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Файл:Ординатура / Хирургия / Библиотека им академика М.И. Перельмана / Книга_3733_Библиотеки_им_академика_М_И_Перельмана.pdf
Procedural Considerations
Timing and Adjunctive Medications
Preoperative embolization is typically performed within several days of
surgical resection. Delaying surgical resection at least 24 hours after
embolization may be beneficial.26 One study suggests the optimal latency for
meningioma resection following embolization may be 7 to 9 days, allowing
for maximal tumor softening, decreased operative times, and lower Simpson
grades.27 However, in tumors that have been embolized with excellent tumor
bed penetration (especially with smaller particle size such as 60 to 150 µm),
delay of surgical resection may lead to significant increases in peritumoral
edema and mass effect.6 Most interventionalists advocate high-dose
intravenous steroids during and after meningioma embolization procedures
where the tumor is large or there is already a significant amount of edema
present.
5,6
Provocative testing with injection of Amytal and/or lidocaine with
simultaneous neuromonitoring or immediate neurologic examination can help
predict the risk of embolization to dangerous territories.28 ECA vasospasm
may occur during the embolization procedure. Prophylactic application of a
transdermal nitroglycerin patch or sublingual calcium channel antagonists
may reduce the occurrence of vasospasm. Administration of papaverine (30
to 60 mg), nitroglycerin (100 to 300 µg), or verapamil (5 to 20 mg) through
the catheter system may reduce vasospasm and allow more predictable
results.
Endovascular Technique
Embolization should be performed by a well-trained neurointerventionalist in
a biplane digital subtraction fluoroscopy suite. Intravenous sedation,
monitored anesthesia care (MAC), or general endotracheal anesthesia should
be provided according to the specific goals and challenges of the procedure.
Arterial endovascular access is obtained most often by puncture of the
common femoral artery and insertion of a 5-Fr or 6-Fr short sheath using the
modified Seldinger technique. Alternatively, embolization may be performed
using a direct puncture technique (DPT).
The patient should be given a bolus of intravenous heparin with a goal
of 2 to 2.5 times the baseline activated clotting time (ACT) to help prevent
thromboembolic complications. If not performed previously, a detailed
angiographic study of the tumor blood supply is then performed via
superselective angiography using microcatheters.
After the decision to proceed with embolization is made, a suitable
guide catheter is selected to allow for a working platform within the major
artery supplying the tumor. The ICA, ECA, or the distal V4 segment of the
VA may be accessed by a 90-cm guide catheter in most patients. However,
vessel tortuosity or patient height may dictate the use of a longer guide
catheter. The outer diameter of the guide catheter is usually 5-Fr or 6-Fr, and
the inner diameter should easily accommodate the desired microcatheter(s).
After the microcatheter is in position within the target arterial pedicle
and the interventionalist is confident that safe embolization can be performed,
the embolic material is selected and prepared. The embolic material is
injected slowly with simultaneous biplane fluoroscopy to identify flow into
the feeding artery and tumor bed. Reduction of tumor blush by 80% or more
following embolization should be the goal, as reaching this threshold may be
necessary to impart a beneficial effect.23 Injection should stop when the
embolic agent no longer reaches the tumor or, in the case of particle
embolization, when there is contrast stagnation of the feeding artery (Fig.
16.1). If there is any identification of embolic material tracking into
undesired territories, or reflux along the microcatheter, the injection should
cease immediately. Deep penetration of embolic agent into the tumor bed
may result in complete devascularization of the tumor, often without
embolization of all of the feeding arteries. In other circumstances, selection
of additional pedicles may be necessary to obtain adequate embolization
results. This typically requires obtaining a fresh microcatheter. After
completion of the embolization, a thorough neurologic examination is
performed to assess for ischemic or hemorrhagic complications. Close
clinical surveillance is indicated over the following hours as delayed
complications such as intratumoral hemorrhage, increased edema, and mass
effect may develop. These complications can usually be quickly and reliably
treated if recognized in a timely manner.
4,5
Route of Embolization
The approach to head and neck tumor embolization varies based on different
factors including, but not limited to, the material chosen, the location of the
tumor, and the comfort level of the operator. The traditional transarterial
route has been used in most meningioma embolization procedures. Rarely,
vascular anatomy prevents appropriate endovascular access to the tumor and,
therefore, prevents intra-arterial treatment. In these situations, a percutaneous
(or transmucosal) DPT may be the only available route for embolization.
23
Occasionally, a previous craniotomy can allow DPT access for the
embolization of intracranial meningiomas (Fig. 16.2). Typically, liquid
agents with 18- to 20-gauge needles are employed for DPT alone or in
combination with the transarterial approach. Although DPT may yield
increased tumor penetration,14 systematic comparisons of transarterial and
DPT embolizations have not been performed. DPT does eliminate the issue
of catheter obstruction. DPT is not without risk of major complications.
29
Care must be taken during DPT as the embolic material is driven by pressure
and it may be pushed through physiologic collaterals into undesired
territories because of the pressure gradient that is created.30 Pain from tumor
necrosis may occur during the DPT procedure. The patient should be aware
of this possibility and may require general anesthesia.
31
CLINICAL APPLICATIONS
Meningiomas
Meningiomas represent approximately 20% of all intracranial tumors.
11,25,28
They usually display benign histopathology and are typically extra-axial or
intraventricular in location. Despite their typical benign pathology, they may
cause seizures and/or neurologic deterioration as a result of their spaceoccupying nature. Tumors that are small and asymptomatic can be followed
with periodic imaging monitoring for enlargement or development of
neurologic dysfunction.
32,33
Symptomatic tumors often require surgical
resection, which is typically curative and results in resolution of symptoms.
28
Angiographic evaluation of meningiomas should be performed with
catheterization of the bilateral external carotid, internal carotid, and vertebral
arteries before embolization. Blood supply to meningiomas can be bilateral
and may be derived from the intracerebral vessels (ICA and VA). On
angiography, meningiomas typically appear as circumscribed areas of
contrast staining that persists well into the venous phase. Large feeders may
show the classic “sunburst” pattern.
15
Surgical resection of meningiomas can result in significant morbidity
and mortality. Chan and Thompson34 reported on the surgical morbidity and
mortality of meningioma resection in a series of 257 patients. The authors
noted a surgical morbidity and a mortality of 30% and 4%, respectively.
34
Advanced age appears to be a significant surgical risk factor. A series of
meningioma resections in an elderly patient population documented a 6.6%
mortality rate and a 48% rate of surgical morbidity.
35
Embolization of arteries supplying the tumor that are not anatomically
accessible during surgery may help to reduce surgical morbidity and
mortality by minimizing intraoperative bleeding or softening of the
tumor.
26,28
A nonrandomized prospective study compared 30 patients who
underwent preoperative embolization in one center with 30 patients in a
second center who were not embolized. Those patients with greater than 90%
tumor embolization had decreased blood loss but no other identified benefit.
No differences in surgical morbidity and mortality were demonstrated
between the two groups.36 This study is limited by inherent selection bias and
potential systematic differences in administration of care between the two
centers. Other studies comparing patients who had preoperative embolization
to those who did not undergo embolization have similar limitations.
Macpherson37 describes a personal series of 52 meningioma patients of
whom 28 patients were embolized and 24 patients were not. The study
reported decreases in surgical difficulty with bleeding, blood transfusions,
surgical complications, and poor outcomes for the patients who were
embolized. This study is influenced by the subjective scoring methods
employed for determination of surgical bleeding difficulties. The operating
surgeon generated scores by comparing the technical difficulty of each
surgery to previous experiences of resecting tumors of comparable size
situated in similar anatomic locations.37 Similarly, in a retrospective
matched-pair analysis of 18 meningioma patients treated with embolization
and 18 patients without embolization, embolized patients had significant
decreases in estimated blood loss and transfusions. This study is limited by a
lack of sufficient detail reported for the methods of determining estimated
blood loss and extent of devascularization achieved.
38
Evidence of postembolization tumor necrosis can be documented via
diminished perfusion on proton spectroscopy, contrast-enhanced CT, and
contrast-enhanced MRI studies.
39–41
Embolization of meningiomas without
subsequent surgical resection has been shown to be beneficial as palliative
therapy in several cases.
39,42
Decisions regarding preoperative meningioma embolization should be
made on a case-by-case basis, considering both the risks and benefits
associated with the procedure. Tumor location, size, overall vascularity, and
specific angiographic features are key factors. Large convexity meningiomas
are often ideal for presurgical embolization. In such cases, significant blood
loss can result during the initial craniotomy before surgical control of the
tumor. The convexity location renders embolization via the middle meningeal
artery relatively low risk. Likewise, surgical resection of skull base
meningiomas, and other vascular tumors, can be challenging due typically to
narrow surgical corridors and firm tumor consistency. Tumor softening and
necrosis can make surgical resection easier by minimizing the need for brain
retraction and/or reducing mechanical injury to adjacent cranial nerves.
Unfortunately, skull base meningiomas often have higher embolization risks
as feeding arteries are often associated with the cranial nerve blood supply
and dangerous anastomoses.
Paragangliomas
Paragangliomas are rare tumors of neural crest cell origin that typically arise
from the temporal bone, carotid body, or nodose ganglion (i.e., glomus
tympanicum, glomus jugulare, carotid body tumor, intravagal
paraganglioma). Because these tumors develop where neural crest cells are
located, the anatomical pattern of the feeding arteries may be predicted by the
tumor size and location. Frequently involved arteries include the ascending
pharyngeal, lingual, posterior auricular, stylohyoid, and occipital. In addition,
the deep cervical artery and the thyrocervical trunk may contribute blood
supply.43 Advanced paragangliomas can seize blood supply from the anterior
tympanic (branch of internal maxillary), caroticotympanic (branch of internal
carotid), and superior tympanic (branch of middle meningeal) arteries.
30
When visualized on angiography, these hypervascular tumors are
characterized by an intense blush.
For larger paragangliomas, the benefits of preoperative embolization
appear to outweigh the associated risks. Perioperative blood loss can be
reduced and surgical time decreased.44 It may be prudent to limit
preoperative embolization to those paragangliomas greater than 3 cm in
diameter as smaller tumors can often be resected with less intraoperative risk.
Small tumors are typically more difficult to embolize. They are associated
with smaller feeding arteries that render injection of embolic material more
difficult without reflux into the parent vessel. In select cases, the DPT can
overcome this challenge.
30,45
In the case of carotid body tumors, balloon
protection of the ICA during embolization is often helpful.
Paragangliomas may be effectively embolized with various materials
(Fig. 16.3). Embolization is most commonly performed transarterially with
PVA particles or liquid embolic agents.30 DPT with NBCA or Onyx has
yielded good results and appears to be effective and safe.
31,46,47
In one report,
the DPT resulted in some degree of devascularization in more than 90% of
patients without permanent complications.
48
Juvenile Nasopharyngeal Angiofibromas
Juvenile nasopharyngeal angiofibromas (JNAs) are benign, yet highly
aggressive and infiltrating, neoplasms that are almost exclusively seen in
adolescent males. These tumors contain vessels that do not have a normal
smooth muscle wall. JNAs are commonly supplied by the internal maxillary,
ascending palatine, ascending pharyngeal, accessory meningeal, and internal
carotid arteries.49 JNAs have significantly larger shunts than most other head
and neck tumors, which may limit the achievable extent of
devascularization.50 Characteristically, angiography demonstrates a
reticulated pattern in the arterial phase and a dense tumor blush that continues
into the venous phase.
The advantages of preoperative embolization for JNAs are compelling.
Studies show diminished intraoperative blood loss, less blood transfusion
needs, more complete resection, and fewer tumor recurrences.
51,52
Blood loss
reduction during postembolization resection is considerable compared to the
other head and neck tumors. JNAs are less likely to recur when the entire
tumor is removed en bloc. Complete devascularization makes this type of
removal easier. DPT may be a useful method for devascularization if all
branches cannot be embolized through the transarterial route (Fig. 16.4).
31
Similar to paragangliomas, multiple embolic materials can be used to
treat JNAs. As JNAs tend to have large arterial shunts, particles greater than
150 µm may be advantageous. Larger particles may be needed if significantly
larger shunts are discovered during angiography. The operator should,
therefore, be prepared to make rapid intraoperative adjustments if necessary.
Particles that travel through a large shunt may cause pulmonary
complications. One potential solution to these high-flow shunts is to use
balloon-augmented embolization to decrease the flow through the target
vessels at the time of embolization.
1,2