Introduction

Thyroid nodules are very common and may be observed by ultrasonography (US) in 50% of the adult population. Thyroid malignancy is relatively rare and is diagnosed in approximately 25,000 patients per year in the United States (1-4). Because ultrasound features alone are not sufficiently specific to exclude malignancy, fine needle aspiration (FNA) biopsy of the thyroid gland is the most cost effective test to definitively evaluate thyroid nodules (5). FNA has high sensitivity and specificity in diagnosing malignancy and thus should be performed early in the evaluation of thyroid nodules (5-6). In experienced hands, FNA is diagnostic approximately 85% of the time. More recently FNA biopsy performed under ultrasound guidance has significantly improved the accuracy (5). There are several reasons for non-diagnostic specimens, including inadequate sampling, incorrect needle placement, inexperienced pathologists or operators, and variable diagnostic criteria for adequacy. The needle lumen size is another variable which may affect sample adequacy. With a small lumen there may not be a sufficient sample for diagnosis, and a larger needle diameter may dilute the aspirate with red blood cells making interpretation of the specimen difficult. Current FNA procedures use needles raging from 21 to 27 gauge (5,7-9). The overall number of FNA biopsy passes necessary to obtain an adequate sample varies. Some suggest an increase in the number of passes yields a lower false negative rate. Others claim more punctures creates more reactive changes within the nodule such as hemorrhage, fibrosis, cystic changes, vascular thrombosis, and even nodule infarction (5,7). There have been very few published studies assessing the most effective needle size or the number of passes needed for thyroid FNA biopsy. Therefore, we compared the adequacy rates between 22 and 25 gauge needles, and the number of passes needed for ultrasound guided FNA biopsy of thyroid nodules.

Materials and Methods

Administration This was a designed retrospective study performed on all thyroid biopsies done at our institution beginning December 2007 through June 2008.

Procedures All FNA biopsies were performed by one of four radiologists with varying levels of experience. (AK 22 years, ES 25 years, SK 15 years, DI 2 years). The patients are positioned supine with their necks extended over a rolled towel. All procedures were performed free-hand under real-time sonographic guidance with a 7.5 Mhz linear array transducer. For each procedure the radiologist randomly chose between using a 22 or 25 gauge needle for each pass. The tip of the needle was placed into the nodule using real time sonographic guidance. The biopsy was performed with a to and fro motion until the hub of the needle filled with fluid or for a maximum of 3 minutes. Three consecutive passes where made into each nodule, with a new needle being used for each pass. After each pass, the FNA material was placed on appropriately labeled glass slides, smeared, fixed in Cytolyt fixative, and was stained with the papanicolaou stain method for immediate interpretation by an onsite laboratory cytoprepatory technician. The material was then sent to pathology to be interpreted for adequacy by one of two experienced cytotechnologists. If adequacy was achieved the procedure was terminated. If more samples were needed, two additional passes where made into the nodule using the above technique, for a maximum of five total passes into each nodule. When preparing the slides from the fourth and fifth passes, the FNA material was flushed from the needle, combined, and cytocentrifuged into a pellet. This was then placed into Cytolyt fixative for Thin Prep (Hologic-Cytyc, Boxborough, Mass) slide preparation method.Cytology specimen evaluation for Adequacy All thyroid nodule cytology specimens were preliminary reviewed by a cytotechnologist for initial adequacy. The adequacy categories were assigned on the basis of criteria given in Table 1. Material was considered adequate according to the following criteria: 10 or more groups of well-preserved follicular cells present with 5 or more cells per group, as defined by the Papanicolaou Society of Cytopathology. (7) For each pass the cytotechnologist recorded if the specimen was adequate. The cytotechnologists were unaware of the needle size used for each pass. A final diagnosis was rendered by one of four pathologists within 24 to 48 hours following review of the material prepared for interpretation. The size of each nodule was recorded on the basis of its largest diameter. Nodules were characterized as solid, complex (more than half of the nodule was solid), or predominantly cystic (more than half of the nodule was cystic). The number of needle passes and the size of the needle used for each pass were recorded. The number of nodules biopsied, age of the patients, and the female/male distribution were also recorded. When the cytology specimen was adequate for diagnosis, the three diagnostic categories were as follows: benign (colloid nodule, goiter, thyroiditis), suspicious for malignancy, or malignancy.

Statistical Analysis Summary data are presented as means, or counts and percentages. Between-group comparisons of non-parametric data were made by calculating the chi-square test of independence or Fisher’s exact test. All values are two-tailed and p-values ≤ 0.05 were considered statistically significant.

ResultsPatient and Nodule Characteristics Over the 6 month period December 2007 through May 2008, 61 patients (12 males and 49 females) ranging in age from 29 to 82 years (mean = 50.5) were referred for ultrasound guided biopsy of thyroid nodules. In total, 83 nodules were sampled, and 16 patients underwent biopsy on two or more nodules during their encounter. Ultrasound examination demonstrated 61 solid nodules (range 0.7- 4.2 cm, mean 1.5 cm), 17 complex nodules (0.8-4.6 cm, mean 2.1 cm), and 5 cystic nodules (1.8- 2.8 cm, mean 1.8 cm). The final diagnoses were: 73% benign; 7% suspicious for carcinoma; 6% carcinoma; and 14% were non-diagnostic.

Needle pass and size analysis Using our technique, on the first pass, a 22 gauge needle was used for biopsy 75 times and 36 (48%) of those specimens were adequate for diagnosis. A 25 gauge needle was used 8 times and a satisfactory specimen was achieved in 4 (50%) specimens. The overall adequacy rate on the first pass was 48%. The difference between using a 22 versus a 25 gauge needle was not statistically significant (p = 1.0). On the second pass, a 22 gauge needle was used for biopsy 55 times and 23 (42%) were sufficient for diagnosis. A 25 gauge needle was used on the remaining 28 attempts and 11 (39%) were satisfactory for diagnosis. The overall adequacy rate on the second pass was 41%. The difference between using a 22 versus a 25 gauge needle was not statistically significant (p = 0.82). On the third pass, a 22 gauge was used for biopsy on 30 FNA biopsy attempts, and 16 were adequate (53%) for diagnosis. A 25 gauge needle was used on the remaining 53 attempts and 20 (38%) proved adequate for diagnosis. The overall adequacy rate on the third pass was 43%. The difference between using a 22 versus a 25 gauge needle was not statistically significant (p = 0.17). An adequate sample was obtained following 3 passes in 51 nodules, yielding an overall adequacy of 61%. In addition, overall analysis of the needle size demonstrated that 22 gauge needles yielded an adequate sample in 47% of the biopsy specimens, while 25 gauge needles yielded 38%. Among the remaining 32 nodules that required additional passes, 31 underwent biopsy, with one patient refusing additional sampling due to pain. Because the biopsy samples from the fourth and fifth needle pass were combined, adequacy for each pass was not recorded. However, the size of the needles used for the fourth and fifth passes was recorded. In 10 nodules, only 22 gauge needles were used, and in 6 instances (60%) an adequate sample for diagnosis was obtained. In 12 nodules only 25 gauge needles were used and 9 (75%) samples yielded sufficient material for diagnosis. In 9 nodules, both 22 and 25 gauge needles were used, and 5 (55%) yielded specimens adequate for diagnosis. Overall, of the 31 nodules requiring additional passes, adequate material for diagnosis was obtained in 20 nodules, yielding an adequacy rate of 65% (Table 2). The overall adequacy rates combing all the passes were as follows: using a 22 gauge needle, there were 81 adequate specimens and 89 inadequate for diagnosis. Using a 25 gauge needle, there were 44 adequate specimens and 57 inadequate for diagnosis. Overall, the difference between using a 22 versus a 25 gauge needle was not statistically significant (p = 0.51) when compared using chi-square analysis.

Discussion There have been numerous recently published articles describing ultrasound features of thyroid malignancy in hopes

to define which ultrasound characteristics are most predictive of malignancy (1-4, 9,10). To date, no single feature carries both a high sensitivity and high positive predictive value for thyroid cancer. The Society of Radiologists in Ultrasound (SRU) convened a consensus conference in 2005 to sort through this complex topic in order to define general recommendations regarding how to manage thyroid nodules detected by ultrasound (2) (Table 3).

Currently, FNA biopsy remains the diagnostic test of choice when evaluating thyroid nodules for malignancy. It carries nearly no morbidity and is the most cost effective procedure available (5). In addition, there has been a demonstrable reduction in the number of patients undergoing surgery for benign thyroid nodules, an increase in the prevalence of malignancy in pathologic thyroid specimens obtained at surgery, and a demonstrable savings to the health care system (11).

However despite its many advantages, ultrasound guided FNA biopsy has some serious limitations, including a specificity of 65%, and a positive predictive value ranging from 33 to 85% depending on the skill of the operator and pathologist. In addition, FNA biopsy has a rate of inadequate specimens that ranges from 1 to 15% in different centers (7,12). An FNA that does not provide a diagnostic specimen should be repeated, and if it remains inadequate, the current recommendation by most experts is to advise the patient to undergo surgery (2,7,10).

The major cause of a non-diagnostic thyroid FNA specimen is the failure to aspirate a sufficient number of cells necessary for diagnosis. (7) Currently, there are no universally accepted guidelines for needle size in the technique of US guided FNA biopsy of the thyroid (5-8). The use of small bore needles may result in too few cells aspirated or poor sampling of the tissue within the nodule (5,13). On the other hand, one of the main problems with using large bore needles is the concern that the interpretation of the cytology will be obscured by red blood cells (5,13). In our experience, we most often used a 22 gauge needle to begin the procedure and if the sample was bloody, then a 25 gauge needle was utilized on subsequent passes. One might also infer that using a larger bore needle may be more painful then a smaller needle, however, when asked, patients did not seem able to perceive a difference in pain when switching from a larger to a smaller gauge needle.

Using two different needle sizes, we reviewed FNA biopsy results in 83 consecutively evaluated nodules at our institution. We found that both 22 and 25 gauge needles can be used to obtain FNA biopsy specimens from thyroid nodules, as there is no statistical significance difference in the adequacy rates between the two sizes. This is similar to the results described by Tangpricha, et al. who compared 21 and 25 gauge needles and found that although a larger bore needle yielded a more cellular sample, it did not produce a higher adequacy rate (5). In addition, a study by Hanbidge and colleagues also found no significant difference in the sample adequacy rates between 23 and 27 gauge needles (8).

With the use of a large bore needle, there is the possibility for a “too bloody” sample for interpretation. However, using cytocentrifugation technique obviates this concern. When thyroid biopsy aspirates are directly flushed into a cytopreservative, the obscuring red blood cells are removed by lysis, which enhances diagnostic yield of large bore needles. In our study, this technique was employed in the 31 nodules undergoing additional FNA biopsy, and showed no significant difference when using exclusively a 22 or 25 gauge needle. In addition, using this technique a sufficient sample was obtained in 65% of the nodules, which was higher than the 61% adequacy rate using the thin prep slide for each individual pass. Thus, the most advantageous procedure may be a thyroid biopsy with a large bore needle flushed into a cytopreservative. This would allow a maximally cellular specimen with the least amount of red blood cell interference. These sentiments have been echoed by Tangpricha in their 2001 study (5), and may be a topic of future study.

In our investigation we saw no significant difference in the adequacy rates performed between the first three passes, with the highest being achieved on the first pass at 48%. The overall sample adequacy rate of 61% following three passes, was much lower than those reported by Redman in 2006, who noted that a total of three needle passes provided an accuracy rate of 98% and included a 90% rate on the first pass (7). This may in part be due to a difference in diagnostic criteria used for the studies as well as the technique and size of the needles utilized which was not specified. Our study also demonstrated that an average of 3.6 passes was needed to acquire an adequate specimen for interpretation, which is similar to that obtained by Redman who reported 3.8 passes (7). It is important to note however, that using our method of three passes, plus an additional two if necessary we achieved an overall diagnostic rate of 86% which is within the acceptable rate of diagnostic samples as reported in the literature (2-5).

It has been reported that immediate interpretation with the use of an onsite cytotechnologist or cytopathologist may affect the number of passes needed to obtain diagnostic material (11). However, our study has shown that immediate interpretation is not essential for all FNA thyroid biopsies. Following three consecutive biopsies, 61% of the FNA biopsies yielded sufficient sample after immediate interpretation, and after five attempts using the combined technique and no immediate interpretation, 86% of the FNAs were sufficient for diagnosis. This is similar to the findings reported in earlier studies which demonstrated no statistically significant difference in adequacy rates for US-guided thyroid nodule FNAB with and without immediate cytopathologic analysis (8,11).

In conclusion, both 22 and 25 gauge needles can be utilized to obtain FNA biopsy samples from thyroid nodules. In addition, beginning the procedure with a larger needle and switching to a smaller needle when a more bloody sample is encountered does not compromise adequacy rates. This study also suggests that using our technique, four needle passes may be performed prior to cytological assessment and that it is not essential for the cytopathologist to attend the FNA biopsy of the thyroid.

Acknowledgments: A special thanks to the ultrasound technologists and the cytotechnologists for data collection and to Dr. Robert Jarski for statistical assistance.

Bibliography 1. Vandermeer F, Wong C. Thyroid nodules: When to biopsy. Journal of Applied Radiology. 2007; Vol 36. No. 3:8-19.2. Frates M, Benson C, Charboneau JW, et al. Management of Thyroid Nodules Detected at US: Society of Radiologists in Ultrasound Consensus Conference Statement . Radiology 2005;237:794-800.3. Hoang J, Lee W, Lee M, et al. US Features of Thyroid Malignancy: Pearls and Pitfalls. RadioGraphics 2007;27:847-860.4. Moon WJ, Jung S, Lee J, et al. Benign and Malignant Thyroid Nodules: US Differentiation—Multicenter Retrospective Study- For the Thyroid Study Group, Korean Society of Neuro- and

Head and Neck Radiology. Radiology 2008; 247: 762 - 770.5. Tangpricha V, Chen B, Swan N, et al. Twenty One Gauge Needles provide more Cellular Samples than Twenty Five Gauge Needles in Fine Needle Aspiration Biopsy of the Thyroid but may

not Provide Increased Diagnostic Accuracy. Thyroid 2001; 11: 973-976.6. Bennedbaek F, Hegedus L. Management of the solitary thyroid nodule: Results of a North American Survey. J Clin Endocrinol Metab 2000;85:2493-2498.7. Redman R, Zalaznick H, Mazzaferri E, et al. The impact of assessing specimen Adequacy and Number of Needle Passes for Fine Needle Aspiration Biopsy of Thyroid Nodules. Thyroid

2006; 16: 55-60.8. Hanbidge A, Arenson A, Shaw P, et al. Needle Size and sample adequacy in ultrasound guided biopsy of thyroid nodules. Can Assoc of Rad J 1995; 46 No. 3: 199-201.9. Strauss E, Iovino A, Upender S. Simultaneous Fine- Needle Aspiration and Core Biopsy of Thyroid nodules and other superficial head and neck masses using Sonographic Guidance. AJR

2008; 190: 1697-1699. 10. Yeung M, Serpell J. Management of the Solitary Thyroid Nodule. The Oncologist 2008;13:105–112. 11. O’Malley M, Weir M, Hahn P, et al. US-guided Fine-Needle Aspiration Biopsy of Thyroid Nodules: Adequacy of Cytologic Material and Procedure Time with and without Immediate

Cytologic Analysis. Radiology 2002; 222:383–387.12. Yang G, Liebeskind D, Messina A. Ultrasound guided fine-needle aspiration of the thyroid assessed by ultrafast Papanicolaou stain: Data from 1135 Biopsies with a two- to six year

followup. Thyroid 2001;11:581-589.13. Hamburger JI, Hamburger SW. Fine Needle biopsy of thyroid nodules: Avoiding the pitfalls. NY State J Med 1986;86:241-249.

Figure 1. Ultrasound demonstrating FNA biopsy of a right thyroid nodule using a 25 Gauge needle

Figure 2. Ultrasound demonstrating FNA biopsy of a isthmus nodule using a 22 Gauge needle

American Osteopathic College of Radiology 2008 Annual ConferenceHilton Head, South Carolina

Correlation Between Needle Size and Sample Adequacy Rates in Ultrasound-Guided Fine Needle Aspiration Biopsy of Thyroid Nodules

Table 1. Adequacy Criteria for Thyroid Nodule FNA Biopsy

Adequacy Rating Criteria Needed

Satisfactory≥10 epithelial groups (≥5 cells per group)

No obscuring factors

Well preserved cells

Unsatisfactory*≤10 epithelial groups with lack of cystic components, colloid, or evidence of thyroiditis

Obscuring factor affecting ≥ 75% of groups*Only one of these two criteria needed to be met to render an unsatisfactory result.

Table 2. Summary Table of Pass Attempt, Number of Attempts, Needle Size and Adequacy Rates

Pass 1 Pass 2 Pass 3 Passes 4 and 5

22 gauge 75 (47%) 55 (42%) 30 (53%) 10 (60%)

25 gauge 8 (50%) 28 (39%) 53 (38%) 12 (75%)

Adequacy rate= 48%

Adequacy rate= 41%

Adequacy rate= 43%

22 and 25 gauge needles= 9 (55%)

Overall adequacy rate for the fourth and fifth passes= 65%

Overall adequacy rate after three passes = 61%

Grand total adequacy rate after five passes = 86%

Table 3. Biopsy Criteria adapted from SRU Consensus Guidelines for US-guided FNA of thyroid nodules >1cm 2

US Feature Nodule Size Biopsy?Microcalcifications ≥ 1cm Strongly Consider FNA

Solid (or almost entirely) or coarse calcification

≥1.5 cm Strongly Consider FNA

Mixed solid and cystic or almost entirely cystic with a

solid mural component

≥ 2cm Consider FNA

Substantial Growth since prior ultrasound

Consider FNA

Presence of abnormal lymph nodes

Should prompt FNA of lymph node and/or ipsilateral

noduleAlmost entirely cystic with none of the above findings and no substantial growth

since prior US

FNA probably unnecessary

Diffusely enlarged gland with multiple nodules of

similar appearance

FNA unlikely necessary

Multiple Nodules Consider FNA of ≥1 with selection prioritized on basis of criteria listed above*

*Majority opinion holds that selection for biopsy should be based on nodule features rather than sizeMinority opinion holds that the larges nodule should undergo FNA, and selection of other nodules should be based on US characteristics

FNA= Fine Needle Aspiration; SRU= Society of Radiologists in Ultrasound; US= Ultrasound

25 Gauge 22 Gauge David Isaacs, DOEli Shapiro, DO