| Authors: J.
Gordon Wright, MD; Roy Nicholson, MD; David E.
Schuller, MD;
William L. Smead, MD.
Country: Columbus, Ohio. USA
Abstract
Methods Results Discussion
Conclusions
References
Send Comments
Abstract
Purpose: Many patients who have advanced cancer of
the neck will have involvement of the internal carotid artery. The management of this
condition remains controversial, and a wide range of therapeutic options have been
suggested including ligation, “shaving” the tumor off the carotid, or en bloc
resection and replacement of the internal carotid artery by polytetrafluoroethylene, vein,
or superficial femoral artery. We reviewed our experience with en bloc resections of the
internal carotid artery in a consecutive series of patients who had malignancies involving
the internal carotid artery at a single institution from 1989 to 1995. Methods: We used a
retrospective chart review based on a list of 20 patients generated by the Hospital Cancer
Registry and our Vascular Surgery clinical database. Results: All patients had their
internal carotid artery removed and replaced with a greater saphenous vein while they were
under general anesthesia. A resection of their cervical malignancy was also performed.
Concomitant myocutaneous flaps were rotated over the carotid bypass in six (30%) patients.
Eight (40%) of the bypass grafts were nonreversed, and 12 (60%) were reversed, with a
clear trend towards using nonreversed veins more recently. Shunts were used in 18 (90%).
Eighteen of the 20 patients had some form of intraoperative contamination including
tracheostomies, pharyngostomies, or fistulas. Half of the patients had intraoperative
radiation therapy, and 16 (80%) patients underwent operation for recurrent cancer. During
the follow-up period two (10%) patients had strokes (one minor and one major), and one
patient had a graft blowout, which was treated by ligation without stroke. One patient had
an asymptomatic occlusion of his graft. Conclusions: From these results we conclude that
the use of the greater saphenous vein to replace the internal carotid artery after en bloc
resection is not attended by a high rate of infectious complications or graft blowout even
in the presence of intraoperative tracheopharyngeal contamination and that the greater
saphenous vein is the conduit of choice for replacing an internal carotid artery after
cancer resections. (J Vasc Surg 1996;23:775-82.)
When attempting a cure for patients with advanced
head and neck cancer, the surgeon will remove all neck metastases along with the primary
tumor while trying to preserve as much function as possible. Occasionally the malignancy
will involve the carotid artery. This poses a special problem, because resection of the
carotid artery (with or without replacement) puts the patient at additional risk for the
potential complications of stroke, graft infection, or graft blowout. In the past, these
complications occurred frequently enough to dissuade many surgeons from undertaking
en-bloc resections that involved the carotid artery. However, we have always believed that
the best way to manage advanced head and neck tumors invading the carotid artery is to use
a team approach that includes vascular surgeons and otolaryngologists. We have not used
the balloon occlusion test routinely to try and predict which patients will be better
treated with carotid ligation alone, because in our experience too many false-negative
test results occur, and the complication rate from carotid replacement is so low that we
simply try and replace the carotid artery in all patients who need carotid artery
resection. Autogenous saphenous vein is our graft conduit of choice, but other materials
may be used. Graft patency and healing require appropriate concomitant soft-tissue
coverage of any overlying mucosal or cutaneous defects. This study reviews the outcomes in
20 consecutive patients treated between 1989 and 1995 at The Ohio State University with en
bloc resection and replacement of the carotid artery for head and neck cancer.
Some controversy exists regarding the value of carotid artery resection and replacement
with respect to its impact on the long-term survival of patients with advanced head and
neck malignancies; however, most authors have suggested that carotid resection does not
increase the long-term survival.1 In a recent
meta-analysis and review of the pertinent literature, Snyderman and D'Amico2 concluded that the impact of carotid resection on long-term
survival remains unproven, but it does improve local/regional control of the disease. We
would agree with their conclusions. Our minimum goal in resecting and replacing the
carotid artery has always been to achieve better local/regional control without subjecting
the patient to undue risk of postoperative stroke regardless of any survival benefit it
may or may not provide.
We believe that ours has been a rational approach, because most series reviewing the
results of unselected carotid ligations (i.e., without revascularization) report a 15% to
30% incidence of postoperative stroke and a 3% to 5% mortality specifically resulting from
strokes. Therefore reduction of stroke risk should be an important goal for any palliative
procedure that might require carotid artery resection, even though the putative survival
benefit of carotid resection remains unproven.
Many investigators have hoped that patients can be selected for a “safe”
ligation of the internal carotid artery (ICA), if some type of temporary balloon occlusion
test (BOT) could reliably predict that permanent occlusion of the internal carotid artery
would not result in a stroke. Unfortunately, no one has demonstrated that any form of BOT
(either by clinical examination alone or in conjunction with electroencephalography,
transcranial Doppler scanning, or single photon emission computed tomography scanning) can
reliably predict which patients can undergo a “safe” ligation of the ICA.
In most published series that have investigated the predictive value of the BOT on the
basis of clinical response alone, the stroke rates after a negative BOT result are
approximately 30%, which is not significantly different from the stroke rate that would be
expected after unselected ligation alone. The predictive value of a negative BOT result
can be increased slightly by adding some adjunctive test of cerebral blood flow (e.g.,
transcranial Doppler scanning, electroencephalography, or single photon emission computed
tomography). In most published series a negative BOT result with some adjunctive test
followed by carotid ligation carries a 10% stroke risk. We believe that even a 10% to 30%
stroke rate is too high among patients who supposedly can have a “safe” ICA
ligation and essentially renders the test useless, because we are able to achieve a major
stroke rate of less than 5% by replacing the internal carotid arteries in all of these
patients without any selection criteria.
We believe that the reason that BOTs have been unsuccessful in predicting postoperative
strokes is because most postoperative strokes do not occur immediately; this is because
most postoperative strokes are due to the embolization of fresh clot that has recently
formed in the ligated distal ICA stump. This opinion is based on our own unpublished
experience with emergency ligations of the carotid artery for tumor erosion or penetrating
trauma and is supported by the recent publication of Meleca and Marks,3 who reported that six of eight of the strokes occurring after
carotid resection had a delayed onset of this complication (typically on postoperative day
2 or 3). In addition, careful review of the literature demonstrates that at least half the
reported strokes occurring after acute carotid ligation for tumor or trauma do not occur
immediately but typically occur a few days later. It seems to us that the temporary
occlusion of an internal carotid artery for 15 or 30 minutes is a poor way to predict what
might happen on the second or third postoperative day.
METHODS
Patients were identified by manual comparison of a
computer-generated list of all patients in the Ohio State University Cancer Registry with
stage 3 or greater head and neck cancers who underwent a resection with another
computer-generated list of all patients in the Vascular Surgery Registry who underwent a
carotid artery procedure. The list was also compared with a list of all patients during
this time period who were billed for a carotid artery procedure and was found to be
complete and comprehensive. All information was obtained from existing patient medical
records or from information obtained during patient interviews. The information was
abstracted onto data sheets and entered into a computer for analysis. Postoperative death
and stroke were defined as occurring during the hospitalization for which the patient
underwent the carotid resection and replacement. Average results are presented as the mean
± SEM. .
RESULTS
Patient population.
From 1989 to 1995, 20 patients had resection of advanced head and neck tumors for which
the internal or common carotid artery was resected and replaced electively. A total of 16
men and four women underwent operation. All the patients were white. The average age was
62.4 ± 4.4 years (range, 20 to 78 years). Eight of the 20 patients were diabetic, 6 had
significant coronary artery disease, and 5 were hypertensive. The patients reported in
this series come from a larger cohort of 80 patients, 60 of whom did not undergo a carotid
resection but had tumor close enough to their carotid artery that they were evaluated with
a carotid angiogram. The mean survival for the 60 patients who did not undergo carotid
resection and replacement was 18.1 months. The mean survival rate for the 20 patients who
did undergo carotid resection and replacement was 19.2 months. This finding is not
dissimilar from what has been reported in other series.1
We excluded from this analysis three patients who required carotid artery ligation to
control exigent hemorrhage caused by tumor invasion. Also excluded from this analysis were
three patients (early in the series) who had carotid artery ligation without an attempt to
replace the carotid artery. We excluded these patients because the focus of this review
was to analyze the septic, thrombotic, neurologic, and hemorrhagic complications of
carotid artery resection and replacement with autogenous greater saphenous vein, and we
were making no attempt to compare resection and ligation alone with resection and
replacement.
Malignancies.
The most common tumor type was squamous cell carcinoma (16, 80%), three patients had
advanced thyroid cancer, and one patient had an advanced basal cell carcinoma. In 16 (80%)
patients the cancer was recurrent. The primary tumors originated from the larynx (six),
pyriform sinus (five), base of the tongue (two), nasopharynx (two), tonsillar fossae
(one), and oropharynx (one). In three patients the primary tumor site was unknown and
could not be determined. All 16 patients with squamous cell carcinoma had a significant
history of alcohol and cigarette consumption, and two of the remaining four patients also
consumed significant amounts of alcohol and cigarettes. Six (30%) patients had
contaminated necks on gross examination including two patients with necrotic tumor, two
with active wound infections from previous biopsies, and two with draining fistulas.
Preoperative evaluation.
All patients had biopsy-proven malignancies. Computed axial tomography (CAT) scans (18),
magnetic resonance imaging studies (6), cerebral angiography (19), cervical
ultrasonography4 studies (6), and BOTs (4) were
routinely obtained when clinically indicated, but none of these tests was obtained in all
patients. CAT scanning was the diagnostic modality that identified tumor invasion most
often, but because it was also the test that was ordered most often, we cannot comment on
the relative accuracy of CAT scanning versus magnetic resonance imaging ultrasonography or
angiography in determining whether the carotid artery is involved with tumor. Indeed, it
is our experience that when we suspect that the carotid might be involved (excluding those
cases in which it is clearly involved or not), a clean tissue plane can be identified
between the tumor and the carotid artery in at least half the cases. Because the Ohio
State University serves as the primary referral center for central Ohio, many of these
patients arrived with their preoperative evaluations complete or nearly complete.
Preoperative treatment.
In all 16 patients with recurrence a previous neck dissection was performed. Seven of
these 16 patients had previously undergone some type of myocutaneous flap procedure.
Preoperative irradiation was performed in 16 of the 20 patients,5
and one patient had previously undergone brachytherapy with I125 seed
implantation.
Operative treatment.
The decision to resect the carotid artery en bloc with the tumor mass was made in the
operating room by the otorhinolaryngologic surgeon. In all cases the tumor either
encircled the carotid artery, or it was so densely adherent that it could not be safely
removed. Before the carotid artery was clamped, the entire tumor mass was mobilized as
much as possible. Heparin was used in all cases except one. The vein harvest site was kept
isolated from the cervical operative site by using separate instruments and by changing
gowns and gloves. Once a suitable length of greater saphenous vein was harvested, heparin
was administered, clamps were applied, and the tumor mass and the involved segment of
carotid artery were removed en bloc. The internal carotid artery was replaced by a greater
saphenous vein in the reversed (12, 60%) or nonreversed (8, 40%) orientation. When the
vein was placed in the nonreversed orientation, a modified Mills valvulotome was used to
cut the valves. Shunts were used in 18 (90%) of the cases. Typically, the entire
extracranial and extrathoracic portion of the carotid artery was removed from a point 3 or
4 cm above the clavicle to a point 1 or 2 cm below the base of the skull. No special
attempts were made to revascularize the external carotid artery, unless the carotid
bifurcation and the external carotid were clearly free of any tumor involvement and the
bypass could be safely terminated proximal to or distal from the bifurcation.
In 18 (90%) of the cases the patient had some form of intraoperative contamination
including tracheostomies, pharyngostomies, or fistulas. Half of the patients had
intraoperative radiation therapy. New concomitant myocutaneous flaps were rotated over the
carotid bypass in six (30%) patients. These included four deltopectoral flaps6 and two pectoralis major flaps.7
In seven other patients flaps had already been fashioned during previous procedures. In
one patient the carotid artery was covered with a skin graft, and in the remaining six
patients the carotid artery was covered with local flaps.
Postoperative management.
Patients were given intravenous antibiotics for at least 24 hours or until all wounds were
healing without signs of infection. Drains were left in and removed by the
otorhinolaryngologic service, typically on postoperative day 2. In four of the patients a
carotid duplex study was performed before discharge to determine graft patency. In the
remaining 16 patients a carotid duplex scan was obtained sometime after discharge. In all
cases except one the initial duplex study demonstrated graft patency. Patients were then
monitored by both the otorhinolaryngologic and Vascular Surgery services with periodic
carotid duplex studies.
Early postoperative complications.
None of the patients died during the early postoperative period. One patient had a major
stroke that manifest on his emergence from anesthesia. This patient had undergone
replacement of his carotid artery without the use of heparin. On removal of the shunt,
clot was noted at the end of the shunt, and poor back bleeding was seen. Therefore a no. 2
Fogarty catheter was passed distally until all retrievable clot was removed. Three
patients had wound infections in the early postoperative period. Two of these were simple
wound infections that resolved with prolonged antibiotics. One of these three was a
phayngocutaneous fistula, which closed spontaneously while the patient was an outpatient.
No other patients had any central neurologic deficit during their hospitalization, nor did
any graft occlusions, graft infections, or graft blowouts occur during the early
postoperative phase.
Late postoperative follow-up.
One patient had a minor stroke 12 months after the operation that was manifest by
contralateral hand and arm weakness that completely resolved during the subsequent 6
weeks. At the time he had his stroke, this patient underwent a carotid duplex scan, which
was normal.
Another patient had arterial hemorrhage from his contralateral neck dissection and
myocutaneous muscle flap. This condition was later diagnosed as being a pharyngeocutaneous
fistula with erosion into the common carotid artery but was on the side opposite our
earlier carotid replacement. However, during the evaluation of this patient's hemorrhage,
he underwent cerebral angiography, which demonstrated an asymptomatic occlusion of the
carotid graft.
A third patient had hemorrhage from his carotid graft approximately 1 month after
discharge. This was the only carotid graft in this series that was covered with a skin
graft. The skin graft was used because the local flaps left approximately 1 square cm of
the carotid graft uncovered. When this patient had exigent hemorrhage 1 month after the
operation, he was treated with ligation of his carotid graft. He did not have any
neurologic deficit. All other patients remained free of complications and had patent
grafts after a mean follow-up of 15.9 ± 7.8 months.
In summary, no graft blowouts or strokes occurred as the result of septic complications.
The only graft blowout that occurred did so after a skin graft coverage, and none of the
remaining 19 patients who had their grafts covered with local flaps or myocutaneous
rotation flaps had a graft blowout. Two (10%) patients had a stroke, one (5%) major stroke
in the immediate postoperative period and one (5%) minor stroke without residual 1 year
after the operation.
DISCUSSION
Elective carotid artery resection in the treatment of patients with advanced malignancies
of the head and neck remains a controversial issue. Tumor invasion or adherence to the
carotid artery may require carotid resection to achieve control of disease. However, the
significant risks of stroke and death and the low cure rate deter many surgeons from
electively resecting the carotid artery.8 This can
result in some patients being denied an appropriate operation and left exposed to the
possibility of carotid rupture or other local tumor problems. Furthermore when these
patients have a recurrent tumor involving the carotid artery, surgical treatment becomes
more treacherous because of the previous neck dissection, irradiation therapy,
myocutaneous flap rotation, and possible fistulae in the field. Unfortunately, few
alternatives exist. Failure to fully resect the segment of the carotid involved with tumor
may result in tumor recurrence or death of carotid rupture.9
Several methods have been described to predict the likelihood of stroke after carotid
artery resection and ligation without replacement. These include intraoperative
electroencephalography, carotid stump pressure monitoring, ocular plethysmography,
somatosensory-evoked cortical potentials, and temporary balloon occlusion with or without
xenon-enhanced computed tomography of cerebral blood flow.
Ehrenfeld et al.10 concluded that a carotid stump
pressure of greater than 70 mm Hg indicates adequacy of collateral circulation sufficient
to avoid a stroke after ligation. They also noted that intermediate carotid stump
pressures (in the range of 55 to 69 mm Hg) represent an intermediate risk of stroke and
that pressures less than 55 mm Hg result in an unacceptable stroke rate. Others, however,
have shown that carotid stump pressure is an inaccurate predictor of subsequent neurologic
compromise.11
Ocular plethysmography as described by Martinez et al.12
allows accurate and reliable prediction of the adequacy of collateral flow to compensate
for carotid artery ligation. Atkinson et al.13 used
somatosensory-evoked cortical potentials in conjunction with carotid stump pressure and
achieved a 17% stroke rate with ligation. Although this is one of the lowest stroke rates
after carotid ligation in the literature, it still seems unacceptably high to us. One of
the most recent advances in this area is the use by de Vries et al.14 of temporary balloon occlusion with xenon-enhanced computed
tomography of cerebral blood flow. This method seems promising, although further studies
are necessary to obtain statistically significant data.
In our opinion none of these methods has produced sufficiently accurate results to justify
the conversion of a patent carotid artery to an occluded carotid artery. The probable
reason these methods are unreliable is simply that most strokes after carotid ligation do
not occur immediately but usually occur from 1 to 5 days after the ligation. Therefore we
should not expect that the effects of acute temporary carotid artery occlusion can predict
what will happen several days after permanent ligation. Furthermore the best series in the
literature has a 17% stroke rate after simple ligation. This result does not compare very
well with the current series and others that have also achieved significantly lower stroke
rates with very acceptable septic and hemorrhagic complications.
Therapeutic options for management of head and neck tumors with invasion of the carotid
artery include irradiation therapy,15-17
palliative carotid peeling,18,19
and resection with20-24 or
without25-30 bypass grafting. A
review of the literature demonstrates a reported stroke rate of 17% to 45% and a death
rate of 8% to 58% when treated with ligation alone,2
and these rates seem to be significantly higher than when patients are treated with
resection and replacement. Radiation therapy carries the additional risk of radiation
arteritis,31 accelerated atherosclerosis,31 and delayed healing,32
but might help achieve better local control of the tumor.
We have used both reversed and nonreversed orientations for the greater saphenous vein and
have found advantages to both. If a significant difference is found in the diameter of the
proximal and distal ends of the harvested veins (distal vein being larger), then we prefer
to use the vein in the nonreversed orientation so we can match up the large end of the
vein with the common carotid artery and the small end of the vein with the internal
carotid artery. Because many of these patients have their entire carotid artery resected
from just above the clavicle to a point within 1 or 2 cm from the base of the skull, the
length of greater saphenous vein is often 20 cm or more, and this often results in a
considerable size differential between the proximal and distal ends of the vein. On the
other hand, if no significant difference is found between the proximal and distal ends of
the vein, then we prefer to use the vein in the reversed orientation to avoid the need for
valve lysis.
In our experience arteriography has not been especially useful in identifying tumor
invasion of the carotid artery. This has also been the experience of Reilly et al.,1 who found that arteriography correctly identified tumor
invasion of the carotid artery in only 1 of 12 patients. In our uncontrolled experience
CAT scans seem to be the most common way that the surgeon is alerted to the possibility of
carotid involvement. Recent reports have suggested that ultrasonography might be the most
accurate method for determining tumor invasion of the carotid artery before operation.33 We are not overly concerned with the preoperative diagnosis
of tumor invasion of the carotid artery, because ultimately this will always be a clinical
judgment based on the findings of the operating surgeon.
CONCLUSIONS
From these results we conclude that the use of the greater saphenous vein to replace the
internal carotid artery after en bloc resection is not attended by a high rate of
infectious complications or graft blowout even in the presence of intraoperative
tracheopharyngeal contamination and that the greater saphenous vein is the conduit of
choice for replacing an internal carotid artery after cancer resections. When comparing
our results with the reported results in the literature after carotid resection and
ligation without replacement, it is clear that carotid replacement has a much lower risk
of postoperative stroke and death. It is unlikely that the resection and replacement of
the carotid artery will achieve significantly better tumor control in these patients with
already advanced malignancies, but further studies might prove this to be the case.
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resection for neoplastic disease: a meta-analysis. Am J Otolaryngol 1992;13:373-80.
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Intraoperative I-125 seed implantation of extensive recurrent head and neck carcinomas.
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internal and common carotid arteries in the treatment of tumors of the neck. Ann Surg
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DISCUSSION
Dr. Ramon Berguer (Detroit,
Mich.).
The mortality and morbidity of head and neck tumors that invade the carotid artery has
changed dramatically since the introduction of en-bloc carotid resection and replacement
with autogenous tissue. The mortality has dropped from 27% in the Sloan-Kettering series
to 0% or 5% in the two series involved in this discussion. Among their 20 patients, the
authors experienced two graft occlusions, two strokes, and one blowout requiring excision
and ligation. In one of the strokes the patient had not received heparin, and the blowout
occurred in a patient who had a skin graft coverage of a vein graft. Both problems
probably could have been avoided. Before 1991 we replaced carotid arteries with saphenous
vein in the manner described by the authors. Sometimes we placed saphenous veins that were
small and posed a problem with size mismatch. We had two saphenous grafts occlude shortly
after their placement. In 1991 we adopted a protocol for carotid replacement using
superficial femoral artery as an autograft while replacing the femoral segment with a
prosthesis of polytetrafluoroethylene (PTFE). Our experience with this protocol was
presented to this society last year. The authors' and our series are comparable in
numbers, age, gender distribution, length of follow-up, and incidence of previous radical
neck dissection. Of the 24 patients in whom we did carotid arterial autograft replacement,
the only neurologic complication noted was in one patient who had a stroke when his
carotid graft was avulsed 6 hours after operation as the surgeons responsible for the
myocutaneous flap were attempting to control bleeding from a muscular vessel. The carotid
artery was ligated, and 24 hours later the patient had a massive stroke and eventually
died. The 23 surviving patients had patent grafts and no strokes at a mean follow-up of 11
months. The other complications were at the site of the donor artery: a silent thrombosis
of the PTFE in the femoral location of one patient and an infected false aneurysm of the
PTFE proximal anastomosis requiring ligation in another. In both cases the legs remained
viable. These numbers are too small to statistically conclude the superiority of one
method over the other. It can be said, however, that because arterial autografts do as
well or better than saphenous vein grafts, that one should consider them a good choice if
the preoperative duplex shows a saphenous vein of inadequate size or quality. We have used
twice a saphenous vein graft in patients that showed atheroma of the superficial artery in
the preoperative duplex. We will continue to use autogenous artery as our first choice
until we accrue numbers that will support or negate this policy, and we will follow with
interest the series of Dr. Wright and associates.
J. Gordon Wright.
I would agree with your comments entirely. I think that the superficial femoral artery
is a good alternate to use in this situation, and clearly the number of cases in our
series precludes a valid a statistical comparison between superior femoral artery and
greater saphenous vein at this point. I think in your hands, you have had good results
with the superficial femoral artery, whereas we have had good results with the greater
saphenous vein. I think the important take-home message from this study is that if you are
faced with a malignant invasion of the carotid, you should not simply ligate and resect;
you should make every reasonable attempt to revascularize because, as you mentioned, the
mortality and morbidity has dropped significantly by adopting a policy of trying to
revascularize all of these. I cannot think of a reason a superficial femoral artery would
be superior except as you have mentioned the theoretic possibilities of less infectious
complications, although we did not see any infectious complications in this particular
series.
Dr. Joseph J. Piotrowski
(Cleveland, Ohio).
I did a number of these resections and replacements with saphenous vein when I was at
the University of Arizona. Similar to your experience, most of our patients had had
previous neck resections and postoperative irradiation. Because of this, we tunneled our
vein grafts into the posterior triangle. I wonder if the single case of blowout that you
experienced could have been prevented by an alternate routing of your vein graft, because
you already were considering covering this with a somewhat scary skin graft.
Dr. Wright.
There is no doubt about that. This blowout was clearly due to an inadequate soft-tissue
coverage, and it could have been prevented by the means you had suggested or by simply
rotating some kind of myocutaneous flap.
Dr. William D. Turnipseed
(Madison, Wis.).
I think your clinical series would suggest that some, but not all, of these patients
require carotid reconstruction. This is born out by the fact that you have lost graft
function in a couple of patients with no clinical consequence. If you could document
before surgery an adequate intracranial collateral system, do you think it might simplify
your surgical approach and eliminate the need for this algorithm in selected patients?
Dr. Wright.
If there were such a test, it would simplify things. However, we do not like the
balloon occlusion test because we have had some patients who have had a negative balloon
occlusion test who were ligated and subsequently stroked. Furthermore, our involvement
with these cases is usually approximately 45 minutes, and many of these procedures take 6
or 8 hours. I am not sure that replacing the carotid in these large head and neck
resections is really adding significantly more complexity to an already complex operation.
Dr. Turnipseed.
You might want to look into the use of magnetic resonance angiography and Diamox
chemical stress testing. Magnetic resonance angiography can clearly define the anatomy of
the circle of Willis. Magnetic resonance angiography can also be used to evaluate blood
flow through watershed areas within the cerebral circulation before and after vasodilation
with Diamox. This may prove to be an accurate preoperative screening test for these
patients.
Dr. Wright.
One other point that is emphasized in the article is that these tests are all acute
tests, and in this series (and others) most patients who have stroke after ligation do not
have stroke immediately but usually stroke on the second or third day after ligation.
Dr. Donald P. Spadone (Columbia,
Mo.).
I would have you entertain another hypothesis for the cause of stroke rather than
inadequate intracerebral collaterals. It is possible that with ligation there is
propagation of thrombus within the ligated internal carotid and propagation or
embolization of thrombus produces stroke 2 or 3 days after ligation. Is there evidence to
support propagation of thrombus or embolization in patients who did have stroke?
Dr. Wright.
Yes, that is exactly what I think happens with most of these patients. There is no
objective evidence to prove or disprove that pathophysiology except as suggested by their
clinical course. The fact that they usually do not have stroke immediately, that they
usually have stroke on the second, third, or fourth postoperative day suggests that it is
the propagation of thrombus into the circle of Willis, which embolizes and causes the
stroke. Once again, this is why we do not like the balloon occlusion test or any other
test of acute temporary occlusion.
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