A new specially designed needle significantly increases sample yield during fine needle aspiration of breast lesions

Background 

A large and increasing number of women in the western world will at some point during their life be investigated morphologically for lumps in the breast. At present there are two main methods for morphological diagnosis of breast lesions, histopathological examination of surgical or core biopsies and cytopathological examination of fine needle aspirates (FNA). Regarding FNA and core biopsy sampling it is of utmost importance to be aware that the diameter of the sampling needle is correlated to the risk of complications, including needle tract seeding [1]. Core biopsies are often associated with side-effects (e.g. local bleeding), increasing the associated costs of this technique, whereas FNA can be performed with virtually no or minimal side-effects [1], [2]. The time consumption for the histopathological examination is considerably longer than the cytopathological examination, making it difficult to incorporate it in ‘a same day diagnostic procedure’. With FNA the best results are obtained when the cytopathologist is present during, or actually performs the aspiration [2], [3], [4], [5]. In this case the probability of obtaining an adequate sample increases significantly by immediately repeating the procedure if the sample is found to be inadequate or non-diagnostic. By using quick staining techniques a final diagnosis can be assessed within 10min, reducing the waiting time and the anxiety for the patient, all of which is not possible with core biopsy. According to the literature the main rationale for choosing core biopsy instead of FNA is the lower frequency of inadequate specimens with the former [6].

The most frequently reported problem with the FNA technique is thus that the obtained sampling yield is too sparse, which is one of the reasons why this patient-friendly technique has not been accepted worldwide. With this in mind it is quite peculiar that standard needles are used, which are designed for blood sampling or infusion therapy (i.e. for gram quantities) whereas the average aspirated sample is in the milligram range. Standard needles have large quantities of residual spaces between the Luer coupling and the cannula stainless steel tube, where the sample can stick to the surface and coagulate (Fig. 1). The standard needle generally used for FNA has residual spaces and permits volumes of approximately 70mg (as water-filled), when attached to the syringe and ready to use.

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Figure 1 Illustration of a standard needle with a diameter of 0.7mm and a length of 50mm (Sterican B) as well as a standard needle with a diameter of 0.6mm and a length of 25mm (Microlance). The arrows indicate the residual spaces.

The compartments are both ill-matched in size and configured sub-optimally regarding air streaming during ejection (Reynolds number, Bernoulli energy distribution) to yield maximal amounts of sample material. Many experienced FNA operators routinely tap the needle hub against the glass slide to increase the yield. Some even use a small brush to empty the hub of sample. Today almost all operators use standard needles from Becton Dickinson (BD) or B. Braun AG (‘Microlance’ and ‘Sterican’ types). The most commonly used needle types have an outer diameter of between 0.5mm and 0.7mm and a length of between 25mm and 50mm. Ultrasonically guided FNA needles may be even longer, with an outer diameter of up to 0.8mm. A few specialised FNA needles are available, but the minor difference compared to standard needles and the non-existent scientific documentation of their stated benefits might explain their sparse usage.

The aim of this study was to develop a new needle specially designed for FNA, which is intended to decrease the discussed problems to a minimum, and to compare this new needle with standard needles regarding the sampling yield.

Materials and methods 

The specially developed FNA needle (Fig. 2) differs from standard needles in three main aspects:

(a)steeper, modified tip angle

(b)thinner wall-thickness (100μm)

(c)added storage compartment that avoids air streaming disturbing residual spaces (c1, c2).

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Figure 2 Outline of the new 0.6mm needle. a=needle tip angle, b=material thickness and c=storage compartment. c1 and c2 indicate the smooth transition in inner diameter which avoids air streaming disturbing residual spaces.

For this study we performed 499 consecutive aspiration procedures of palpable breast lesions at the Stockholm Breast Clinic, according to a Swedish ethical approval. All male patients and female patients with cystic lesions were excluded from the study. This clinic practices state-of-the-art same day diagnostic procedures, which include physical examination, ultrasound/mammography and morphology-based diagnostics. MRI is added when other imaging techniques failed or resulted in inconclusive outcome. All aspiration procedures were performed by the same sampling operator and cytopathologist (G.A.). The procedures were divided into three protocols using three different needles (outer diameter):

(a)Standard 0.6mm (BD, Microlance) (n=255)

(b)Standard 0.7mm (B. Braun, Sterican) (n=144)

(c)The new needle 0.6mm (n=100).

No differences in inclusion criteria were evident between the protocols. After physical examination of the breast lesions the skin around the puncture site was cleaned with ethanol. Subsequently the palpable lesion was fixed with one hand and punctured with the other using a standard syringe pistol hand-piece (Cameco, Medical Ltd., London, UK), equipped with a 10-ml syringe. When the needle was placed in the lesion low pressure was created and the needle was passed an average of 10–15 times through the lesion in different directions. The passes included both rotational and longitudinal movements. Before finally retracting the needle the low pressure was equalised to the ambient pressure by spontaneous release of the syringe plunger. The yield of sample was assessed by weighting the syringe and the needle using a precision balance (type Sartorius CP64, resolution 100μg) before sampling, after sampling and after ejection of the sample (V.E.). Finally, the cell material was examined by ejecting it onto a glass slide, where it was fixed, quick-stained and examined cytomorphologically.

Results 

The average total amounts of harvested sample were 10.5mg, 25.2mg and 20.2mg of which 20%, 35% and 28%, respectively, was present in the syringe using the standard 0.6mm needle, the standard 0.7mm needle and the new needle, respectively. The rest of the material was located in the needle. The average ejected sampling yield originating from the syringe and the needle using the standard 0.6mm and 0.7mm needles was 2.6mg and 7mg, respectively (Table 1). The average ejected sampling yield from the new needle was 7.8mg. Thus the new needle provided three times more material than a standard needle of the same diameter. The needle efficiency, i.e. the percentage of the total harvested material which was ejected onto the slide after sampling, was 25% for the standard 0.6mm needle, 28% with the standard 0.7mm needle and 39% with the new needle.

Table 1. Ejected sample amount and needle efficiency

	Type	n	Average ejected sample (mg)	t-test	Needle efficiency (%)	25% and 75% quartile (mg)
	Standard 0.6mm needle
	All cases	255	2.6	***	25	0.5–3
	No sample in syringe	96	1.6	***	27	0.4–2.2
	Total sample<4mg	89	0.6	***	30	0.3–0.8
	Standard 0.7mm needle
	All cases	144	7	***	28	1.3–8.5
	No sample in syringe	50	3.1	***	31	1.1–4.1
	Total sample<4mg	34	0.9	***	50	0.5–1.2
	New needle
	All cases	100	7.8	–	39	3.4–10.3
	No sample in syringe	34	5.8	–	62	3.3–7.9
	Total sample<4mg	9	1.9	–	72	1.6–2.1

*p<0.05, **p<0.01, and ***p<0.001 (unpaired two sided t-test). In all groups data were log transformed to fit normal distribution. Needle efficiency is the percentage of ejected sample compared to the total harvested sample weight.

If the cases for which residual material was present in the syringe were neglected, approximately 62–66% of the cases for all protocols, the needle efficiency increased to above 62% for the new needle. The trend for the standard needles was less pronounced, 27% (0.6mm) and 31% (0.7mm). The average total amount of harvested sample for this analysis was 5.9mg (standard 0.6mm needle), 10.1mg (standard 0.7mm needle) and 9.4mg for the new needle. Hence the new needle ejects more than three times more sample compared to the standard 0.6mm needle and almost twice as much as the standard 0.7mm needle.

Thirty-five percent, 24% and 9% of the procedures encompassed total harvested material of less than 4mg for the standard 0.6mm needle, the standard 0.7mm needle and the new needle, respectively. The needle efficiency of the new FNA needle increased to 71.7% in this group.

Discussion 

In order to minimise the frequency and extension of complications there is a need to establish routines to achieve final diagnosis using needles of minimal diameter. The diameter of the core biopsy instruments is several times greater than that of the FNA needles, with diameters of up to 3.2mm. Since a doubling of the diameter increases the cutting area by four times and has been estimated to increase the seeding risk by 60 times [7], needle trauma and the risk of tumour cell seeding increase rapidly with increasing diameter. The bevel configuration might also have an effect on the mentioned risks.

Core biopsy is able to provide a more definitive diagnosis of in situ and early invasive carcinomas, which is generally difficult using FNA [6]. Nonetheless the sensitivity and specificity of FNA can be sufficiently high [4], [8], [9], but varies greatly with the skill of the aspiration operator and the judging cytopathologist. In addition, objective molecular diagnostic parameters will be introduced in the near future, changing the indication for core biopsies. FNA material is ideal for such methods by providing intact individual cells and cell nuclei without cutting artefacts [1]. The reported accuracy of ultrasonically guided FNA varies greatly depending upon the skill of the aspirators [5], [10]. If increased sensitivity is reported it is mainly due to a higher degree of sufficient aspirates.

The authors have previously investigated the possibility of using sterile inserts in the needle hub on standard needles to abate a significant amount of the discussed residual storage spaces to enhance ejection. However, the attachments made the sample go into the syringe and the material was still lost, indicating the necessity of a larger and well designed storage compartment in the needle. The new FNA needle increased the weight of the ejected material by more than three times compared to the standard needle of the same outer diameter. Additionally, the new 0.6mm needle provided more ejected material than the standard 0.7mm needle. The frequency of needles with sparse harvested material (sample<4mg) was less with the new needle (9%) compared to its standard counterpart (35%), which is the result of increased harvesting. The most interesting finding is that the new needle provides almost twice as much material compared to the standard 0.7mm needle in cases where no sample is present in the syringe.

The increased needle efficiency is due to the added storage compartment. The length, shape and diameter of this compartment must be carefully selected in order to be able to retain the sample in the needle, not in the hub residuals or syringe, and to finally be able to eject it. The transitions in inner diameter ought to be smoothly configured, removing the residual spaces present in standard needles. If the storage diameter is too large the air stream velocity-profile is too low to successfully eject the sample. Moreover, if the length of the compartment is too short, sample droplets will be thrust into the hub or syringe due to the high kinetic energy, and will be more difficult to eject, as documented in the protocols with inserts as discussed above.

The increased harvesting with the new needle is mainly due to an increased sampling area (area of the needle opening) compared to in standard needles, this being obtained by decreasing the material thickness and modifying the tip angle and configuration. The sampling areas of the new 0.6 needles were 40% and 216% greater than of the standard 0.7mm and 0.6mm needles, respectively. It should be noted that the presented results were obtained by a very skilled sampling operator. Thus for the average experienced sampling operator who probably obtains more samples in the spare range, the new dedicated FNA needle should have even more added value.

Conclusion 

Critical reviews of the FNA methodology and technology have, with few good exceptions [11], been relatively sparse since FNA was introduced approximately 60 years ago. Our group believes that the use of non-optimised technology and diverging methodology is one of the main reasons why this patient-friendly technique has difficulty in being generally accepted. The development of a new dedicated FNA needle is advance in improving the technique. The new needle significantly increased the sample volume, especially in cases where the sparse material obtainable with the standard needle would not allow a final cytopathologic diagnosis.

Conflict of interest 

The authors in this study are also interested in commercialising the findings in this study.