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Файл:Ординатура / Хирургия / Библиотека им академика М.И. Перельмана / Книга_5225_Библиотеки_им_академика_М_И_Перельмана.pdf
5 Imaging-Based Navigation: Applications Beyond Instrumentation
55
The following case example was a patient that presented to our institution with
several months of worsening numbness in the bilateral lower extremities, as well as
worsening balance and gait instability. The patient had previously been diagnosed
with spinal tuberculosis and undergone multidrug therapy in another country but
had no prior surgical intervention. Although uncommonly seen in many parts of the
developed world, tuberculosis continues to affect a large amount of the global population. Although only a minority of patients are symptomatic, the spinal ramications of mycobacterium tuberculosis infection can lead to great disability. Unlike
typical bacterial osteomyelitis and discitis, spinal tuberculosis tends to begin and
center at the vertebral body, with the disc space remaining relatively spared.
Eventually this leads to cold abscess formation, bony destruction, and ultimately
kyphotic deformity [49].
The patient’s MRI imaging at the time of presentation to our institution is shown
in Fig.5.9, demonstrating signicant bony destruction of the 11th thoracic vertebra
with large abscess formation, causing signicant kyphotic deformity as well as
mass effect on the spinal cord. Figure5.10 shows the patient’s preoperative CT,
highlighting the extent of bony destruction.
The patient was planned for a staged procedure with posterior instrumentation
performed in the rst stage, along with laminectomy decompression from T9
through T11 and bilateral facetectomies at T10/T11 to allow for access, tissue collection, and debridement of the abscess. Due to the distortion of the anatomy, navigated instruments including the navigated probe were utilized throughout to ensure
adequate access into the abscess. Figure5.11 demonstrates partial reduction of the
patient’s kyphotic deformity with temporary stabilization following the rst stage
debridement. On initial postoperative assessment, the patient noted improvement in
bilateral lower extremity numbness and began working with therapies. The patient
returned to the operating room for a second stage debridement with left-sided T10
Fig. 5.9 TB preoperative MR
56
Fig. 5.10 TB
preoperative CT
Fig. 5.11 TB initial
instrumentation/
debridement/reduction
intra-op
K. S. Heidari and C. J. Kleck
5 Imaging-Based Navigation: Applications Beyond Instrumentation
Fig. 5.12 TB nalization/
cage intra-op
57
and T11 rib resection for costotransversectomy approach with partial corpectomies.
Further tissue was collected for analysis. Although cultures were negative, PCR
testing conrmed the diagnosis. The patient subsequently returned for the third and
nal stage with reinstrumentation, completion of corpectomies, and discectomies
with right-sided pediculectomy at T10 and T11. Finally, the cage was inserted from
the left and expanded to restore height. Following resection, CT imaging was
obtained intraoperatively to ensure adequate resection and assist in mapping the
space for planned cage placement, and then again following cage placement to
ensure satisfactory hardware placement. Figure5.12 shows intraoperative CT image
obtained following cage placement. The patient did well postoperatively and was
able to be discharged home on postoperative day ve from nalization. At six weeks
postoperative the patient reported signicant improvement in their symptoms and
was ambulating without assistive devices. Radiographs obtained at six weeks postoperative are shown in Fig.5.13.
58
K. S. Heidari and C. J. Kleck
Fig. 5.13 TB 6 weeks postoperative
Radiofrequency Ablation ofTumors
Radiofrequency ablation (RFA) has presented a useful adjunct in the treatment of
spinal tumors. RFA utilizes high-frequency radio waves to create and convert an
electrical current into heat, thereby inducing thermal necrosis of targeted tissue
around the RFA probe. This modality is useful not only as an adjunct treatment to
help for local control of tumors, but also to assist in pain relief, without disrupting
systemic therapies. It can be used as part of palliative treatment or as an adjunct
during surgical treatment or radiation treatment. The size of ablation corresponds to
the intensity and duration of energy released, as well as the tissue characteristics,
which can contribute to impedance. Increased impedance results in increased power
requirements to maintain current across tissues [50–54].
Cooled probes are often utilized in bone as they can facilitate a larger energy
delivery. These probes house an inner chamber through which a cold solution is
cycled [54]. The probe is temperature controlled, maintaining a lower temperature
at the tip than between electrodes. Meanwhile, real-time temperature monitoring
helps to avoid thermal damage to adjacent structures. The probe also utilizes an
impedance cutoff, in which the system pauses ablation if impedance is too high,
which would prevent tissue from rehydration [50, 54].
5 Imaging-Based Navigation: Applications Beyond Instrumentation
59
Simultaneous bipedicular vertebral body ablation allows for time efciency in
addition to added safety and decreased risk to surrounding tissue, as it allows for
decreased heat propagation compared to single electrode treatment. Tomasian
describes the safety of concurrent ablation and cement augmentation through the
same cannulation, with a bipedicular approach [52]. Figure5.14 shows an example
of real-time monitoring during radiofrequency ablation using bipedicular probes
simultaneously targeting the vertebral body. As the monitor shows: time, temperature, power, as well as impedance are displayed throughout the ablative process, as
well as the selected settings.
Navigation has provided methods to utilize RFA while minimizing risk to the
spinal cord and neural elements. Navigated probes can be inserted through the pedicle and into the vertebral bodies [26]. A projection can then be created to map and
plan the area of treatment, ensuring a safe corridor while maximizing treatment
ability for local control of tumor during or following resection or debulking. The
planning projection also allows for selection of the desired probe tip, matching the
ablation zones by tip length. For example, in the Medtronic OsteoCool (Medtronic,
Minneapolis, MN) series, the 7mm active tip carries a 11 × 10mm ablation zone,
while the 20mm carries a 29 × 21mm ablation zone.
RFA can be utilized with percutaneous techniques, or in combination with open
techniques, including during en bloc resections to assist inlocal control. The access
Fig. 5.14 RFA (Medtronic Osteocool) screen showing simultaneous probe temperature readings
from bipedicular RFA in the T6 vertebral body
60
K. S. Heidari and C. J. Kleck
tract can also be ablated with selection of specic settings while slowly retracting
the probe, although care must be taken to terminate the process when approaching
skin to avoid thermal necrosis injury. RFA can also be combined with concurrent
kyphoplasty or vertebroplasty, which can utilize the same transpedicular tracts for
cement introduction [26, 53].
We present here for illustration the case of a young patient who presented with
progressive thoracic myelopathy symptoms and bilateral lower extremity numbness. Figures5.15, 5.16, 5.17, and 5.18 demonstrate preoperative CT and MRI of a
locally aggressive tumor. Biopsy of the lesion was performed and was consistent
Fig. 5.15 Axial CT image
through T6 giant cell
tumor of bone lesion
Fig. 5.16 Sagittal CT
image depicting locally
aggressive giant cell tumor
of bone
5 Imaging-Based Navigation: Applications Beyond Instrumentation
Fig. 5.17 Axial
T2-weighted MR image of
giant cell tumor of bone
demonstrating severe
spinal cord compression
Fig. 5.18 Sagittal
T2-weighted MR image
demonstrating involvement
of left pedicle
61
with giant cell tumor of bone. He was subsequently referred to our institution and a
total resection was planned with RFA as adjunctive treatment. The patient was
brought to the operating suite and after induction of anesthesia and endotracheal
intubation was positioned prone on the operating table. Open posterior approach to
the mid-thoracic spine was performed and the navigation array afxed to an exposed
spinous process.
62
K. S. Heidari and C. J. Kleck
Intraoperative 3D imaging was obtained and the navigated awl was utilized to
create transpedicular tracts into the T6 vertebral body which contained the majority
of the tumor. This was done during the placement of pedicle screws at the adjacent
levels to optimize workow. The navigated probe was then placed down into the
tracts and navigation software then utilized to create, size, and save projections as
plans for the desired ablative zones in the vertebral body, which are shown in
Figs.5.19 and 5.20. Utilizing these projections, the appropriate probes were selected
and used for ablation of the tumor in T6. An RFA probe was inserted on each side
through the pedicle tracts and held in position just above the oor of each tract. The
ablation was performed utilizing both transpedicular probes simultaneously as
described with the bipedicular technique.
Once this was complete, the navigated probe was again utilized within the left
pedicle, which was heavily involved with tumor mass, to plan a precise projection
for a controlled burn within the pedicle, which is shown in Fig.5.21. Another probe
was inserted to the planned depth and a second ablation through this single probe
was performed.
Fig. 5.19 Planning area for left-sided tumor RFA in the vertebral body
5 Imaging-Based Navigation: Applications Beyond Instrumentation
Fig. 5.20 Navigation imaging demonstrating the saved plan for left-sided RFA in the vertebral
body, as well as the planning for the right-sided RFA probe
63
Fig. 5.21 Navigation imaging demonstrating the projected plan for RFA within the left pedicle
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K. S. Heidari and C. J. Kleck
En Bloc Tumor Resection
Navigation can also be utilized to plan and execute en bloc tumor resections, aiding
the surgeon in mapping out appropriate soft tissue dissection and bony resection and
osteotomies to safely remove tumor mass while maintaining negative margins. As
previously described, the navigated instrument can be used throughout the resection
to help navigate in real time, ensuring not only depth and adequacy of resection, but
also safety to surrounding structures. This is of incredible importance in tumors of
the spine, as the proximity of the neural and vascular structures necessitates incredible care and accuracy to avoid injury. One systematic review found a complication
rate of 50% in 145 en bloc resections of lumbar spine tumors [55]. When en bloc
resection is not possible, due to unacceptable risk of compromise to vital structures
such as the spinal cord, tumor gross total resection can still be undertaken with navigated assistance to ensure safe and complete resection [5, 26, 55–59].
In their study comparing en bloc navigated resection with curettage of metaphyseal and/or epiphyseal locally aggressive primary bone tumors, Farfalli etal. found
no local recurrences in the navigated resection group, although the low sample size
precluded detection of meaningful difference between the two groups with regards
to recurrence risk, complications, and functional scores [57]. In giant cell tumors of
the spine, recurrence rates have been reported to range from 22% to 41% [59].
Additionally, giant cell tumors of bone do carry risk of sarcomatous change. En bloc
or gross total resection is therefore recommended to minimize risk of local recurrence, as was planned in our representative patient (Fig.5.14).
Following intraoperative RFA treatment of the previously presented patient’s
tumor, the navigated probe was utilized to trial and map and plan soft tissue dissection and osteotomy pathways to allow for complete resection of the tumor.
Figures5.22 and 5.23 depict utilizing a navigated probe to plan resection cuts in our
representative case. Care was taken to select pathways that would minimize risk to
vital structures while also minimizing tumor violation and seeding. As Fig.5.22
shows, a pathway was selected above the facet joint of the superior vertebra which
had some tumor involvement on the left side. This allowed for precise resection of
that area of involvement, including a portion of the pedicle, without necessitating
compromise of the entire vertebral segment. Given the lack of additional involvement of that segment, a pedicle screw was placed on the right side under navigated
guidance. Figure5.23 depicts the inferior resection trajectory on the left side, utilizing the disc space to help effect a complete spondylectomy of the heavily involved
segment.
As the resection was carried out, the navigated probe was utilized throughout to
ensure safety of the resection as well as depth and maintenance of margins between
osteotome cuts. Figures5.24, 5.25, and 5.26 depict this process at different points
of the resection in our patient’s case. Figures5.27 and 5.28 are the patient’s postop-
erative upright radiographs.