Comparing Ultrasound-Guided Fine Needle Aspiration Techniques for Thyroid Nodules - Is The Short Axis Better Than The Long Axis?


 Background: Ultrasound-guided fine needle aspiration cytology (FNAC US) has been proven to be an accurate and efficient tool in thyroid nodule evaluation. Thyroid nodule aspiration can be acquired with either of two techniques: the short axis, in which only the tip of the needle is observed, and the long axis, in which the entire length of the needle is observed. Our retrospective study aimed to compare the adequacy of the two techniques. Methods: FNAC US was performed in 357 thyroid nodules between January 2019 and December 2019. Data on the technique and the diagnostic accuracy were collected. Results: A total of 181 nodules were aspirated using the long axis technique, and 176 nodules were aspirated using the short axis technique. The diagnostic adequacies of the long axis technique were significantly higher than those of the short axis technique. technique (93% versus 83%, respectively, p< 0.001). Conclusion: In our study, the long axis technique provided more accurate cytological evaluation than the short axis technique.


Introduction
Thyroid nodules are very common and are diagnosed in 34% (27% in men, 41.7% in women) of the adult population. The majority of nodules are benign, while 5%-15% of those nodules are malignant. Ultrasonography (US) is the most important diagnostic tool in the workup of thyroid nodules.
The clinical importance of thyroid nodule diagnosis rests with the need to exclude thyroid cancer, which occurs in 7%-15% of cases with correspondence to age, sex, previous exposure to ionizing radiation, family history, and other factors. 3 The most acceptable US classi cation for thyroid nodules is the American College of Radiology Thyroid Imaging, Reporting and Data System (ACR TI-RADS). The score is based on the shape, echogenicity, composition, and margins of the nodule.
In the last decade, the US-guided ne needle aspiration cytology (FNAC) diagnostic method has been the gold standard for cytopathology differentiation between benign and malignant nodules. US-guided FNAC has been shown to have high rates of sensitivity and speci city, as well as diagnostic accuracy. The Bethesda system for reporting thyroid cytopathology (TBSRTC) was set up in 2007 by the National Cancer Institute, which standardized the reporting of thyroid cytopathology. The six diagnostic categories de ned in this system are linked to certain ranges of malignancy risk and clinical management guidelines.
In TBSRTC, inadequate samples are pathologically reported as Category I. This category applies to samples that are nondiagnostic or unsatisfactory due to obscuring blood, overly thick smears, air drying Page 3/9 of alcohol-xed smears, or an inadequate number of follicular cells.
Despite the established e cacy of US-guided FNAC in the workup of thyroid masses, relatively high nondiagnostic (Category I) rates continue to hinder the full potential of FNAC. These rates for ultrasoundguided FNAC in the literature range widely from 2 to 29%. Such nondiagnostic results increase costs, patient stress, and time to diagnosis. Most importantly, studies have shown that initial nondiagnostic samples can harbor a malignancy in 1-4% of cases.
The US-guided FNAC procedure can be performed using either the short axis (perpendicular) or a long axis (parallel) approach to visualize the needle as it is advanced toward the desired nodule. In a short axis approach, the ultrasound transducer is oriented transversely to the thyroid nodule. When the needle is inserted perpendicular to the transducer, it bisects the plain of imaging and therefore appears as a hyperechoic "dot" on the ultrasound screen ( We hypothesized that US-guided FNAC performed on the long axis will produce more accurate results since the needle can be visualized throughout its course. The purpose of this study was to compare the long-and short-axis approaches and the rate of nondiagnostic FNAC results (Category I).

Patients
A retrospective study review was performed on 357 patient les with thyroid nodules who underwent US FNAC in our institution between January 2019 and December 2019.
Medical records, ultrasound ndings, and cytologic results in all patients were retrospectively reviewed.
Thyroid nodule evaluation using ACR TI-RADS was performed prior to FNAC by the attending specialist.
All methods were carried out in accordance with relevant guidelines and regulations.
All experimental protocols were approved by the Ziv Medical Center human ethics Helsinki committee.
Informed consent was obtained from all subjects and/or their legal guardian(s).

US-Guided FNAC Procedure.
US-guided FNAC was performed by two expert physicians with more than 5 years FNAC US guided experience. As a routine, one expert uses the short axis approach, while the other uses the long axis approach. Patients are referred to either expert according to on-site availability.
All FNACs were performed using a 5-12 MHz linear transducer.

Cytologic preparation and diagnosis.
The collected material was expelled on glass slides, smeared and xed in 95% ethyl alcohol immediately following FNAC. Staining was performed using the Papanicolaou method.
An adequate sample was de ned as having at least six clusters of thyroid follicular cells (15- The rate of nondiagnosis (category I) between the two techniques mentioned above were compared, as well as other categories of the samples that were obtained .All slides were reviewed rst by the attending cytopathologist, and subsequently con rmed by chief cytopathologist.

Statistical analysis
For categorical variables, summary tables will provide giving sample size, and relative frequencies .For continuous variables, a summary will provide the arithmetic mean and standard deviation (SD) .Quantitative data are shown as the mean ± standard deviation, whereas numbers and percentage were provided for the qualitative data .Pearson's chi-squared was applied to test the correlations between the study groups for the categorical parameters . AP-value of 5% or less will be considered statistically signi cant .Statistical analyses were performed using SPSS version 25 (SPSS Inc., Chicago, IL, USA).

Data collection:
Patient les were reviewed for ND results (category I) to compare the two techniques .The following data were collected and analyzed: age, sex, anatomic location of the biopsy, thyroid nodule size, biopsy technique, TIRADS and FNA Bethesda results.

Results
A total of 357 patient les were reviewed; 290 (81%) were females, and 67 (19%) males with mean age of 56.9±13.5 years. Demographic data of the two groups is presented in Table 1. No signi cant differences were found between the groups in terms of sex, age and nodule location and ACR-TIRADS scores (table 1  and table 2a and 2b). A total of 357 samples were obtained. 181 in the long axis approach and 176 in the short axis approach. The overall diagnostic adequacy of specimens obtained using the long axis approach, was signi cantly higher than that using the short axis approach (92.8% versus 83.3%, respectively, P=0.006).   Discussion US-guided FNAC is an accurate and effective tool in the workup of thyroid nodules. As mentioned, there are two accepted approaches for thyroid gland biopsy. In this study, we compared the adequacy of the two techniques. As hypothesized, our study showed that performing FNAC US guided using the long axis approach yields fewer ND (category I) results than the short axis (7.2% vs 16.6%).
Although FNAC is a common procedure. Only one prior relatively small sample study has compared the short axis vs long axis approaches for FNAC in the thyroid gland. Kandil  access ultrasound guidance, also stated that long access is associated with improved visibility of the needle tip during vessel puncture. They concluded that this approach helps decrease complications associated with ultrasound-guided central venous catheterization.

Conclusion
In summary, we found that the long axis approach for US-guided FNAC US guidance is independently more accurate and produces signi cantly fewer ND (category I) results than the short axis approach. This is the rst large study comparing the two FNAC US-guided techniques regarding an accurate diagnosis.
Therefore, we suggest to prefer this technique for thyroid nodule FNAC.