Clinical Value Of Coaxial Trocar Needles in Reducing Core Biopsy Passes

 Exemplified by Liver, Kidney, and Lung Biopsies

https://www.cookmedical.com/products/ir_dtn_webds/

In modern interventional radiology and ultrasound-guided biopsy, "reducing core biopsy passes" has become a central objective for enhancing patient safety and diagnostic accuracy. Traditional core biopsy needles (e.g., Tru-Cut needles) require re-puncturing of the skin and successive tissue layers with every sampling attempt. This not only increases the risks of bleeding, pneumothorax, and needle tract seeding, but also tends to exacerbate patient pain and cause sample crush artifacts. In contrast, the coaxial trocar system-composed of a sharp inner obturator/trocar paired with an outer cannula-enables the practitioner to withdraw the inner stylet after the initial puncture while leaving the outer cannula in situas a working channel. Subsequent biopsy needle insertions advance through this cannula for multiple samplings, significantly reducing the actual number of penetrating core biopsy passes through the tissues.

Clinical data demonstrate that under ultrasound guidance, coaxial trocar biopsy of small hepatocellular carcinomas (≤2 cm) achieves a diagnostic yield of 95.6%, surpassing the 89% rate of non-coaxial techniques. Concurrently, the incidence of pneumothorax drops from 3.2% to approximately 0.5%, and the risk of bleeding decreases by over 60%. The underlying mechanism is as follows: the initial puncture is performed with the trocar and obturator assembly; the three-faceted or pyramidal tip design reduces resistance upon skin entry and prevents healthy tissue from clogging the cannula. Once the channel is established, the outer cannula isolates the biopsy needle from normal tissues, so subsequent samplings no longer require repeated transgression of the pleura, peritoneum, or organ capsules-truly realizing the "single puncture, multiple cores" philosophy of pass reduction.

The geometric shape of the trocar tip also influences core quality-a triple-edge or three-sided pyramidal tip (3-faced trocar tip) causes less tissue drag than a standard beveled edge. Combined with appropriate diameter (commonly 14G–18G) and length (70 mm–200 mm depending on anatomical depth), it effectively minimizes fragmentation and tissue crush artifacts. For deep-seated organs such as the kidney and hilar lymph nodes, the coaxial trocar system further streamlines the procedure by allowing injection of thrombin or contrast agent through the trocar lumen for real-time hemostasis and localization.

It is worth noting that reducing core biopsy passes via the trocar technique does notmean reducing the total amount of sampled tissue. On the contrary, thanks to the stable channel and the ability to adjust the cannula tip angle, 3–5 cores can be obtained from different directions within the same lesion using only a single percutaneous puncture. This markedly increases the probability that the pathology department receives intact, structurally preserved tissue strips. This is precisely why interventional departments in tertiary hospitals and image-guided biopsy centers increasingly designate coaxial trocar needles as the preferred tool for liver, kidney, peripheral pulmonary nodules, and pancreatic masses.

Selection recommendations:​ For liver/kidney, 14G–16G cannulas with graduated markings are recommended (length ≥150 mm); for peripheral lung nodules, 18G–20G thin-walled cannulas paired with blunt-tip obturators to reduce alveolar injury; for breast and superficial lymph nodes, 14G coaxial trocars combined with vacuum-assisted biopsy needles may be used. All products should conform to the ISO 13485 medical device quality management system, with 304/316L stainless steel being the optimal material choice, and surfaces treated with electropolishing to minimize tissue adhesion.