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If there is one “lightning rod” topic addressed by the vascular neurosurgery
community, radiosurgery vs. CCMs is that topic. While both CCMs and radiosurgery have
been around for decades, CCMs are, at best, poorly understood. CCM natural history
has only been documented in depth and number within the last 10 years, thanks mostly
to the advent of MRI. Medical science has not yet determined the root cause and
predictive hemorrhaging behavior of CCMs. Developing a “cure” or a process to deal
with an entity of unknown origin and pattern of behavior is problematic at best.
The resultant schism divides most of the neurosurgical community into
two camps (assuming we’re dealing with an aggressive lesion requiring
some type of action, not “expectant management”): those who advocate
conventional surgery for CCM removal (the majority), and those who think
radiosurgery has a role in the reduction of CCM hemorrhagic potential.
There are very few neurosurgeons who take the middle ground by
equally favoring both solutions to this issue.
Why the great divide? There
has not yet been a 100% conclusive study that radiosurgery is an
effective solution. While a few retrospective studies have been done, to date, not one
randomized prospective study has been completed. Irrefutable evidence does not
exist showing that radiosurgery reduces or eliminates future hemorrhagic
events versus the natural history of the disease. Also, there have been cases
where longer term results from radiosurgery have been less than ideal, causing
patients to seek conventional surgical resection to alleviate persistent symptoms.
In many cases, the radiation was a complicating factor, reducing
the effectiveness of the follow-on conventional surgery.
Some radiosurgery studies, Gamma Knife studies in particular, indicate
that there is a reduction in longer term hemorrhage rate after the
procedure [Kondziolka], [Hasegawa], while other studies also show higher
complication rates [Steinberg]. Even with Gamma Knife, some complication
rates were unacceptably high [Pollock et al]. Pollock and Karlsson both agree
that,
“whatever limited hemorrhage protection is provided by radiosurgery is not
sufficient to accept the high risk of delayed radiation-related
complications associated with radiosurgery of CMs.” [Pollock]
Most importantly, radiosurgery does not remove or obliterate the lesion
[Gerwitz et al]. Changes in lesion size cannot be indexed conclusively to
radiosurgery. In many cases, lesions are dynamic, and it is impossible to
attribute change in size or volume to an external procedure.
One proposed hypothesis attempts to explain why radiosurgery surgery may
not be suited for CCMs:
Avoiding the haemosiderin fringe is difficult in practice because of
the intimate relationship of the ring to the periphery of the
cavernoma and uncertainty in accurately determining the lesion’s
edge… The haemosiderin fringe surrounding the cavernous malformation
is therefore likely to be generously dosed during radiosurgery. [St.
George]
In other words, the properties of the “haemosiderin” (aged blood
products; “hemosiderin is the American spelling) ring make it
difficult to ascertain the exact boundary of where the lesion ends and
healthy, albeit hemosiderin stained, brain tissue begins. This is in
spite of the fact that:
Most authors agree,without venturing a scientific aetiological basis
for their observations, that there is a higher incidence of sub-acute
radiation reactions following radiosurgery for cavernous angiomas as
compared to AVM or other targets, not withstanding lower recommended
marginal doses than employed for AVM targets [St. George].
This report stipulates that despite using lower dosage rates in CCM vs. AVM
cases, more radiation-induced complications were seen with the CCM
cases.
Finally, neurosurgeons at the Barrow Institute commented on the efficacy
of radiosurgery radiosurgery in the treatment of CCMs:
“First, radiation treatment of angiographically occult vascular malformations
does not 'cure' these lesions. Hence, even after treatment,
here is a continued risk of hemorrhage. Radiographic documentation of
a lesion eliminated after radiosurgery has yet to be published.
Second, the risk of radiation injury is significant and must be
considered and compared with the outcomes of conventional surgical
treatment of these lesions. Third, patients who had received radiation
therapy before surgical resection had the worst postoperativecourse.”
[Gerwitz].
On the other hand, conventional surgery in most cases can remove 100% of
the lesion. Dramatic improvements in microsurgical techniques and experience
now allow successful resection of malformations, which would not have been
touched five years ago. There is at least one neurosurgeon who has changed
positions in this debate and has stopped performing radiosurgery as the
primary means to treat deeply seated cavernous malformations
The downside is that conventional surgery brings with it a longer and
non-trivial patient recovery time. In some cases if the lesion is not
completely resected, it can and does regenerate. Of
course, there are instances where the lesion is both aggressive and
surgically inaccessible without undue risk of mortality. It is this
subset of patients, when all other alternatives have been considered
and discarded, to which Gamma Knife may be most suited.
Until a definitive, randomized, multi-centered prospective study is
completed, radiosurgery as a treatment modality for CCMs will continue
to polarize the neurosurgical community.
Personal Story
Visit our Stories section for a description of
one member's experience of the radiosurgery procedure.
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