# Patent

## Title
Self-contained, self-piercing, side-expelling marking apparatus

## Abstract

A marking apparatus includes a rigid cannula having a peripheral wall forming a lumen that carries an imaging marker. A lateral opening in the peripheral wall is open to the lumen. The lateral opening has a proximal extent and a distal extent. A closed-off distal portion is distal to the lateral opening. A resilient end wall extends downwardly from the peripheral wall at the distal extent of the lateral opening. A stylet has a distal end having a ramp. The stylet is slidably received within the lumen of the rigid cannula for movement in the lumen. The resilient end wall of the rigid cannula is configured to engage the ramp of the distal end of the stylet when the stylet is advanced through the lumen of the rigid cannula to an extended position to substantially close off the lateral opening of the rigid cannula.

## Background
CROSS-REFERENCE TO RELATED APPLICATIONS
This application is a divisional of U.S. application Ser. No. 15/078,847, filed Mar. 23, 2016, which is a continuation of U.S. application Ser. No. 12/850,844 filed Aug. 5, 2010, now abandoned, which is a continuation of U.S. application Ser. No. 11/275,918 filed Feb. 3, 2006, now U.S. Pat. No. 7,819,820, which is a continuation of U.S. application Ser. No. 10/710,587 filed Jul. 22, 2004, now abandoned, and is a continuation-in-part of U.S. application Ser. No. 10/707,044 filed Nov. 17, 2003, now U.S. Pat. No. 7,424,320, issued Sep. 9, 2008, which claims the benefit of U.S. provisional application Ser. No. 60/427,048 filed Nov. 18, 2002, all of which are incorporated herein by reference in their entirety.


BACKGROUND OF THE INVENTION
Field of the Invention
This invention relates generally to an apparatus for the percutaneous positioning of an imaging marker for identifying the location of a lesion in a biopsy procedure. More particularly, the invention relates to a self-contained marking apparatus that expels the imaging marker through the side of the marking device.
Description of the Related Art
Tissue biopsies are commonly performed on many areas and organs of the body where it is desirable to ascertain whether or not the biopsied tissue is cancerous. Often, a lesion or other tissue to be biopsied is identified through use of an imaging technique such as a computerized axial tomography (CAT) scan, ultrasonography, magnetic resonance imaging, and mammography.
One problem commonly encountered, especially in breast biopsies, is that the lesion is so small that the biopsy reduces its size to the extent that it is no longer visible by the imaging method employed. In such circumstances, it is desirable to place an imaging marker at the site of the biopsy to enable the medical practitioner subsequently to locate the lesion quickly and accurately in the event complete removal of the affected tissue is indicated. This problem is currently met by placing an imaging marker at the biopsy area by means of a cannula or similar device housing the marker.
There are currently two primary types of marking devices. One of the primary types is referred to as vacuum assisted biopsy devices (VAB's). The VAB devices are many times integrated with a mammography imaging system. They include a large diameter cannula, approximately 9 to 12 gage, or probe that is inserted into the breast tissue. Instruments, such as a biopsy device and a marking device, are introduced into the breast tissue through the large diameter cannula to take biopsy samples or mark a biopsy location.
The other primary type is self-contained marking devices comprising a small diameter, approximately 14 to 17 gage, open-end cannula and a stylet slidably received within the cannula. A marker is located in the cannula and expelled out the open-end upon the advancing of the stylet relative to the cannula.
One disadvantage of the VAB system is the biopsy and marking tools are integrated with the mammography imaging system. The capital investment of this type of system is substantial. Also, the biopsy and marking tools are typically designed to work only with the large diameter probe, which tends to lock the hospital or medical professional into the same source for the imaging system and the biopsy and marking tools. The VAB systems are also intended for the same components to be reused, which requires sterilization after each step. The various components are also typically flexible to help insert them through the probe. The VAB systems also have a relatively large diameter probe, which, all things being equal, the larger the diameter, the greater trauma to the surrounding tissue and the greater the pain or discomfort for the patient.
The self-contained marking devices address these disadvantages of the VAB systems. Since the self-contained marking device is not integrally incorporated with a particular imaging system, the self-contained marking devices can be used with any suitable imaging system and are not limited to just mammography. This permits the hospital or medical professional to mix and match the available imaging systems and self-contained marking devices to obtain the desired performance and cost-effectiveness.
The self-contained marking devices are typically disposable, which negates the need to sterilize them after each use. They also have a much smaller diameter, resulting in much less trauma to the surrounding tissue and pain to the patient.
A disadvantage of the self-contained systems is that the cannula has an open tip through which the marker is expelled. The open tip is generally closed by the marker residing in the cannula. However, the marker does not completely close off the open tip and it is possible for tissue to enter the open end of the cannula during the positioning of the marking device. The presence of tissue inside the open end of the cannula can interfere or make more difficult the expelling of the marker from the cannula.
The possibility for tissue being present in the open end of the cannula is, to some extent, related to the distance that the cannula is inserted through the tissue to the marking site. Thus, the manner in which the marking device is located at the biopsy site can impact the presence of tissue in the open end of the cannula. For example, the self-contained systems are sometimes used in combination with a positioning cannula that is inserted into the tissue mass with a stylet closing the end of the positioning cannula. In such a configuration, the stylet is removed once the positioning cannula is properly located relative to the biopsy site. Both the biopsy device and the marking device can be inserted and withdrawn through the positioning cannula. The use of the positioning cannula reduces the distance that the open end of the marking device cannula must travel through the tissue.
Alternatively, the marking device can be inserted without the positioning cannula. This is most common when it is desirable to place a marker without taking a biopsy. Under such circumstances, it is more likely that tissue will be received within the open end of the cannula. Therefore, it is more likely that the tissue will interfere with the expelling of the marker.
Therefore, it is desirable to have a self-contained marking device that can be used with or without a positioning cannula and which does not receive tissue within the open end of the cannula that might interfere with the expelling of the marker.
SUMMARY OF THE INVENTION
The invention relates to a marking apparatus for the percutaneous placement of an imaging marker at a predetermined location in a tissue mass to facilitate subsequent determination of the predetermined location. The marking apparatus comprises a handle, cannula, and plunger. The handle is to be grasped by a user to aid in the placement of the marker.
The cannula comprises a peripheral wall forming a lumen, with a proximal end carried by the handle, and a distal end terminating in a self-piercing tip. A lateral opening is formed in the peripheral wall and is open to the lumen.
A plunger having a distal end is slidably received within the lumen for movement between a ready position, where the distal end is spaced inwardly from the self-piercing tip to form a marker recess in communication with the lateral opening and sized to receive an imaging marker, and an expelled position, where the distal end is advanced a sufficient distance into the marker recess to expel a marker contained therein through the lateral opening.
One or more imaging markers can be positioned within the marker recess.
The handle, cannula, plunger are operably coupled such that they form a self-contained marking apparatus that can be easily and conveniently handled by a user to effect operation of the marking apparatus from the ready position to an expelled position.
The cannula is preferably sufficiently rigid and a distal end of the cannula is pointed to form the self-piercing tip. The cannula is 13 gage or less.
A ramp can be provided on at least one of the plunger and cannula to aid in expelling an imaging marker. The ramp can be located in the lumen adjacent the lateral opening. The distal end of the plunger can be flexible to be deflected toward the lateral opening by the ramp when the plunger is moved to the expelled position. The ramp can also be located on the distal end of the plunger.
The invention, in one form thereof, is directed to a marking apparatus for the percutaneous placement of an imaging marker in a tissue mass. The marking apparatus includes a handle to be grasped by a user, a rigid cannula and a stylet. The rigid cannula has a peripheral wall forming a lumen that carries the imaging marker, a proximal end coupled to the handle, a lateral opening in the peripheral wall that is open to the lumen, and a closed-off distal portion having a ramp adjacent the lumen. The closed-off distal portion extends distally from the ramp to terminate at a tissue piercing pointed tip. The ramp of the rigid cannula is curved to transition from the peripheral wall of the rigid cannula to the lateral opening of the rigid cannula. A stylet has a distal end, with at least the distal end of the stylet being flexible. The stylet is slidably received within the lumen of the rigid cannula for movement in the lumen. The ramp of the rigid cannula is adapted to engage the distal end of the stylet as the stylet is advanced through the lumen of the rigid cannula to guide the distal end of the stylet to a position to substantially close off the lateral opening of the rigid cannula having the tissue piercing tip.
The invention, in another form thereof, is directed to a marking apparatus for the percutaneous placement of an imaging marker in a tissue mass. The marking apparatus includes a handle to be grasped by a user, a cannula, and a stylet. The cannula has a peripheral wall forming a lumen that carries the imaging marker, a proximal end coupled to the handle, a lateral opening in the peripheral wall that is open to the lumen, and a closed-off distal portion having a ramp adjacent the lumen. The closed-off distal portion extends distally from the ramp to terminate at a tissue piercing pointed tip. The stylet has a distal end with an angled surface. The stylet is disposed in the lumen and movable in the lumen between a ready position and an expelled position, such that when the stylet is advanced through the lumen to the expelled position the ramp deflects the distal end of the stylet toward the lateral opening such that at the expelled position the angled surface is flush with the peripheral wall of the cannula at the lateral opening of the cannula.
The invention, in another form thereof, is directed to a marking apparatus for the percutaneous placement of an imaging marker in a tissue mass. The marking apparatus includes a handle to be grasped by a user, a cannula, and a stylet. The cannula has a peripheral wall forming a lumen that carries the imaging marker, a proximal end carried by the handle, a closed-off distal portion terminating in a self-piercing tip, a ramp integrated with the closed-off distal portion, and a lateral opening in the peripheral wall. The lateral opening extends in a region between the proximal end and the closed-off distal portion of the cannula. The lateral opening has a proximal extent and a distal extent, the distal extent being closer to the self-piercing tip than the proximal extent. The stylet includes a distal end. The stylet is slidably received within the lumen for movement between a ready position, wherein the distal end of the stylet is spaced inwardly from the self-piercing tip to form a marker recess in communication with the lateral opening, and an expelled position, wherein the distal end of the stylet is advanced a sufficient distance into the marker recess to expel the imaging marker contained in the lumen through the lateral opening of the cannula. When the distal end of the stylet is at the expelled position the distal end of the stylet is deflected by the ramp to close off the lateral opening of the cannula between the proximal extent and the distal extent of the lateral opening.
The invention also relates to a method for percutaneously placing a marker at a predetermined location in a tissue mass using a self-piercing, side-ejecting, self-contained marking apparatus comprising a cannula defining a lumen and terminating in a self-piercing tip, with a lateral opening in communication with the lumen, and a plunger slidably received within the lumen for expelling a marker in the lumen through the lateral opening. The method comprises: inserting the cannula into the tissue mass by puncturing an exterior of the tissue mass with the self-piercing tip, and expelling the marker through the lateral opening by sliding the plunger within the lumen.
The inserting step can comprise locating the lateral opening near a predetermined location in the tissue mass where it is desired to be marked. Preferably, the lateral opening is located beneath the predetermined location.
The expelling step comprises expelling multiple markers into the tissue mass. At least one of the multiple markers can be expelled at a different location in the tissue mass than another of the multiple markers.



BRIEF DESCRIPTION OF THE DRAWINGS
In the drawings:
FIG. 1 is a plan view of a self-contained, self-piercing, and side-expelling marking apparatus comprising an actuator, a cannula with a side opening, and a stylet for laterally expelling a marker through the side opening in accordance with the invention.
FIG. 2 is an enlarged sectional view of the area II of FIG. 1, illustrating the relationship between the cannula, stylet and marker prior to the expelling of the marker.
FIG. 3 is an enlarged top view of the cannula tip of FIG. 2.
FIG. 4 is an enlarged sectional view of a portion of the actuator.
FIG. 5 is a sectional view of the marking device inserted into a tissue mass such that the cannula side opening is adjacent an area to be marked, with the stylet shown in a ready position and the marker still retained within the cannula lumen.
FIG. 6 is an enlarged sectional view of the cannula tip of FIG. 5.
FIG. 7 is a sectional view of the marking device inserted into a tissue mass such that the cannula side opening is adjacent an area to be marked, with the stylet shown in a expelled position and the marker expelled through the side opening into the surrounding tissue mass.
FIG. 8 is an enlarged sectional view of the cannula tip of FIG. 7.
FIG. 9 is a sectional view of an alternative design for the cannula and stylet according to the invention, with the stylet having a flexible tip and shown in the ready position.
FIG. 10 is a sectional view of the cannula and stylet of FIG. 9 with the stylet shown in the expelled position.
FIG. 11 is a sectional view of a second alternative design for the cannula and stylet according to the invention, with the stylet having a ramped tip and shown in the expelled position.



DETAILED DESCRIPTION
FIGS. 1-4 illustrate a self-contained, self-penetrating, side-expelling marking apparatus 10 according to the invention, which is capable of the percutaneous placement of a imaging marker at a desired location, such as at a tissue biopsy site or a lesion site in a breast. The marking apparatus 10 comprises an introducer 12 and an imaging marker 14 (FIG. 2) contained within the introducer 12. The introducer 12 includes an actuator 16 having a hollow interior 18. The actuator 16 comprises a grip portion 20 from which extends a tapered nose portion 22. The grip portion 20 defines a rear opening 24 that provides access to the hollow interior 18. A pair of detents 26 are formed in the grip portion 20 near the rear opening 24. Channels 28 are formed on the interior surface of the grip portion 20 and extend from the rear opening 24 to the detents 26.
The nose portion 22 comprises a guide passage 30 extending from the tip of the nose portion 22 to the hollow interior 18 of the actuator 16. The guide passage 30 decreases in diameter inwardly from the tip of the nose portion to form a cannula seat 32 (FIG. 5).
A plunger 50 comprises a cylindrical body 52 from which extend a pair of catches 54 at diametrically opposed positions. The cylindrical body 52 is sized so that it is slidably received within the rear opening 24 of the actuator 16 where it is so oriented with respect to the actuator such that the catches 54 are aligned with the guide channels 28. The plunger is free to reciprocate within the grip portion 20 of the actuator 16.
A cannula 60 is mounted to the introducer 12. The cannula 60 defines a hollow interior in the form of a lumen 62 and comprises a proximal end 64 and a distal end 66. The proximal end 64 (FIG. 5) is mounted within the cannula seat 32 to secure the cannula 60 to the introducer 12. The distal end 66 terminates in a closed-off tip 68 to provide the marking apparatus with self-piercing functionality. The closed-off tip 68 is illustrated as being pointed, but other suitable shapes are possible.
The cannula 60 is preferably 13 gage or less in size. The cannula 60 is also preferably rigid. That is, the cannula does not substantially flex. The rigidity of the cannula aids in inserting the cannula into a tissue mass, without the aid of a guide needle or guide cannula.
A side opening 70 is formed in the cannula 60 and extends entirely through the cannula such that the lumen 62 is in communication with the exterior of the cannula 60 through the side opening 70. The side opening is preferably located behind the closed-off tip 68.
A ramp 72 is provided on the interior of the cannula 60. The ramp 72 is illustrated as being integrally formed with the closed-off tip 68. Such a configuration can result in a solid distal end 66 as illustrated. However, the distal end can be hollow and the ramp 72 can be formed by separately from the distal end 66.
The ramp 72 extends diametrically across the lumen 62 and terminates at the side opening 70. With this configuration, the ramp 72 aids in directing an imaging marker 14 stored in the lumen through the side opening 70 and beyond the exterior of the cannula.
A stylet 80 comprising a shaft 82 and a base 84 is received within the hollow interior 18 of the actuator 16 in a manner such that the shaft 82 extends through the guide passage 30 and into the cannula interior 62 and the stylet base 84 lies within the hollow interior 18 and is mounted to the plunger 50. Thus, the reciprocation of the plunger 50 relative to the grip portion 20 results in a reciprocation of the stylet 80 within the cannula 60.
The stylet 80 terminates in a distal end 86, which, when the marking apparatus is in the ready position, is spaced from the distal end 66 of the cannula 60 to form a marker recess therebetween. As illustrated, a single marker 14 is stored within the marker recess. It is within the scope of the invention for multiple markers to be received within the marker recess.
As is shown, the foregoing construction provides a marking apparatus that is preassembled as a self-contained unit and prepackaged, all under sterile conditions, thereby affording the practitioner substantially greater convenience and reliability, while eliminating the need for sterilizing the self-contained unit after use. Preferably, the self-contained unit is disposed of after it is used.
Referring to FIGS. 5-8, in operation, the introducer 12 begins in the ready condition shown in FIGS. 5 and 6. In this condition, the distal end 86 of the stylet 80 is received within the cannula and spaced from the closed-off distal end 66 of the cannula to define a marker recess in which a marker 14 is stored. The plunger 50 is in a position relative to the grip portion 20 in which the catches are outside the grip portion; that is, they are not received within the detents 26. However, the plunger 50 is so oriented with respect to the grip portion that the catches 54 are aligned with the guide channels 28.
With the introducer in the ready condition, the cannula is positioned within the tissue mass such that the side opening 70 is at or near the location of a tissue mass where it is desired to place the marker. In the case of marking a biopsy site, the side opening is preferably placed adjacent the biopsy site.
To place the side opening adjacent the site to be marked, the medical professional grasps the grip portion 20 of the actuator and presses the closed-off tip 68 against the exterior of the tissue mass to puncture the tissue mass. The medical professional continues applying force to the grip portion 20 to drive the cannula 60 to the desired location within the tissue mass.
The closed tip 68 helps separate the tissue of the tissue mass to make it easier to insert the cannula within the tissue mass to the desired location. A starter incision can be made in the exterior of the tissue mass to reduce the initial force needed to start the insertion.
The used of a side opening 70 instead of a tip opening found in the prior art self-contained devices helps prevent the accumulation of tissue within the lumen 62 upon the insertion of the cannula 60 into the tissue mass. The closed tip 68 also helps in that it separates the tissue to form a path through which the side opening passes. Since the side opening is parallel to the path, there is much less tendency for the insertion of the cannula to force tissue into the side opening as could occur in the prior-art front opening cannulae.
Typically, a suitable imaging system will be used by the medical professional to help guide the cannula to the desired location within the tissue mass. Examples of contemporary imaging systems include: stereotactic, x-ray, ultrasound, CAT scan, or MRI. The invention is not limited to any particular type of imaging system.
Once the cannula is positioned at the desired location, the plunger 50 is moved from a first or ready condition as illustrated in FIGS. 5 and 6 to a second or expelled condition as illustrated in FIGS. 7 and 8. As the plunger is moved, the stylet 80 is advanced into the marker recess to drive the marker 14 up the ramp 72. The continued advancement of the stylet 80 ultimately drives the marker 14 through the side opening 70 and into the adjacent tissue.
Once the stylet is in the expelled position, the cannula can be withdrawn to leave the marker in the tissue. To withdraw the cannula, the medical professional pulls on the actuator to withdraw the cannula from the tissue mass. After use, the marking apparatus is disposed of, negating the need for sterilization.
As illustrated, the rigid cannula in combination with the closed-off tip 68 provides an ideal structure for inserting the device directly into the tissue without the need for a guide needle or cannula. This is advantageous in that it reduces the size of the opening formed in the tissue and thereby reducing the trauma to the patient. The closed-off tip is used to puncture the exterior of the tissue mass. While the marking apparatus of the invention can be used with a guide needle or cannula, there is no need to do so because of the self-piercing nature of the invention.
FIGS. 9 and 10 illustrate an alternative design for the stylet in the ready and expelled conditions, respectively. The alternative stylet 80′ is essentially identical to the stylet 80, except that the distal end 66′ is made from a resilient material and has an angled surface 90′. The resilient material permits the distal end 66′ to deflect when contacting the ramp 72′, such that the distal end 66′ generally follows the shape of the ramp 72′. The angle of the angled surface 90′ is preferably selected such that the angled surface substantially closes off the side opening 70′ when the stylet is in the expelled condition, which will ensure that the marker is completely expelled through the side opening 70′. It will also ensure that no portion of the marker 14 will be pulled back into the side opening 70′ due to the vacuum forces created upon the withdrawal of the cannula. The angled surface 90′ functions like the ramp 72 in that it helps to deflect the marker 14 through the side opening.
FIG. 11 illustrates another alternative design for the stylet and cannula. In this alternative design, the distal end 66′′ of the stylet 80′′ includes a ramp 72′′. A resilient end wall 92′′ is used instead of the ramp 72 of the cannula. The space between the ramp 72′′ and the resilient end wall 92′′ defines the marker recess in which multiple markers 14′′ are stored. The advancement of the stylet from the ready condition to the expelled condition drives the markers up the ramp 72′′. When contacted by the ramp 72′′, the resilient end wall 92′′ deflects to permit the ramp 72′′ to slide beneath and into the distal end closed tip 68′′ of the cannula.
In all of the embodiments, multiple markers can be located within the cannula and expelled at the same or different locations within the tissue mass.
While the invention has been specifically described in connection with certain specific embodiments thereof, it is to be understood that this is by way of illustration and not of limitation, and the scope of the appended claims should be construed as broadly as the prior art will permit.

## Claims

1. A marking apparatus for the percutaneous placement of an imaging marker in a tissue mass, the marking apparatus comprising:
a handle configured to be grasped by a user, the handle having a rear opening;
a rigid cannula having:
a proximal end coupled to the handle;
a peripheral wall forming a lumen that carries the imaging marker;
a lateral opening in the peripheral wall that is open to the lumen, the lateral opening having a proximal extent and a distal extent;
a closed-off distal portion distal to the lateral opening; and
a resilient end wall extending downwardly from the peripheral wall at the distal extent of the lateral opening;

a stylet having a proximal end and a distal end, the distal end of the stylet having a ramp, the stylet being slidably received within the lumen of the rigid cannula for movement in the lumen, the resilient end wall of the rigid cannula being configured to deflect upon engagement of the ramp such that the ramp of the distal end of the stylet passes beneath the resilient end wall and into the closed-off distal portion when the stylet is advanced through the lumen of the rigid cannula to an extended position to substantially close off the lateral opening of the rigid cannula; and
a plunger received in the rear opening of the handle, the plunger connected to the stylet and configured to move relative to the handle.

2. The marking apparatus of claim 1, wherein only the distal end of the stylet and the resilient end wall close off the lateral opening when the stylet is in the extended position.

3. The marking apparatus of claim 1, configured such that the stylet has a ready position wherein the distal end of the stylet is positioned in the lumen proximal to the extended position, in the ready position the stylet is spaced inwardly from the closed-off distal portion to form a marker recess that is in communication with the lateral opening and that is sized to receive the imaging marker, and configured such that when the stylet is moved to the extended position, the ramp engages and expels the imaging marker contained in the lumen of the rigid cannula through the lateral opening, and wherein the resilient end wall engages the ramp at the distal end of the stylet to substantially close off the lateral opening of the rigid cannula only after the imaging marker is expelled.

4. The marking apparatus of claim 3, further comprising multiple imaging markers contained within the marker recess.

5. The marking apparatus of claim 1, wherein the handle, the rigid cannula, the stylet, and the plunger are operably coupled to form a self-contained marking apparatus.

6. The marking apparatus of claim 1, wherein the handle has a detent, and the plunger has a catch configured to selectively engage the detent of the handle to latch the stylet in the extended position.

7. A marking apparatus for the percutaneous placement of an imaging marker in a tissue mass, comprising:
a handle configured to be grasped by a user, the handle having a rear opening;
a cannula having:
a peripheral wall forming a lumen that carries the imaging marker,
a proximal end coupled to the handle,
a lateral opening in the peripheral wall that is open to the lumen,
a closed-off distal portion having a distal void and a pointed tip, wherein the distal void is distal to the lateral opening and is proximal to the pointed tip, and
a resilient end wall proximal to the distal void;

a stylet having a distal end with an angled surface, the stylet being disposed in the lumen and movable in the lumen between a ready position and an expelled position, the stylet being configured to advance through the lumen to the expelled position, the resilient end wall being configured to deflect distally and beneath the resilient end wall and into the distal void as the stylet advances through the lumen into the expelled position, the angled surface of the stylet being configured to drive the imaging marker out of the lumen through the lateral opening of the cannula as the stylet advances into the expelled position; and
a plunger received in the rear opening of the handle and configured to move relative to the handle, the plunger being connected to the stylet.

8. The marking apparatus of claim 7, wherein the resilient end wall cantilevers from the peripheral wall of the cannula to separate the distal void from the lateral opening.

9. The marking apparatus of claim 7, wherein the stylet closes off the lateral opening when the stylet is in the expelled position.

10. The marking apparatus of claim 7, wherein the handle has a detent, and the plunger has a catch configured to selectively engage the detent of the handle to latch the stylet in the extended position.

11. A marking apparatus for the percutaneous placement of an imaging marker in a tissue mass, the marking apparatus comprising:
a handle having a rear opening;
a cannula having:
a peripheral wall forming a lumen that carries the imaging marker,
a proximal end carried by the handle,
a closed-off distal portion terminating in a self-piercing tip,
a lateral opening in the peripheral wall, wherein the lateral opening extends in a region between the proximal end of the cannula and the closed-off distal portion of the cannula, the lateral opening having a proximal extent and a distal extent, and
a cantilever end wall extending into the lumen from the peripheral wall at the distal extent of the lateral opening, the cantilever end wall having a distal free end that is suspended in the lumen above the peripheral wall;

a stylet having a proximal end and a distal end, the stylet being slidably received within the lumen for movement between a ready position, wherein the distal end of the stylet is spaced inwardly from the self-piercing tip to form a marker recess in communication with the lateral opening, and an expelled position, wherein the distal end of the stylet is advanced a sufficient distance into the marker recess to expel the imaging marker contained in the lumen through the lateral opening of the cannula, the cantilever end wall of the cannula being configured to deflect upon engagement of the distal end of the stylet such that the distal end of the stylet passes beneath the cantilever end wall and into the closed-off distal portion; and
a plunger received in the rear opening of the handle and configured to move relative to the handle, the plunger being connected to the proximal end of the stylet.

12. The marking apparatus of claim 11, wherein a portion of the stylet including the distal end includes an angled surface, the distal end of the stylet being configured to engage the cantilever end wall when the stylet is latched in the expelled position.

13. The marking apparatus of claim 11, wherein a portion of the stylet including the distal end includes a ramp, wherein when the distal end of the stylet is moved toward the expelled position to close off the lateral opening of the cannula, the cantilever end wall is deflected by the ramp.

14. The marking apparatus of claim 11, wherein the handle has a detent, and the plunger has a catch configured to selectively engage the detent of the handle to latch the stylet in the extended position.