Retroperitoneal adenopathies are frequently encountered in clinical practice and can be associated with a wide range of both benign and malignant conditions. Accurate diagnosis is critical for guiding appropriate management, but the deep and complex anatomical location of retroperitoneal lymph nodes poses significant challenges for tissue sampling. Percutaneous biopsy, performed under image guidance, has emerged as a minimally invasive technique for obtaining diagnostic tissue while minimizing patient morbidity.

     Technique

The retroperitoneal space is a complex anatomical region that can pose challenges when performing percutaneous biopsy of anatomical structures located in this area (Figure 1).

Fig 1: The retroperitoneal space is a complex anatomical region that can pose challenges when performing percutaneous biopsy of anatomical structures located in this area (L-liver, S-stomach, Sp-spleen, P-pancreas, D-duodenum, AC-ascending colon, DC-descending colon, K-kidney, IVC-inferior vena cava, Ao-aorta, A-adenopathies)

After evaluating the pre-procedural CT scan and performing an ultrasound assessment, the optimal access route is selected, primarily depending on the location of the adenopathy and its anatomical relationship with vital structures. The most commonly chosen approaches are the anterior transperitoneal or the retroperitoneal paravertebral routes.

When these approaches are not feasible, access to the adenopathy can also be achieved via a transhepatic route (avoiding the gallbladder, dilated bile ducts, and porta hepatis), transgastric, or transduodenal routes (Figure 2).

Fig 2: Common (black arrows) and uncommon (dotted black arrow) needle pathways to the adenopathies including the (a) paravertebral, (b) pararenal, (c) transperitoneal and (d) transhepatic approach

The choice of imaging modality for performing the percutaneous biopsy depends on the location of the adenopathy and whether ultrasound provides good visualization of the adenopathy, surrounding structures, and the biopsy needle's trajectory.

Computed tomography (CT) offers the advantage of better visualization of loco-regional anatomical structures, while ultrasound allows real-time visualization of the biopsy needle. A combined guidance approach using ultrasound and CT may be employed when the biopsy needle tip is difficult to identify solely under ultrasound guidance (Figure 3).

Fig 3: Suboptimal visualization of the biopsy needle tip within the lesion may necessitate the use of alternative imaging modalities for accurate confirmation

When ultrasound guidance makes biopsy needle localization difficult, CT examination can offer additional information and enhance procedural safety to minimize the risk of complications. (Figure 4).

Fig 4: CT scan to verify the position of the biopsy needle tip to avoid potential complications due to the proximity of the target lesion to the aorta

Semi-automatic side-cutting biopsy needles (18G or 20G) are used in a coaxial system along with a coaxial trocar, enabling the collection of multiple biopsy fragments (Figure 5).

Fig 5: The parts and mechanism of action of a side-cutting percutaneous biopsy needle along with the trocar used in the coaxial technique for tissue sampling

The choice of needle size is based on the selected pathway, the size of the adenopathy, and its proximity to vital structures, aiming to minimize the risk of complications.

Local anesthesia is administered using 1% lidocaine injected along the entire biopsy needle path.

Subsequently, the biopsy needle trocar is advanced to the adenopathy, followed by the insertion of the biopsy needle and the collection of tissue samples (Figure 6, Figure 7).

Fig 6: Coaxial biopsy needle sampling technique: The needle set, consisting of the outer cannula (red) and inner stylet (black), is advanced to the edge of the lesion (A). The inner stylet is then pushed forward beyond the margin of the supporting cannula inside the target lesion (B). When the plunger is fired, the cannula advances over the stylet, cutting the tissue trapped inside the stylet’s notch (C). Finally, the biopsy needle is withdrawn from the patient, and the outer cannula is retracted to reveal the collected tissue sample

Fig 7: Gradual advancement of the biopsy needle’s sample notch to ensure optimal tissue fragment collection from the lesion with precision while preserving the integrity of adjacent vital structures