- Email: [email protected]
Pediatric Image-Guided Nonvascular Musculoskeletal Interventions
Pediatric Image-Guided Nonvascular Musculoskeletal Interventions Jack-Nghia Vo, MD, Fredric A. Hoffer, MD, FSIR, and Dennis W.W. Shaw, MD Image-guided procedures involving the musculoskeletal (MSK) system of children can be challenging because of the variability posed by the child’s age, skeletal maturity, and the stage of development. The imaging findings of the maturing MSK system and the underlying diseases affecting children, particularly those that are skeletally immature, can differ significantly from typical adults. The breadth of possible MSK procedures performed by an interventional radiology service depends on the availability of local expertise/experience as well as the referral patterns. In our practice, the majority of nonvascular MSK procedures involve children with a sequela of pain and in need of a therapeutic intervention. We describe our techniques for our more commonly performed MSK procedures, including corticosteroid injections, treating osteoid osteomas, and performance of image-guided bone biopsies and foreign body removal. Tech Vasc Interventional Rad 13:214-221 © 2010 Elsevier Inc. All rights reserved. KEYWORDS children, image guidance, joint injections, radiofrequency ablation, biopsy, foreign body retrieval
Corticosteroid Joint Injections Juvenile idiopathic arthritis (JIA) is a generic term for a set of diseases that result in chronic joint inflammation before adulthood and manifests as arthritis for which no specific etiology is identified.1 It is the most common rheumatic disease affecting children with a prevalence of 7-400 per 100,000. Pauci-articular (affecting 1-4 joints) is the most common subgroup, but polyarthritis is not uncommon. JIA can frequently extend into early adulthood and, if the inflammatory reaction is permitted to progress uncontrolled, may result in severe joint destruction and deformity.2 Intra-articular corticosteroid injections (IACI) in children with JIA has traditionally been reserved for use when nonsteroidal anti-inflammatory drugs (NSAIDs) have been ineffective/insufficient at controlling the inflammation or to treat a painful symptomatic flare in a child who is al-
Department of Radiology, Seattle Children’s Hospital and The University of Washington, Seattle, WA. Address reprint requests to Jack-Nghia Vo, MD, Seattle Children’s Hospital and The University of Washington, Department of Radiology, Section of Pediatric Interventional Radiology, Pediatric Radiology and Vascular Interventional Radiology, 4800 Sand Point Way NE, Seattle, WA 98105. E-mail: [email protected]
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ready managed with systemic therapy. Increasingly, pediatric rheumatologists are considering IACI earlier in the disease course with the goal of directing potent anti-inflammatory treatment directly into an actively inflamed joint and may permit the withdrawal or avoid the need for systemic therapy.1 There are a variety of corticosteroid preparations available. Triamcinolone hexacetonide (Sandoz, Princeton, NJ) is our agent of choice and is available as a preparation of 20 mg/mL. It has low solubility with excellent efficacy.3,4 The typical dose we use is 1 mg/kg (max. of 40 mg) in large joints (shoulders, hips, and knees); 0.5 mg/kg (max. of 20 mg) for medium joints (wrist, elbow, ankle, subtalar); and up to 5 mg into small joints of the hands and feet. When triamcinolone hexacetonide is not available, we will use triamcinolone acetonide (Bristol-Myers Squibb, Princeton, NJ), available in a preparation of 40 mg/mL. Although the risk of inducing an infection is low, the results of such a complication can be significant. Therefore, we use strict aseptic techniques during IACI. The most common local complications or adverse side effects involve subcutaneous atrophy and skin pigmentation changes because of leakage of steroid into the subcutaneous tissue along the needle tract. Both are usually selflimiting, resolving spontaneously. The risk can be reduced
Pediatric image-guided nonvascular MSK interventions by clearing the needle of residual steroid then compressing the site during and after needle removal. A post injection “flare” can occur in which there is a local increase in the inflammation that develops within hours of the IACI and can last several days; the exact cause is uncertain, but some feel that this may be induced by the formation of microcrystalline particles resulting in crystal-induced arthritis.5 This is also typically self-limiting. Contra-indications to IACI include an active infection of the joint or overlying soft tissues, hemorrhagic diathesis, and a child who is actively on anticoagulation or antiplatelet therapy. We feel that it is prudent to wait until the INR is ⬍2 before performing an elective IACI. We do not inject a single joint more than three times a year or within 6 weeks of a prior injection. Caution should be taken when considering adding a mixture of local anesthetic (LA) to a
215 corticosteroid preparation for a joint injection. We do not use any epinephrine-containing LA formulation due to a demonstrated increased risk and rate of chondrocyte apoptosis.6
Technique for Corticosteroid Joint Injections Cooperation of the child is required to accurately and safely position an access needle into an appropriate intraarticular location for corticosteroid injection. The child’s maturity and ability to cooperate determines the level of sedation required, if any. Older adolescents frequently only require a LA and moral support; child life specialists can be useful. When ultrasound (US) is not used for image guidance, we start with a needle-free air injection device (J-Tip) to infiltrate 0.5 mL of 1% lidocaine into the skin
Figure 1 A 10-year-old boy with JIA and hip pain. (A) A 22gauge spinal needle is introduced using an oblique trajectory to the lateral junction of the right femoral head and neck. A small volume of water-soluble contrast “flows” away from the needle tip and confirms an intra-articular position before the introduction of the steroid preparation. (B) A different child in whom contrast does not easily “flow” away from the needle tip and forms a persistent dense contrast blush. In this circumstance, there was “resistance” during the contrast injection and the needle tip is only partially in the joint as evident by some contrast opacifying the joint while the majority forms a persistent blush (arrow) (C).
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surface (National Medical Products, Irvine, CA). We also apply EMLA cream to the skin surface 30-45 minutes before the procedure while the patient is in the holding area. Fluoroscopy is the modality we most frequently rely on for image-guided IACI. This offers the ability in real-time, using contrast, to confirm an intra-articular needle position immediately before the introduction of the corticosteroid. An intra-articular position is confirmed by the sensation of low resistance during the injection along with the direct observation of the contrast “flowing” away from the needle tip within the joint. With an extra-articular location, the contrast will not diffuse away from the needle tip but rather form a persistent “blush” in the peri-articular soft tissue and continue to demonstrate some tactile resistance to the injection (Fig. 1). Injection procedures performed without image guidance leads to an extra-articular joint injection rate as high as 50%-60%.7 Hip Joint With the hip in anteroposterior position, a 22-gauge spinal needle is directed to the lateral junction of the femoral head and neck with an oblique trajectory (Fig. 1). Once the spinal needle is in contact with the bone surface, the needle is rotated 180 degrees and the inner stylet removed. A short connector tubing is than attached for contrast confirmation followed by the introduction of the corticosteroid preparation. With large and medium joints, either a small volume of water-soluble contrast or air can be used as a contrast agent. The needle rotation and attachment of the connector tubing is a standard routine performed for nearly all of our joint injections. Shoulder Joint We use an anterior approach with fluoroscopy for shoulder joint injections. The hand is placed at the child’s side with the hand supinated (a sandbag can help maintain this position), and a 22-gauge spinal needle is directed to the elliptic shadow formed by the medial aspect of the humeral head and the lateral margin of the glenoid (Fig. 2). Knee Joint US is used to detect for the presence of a joint effusion. If present, as much synovial fluid will be aspirated as possible before introducing the corticosteroid. In the absence of an effusion, a fluoroscopically guided suprapatellar bursa or a retropatellar approach is applied. With a suprapatellar approach, a 22-gauge spinal needle may need to be advanced beyond the midline of the knee and slowly withdrawn until there is a loss of resistance and diffusion of the contrast (or air) away from the needle tip. The suprapatellar bursa is a redundant sac when not distended and may require a “double wall” puncture technique similar to venous punctures. Subtalar and Tibiotalar (Ankle) Joint Tibiotalar (ankle) joint injections do not routinely treat subtalar synovitis. These joints should be treated independently when symptomatic. The subtalar joint is a complex articulation and image guidance is critical for reliable IACI. We use a lateral-oblique approach in which the pos-
Figure 2 A 17-year-old boy with JIA and right shoulder pain. (A) Frontal radiograph of the right shoulder demonstrating the elliptic shadow formed by the overlapping shadows of the humeral head and glenoid (arrowheads). (B) A 22-gauge spinal needle in place with the tip directed to the elliptic shadow target followed by contrast injection confirming an intra-articular position.
terior facet of the joint is placed in profile fluoroscopically. We have also started to use a high-frequency linear US probe for real-time guidance during advancement and positioning of a 22-gauge spinal needle. However, we continue to use brief fluoroscopy to confirm contrast spread within the subtalar joint (Fig. 3). With the lateral fluoroscopic view used for the subtalar joint, the tibiotalar joint is also seen in profile. The joint is most easily entered anteriorly from an inferior to superior trajectory along the lateral third of the joint, to avoid the anterior tibial artery. US is also frequently capable of demonstrating the joint and is useful for real-time advancement of the access needle (Fig. 3). Elbow and Wrist Joints The elbow is flexed to 90 degrees in the lateral position. Using a lateral approach, the radial-capitulum joint is placed in profile under fluoroscopy for access using a 22gauge spinal needle. Contrast will typically flow into the anterior and/or posterior joint capsule and with sufficient volume can reproduce the infamous elevated “fat pad” sign that radiology residents are so familiar with. For wrist injections the radial-carpal joint is placed in profile
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Figure 3 A 3-year-old girl with JIA. US was used to advance a 22-gauge spinal needle into each joint then brief fluoroscopy was used for confirmation. (A) Lateral fluoroscopic view shows that contrast opacifies the posterior facet of the subtalar joint. (B) The foot is maintained in the same fluoroscopic view and again confirms an intra-articular needle position in the tibiotalar joint. Note that the contrast in the subtalar joint is diluted following the introduction of the corticosteroid. (C) Coronal US image of the subtalar region using a high frequency linear “Hockey Stick” probe from a lateral approach. Note the echogenic epiphysis of the distal fibula (arrow) and the oblique course of the superior-lateral margin of the calcaneus (CALC). A 22-gauge spinal needle tip (arrowhead) is slipped along the upper margin of the calcaneus and below the fibula toward the subtalar joint. (D) US image of the tibiotalar region from a sagital frontal view. The joint is positioned between the anterior tibia (AT) and the talar dome (TD). A 22-gauge spinal needle tip (arrowhead) is positioned into the joint.
and accessed near the radial tubercle using a dorsal approach.
Radiofrequency Ablation of Osteoid Osteoma: How We Do It Children with presumed osteoid osteoma (OO) are referred by local pediatricians or more often through our hospital orthopedists for a percutaneous image-guided radiofrequency ablation (RFA). A consult is performed in our interventional radiology clinic to confirm the diagno-
sis of OO. A CT or MRI study will be reviewed or ordered if not already completed. We perform all RFA procedures for OO with CT guidance under general anesthesia. Clinically, the typical patient will have pain worse at night that awakens them. NSAIDs can effectively treat the pain, but the pain can worsen with time and the medication may eventually be required around the clock.8 The pain can progress to the point of severe debilitation; an OO located in the lower extremity can alter the child’s gait and affect their ability to ambulate. The typical imaging pattern is a nidus under 1 cm in diameter that is cortically based in the bone, most often involv-
J.-N. Vo, F.A. Hoffer, and D.W.W. Shaw
218 ing the tibia or femur. The nidus is lytic and when outside the joint frequently induces an intense periosteal bone thickening and reaction. Cortical lesions that are within the joint capsule often lack the periosteal new bone formation. All lesions will have increased uptake on skeletal scintigraphy
and periosteal and endosteal reaction on MRI. The nidus will enhance on MRI but is often more conspicuous on noncontrast CT. The nidus is localized with CT and an appropriate approach is planned, avoiding large vessels, nerves and ten-
Figure 4 A 4-year-old boy with left leg pain typical of OO. (A) CT image demonstrates a 4-mm lytic lesion with a tiny central nidus in the proximal femur. (B) Coronal image shows the OO with a sclerotic reactive halo. (C) A 13-gauge bone biopsy guiding cannula is advanced with CT guidance to the cortical margin of the OO; this served essentially as a guiding trocar for a drilling a path through the cortex with a K-wire. (D) A 7-mm burn diameter RFA probe is positioned within the nidus. Note the guiding cannula (arrow) has been retracted well away from the active tip to reduce risk of causing a skin burn.
Pediatric image-guided nonvascular MSK interventions dons. Two grounding pads are placed on the legs in a transverse orientation away from any superficial bony structures. For a femoral lesion, one grounding pad can be placed under the thigh on the ipsilateral leg and the other over the thigh on the opposite leg. For a lower leg lesion, two grounding pads can be placed on the ipsilateral thigh, front and back. It is important to insulate the skin between the two legs with a towel to avoid skin-to-skin conduction pathways and skin burns. We routinely reduce the CT technique, as much as 50%, and are able to maintain sufficient image quality for guidance. This is consistent with the principle of “Image Gently, Step Lightly” campaign of the Alliance for Radiation Safety, which is to improve radiation safety in pediatric interventional radiology.9 A small 3- to 5-mm skin incision is made to accommodate needle passage. Most OO can be treated without a biopsy. However, we do perform a biopsy for the occasional case where the diagnosis remains in doubt. If the nidus is on the surface of the bone, we favor biopsying the lesion with a 16-gauge Ackermann needle (Cook Medical, Bloomington, IN) or a similar trephine needle that is used coaxially through a 10-cm, 13-gauge Osteosite needle (Cook Medical). If the nidus is buried under thickened periosteal bone, we use an 11-gauge, 10-cm Jamshidi needle (Cardinal Health, Mcgaw Park, IL) to localize the path and engage the periosteum. A power drill with a 0.062inch diameter K wire is used to drill a path through the thickened bone then 5 mm beyond the center of the nidus. A 17-gauge Cool-Tip RF probe (Valley Lab, Covidien, Mansfield, MA) with a 7-mm or 1- cm active tip is placed through the coaxial needle and positioned with the active tip centered on the nidus. The coaxial needle is pulled back as far as possible on the probe and a sterile steri-strip used to tape the probe hub to separate the coaxial needle from the active tip. This helps to avoid conduction of RF along the coaxial needle which could cause severe skin burns. Final position is confirmed with a localized CT image before ablation (Fig. 4). The generator timer is set for a 7-minute burn cycle and the energy is gradually increased over 1-2 minutes until the temperature at the probe tip registers 80°C. If there is a portion of the nidus that is further than 5 mm away from the active portion of the probe, a second path is formed and the RF probe is redeployed for another burn cycle. Occasionally, when the periosteal new bone formation is abundant, the initial impedance is over 1000 ⍀ and the generator will not function. Various methods can be employed to bring down the impedance, including, twisting the RF probe slightly around in the tract, adding more grounding pads, pulling back the RF probe partially into the soft tissues superficial to the nidus (caution not to withdrawal the probe to the point in which skin burn could be an issue), enlarging the drilled or biopsied pathway, or placing a small amount of saline into the drilled bone. If the OO is in the spine, two precautions are suggested to avoid nerve damage (Fig. 5). The smaller 7-mm active tip RF,
219 Cool-Tip probe is used and a separate temperature probe is placed with the tip near or in the neuroforamen or spinal canal.10 If the temperature in the probe near vital nerve structures approaches 45°C, the RF energy is turned off. The patient is instructed to continue NSAIDs as necessary. However that first evening many children are painfree for the first time in months. Patients can typically differentiate the “soreness” that may be present because of the coaxial needle path through the soft tissues compared with the typical pain associated with their OO. Nearly all patients are pain-free by 2 weeks. Occasionally, children treated with RFA for a presumed OO may not have adequate clinical relief of symptoms. In these circumstances, the imaging needs to be reviewed to ensure that appropriate positioning of the RFA probe was accomplished during the procedure to achieve adequate treatment of the lesion and nidus. In addition, the actual diagnosis of OO may need to be revisited.
Bone Biopsies The two most common primary bone tumors encountered in pediatrics are Ewing sarcoma and osteosarcoma. Both usually have a soft tissue mass outside the primary bone lesion. Obtaining a sample from the soft tissue mass, bone mass and its interface is most helpful. The Osteosite 11- or 13-gauge needle will permit the coaxial passage of a trephine Ackermann needle (15- and 16-gauge, respectively) to complete the bone biopsy. Additional samples of the soft tissue mass can be obtained with a spring-loaded 16gauge biopsy needle device through the Osteosite needle. Osteosarcoma is more likely to produce new exuberant bone in the soft tissue mass. When biopsying an osteosarcoma, one needs to communicate clearly with the orthopedist and use a percutaneous needle path that can easily be resected with a subsequent surgical resection after neoadjuvant chemotherapy.
Figure 5 CT during RFA of lumbar right laminar OO, which was causing the patient 10/10 pain unless on pain medication. Whereas the 17-gauge, 7-mm active tip RF probe (arrowhead) in the nidus measured 90°C, the smaller 20-gauge temperature probe (arrow) near the neuroforamen measured less than 45°C. The patient suffered no nerve damage.
J.-N. Vo, F.A. Hoffer, and D.W.W. Shaw
220 Ewing sarcomas may have necrotic areas and only the viable areas will be diagnostic. Having an MRI or FDG PET before the biopsy or color flow Doppler US during the biopsy is helpful to aim for the viable tissue. Unlike osteosarcoma the tract does not have to be resected and some of the material can be sent fresh in normal saline or RPMI 1640 transport medium for potential molecular pathology, fluorescent in-site hybridization (FISH) or cytogenetics to determine if there is translocation, t(11;22) diagnostic of ESFT.11
Image-Guided Foreign Body Removal Foreign bodies (FB) consisting of glass, wood, or other vegetative fragments (thorns, etc.) embedded in the soft tissue is a common problem that lead children to seek care in emergency departments. Wood is highly echogenic by US with variable acoustic shadowing, depending on the angle of insonation and therefore generally very conspicuous.12 US imaging is our method of choice for investigation of the superficial soft tissues because it has a high sensitivity and specificity.13 US is capable of providing real-time guidance for FB retrieval. Our typical technique is to localize the FB with a high-frequency linear US probe and determine the best trajectory for retrieval. The skin is prepared and an incision is made wide enough to insert the leading interface of a device capable of grasping the FB (eg, hemostat, forceps, or sterile tweezers). It is best for a single operator to perform the real-time imaging with US and manipulate the retrieval device.14 We find that imaging initially parallel to the long axis of the FB and hemostat passage path facilitates its rapid advancement through the soft tissue toward the FB for successful grasping and removal. Just before reaching the FB with the hemostat, the US probe can be turned into the transverse scanning plane to visualize in real time the opening and closing of the clamp around the FB to obtain a firm grasp (Fig. 6). (Note, if the mouth of the grasping device does not circumscribe but is positioned adjacent to the FB, it will displace the FB side-to-side with opening and closing of the clamp.) We treat the patient with an additional 1-week course of antibiotics (amoxicillin and clavulanic acid).12
References
Figure 6 A 3-year-old girl with longstanding history of disliking shoes and the preference to walk barefoot. Patient developed progressive increase in localized foot pain. Mother did not recollect any specific injury or incident. (A) US shows an echogenic 3-mm FB embedded into child’s foot with a hypoechoic halo of edema and granulomatous formation, indicating at least a subacute event. (B) Forceps positioned with mouth open (arrowheads) around the FB before closure to obtain a firm grasp for removal.
1. Cleary AG, Murphy HD, Davidson JE: Intra-articular corticosteroid injections if juvenile idiopathic arthritis. Arch Dis Child 88:192-196, 2003 2. Mari P, Molinari L, Bolt IB, et al: Factors influencing the efficacy of intra-articular steroid injections in patients with juvenile idiopathic arthritis. Eur J Pediatr 167:425-430, 2008 3. Eberhard BA, Sison MC, Gottlieb BS, et al: Comparison of the intraarticular effectiveness of triamcinolone hexacetonide and triamcinolone acetonide in treatment of juvenile rheumatoid arthritis. J Rheumatol 31:2507-2512, 2004 4. Zulian F, Martini G, Gobber D, et al: Triamcinolone acetonide and hexacetonide intra-articular treatment of symmetrical joints in juvenile idiopathic arthritis: A double blind trial. J Rheumatol 43:1288-1291, 2004 5. MacMahon PJ, Eustace SJ, Kavanagh EK: Injectable corticosteroids and local anesthetic preparations: A review for radiologists. Radiology 252: 647-662, 2009 6. Dragoo JL, Korotkova T, Kanwar R, et al: The effect of local anesthetics administration via pain pump on chondrocyte viability. Am J Sports Med 36:1484-1488, 2008 7. Sibbitt WL, Peisajovich A, Michael AA, et al: Does sonographic needle guidance affect the clinical outcome of intraarticular injections? J Rheumatol 36:1892-1902, 2009 8. Torriani M, Rosenthal DI: Percutaneous radiofrequency treatment of osteoid osteomas. Pediatr Radiol 32:615-618, 2002 9. Sidhu MK, Goske MJ, Coley BJ, et al: Image gently, step lightly: Increasing radiation dose awareness in pediatric interventions through an international social marketing campaign. J Vasc Interv Radiol 20:1115-1119, 2009 10. Dupuy DE, Hong RJ, Oliver B, et al: Radiofrequency ablation of spinal tumors: Temperature distribution within the spinal canal. AJR Am J Roentgenol 175:1263-1266, 2000
Pediatric image-guided nonvascular MSK interventions 11. Hoffer FA: Gianturco LE, Fletcher JA, et al: Percutaneous biopsy of peripheral primitive neuroectodermal tumors and Ewing’s sarcoma for cytogenetic analysis. AJR Am J Roentgenol 162:1141-1142, 1994 12. Peterson JJ, Bancroft LW, Kransdorf MJ: Wooden foreign bodies: Imaging appearance. AJR Am J Roentgenol 178:557-562, 2002
221 13. Callegari L, Leonardi A, Bini A, et al: Ultrasound-guided removal of foreign bodies: Personal experience. Eur Radiol 19:1273-1279, 2009 14. Shiels WE, Babcock DS, Wilson JL, et al: Localization and guided removal of soft-tissue foreign bodies with sonography. AJR Am J Roentgenol 155:1277-1281, 1990
Corticosteroid Joint Injections Juvenile idiopathic arthritis (JIA) is a generic term for a set of diseases that result in chronic joint inflammation before adulthood and manifests as arthritis for which no specific etiology is identified.1 It is the most common rheumatic disease affecting children with a prevalence of 7-400 per 100,000. Pauci-articular (affecting 1-4 joints) is the most common subgroup, but polyarthritis is not uncommon. JIA can frequently extend into early adulthood and, if the inflammatory reaction is permitted to progress uncontrolled, may result in severe joint destruction and deformity.2 Intra-articular corticosteroid injections (IACI) in children with JIA has traditionally been reserved for use when nonsteroidal anti-inflammatory drugs (NSAIDs) have been ineffective/insufficient at controlling the inflammation or to treat a painful symptomatic flare in a child who is al-
Department of Radiology, Seattle Children’s Hospital and The University of Washington, Seattle, WA. Address reprint requests to Jack-Nghia Vo, MD, Seattle Children’s Hospital and The University of Washington, Department of Radiology, Section of Pediatric Interventional Radiology, Pediatric Radiology and Vascular Interventional Radiology, 4800 Sand Point Way NE, Seattle, WA 98105. E-mail: [email protected]
214
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ready managed with systemic therapy. Increasingly, pediatric rheumatologists are considering IACI earlier in the disease course with the goal of directing potent anti-inflammatory treatment directly into an actively inflamed joint and may permit the withdrawal or avoid the need for systemic therapy.1 There are a variety of corticosteroid preparations available. Triamcinolone hexacetonide (Sandoz, Princeton, NJ) is our agent of choice and is available as a preparation of 20 mg/mL. It has low solubility with excellent efficacy.3,4 The typical dose we use is 1 mg/kg (max. of 40 mg) in large joints (shoulders, hips, and knees); 0.5 mg/kg (max. of 20 mg) for medium joints (wrist, elbow, ankle, subtalar); and up to 5 mg into small joints of the hands and feet. When triamcinolone hexacetonide is not available, we will use triamcinolone acetonide (Bristol-Myers Squibb, Princeton, NJ), available in a preparation of 40 mg/mL. Although the risk of inducing an infection is low, the results of such a complication can be significant. Therefore, we use strict aseptic techniques during IACI. The most common local complications or adverse side effects involve subcutaneous atrophy and skin pigmentation changes because of leakage of steroid into the subcutaneous tissue along the needle tract. Both are usually selflimiting, resolving spontaneously. The risk can be reduced
Pediatric image-guided nonvascular MSK interventions by clearing the needle of residual steroid then compressing the site during and after needle removal. A post injection “flare” can occur in which there is a local increase in the inflammation that develops within hours of the IACI and can last several days; the exact cause is uncertain, but some feel that this may be induced by the formation of microcrystalline particles resulting in crystal-induced arthritis.5 This is also typically self-limiting. Contra-indications to IACI include an active infection of the joint or overlying soft tissues, hemorrhagic diathesis, and a child who is actively on anticoagulation or antiplatelet therapy. We feel that it is prudent to wait until the INR is ⬍2 before performing an elective IACI. We do not inject a single joint more than three times a year or within 6 weeks of a prior injection. Caution should be taken when considering adding a mixture of local anesthetic (LA) to a
215 corticosteroid preparation for a joint injection. We do not use any epinephrine-containing LA formulation due to a demonstrated increased risk and rate of chondrocyte apoptosis.6
Technique for Corticosteroid Joint Injections Cooperation of the child is required to accurately and safely position an access needle into an appropriate intraarticular location for corticosteroid injection. The child’s maturity and ability to cooperate determines the level of sedation required, if any. Older adolescents frequently only require a LA and moral support; child life specialists can be useful. When ultrasound (US) is not used for image guidance, we start with a needle-free air injection device (J-Tip) to infiltrate 0.5 mL of 1% lidocaine into the skin
Figure 1 A 10-year-old boy with JIA and hip pain. (A) A 22gauge spinal needle is introduced using an oblique trajectory to the lateral junction of the right femoral head and neck. A small volume of water-soluble contrast “flows” away from the needle tip and confirms an intra-articular position before the introduction of the steroid preparation. (B) A different child in whom contrast does not easily “flow” away from the needle tip and forms a persistent dense contrast blush. In this circumstance, there was “resistance” during the contrast injection and the needle tip is only partially in the joint as evident by some contrast opacifying the joint while the majority forms a persistent blush (arrow) (C).
216
J.-N. Vo, F.A. Hoffer, and D.W.W. Shaw
surface (National Medical Products, Irvine, CA). We also apply EMLA cream to the skin surface 30-45 minutes before the procedure while the patient is in the holding area. Fluoroscopy is the modality we most frequently rely on for image-guided IACI. This offers the ability in real-time, using contrast, to confirm an intra-articular needle position immediately before the introduction of the corticosteroid. An intra-articular position is confirmed by the sensation of low resistance during the injection along with the direct observation of the contrast “flowing” away from the needle tip within the joint. With an extra-articular location, the contrast will not diffuse away from the needle tip but rather form a persistent “blush” in the peri-articular soft tissue and continue to demonstrate some tactile resistance to the injection (Fig. 1). Injection procedures performed without image guidance leads to an extra-articular joint injection rate as high as 50%-60%.7 Hip Joint With the hip in anteroposterior position, a 22-gauge spinal needle is directed to the lateral junction of the femoral head and neck with an oblique trajectory (Fig. 1). Once the spinal needle is in contact with the bone surface, the needle is rotated 180 degrees and the inner stylet removed. A short connector tubing is than attached for contrast confirmation followed by the introduction of the corticosteroid preparation. With large and medium joints, either a small volume of water-soluble contrast or air can be used as a contrast agent. The needle rotation and attachment of the connector tubing is a standard routine performed for nearly all of our joint injections. Shoulder Joint We use an anterior approach with fluoroscopy for shoulder joint injections. The hand is placed at the child’s side with the hand supinated (a sandbag can help maintain this position), and a 22-gauge spinal needle is directed to the elliptic shadow formed by the medial aspect of the humeral head and the lateral margin of the glenoid (Fig. 2). Knee Joint US is used to detect for the presence of a joint effusion. If present, as much synovial fluid will be aspirated as possible before introducing the corticosteroid. In the absence of an effusion, a fluoroscopically guided suprapatellar bursa or a retropatellar approach is applied. With a suprapatellar approach, a 22-gauge spinal needle may need to be advanced beyond the midline of the knee and slowly withdrawn until there is a loss of resistance and diffusion of the contrast (or air) away from the needle tip. The suprapatellar bursa is a redundant sac when not distended and may require a “double wall” puncture technique similar to venous punctures. Subtalar and Tibiotalar (Ankle) Joint Tibiotalar (ankle) joint injections do not routinely treat subtalar synovitis. These joints should be treated independently when symptomatic. The subtalar joint is a complex articulation and image guidance is critical for reliable IACI. We use a lateral-oblique approach in which the pos-
Figure 2 A 17-year-old boy with JIA and right shoulder pain. (A) Frontal radiograph of the right shoulder demonstrating the elliptic shadow formed by the overlapping shadows of the humeral head and glenoid (arrowheads). (B) A 22-gauge spinal needle in place with the tip directed to the elliptic shadow target followed by contrast injection confirming an intra-articular position.
terior facet of the joint is placed in profile fluoroscopically. We have also started to use a high-frequency linear US probe for real-time guidance during advancement and positioning of a 22-gauge spinal needle. However, we continue to use brief fluoroscopy to confirm contrast spread within the subtalar joint (Fig. 3). With the lateral fluoroscopic view used for the subtalar joint, the tibiotalar joint is also seen in profile. The joint is most easily entered anteriorly from an inferior to superior trajectory along the lateral third of the joint, to avoid the anterior tibial artery. US is also frequently capable of demonstrating the joint and is useful for real-time advancement of the access needle (Fig. 3). Elbow and Wrist Joints The elbow is flexed to 90 degrees in the lateral position. Using a lateral approach, the radial-capitulum joint is placed in profile under fluoroscopy for access using a 22gauge spinal needle. Contrast will typically flow into the anterior and/or posterior joint capsule and with sufficient volume can reproduce the infamous elevated “fat pad” sign that radiology residents are so familiar with. For wrist injections the radial-carpal joint is placed in profile
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Figure 3 A 3-year-old girl with JIA. US was used to advance a 22-gauge spinal needle into each joint then brief fluoroscopy was used for confirmation. (A) Lateral fluoroscopic view shows that contrast opacifies the posterior facet of the subtalar joint. (B) The foot is maintained in the same fluoroscopic view and again confirms an intra-articular needle position in the tibiotalar joint. Note that the contrast in the subtalar joint is diluted following the introduction of the corticosteroid. (C) Coronal US image of the subtalar region using a high frequency linear “Hockey Stick” probe from a lateral approach. Note the echogenic epiphysis of the distal fibula (arrow) and the oblique course of the superior-lateral margin of the calcaneus (CALC). A 22-gauge spinal needle tip (arrowhead) is slipped along the upper margin of the calcaneus and below the fibula toward the subtalar joint. (D) US image of the tibiotalar region from a sagital frontal view. The joint is positioned between the anterior tibia (AT) and the talar dome (TD). A 22-gauge spinal needle tip (arrowhead) is positioned into the joint.
and accessed near the radial tubercle using a dorsal approach.
Radiofrequency Ablation of Osteoid Osteoma: How We Do It Children with presumed osteoid osteoma (OO) are referred by local pediatricians or more often through our hospital orthopedists for a percutaneous image-guided radiofrequency ablation (RFA). A consult is performed in our interventional radiology clinic to confirm the diagno-
sis of OO. A CT or MRI study will be reviewed or ordered if not already completed. We perform all RFA procedures for OO with CT guidance under general anesthesia. Clinically, the typical patient will have pain worse at night that awakens them. NSAIDs can effectively treat the pain, but the pain can worsen with time and the medication may eventually be required around the clock.8 The pain can progress to the point of severe debilitation; an OO located in the lower extremity can alter the child’s gait and affect their ability to ambulate. The typical imaging pattern is a nidus under 1 cm in diameter that is cortically based in the bone, most often involv-
J.-N. Vo, F.A. Hoffer, and D.W.W. Shaw
218 ing the tibia or femur. The nidus is lytic and when outside the joint frequently induces an intense periosteal bone thickening and reaction. Cortical lesions that are within the joint capsule often lack the periosteal new bone formation. All lesions will have increased uptake on skeletal scintigraphy
and periosteal and endosteal reaction on MRI. The nidus will enhance on MRI but is often more conspicuous on noncontrast CT. The nidus is localized with CT and an appropriate approach is planned, avoiding large vessels, nerves and ten-
Figure 4 A 4-year-old boy with left leg pain typical of OO. (A) CT image demonstrates a 4-mm lytic lesion with a tiny central nidus in the proximal femur. (B) Coronal image shows the OO with a sclerotic reactive halo. (C) A 13-gauge bone biopsy guiding cannula is advanced with CT guidance to the cortical margin of the OO; this served essentially as a guiding trocar for a drilling a path through the cortex with a K-wire. (D) A 7-mm burn diameter RFA probe is positioned within the nidus. Note the guiding cannula (arrow) has been retracted well away from the active tip to reduce risk of causing a skin burn.
Pediatric image-guided nonvascular MSK interventions dons. Two grounding pads are placed on the legs in a transverse orientation away from any superficial bony structures. For a femoral lesion, one grounding pad can be placed under the thigh on the ipsilateral leg and the other over the thigh on the opposite leg. For a lower leg lesion, two grounding pads can be placed on the ipsilateral thigh, front and back. It is important to insulate the skin between the two legs with a towel to avoid skin-to-skin conduction pathways and skin burns. We routinely reduce the CT technique, as much as 50%, and are able to maintain sufficient image quality for guidance. This is consistent with the principle of “Image Gently, Step Lightly” campaign of the Alliance for Radiation Safety, which is to improve radiation safety in pediatric interventional radiology.9 A small 3- to 5-mm skin incision is made to accommodate needle passage. Most OO can be treated without a biopsy. However, we do perform a biopsy for the occasional case where the diagnosis remains in doubt. If the nidus is on the surface of the bone, we favor biopsying the lesion with a 16-gauge Ackermann needle (Cook Medical, Bloomington, IN) or a similar trephine needle that is used coaxially through a 10-cm, 13-gauge Osteosite needle (Cook Medical). If the nidus is buried under thickened periosteal bone, we use an 11-gauge, 10-cm Jamshidi needle (Cardinal Health, Mcgaw Park, IL) to localize the path and engage the periosteum. A power drill with a 0.062inch diameter K wire is used to drill a path through the thickened bone then 5 mm beyond the center of the nidus. A 17-gauge Cool-Tip RF probe (Valley Lab, Covidien, Mansfield, MA) with a 7-mm or 1- cm active tip is placed through the coaxial needle and positioned with the active tip centered on the nidus. The coaxial needle is pulled back as far as possible on the probe and a sterile steri-strip used to tape the probe hub to separate the coaxial needle from the active tip. This helps to avoid conduction of RF along the coaxial needle which could cause severe skin burns. Final position is confirmed with a localized CT image before ablation (Fig. 4). The generator timer is set for a 7-minute burn cycle and the energy is gradually increased over 1-2 minutes until the temperature at the probe tip registers 80°C. If there is a portion of the nidus that is further than 5 mm away from the active portion of the probe, a second path is formed and the RF probe is redeployed for another burn cycle. Occasionally, when the periosteal new bone formation is abundant, the initial impedance is over 1000 ⍀ and the generator will not function. Various methods can be employed to bring down the impedance, including, twisting the RF probe slightly around in the tract, adding more grounding pads, pulling back the RF probe partially into the soft tissues superficial to the nidus (caution not to withdrawal the probe to the point in which skin burn could be an issue), enlarging the drilled or biopsied pathway, or placing a small amount of saline into the drilled bone. If the OO is in the spine, two precautions are suggested to avoid nerve damage (Fig. 5). The smaller 7-mm active tip RF,
219 Cool-Tip probe is used and a separate temperature probe is placed with the tip near or in the neuroforamen or spinal canal.10 If the temperature in the probe near vital nerve structures approaches 45°C, the RF energy is turned off. The patient is instructed to continue NSAIDs as necessary. However that first evening many children are painfree for the first time in months. Patients can typically differentiate the “soreness” that may be present because of the coaxial needle path through the soft tissues compared with the typical pain associated with their OO. Nearly all patients are pain-free by 2 weeks. Occasionally, children treated with RFA for a presumed OO may not have adequate clinical relief of symptoms. In these circumstances, the imaging needs to be reviewed to ensure that appropriate positioning of the RFA probe was accomplished during the procedure to achieve adequate treatment of the lesion and nidus. In addition, the actual diagnosis of OO may need to be revisited.
Bone Biopsies The two most common primary bone tumors encountered in pediatrics are Ewing sarcoma and osteosarcoma. Both usually have a soft tissue mass outside the primary bone lesion. Obtaining a sample from the soft tissue mass, bone mass and its interface is most helpful. The Osteosite 11- or 13-gauge needle will permit the coaxial passage of a trephine Ackermann needle (15- and 16-gauge, respectively) to complete the bone biopsy. Additional samples of the soft tissue mass can be obtained with a spring-loaded 16gauge biopsy needle device through the Osteosite needle. Osteosarcoma is more likely to produce new exuberant bone in the soft tissue mass. When biopsying an osteosarcoma, one needs to communicate clearly with the orthopedist and use a percutaneous needle path that can easily be resected with a subsequent surgical resection after neoadjuvant chemotherapy.
Figure 5 CT during RFA of lumbar right laminar OO, which was causing the patient 10/10 pain unless on pain medication. Whereas the 17-gauge, 7-mm active tip RF probe (arrowhead) in the nidus measured 90°C, the smaller 20-gauge temperature probe (arrow) near the neuroforamen measured less than 45°C. The patient suffered no nerve damage.
J.-N. Vo, F.A. Hoffer, and D.W.W. Shaw
220 Ewing sarcomas may have necrotic areas and only the viable areas will be diagnostic. Having an MRI or FDG PET before the biopsy or color flow Doppler US during the biopsy is helpful to aim for the viable tissue. Unlike osteosarcoma the tract does not have to be resected and some of the material can be sent fresh in normal saline or RPMI 1640 transport medium for potential molecular pathology, fluorescent in-site hybridization (FISH) or cytogenetics to determine if there is translocation, t(11;22) diagnostic of ESFT.11
Image-Guided Foreign Body Removal Foreign bodies (FB) consisting of glass, wood, or other vegetative fragments (thorns, etc.) embedded in the soft tissue is a common problem that lead children to seek care in emergency departments. Wood is highly echogenic by US with variable acoustic shadowing, depending on the angle of insonation and therefore generally very conspicuous.12 US imaging is our method of choice for investigation of the superficial soft tissues because it has a high sensitivity and specificity.13 US is capable of providing real-time guidance for FB retrieval. Our typical technique is to localize the FB with a high-frequency linear US probe and determine the best trajectory for retrieval. The skin is prepared and an incision is made wide enough to insert the leading interface of a device capable of grasping the FB (eg, hemostat, forceps, or sterile tweezers). It is best for a single operator to perform the real-time imaging with US and manipulate the retrieval device.14 We find that imaging initially parallel to the long axis of the FB and hemostat passage path facilitates its rapid advancement through the soft tissue toward the FB for successful grasping and removal. Just before reaching the FB with the hemostat, the US probe can be turned into the transverse scanning plane to visualize in real time the opening and closing of the clamp around the FB to obtain a firm grasp (Fig. 6). (Note, if the mouth of the grasping device does not circumscribe but is positioned adjacent to the FB, it will displace the FB side-to-side with opening and closing of the clamp.) We treat the patient with an additional 1-week course of antibiotics (amoxicillin and clavulanic acid).12
References
Figure 6 A 3-year-old girl with longstanding history of disliking shoes and the preference to walk barefoot. Patient developed progressive increase in localized foot pain. Mother did not recollect any specific injury or incident. (A) US shows an echogenic 3-mm FB embedded into child’s foot with a hypoechoic halo of edema and granulomatous formation, indicating at least a subacute event. (B) Forceps positioned with mouth open (arrowheads) around the FB before closure to obtain a firm grasp for removal.
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