid-based preservation medium for cytopathology, immunohistochemistry, or genetic testing. Complications are managed by protocol: bleeding demands immediate needle withdrawal and pressure, infection is rare and treated with antibiotics, and pain is typically mild and self-limiting.

The guideline closes by looking forward. Its authors frame the document as a standardized, integrative framework harmonizing conventional imaging, refined TI-RADS stratification, contrast-enhanced ultrasound, elastography, and evidence-based biopsy recommendations into a single decision pathway. The next frontier, they argue, lies in artificial intelligence for automated nodule detection and characterization, molecular and contrast-based biomarkers for noninvasive risk prediction, and maturing elastographic and fusion imaging techniques, all validated across multiple institutions. If those technologies mature as hoped, the humble 9-to-16-megahertz probe may evolve from a diagnostic camera into a personalized risk-prediction engine, reducing unnecessary surgeries for benign nodules while catching the aggressive few that truly need treatment.

Subject of Research: Standardized ultrasound imaging protocols and risk stratification for diagnosing thyroid tumors

Article Title: CACA technical guidelines for ultrasound imaging diagnosis of thyroid tumors

Article References: Wei, X., Li, A., Wu, W., Jing, X., Wu, J., Liu, M., Cheng, W., Li, P., Li, Q., Wang, Y., Zhou, J., & Zhu, J. (2026). CACA technical guidelines for ultrasound imaging diagnosis of thyroid tumors. Holistic Integrative Oncology, 5(1), Article 51. https://doi.org/10.1007/s44178-026-00263-y

Image Credits: AI Generated

DOI: 10.1007/s44178-026-00263-y

Keywords: thyroid nodules, ultrasound imaging, TI-RADS, CACA guidelines, contrast-enhanced ultrasound, elastography, fine-needle aspiration biopsy, thyroid cancer, risk stratification, cervical lymph nodes, medical imaging, clinical guidelines