A core biopsy needle is a medical device used to extract a sample of tissue from organs like the breast, prostate, liver, thyroid, or kidneys for examination under a microscope. The size of a core biopsy needle varies based on the site being biopsied and the amount of tissue needed for analysis.
What is a core biopsy needle?
A core biopsy needle consists of an outer cutting cannula that slides over an inner stylet. The stylet fills the hollow space inside the cannula and protrudes slightly beyond the tip. When inserted into tissue, the stylet pierces and advances into the site while the cutting cannula follows. As the stylet is withdrawn, a small cylinder of tissue is captured in the notch of the cannula and removed.
Core biopsy needles are available in a range of diameters from 14 gauge to 18 gauge. The lower the gauge number, the wider the diameter of the needle. For example, a 14 gauge needle is thicker than an 18 gauge needle. The gauge needed depends on the amount of tissue required for diagnosis and the accessibility of the biopsy site.
Typical sizes of core biopsy needles
Here are some typical core biopsy needle sizes:
- Breast biopsy: 14 gauge or 16 gauge
- Prostate biopsy: 18 gauge
- Liver biopsy: 16 gauge or 18 gauge
- Thyroid biopsy: 18 gauge or 20 gauge
- Kidney biopsy: 16 gauge or 18 gauge
For breast biopsies, radiologists usually prefer 14 gauge or 16 gauge core needles which harvest larger tissue samples. For more delicate organs like the prostate, thyroid and kidneys, finer 18 gauge needles are commonly used to minimize trauma.
14 Gauge Core Biopsy Needle
A 14 gauge core biopsy needle has an outer diameter of 2.1 mm and inner diameter of 1.6 mm. It retrieves a core sample approximately 20 mm long and 1.6 mm wide.
The relatively large diameter of a 14 gauge needle allows harvesting of a generous core tissue sample. This helps the pathologist make an accurate diagnosis.
Due to the larger caliber, 14 gauge needles may cause more pain and bleeding during insertion. However, the procedure is usually quick and well-tolerated under local anesthesia.
Uses of a 14 Gauge Core Biopsy Needle
- Breast biopsy
- Liver biopsy
- Prostate biopsy
- Kidney biopsy
- Lymph node biopsy
Advantages
- Obtains a large, intact core sample
- Provides ample tissue for histopathology
- May allow complete removal of small lesions
Disadvantages
- May cause more pain and bleeding
- Higher risk of tumor seeding along the needle tract
16 Gauge Core Biopsy Needle
A 16 gauge core biopsy needle has an outer diameter of 1.65 mm and an inner diameter of 1.19 mm. Each pass retrieves approximately a 17 mm long by 1.19 mm wide core.
The 16 gauge needle is only slightly thinner than the 14 gauge. It obtains a reasonably sized tissue sample with minimal discomfort.
Uses of a 16 Gauge Core Biopsy Needle
- Breast biopsy
- Liver biopsy
- Prostate biopsy
- Kidney biopsy
- Soft tissue tumor biopsy
Advantages
- Obtains a good sized core sample
- Lesser pain and bleeding risk than 14 gauge needle
- Preferred size for breast biopsies
Disadvantages
- Smaller sample than 14 gauge needle
18 Gauge Core Biopsy Needle
An 18 gauge core biopsy needle has an outer diameter of 1.27 mm and an inner diameter of 0.97 mm. It cuts a core sample approximately 17 mm long by 0.97 mm wide.
The slender 18 gauge needle is ideal for superficial organs or small lesions. Rapid needle insertion reduces organ motion artifact.
Uses of an 18 Gauge Core Biopsy Needle
- Prostate biopsy
- Thyroid nodule biopsy
- Kidney biopsy
- Lymph node biopsy
Advantages
- Thin diameter decreases pain and bleed risk
- Allows easy access to small or hard-to-reach lesions
- Rapid needle insertion reduces motion artifact
Disadvantages
- Small core size provides limited tissue for diagnosis
- Prone to crush artifact during firing
How is core needle size measured?
Core biopsy needles are sized according to the Stainless Steel Gauge (SSG) or Birmingham Wire Gauge (BWG) system. This measuring system is based on the outer diameter of the needle.
For example, an 18 gauge needle has an external diameter of 1.27 mm. This decreases incrementally by 0.13 mm with each gauge increase. So a 19 gauge needle measures 1.14 mm while a 21 gauge is only 0.91 mm wide.
The inner diameter varies according to the needle wall thickness. Larger needles have thicker walls than finer needles. The inner space fits the stylet which is 0.08 mm less than the outer diameter.
What affects the choice of core needle size?
Several factors influence the choice of an appropriately sized core biopsy needle:
- Amount of tissue required: Larger needles harvest more tissue for analysis.
- Lesion size: Fine needles are preferable for tiny lesions to minimize damage.
- Organ depth: Short needles may be inadequate to reach deep-seated organs.
- Tissue texture: Hard, fibrotic tissue may require a larger gauge for adequate samples.
- Location: Superficial or highly innervated sites like thyroid need thinner needles to reduce trauma.
- Diagnostic purpose: Immune profiling or genetic analysis need minimal tissue unlike histopathology.
- Skill level: Beginners may prefer thinner needles which are easier to manipulate.
The radiologist selects a needle size capable of acquiring sufficient representative tissue with minimal passes and side effects.
Comparison of Core Biopsy Needle Sizes
This table summarizes the typical sizes of commonly used core biopsy needles:
| Needle Gauge | Outer Diameter | Inner Diameter | Sample Length | Sample Width |
| 14 | 2.1 mm | 1.6 mm | 20 mm | 1.6 mm |
| 16 | 1.65 mm | 1.19 mm | 17 mm | 1.19 mm |
| 18 | 1.27 mm | 0.97 mm | 17 mm | 0.97 mm |
The table shows the outer and inner diameters of 14, 16 and 18 gauge needles. It also displays the approximate length and width of core samples obtained.
We can see that the 14 gauge needle retrieves the longest and widest core, while the 18 gauge has the narrowest sample. The sample length remains fairly constant at 17-20 mm regardless of caliber.
How to choose the right core needle size
Selecting the ideal core needle size for a particular biopsy requires consideration of these elements:
- Organ depth: Longer needles for deep targets, shorter for superficial.
- Tissue density: Dense fibrotic tissue needs wider needles.
- Lesion size: Small lesions require thinner needles.
- Amount of tissue: More tissue needs wider gauge.
- Location: Delicate areas like thyroid prefer smaller needles.
- Purpose: Immune assays need minimal tissue versus histopathology.
- Sonographic features: Highly vascular lesions may bleed with larger needles.
- Patient pain threshold: Low tolerance merits smaller needle.
The clinical context helps select the optimal core needle size to safely procure adequate diagnostic tissue. Customizing needle choice for the specific biopsy target and purpose results in the best outcomes.
Does needle size affect biopsy accuracy?
Needle size can impact biopsy diagnostic accuracy in a few ways:
- Smaller needles provide scant tissue which may not represent the lesion pathology.
- Larger needles retrieve abundant tissue but increase trauma and crush artifact.
- Thinner needles are more prone to sample errors from needle deflection by hard fibrotic tumors.
- Wider gauge needles allow immuno-analyses which require substantial tissue.
For palpable masses, a 14 or 16 gauge needle optimizes correct targeting and adequate sample size. For impalpable lesions seen only on imaging, 18 gauge needles minimize artifact and allow precise targeting.
Overall, an appropriate needle size for the lesion size, depth and tissue composition enhances biopsy accuracy.
Specialty core biopsy needles
While standard core biopsy needles suffice for most situations, some applications require specialized devices:
- Coaxial needle: Outer guide cannula directs inner sampling needle. Enables multiple samples through one skin puncture.
- Temno biopsy needle: Advanced 14, 16 or 18 gauge core needle with clamshell notch improves tissue capture and reduces trauma.
- Vacuum-assisted device: Uses suction to draw tissue into the needle notch to cut larger samples.
- Fine needle biopsy gun: Automated spring-loaded device fires needle rapidly into lesion for accurate sampling.
Additional innovations like 3D needle guides and robotic biopsy assistance further refine core needle biopsy procedures to enhance the quality and diagnostic utility of samples obtained.
Conclusion
In summary, core biopsy needles come in a selection of sizes from 14 to 18 gauge, with external diameters spanning 2.1 to 0.91 mm. Needle caliber is chosen based on the amount of tissue required, site accessibility, lesion depth, organ texture and location.
While larger needles obtain more tissue, finer needles minimize trauma and allow precise targeting. An appropriate gauge is selected to safely procure tissue adequate for histopathologic and cytologic diagnosis or ancillary studies.
Careful needle size selection for each clinical scenario helps maximize biopsy accuracy while limiting patient discomfort and complications.
