Image guided Biopsies [1,2]:
Image-guided MSK biopsies are safe,
minimally invasive,
and effective procedures with high diagnostic accuracy,
lower risk,
better recovery ,
lower patient morbidity,
lower cost compared with open biopsies.
Technique:
Fig. 7: Examples of trephine bone biopsy needles. ( A ) 14.5G Ostycut needle (Angiomed/Bard, Karlsruhe, Germany). ( B ) 11G Cook bone biopsy needle (Cook, Bloomington, Indiana).
References: Lee Et Al. Image-Guided Musculoskeletal Biopsies . Semin Intervent Radiol 2010;27:191–198
Fig. 8: Bone marrow biopsy technique using the Westerman-Jensen needle
References: George A. Fritsma. Bone Marrow Examination
Percutaneous Tumour ablation [3,4] :
Chemical Ablation : Alcohol ablation
- Ethanol causes cell dehydration and thrombosis of the tumor vessels.
- In cases of vascular tumors,
such as vertebral hemangiomas,
ethanol injection has been introduced as the preferred ablation method because generating temperatures in a hemangioma that are adequate to initiate cell death may be impossible with thermal ablation because of the cooling effect of flowing blood .
- The recommendation is to inject a mixture of 1% lidocaine and contrast material into the tumor under CT or fluoroscopic guidance before ablation to estimate tumor perfusion followed by injection of 3–25 mL of 96% ethanol using one or more 18-gauge spinal needles.
Thermal Ablations: Radiofrequency,
Microwave,
Laser,
or Cryoenergy
- The goal of thermal ablation is to induce cell death by introducing an extreme change of temperature,
either cold or hot,
that is applied using a probe in or adjacent to a tumor.
- On the basis of preoperative imaging findings,
one or more probes are positioned so that the lethal ablation zone extends beyond the margin of the tumor if warranted.
Radiofrequency ablation—RFA generates heat by application of high-energy frequency electric current.
The active electrode delivers the energy through the tip of the probe at the treatment site.
The current then flows through the patient to the return electrodes in the dispersive pads where the energy is dissipated away from the body.
Usually the heating during RFA of osteoid osteomas is performed for 6 minutes after achieving temperatures of approximately 90°C.
Microwave ablation—Thermal ablation is achieved by application of microwave energy through antennas that generate an oscillating electromagnetic field.
This electromagnetic field in turn leads to energy absorption and tissue heating due to dielectric hysteresis.
The mechanism of hysteresis is that the polar molecules,
such as water,
attempt to continuously align with the oscillating electromagnetic field; with rapid oscillations,
the inability of the polar molecules to align properly creates energy deposition in the tissue and heat.
The optimal frequencies used for microwave ablation are reported to be 915 MHz and 2.45 GHz.
Laser ablation—In laser ablation,
photocoagulation is achieved by transmitting infrared light energy through an optical fiber of near infrared wavelength,
which leads to the direct deposition of energy and heating.
The infrared light used commonly originates from neodymium:yttrium-aluminum-garnet (Nd:YAG) diode laser fibers and ranges from 800 to 1100 nm.
Cryoablation—small-bore insulated ablation probes use compressed argon and helium gas to cool and thaw tissue according to the Joule-Thompson effect .
When activated,
cryotherapy probes are able to freeze a volume of tissue to extremely cold temperatures that ultimately result in cell death.
MR-HIFU (MRI-guided High Intensity Focused Ultrasound)- This involves focusing high intensity ultrasound beam in the desired tissue to be treated.
The ultrasound waves cause heat generation in the tissue with coagulative necrosis.
MRI is used to guide the treatment.
Fig. 9: Radiofrequency ablation of osteoid osteoma of talus
Fig. 10: Radiofrequency ablation of osteoid osteoma greater trochanter in a 6 month old child
Fig. 11: Intersticial Laser Photocoagulation of osteoid osteomas
References: 2000-2018 by the Plone Foundation
Trans arterial embolization of tumors [5,6,2]:
- Indicated in primary or metastatic bone tumors to reduce operative hemorrhagic risks,
to simplify or allow more definitive surgery,
or in the context of pain palliation,
fever,
bleeding,
or hypercalcemic and other factors.
- Preoperative arterial embolization improves surgical vision and allows safer and faster surgery by decreasing bleeding from the surgical site.
To maximize the effects of the embolization,
the planned surgery should be conducted within 24 to 48 hours.
- Embolization is also used as a palliative treatment in painful bone metastasis when surgery cannot be performed because of the size or location of the tumor or the general status of the patient.
Pain relief is possibly achieved by inhibiting and reducing tumor growth that decreases the pressure on adjacent neural structures.
- Sequential embolization has also been described as a primary treatment alternative for hypervascular bone tumors,
such as aneurysmal bone cyst and giant cell tumor.
This method is recommended when the tumor is inoperable or surgery is technically difficult or may result in considerable morbidity .
In pelvic and spinal tumors,
arterial occlusion has been reported to devascularize tumors,
cause calcification of their margins,
alleviate pain,
and even result in complete growth arrest of the lesions.
Technique:
- Initially,
a diagnostic angiogram is done to define the supplying vessels following which embolization is performed.
- The choice of catheter will depend upon the situation and size of feeding vessel.
Usually a 4- or 5-French diagnostic catheter used for the initial angiogram and continue the same catheter for embolization where the feeding vessel is large or add a standard 2.3- to 2.5-French microcatheter as a coaxial technique.
Embolic agents :
- Gelfoam is the embolization material of choice for pre-operative embolization.
- In cases where serial embolization is required,
particulate agents like polyvinyl alcohol (PVA) or embospheres is used.
- Coils are used where parent vessel occlusion is required or when protection of distal vasculature is necessary.
- Liquid embolics like N-butyl cyanoacrylate be advantageous where definitive treatment is desired .
Fig. 12: Pre-operative trans arterial embolization in epithelial sarcoma of right arm.
Fig. 13: Pre-operative trans arterial embolization in metastases of left acetabulum from carcinoma thyroid
Intra-arterial chemotherapy[7]:
- Intra-arterial chemotherapy under image guidance provides shrinkage of tumour volume prior to surgical resection in cases refractory to systemic chemotherapy.
- This approach permits higher cytotoxic concentrations to be directed to the targeted lesion.
- Preoperative intra-arterial chemotherapy has resultant benefits of :
- controlling micrometastasis,
- analysing the response of the tumor to chemotherapy
- promote limb salvage surgery by reducing and consolidating the tumor volume
- control local lesions very effectively.
- Intra-arterial chemotherapy is used mainly for osteogenic sarcoma,
melanoma,
malignant fibrous histiocytoma and soft tissue sarcomas.
Cementoplasty [2]:
- Vertebroplasty consists in the percutaneous injection of cement into vertebral collapses in order to obtain pain relief and mechanical strengthening of the vertebral body.
- Indications: to treat painful vertebral compression fractures which have failed conventional medical therapy.
- Contraindications: uncorrectable coagulopathy,
spinal infection,
vertebral infection and allergy to bone cement.
Technique:
- Generally,
an 11 G needle is preferred for lower dorsal and lumbar vertebrae while a 13 G needle may be used for upper dorsal vertebrae.
- Generally,
two approaches are used to enter the vertebral body- the transpedicular approach and the parapedicular approach.
- The transpedicular approach has an advantage of protecting the nerve roots and the paravertebral tissue due to the long intraosseous course.
The first step is to align the affected vertebral body in such a way that the spinous process is in the midline,
the vertebral edges overlap and the pedicle is in the centre of that half of the vertebral body.
The entry point is marked on the skin at about 10 O'Clock position with respect to the pedicle that will be traversed.
Needle is inserted from the planned entry point.
For transpedicular approach,
it is most important to keep the needle,
lateral to the medial margin and superior to the inferior margin of the pedicle.
This takes care that the needle is in the confines of the pedicle.
The needle position could be checked on AP and lateral view on fluoroscopy.
Once the needle reaches the posterior margin of the vertebral body,
it should be further advanced till the anterior third of the vertebral body in lateral view and till the midline on AP view.
Unipedicular approach would suffice if the cement crosses to the opposite side.
Otherwise,
a bipedicular approach is required .
- For parapedicular approach,
the vertebral body is directly entered and thus the needle is kept lateral to the lateral margin of the pedicle.
- The cement commonly used is Polymethyl Methacrylate (PMMA).The endpoints for cement injection include passage of cement beyond the marrow space and cement reaching the posterior quarter of the vertebral body.
- Kyphoplasty: Before injecting cement,
kyphoplasty involves an additional step of increasing the size of the vertebral body.
This is achieved with a kyphoplasty balloon.
Later,
a dedicated Vertebroplasty injector system can be used to inject PMMA for khyphoplasty.
It is recommended to treat up to 3 vertebral levels at a sitting to prevent the complications arising due to marrow fat embolizations .
Fig. 14: Vertebroplasty : Diagram showing that the needle tip should not cross the medial border of the pedicle on the anteroposterior view (left ) before it has reached the posterior cortex of the vertebral body on the lateral view (center).
References: Jean-Denis Laredo and Bassam Hamzé. Complications of Percutaneous Vertebroplasty and Their Prevention
Joint injections [8] :
- Appropriate needle gauge and length depend on the joint being targeted.
- The fluoroscopic approaches rely on aligning the fluoroscopic beam with the needle trajectory so the needle appears as a small dot (bull’s-eye technique).
Centering the beam on the skin entry site avoids parallax and distortion.
- Ultrasound : An in-plane approach,
with the needle positioned parallel to the midline of the long axis of the transducer,
is generally preferable to the out-of-plane technique so that the needle can be seen throughout the procedure.
Planning a skin entry site that allows a shallow needle trajectory maximizes needle visibility: visualization markedly diminishes with angles approaching 40°.
One strategy to accomplish this is to place the puncture site farther from the probe to achieve a longer but flatter trajectory with respect to the transducer.
“Toeing-in” the probe can also help to produce an angle between the transducer and the needle that is closer to parallel (fig 15).
Fig. 15: Concept of toeing-in of ultrasound probe. A, Three-dimensional image shows probe before it is pressed into skin. B, Three-dimensional image shows edge of probe opposite needle has been pressed into skin while nearer edge is gently lifted. Maneuver flattens angle between probe and needle, facilitating visualization of needle.
References: O. Kenechi Nwawka,Theodore T. Miller. Ultrasound-Guided Peripheral Nerve Injection Techniques. DOI:10.2214/AJR.16.16378
Nerve blocks [9]:
- The needle trajectory should be as close to perpendicular to the transducer beam as possible to maximize visualization of the needle.
- Nerve injected as visualized in the short axis and in-plane with the transducer.
This technique will allow visualization of the margins of the nerve and the tip of the needle at all times during the injection and has been shown to have a lower risk of intra neural injection.