Applicazioni cliniche del B-flow twinkling sign nello studio del carcinoma papillifero della tiroide

INTRODUCTION. The thyroid nodule represents one of the most common situations in ultrasound (US) examination of the neck and often occasional finding. Infact is a particularly frequent disease, with a prevalence in the general population between 20 and 50% (prevalence of malignancy reported in literature between 5 and 20%). The malignancy of thyroid represents about 1% of all cancers and are steadily increasing with approximately 20000 new cases per year in the United States. Papillary thyroid carcinoma (PTC) is the most common form (over 80% of thyroid carcinomas). The PTC is characterized by indolent course and by a low mortality rate and is therefore associated, in most cases, with a slow progression and a low mortality. PTC cells also have a particular attitude for iodine concentration and, therefore, are highly susceptible to an effective treatment with radioactive iodine (I-131). However, the ability to uptake the 131-I is lost by about 1/3 of the patients in the disease course, which implies a considerable worsening of the prognosis. Fundamental is the role of diagnostic imaging, which can help identify early primitive carcinoma as well as any distant metastases sites both in staging and in follow-up. In particular US stands as a diagnostic method of choice for the study of thyroid nodular pathology. The "Ultrasound Consensus Conference Statement” of 2005 showed the following parameters to be tested: microcalcifications, irregular margins, absence of halo, predominantly solid composition, intranodular vascularity, hypoechogenicity. Particularly important is the microcalcifications search whose presence leads to an increase of about three times the risk of malignancy. The microcalfications represent the most specific sign of PTC but with low sensitivity (35 percent). B-flow Imaging (BFI) is a new imaging technique, which is not based on the Doppler principle and allows the direct visualization of blood flow in grey scale. During evaluation and characterization of microvascular abnormalities of suspicious nodules, recently it is identified a new sign that we called ultrasound B-flow twinkling sign (BFI-TS), with similar characteristics to the color-Doppler TS observed in renal and ureteral lithiasis. The sign is characterized by a small and quick sparkle produced by a solid, not homogeneous and stationary object as the thyroid microcalcifications that are formed from the aggregation of primary psammoma bodies (PBS), having high reflecting power. Aim of our study was to assess patients afflicted with PTC for pre-surgical staging by B-mode ultrasound examination integrated by color-Doppler analysis and B-flow imaging, researching this sign also in ipsilateral and contralateral laterocervical lymph nodes towards the thyroid lesions. MATERIALS AND METHODS. 37 patients (age: from 21 to 74 years, average age: 42.2 ± 9.3 years; 11 males and 26 females) with known PTC were undergone to a preoperative US evaluation of the thyroid parenchyma and latero-cervical lymph nodes. US and BFI examinations were performed with Philips IU22 and GE Logiq 9 systems with a 9-14 and 6-8 Mhz linear erray transducer. Examinations performed separately by two radiologist. The following US features were recorded for each nodule: size, parenchymal composition, echogenicity, presence or absence of halo, margin appearance and presence of absence of microcalcifications. The following US features were recorded for each lymph node: round shape (ratio of short to long axis > 0.5), absence of echogenic hilum, microcalcifications, cystic changes and peripheral vascularization. BFI imaging has evaluated the presence of the BFI-TSs present within the lymph node under consideration. Lymph node localization was carried out according to the segmentation of laterocervical stations as reported in the literature. Positive patients to traditional US B-mode method and/or the BFI-TS were undergone to ipsilateral laterocervical lymphadenectomy, the others to follow-up with postoperative baseline thyroglobulin dosage and after stimulation with recombinant TSH and US evaluation of laterocervical LN stations. RESULTS. The specificity and sensitivity of the BFI-TS for the PTC with ≥ 4 BFI-TS are respectively 97% and 89%, significantly higher than the values obtained by US conventional findings and also respect to reported values in literature. Respect to the evaluation of latero-cervical lymph nodes the BFI-TS presents values of sensitivity (83%) and specificity (100%) higher than the other parameters of the traditional US examination (presence of cystic component and microcalcifications, evidence of metastasis in patients suffering PTC with very low sensitivity values: 23 % and 8 %). DISCUSSION. The punctuate calcifications on US represent the most reliable indicators for the assessment of malignancy because they correspond to PBS (psammoma bodies), laminated calcified structures, most commonly found in neoplasms such as meningioma, papillary carcinoma of the ovary and PTC. The BFI appears to be able to detect the microcalcifications generated by PBS in solid thyroid nodules and in thyroid metastatic lymph nodes through finding BFI-TSs. The BFI-TS has allowed in our study to identify a number of microcalcifications significantly higher than US B-mode examination: 36 BFI-TS positive thyroid nodules (4 or more signs/scan), compared to 24 identified by US B-mode. Cytology showed that 34 of 36 BFI-TS positive thyroid nodules were malignant (94%) and 2 were benign (6%). 18 PTC-associated microcalcifications were detected only by the BFI-TS and not by US B-mode, so the BFI-TS is more sensitive than US-B mode in detection of PBS (sensitivity: 89% vs 42%) indicating that the nodules with at least 4 signs/scan are highly suspicious for malignancy. The BFI-TS allows to identify the presence of microcalcifications generated by aggregation of PBS and aggregates of colloid crystals in lymph node metastasis of PTC with higher sensitivity compared to conventional US. Only the presence of microcalcifications and cystic component (US B-mode features) shows a specificity comparable to that of the BFI-TS, but with a significatively lower sensitivity (respectively 8 and 23% vs 83% of the BFI-TS). The BFI imaging, often chosen only for the study of vascular pathologies, can be applied to nodular thyroid disease both in diagnosis and staging, allowing the evaluation also of the laterocervical lymph nodes, first site of PTC metastasization with higher sensitivity and specificity than traditional US B-mode.