Keywords
percutaneous CT-guided biopsy - saline instillation technique - soft-tip stylet
Background
Percutaneous computed tomography (CT)-guided needle biopsy is an established technique
for obtaining tissue sample from deep-seated lesions. However, sometimes it is difficult
to find a safe needle path due to concern for injuring a vital structure. Many techniques
like saline instillation technique or changing patient's position have been used to
displace vital structures out of needle path.[1]
[2]
[3]
[4] A soft-tip also referred to as blunt-tip stylet for the introducer cannula is provided
with some coaxial biopsy sets in additional to standard sharp-tip stylet. Although
its use has been described in medical literature, many radiologists are still not
utilizing this tool to its full potential.[5] The combination of saline instillation and use of soft-tip stylet further increased
safety of the procedure.
While using a sharp-tip stylet, it is important to create a wider saline window for
safely advancing the needle without injuring adjacent structures. With a soft-tip
stylet, usually a small amount of saline instillation is enough to dissect the fascial
plane and displace any membranous structures, and this makes enough room for advancing
the introducer cannula. Many a times, even saline instillation is not needed if introducer
cannula along with soft-tip stylet is sliding smoothly without transgressing the anatomical
structures.
Illustrative Cases
In all representative cases shown in this exhibit, percutaneous CT-guided biopsies
were performed using an 18- or 20-gauge coaxial biopsy set (Bard Mission Core Biopsy
Instrument, BARD, Arizona, United States) ([Fig. 1]). While a sharp-tip stylet is fitted with introducer cannula for piercing skin,
muscle, and fascia, a soft-tip stylet may be used for avoiding injury to structures
like lung, vessels, and bowel loops especially while advancing cannula through fatty
tissue or between fascial planes ([Fig. 2]). The soft-tip stylet tends to displace the vital structures or slide over them
rather than injuring them. Important applications of soft-tip stylet have been described
below, and in some cases used in combination with saline instillation.
Fig. 1 Introducer cannula (1) of coaxial biopsy set with a soft-tip or blunt-tip stylet
(2) and a sharp-tip stylet (3).
Fig. 2 Illustrating the technique (same case as shown in [Fig. 6]). Initially the outer cannula is advanced in the paravertebral location. While crossing
the chest wall a sharp-tip stylet is used; however, when the needle reaches close
to the lung it is exchanged with soft-tip stylet for safety. Saline instillation is
done to push the lung away and create a window. While advancing needle toward the
lesion, again a soft-tip stylet is used as it will not pierce the pleura. Finally,
when outer cannula reaches the lesion margin, then a sharp-tip stylet can be used
to get into the lesion.
Neck region: A soft-tip stylet can be used to insert cannula close to the thyroid gland, pharynx,
esophagus, and neck vessels ([Fig. 3]).
Fig. 3 (A) Lytic destruction of cervical vertebra with associated soft tissue mass, biopsy
was performed from an anterior approach. (B) Soft-tip stylet used to avoid injury to carotid artery and esophagus. (C) Final cannula position in the lesion.
Mediastinum (anterior parasternal approach): A soft-tip stylet is helpful to slide the introducer cannula close to the ascending
aorta, internal mammary arteries, pulmonary artery, and pleura ([Figs. 4] and [5]).
Fig. 4 (A) Internal mammary artery (thin arrow) is coming in the needle path while choosing
right parasternal approach for the biopsy of prevascular nodal mass (thick arrow).
(B) Soft-tip stylet was used to avoid injury to the lung and internal mammary artery.
Final cannula position in the lesion.
Fig. 5 (A) Anterior mediastinal mass close to main pulmonary artery is noted. Lung was coming
in the biopsy path and main pulmonary artery was also in close proximity. (B) A combination of saline instillation technique and soft-tip was used to target the
lesion without injuring the lung and vessels. This was biopsy-proven case of invasive
thymoma with pleural metastasis along oblique fissure.
Mediastinum (posterior paravertebral approach): A soft-tip stylet helps to avoid injury to the spinal nerve roots, descending aorta,
esophagus, lung, and azygos vein ([Fig. 6]).
Fig. 6 (A) Anterior approach was not possible for this right paratracheal node due to superior
vena cava. (B) Long posterior paravertebral route was taken. Initially saline instillation
was performed to displace the pleural laterally. Initially the needle trajectory was
going close to the trachea. (C) Needle was partially withdrawn, redirected, and advanced
close to pleura using soft-tip stylet.
Abdomen: A soft-tip stylet is used to slide introducer cannula over the kidney, liver, splenic
capsule, and displacing the ureters or bowel loops ([Figs. 7], [8], [9]). It is also used for avoiding injury to mesenteric, splenic, epigastric, and iliac
arteries ([Fig. 10]). The soft-tip stylet has also been used as a lever to displace a structure manually
especially the bowel loops.[1]
Fig. 7 (A) Necrotic periportal node (star) developed in a previously operated case of cholangiocarcinoma.
Another smaller node (arrow) noted close to the larger node. (B) Soft-tip stylet used to avoid injury to stomach and small perigastric blood vessels.
Fig. 8 (A) Recurrent peritoneal deposit in a case of operated gastrointestinal stromal tumor.
(B) Soft-tip stylet was used while advancing introducer cannula close to small bowel
loops.
Fig. 9 (A) Elderly lady presented with a mass medial to descending colon (arrow). No posterior
approach was available due to iliac blade. (B) Soft-tip stylet used to cross the narrow window available between large bowel loops.
Fig. 10 (A) Pancreatic head mass (arrow) with common bile duct (CBD) stent in situ. (B) Soft-tip stylet used to avoid injury to mesenteric vessels and bowel loops. Final
position of introducer cannula.
Retroperitoneum (posterior approach): A soft-tip stylet is used to slip close to the kidney capsule, ureter, colon, vertebra,
or spinal nerves. Similarly, it can be used to avoid injury to the inferior vena cava
([Figs. 11] and [12]).
Fig. 11 In a case of gall bladder carcinoma with enlarged aortocaval lymph node (thick arrow)
biopsy was performed to know the nature of the node. (A) Soft-tip stylet was used while advancing cannula near the renal capsule, ureter
(thin arrow), vertebra, and inferior vena cava (arrowhead). (B) Final position of introducer cannula.
Fig. 12 (A) Pancreatic uncinate process mass (black arrow) with negative endoscopic ultrasound-guided
biopsy. Inferior vena cava (IVC) (white arrow) is coming in the needle path. (B) Soft-tip stylet was used to slip the introducer cannula over the IVC without transgressing
it. Final position of cannula with specimen notch of biopsy needle advanced inside
the mass.
Pelvis: A soft-tip stylet is used to avoid injury to the iliopsoas muscle, iliac vessels,
ureter, colon, and urinary bladder ([Fig. 13]).
Fig. 13 (A) In a follow-up case of carcinoma cervix, a recurrent mass developed involving left
lower ureter (ureteric stent in situ). (B) Contrast mixed saline used to displace small bowel loops from needle path. (C) Soft-tip stylet was used to avoid bladder injury while steering the introducer cannula
toward main bulk of mass.
Other Uses
During vertebral or paravertebral biopsies, often the needle path runs close to exiting
nerve, again a soft-tip stylet may help push the nerve aside while advancing the introducer
cannula ([Fig. 14]). It is also useful for slipping introducer cannula close to bones without injuring
periosteum which is a pain-sensitive structure.
Fig. 14 Lytic lesion of lumbar vertebra in a suspected case of spinal tuberculosis. (A) The exiting nerve (arrow) was coursing close to the needle path. (B) Final position of introducer cannula.
During lung biopsies, giving local anesthesia to the pleura is important as it is
a pain-sensitive structure. Pleural anesthesia is even more important during targeting
small lung nodules, as these patients need to hold the breath at the time of advancing
the needle into the lung; however, if the pleura is not anesthetized, the sharp pain
of pleural puncture may cause movement or improper breath holding. Anesthetizing the
pleura makes insertion of needle pain-free from chest wall into the lung. While manipulating
the introducer cannula close to the pleura, soft-tip stylet is safer than sharp-tip
stylet which may inadvertently cause pneumothorax ([Fig. 15]). A flat-tip bevel of the introducer cannula ([Fig. 1]) can also be manipulated close to the pleura safely and intercostal muscles may
be pierced by making rotatory motions.
Fig. 15 Soft-tip stylet used while manipulating introducer cannula close to the pleura. The
intercostal muscles were pierced using rotatory movement with the flat tip bevel of
the introducer cannula. This helps in giving pleural anesthesia without risk of inadvertent
pleural puncture and pneumothorax.
Limitations
Soft-tip stylet cannot be used to pierce tough structures like the skin, fascia, or
muscles. It can distort the anatomy by pushing the anatomical structures rather than
sliding over them; however, when used in between the fascial planes in conjunction
with saline instillation, usually the introducer cannula slips easily over the anatomical
structures. Similarly, the soft-tip stylet can be advanced through the fatty tissue
while making gentle rotatory movements with little resistance.
Conclusion
During insertion of introducer cannula for coaxial CT-guided percutaneous biopsy,
a soft-tip or blunt-tip stylet can be used for avoiding injury to structures like
vessels and bowel loops especially while advancing the cannula through fatty tissue.
Additionally, it is also useful for avoiding injury to nerves, muscles, and giving
pleural anesthesia. A combination of saline instillation technique with soft-tip stylet
further reduces the complications.
