Brain, Vol. 123, No. 1, 190-192,
January 2000
© 2000 Oxford University Press
Book reviews |
ARTERIOVENOUS MALFORMATIONS IN FUNCTIONAL AREAS OF THE BRAIN.
.
Neurochirurgische Universitatsklinik, Bonn, Germany
For Arteriovenous Malformations (AVMs) in so-called `non-eloquent' brain regions, the therapeutic regimen is rather straightforward unless they are giant (>6 cm): in experienced hands microsurgical removal has the highest success rates with regard to complete AVM elimination as well as to associated morbidity when compared with the other treatment modalities. In patients with giant AVMs or with AVMs in `eloquent' (i.e. functional) regions, however, morbidity—transient and permanent—may be high. They may be subject to various therapeutic options from microsurgery or radiosurgery alone to combined approaches (e.g. embolization + radiosurgery or embolization + microsurgery + radiosurgery) depending on size and location. It needs to be pointed out that even in these difficult lesions the ultimate goal of any therapeutic approach in AVM patients remains complete DSA-controlled obliteration of the AVM in order to avoid subsequent rupture with the potential for life-threatening bleeding.
Few books deal with cerebral AVMs in detail, and Professor Shokei Yamada has undertaken the task to report on his surgical experience with 135 AVMs located in `functional' brain regions. The book is structured in 12 chapters, with five written by Professor Yamada himself and the remaining seven by renowned experts in their respective fields.
On initial browsing some technical shortcomings of the book become evident. First, most chapters of the book are subdivided into subsections, which are not mentioned in the index of contents. Secondly, many intraoperative photographs and angiographic pictures are dark and not in focus. Thirdly, the figures drawn by the medical illustrator tend to be too simplistic, in particular, when it comes to descriptions of surgical technique, where elaborate drawings could be of great value to foster understanding. Fourthly, some figure legends are incomplete: What is the meaning of the three arrows in Figure 10C, etc.? Last but not least, in the preface, the names of three eminent neurosurgeons and neuroradiologists are misspelled.
Chapter 1—`Surgical Approach to Arteriovenous Malformations in Functional Areas of the Brain'—covers half of the book and is written by Yamada. It starts with a description of his pathoanatomical concept of shunting arterioles and communicating venules, the latter of which connect the AVM core with the larger collecting draining veins, and the description of his particular surgical techniques for the removal of AVMs in eloquent areas which `avoid removal of the neurons involved in motor, sensory, and speech functions'. He approaches AVMs by isolation of the main draining vein, following it towards the AVM core, coagulates shunting arterioles and communicating venules, and isolates the AVM from surrounding brain tissue `with avoidance of removal of functional brain tissue ... and protection of the neuronal fibers'. Then, the nidus is shrunken, and the major draining veins are interrupted. Thereby he describes excellent results with four mild new permanent neurological deficits in his series of 135 AVMs in functional brain areas, which would be indeed a formidable result. The numbers, however, are not easy to interpret, and some facts remain unclear, such as why none of his patients held a full-time occupation preoperatively.
The author presents a few concepts worth discussing and relevant criticism is mentioned as follows. He introduces one hemodynamic AVM-type, supplied by one penetrating artery only, with the example of an occipital AVM and states that `embolization is usually effective, although homonymous hemianopia must be anticipated as a complication'. This is an important issue, which should be dealt with in the discussion, because the chance of complete AVM obliteration by endovascular therapy alone is less than 15% in best hands. And if complete homonymous hemianopia is anticipated, why should one put the patient at risk of significant morbidity due to a neuroradiological intervention with uncertain success, if the same small AVM could be removed microsurgically with a 99% success rate and the same morbidity?
Another interesting subsection is that on the resection of capsulocaudothalamic AVMs: `Surgical procedures for diffuse AVMs is limited to the cauterization of the individual AVM vessels. ... Large diffuse AVMs can be cauterized from the distal side in the caudate nucleus, putamen, and upper thalamus to reduce the AVM size to 2.5 cm or less in diameter.' What is the goal of such surgery—shrinking the AVM for prevention of rupture?
Another technique is that of the `stereotactic approach to AVMs located mesially or deep in white matter': thereby, a Kirschner wire is brought as close as `2 mm short of the target depth' as a `process in preparation for the dissection of the AVM with superselective interruption of the shunting arterioles and communicating venules.' This seems unnecessarily hazardous with neuronavigation being available nowadays.
Some figures and legends are irritating (e.g. Figures 2A and B, showing lateral and AP-angiograms of the same AVM located within the basal ganglia). Professor Yamada states that these angiograms are `showing brain tissue between abnormal arteriovenous loops. The AVM vessels were approached stereotactically, cauterized, and subtotally eliminated.' First, from an angiographic picture one cannot readily draw conclusions about intervening parenchyma between abnormal vessels. Secondly, what is the use of a stereotactic approach and cauterization with only subtotal elimination of the AVM?
A number of technical deficiencies should not have escaped editing. Included in the chapter is a short section with figures on spinal AVMs, which does not connect with the other neighboring sections. References are missing on the natural history of AVMs (e.g. those of Ondra and Kondziolka), which are very important for patient information and calculation of the bleeding risk. Professor Yamada introduces an interesting concept of AVM surgery (neuroendoscopically guided cauterization). The interested reader is referred to Chapter 2, section 5 for more details. Unfortunately, this section does not exist. Professor Yamada is a proponent of staged AVM surgery. It is not clear, however, how many procedures were performed in a staged manner, at what intervals, and whether DSA control was performed or not. Two ventricular hemorrhages were encountered in his series. Can staged resection then be regarded as safe, unless one is given the respective numbers?
Chapter 3 on `Blood Flow to Arteriovenous Malformations and the Brain, and Cerebral Metabolism' is authored by Yamada, and based on his previous publications again. Other relevant references are missing (e.g. those of the AVM study project from Columbia University). Distinctions between angiographic and true CBF-steal are not clearly made, and assumptions are drawn from small and hetereogenous patient groups. He explains preoperatively lower CBF in AVM-patients with hemorrhage-induced vasospasm. But where is proven evidence of this phenomenon? On 135 he states that due to `the uniqueness of the author's resection technique' with `interruption of only shunting arterioles and communicating venules' he has not encountered normal perfusion pressure breakthrough (NPPB) syndrome. But NPPB is a phenomenon based on vascular events—no matter whether a small rim of parenchyma has been removed additionally or not—and this applies to Professor Yamada's technique as well.
Some concepts are irritating: in Chapter 4, on `Anesthesia Requirements', which is written by an anesthesiologist, the author suggests `Triple H' therapy, that is, hypervolemia, hypertension and hemodilution for the management of NPPB. However, to the understanding of this reviewer, this may further aggravate NPPB, and thus, the proposed rationale is difficult to understand. Another example is given by the second chapter—on postoperative care of the AVM-patient—where Yamada suggests phlebotomy `immediately before surgery if hematocrit is 39 or greater'.
Chapter 5, `Arteriovenous Malformations in Functional Areas', is written by a clinical neuroscientist. This is appealing, since the treatment of AVMs involves more and more elaborate neurological testing and preresectional evaluation of higher cortical functions. This can be achieved in a setting as is provided by large centres, because neurologists have the test paradigms available, which are necessary in conjunction with modern functional imaging techniques. The author, however, gives another review on the historical background of AVM treatment, localization, NPPB-theory and on anesthesia. Another problem arises from his classification by size (<2–3, 2.5–5 or >5 cm), which is different from the generally accepted one by Spetzler and Martin (<3, 3–6 or >6 cm), which helps when comparing different series from various groups.
The statement that very large AVMs can `be treated by endovascular therapy alone' is not substantiated by the current literature. The author favors AVM surgery to be performed under local anesthesia with the possibilty of intraoperative functional testing. However, AVM-surgery may be looked at differently in terms of length of the operation itself and the imminent needs of microsurgical vascular repair—in a patient who may be awake and whose head is placed on a padded headrest only. With this in mind it is difficult to follow the author's conclusion that `it is precisely the use of local anesthesia that has taught us that it is not necessary in all cases'.
Chapter 6 is about cavernous malformations of the brainstem. It is very well written and concise. The illustrations and photographs are of excellent illustrative character, especially for the explanation of the surgical approaches. Numbers and tables are very clear, and do not leave out the complicated courses with the vast surgical experience gained at the Barrow Neurological Institute with this rare pathological entity. This is the way a book chapter should be written—including the extensive reference list. Only one question arises: what is a chapter on brainstem cavernous malformations doing in a book about AVMs in functional areas of the brain?
Chapter 7 is about the multimodality treatment for cerebral AVMs. It includes an elaborate subsection on the necessity of the team approach towards AVMs in functional brain regions taking into account the presently available techniques—microsurgical resection, embolization and radiosurgery, or a combination of those. Unfortunately, this chapter lacks the scientific precision of the preceding one (`approximately 300 patients ...', `... obliteration in 80–85% of patients ...', `... most patients have not had their 2-year follow-up studies.'). It remains unclear why some patients were operated on upon failure of radiosurgical treatment and others were irradiated again. It is surprising that two patients with radiosurgical failure had only `subtotal resection', leaving them at risk for hemorrhage (p. 189). It would have been helpful had the authors explained the difficulties in their decision stages in patients with complex AVMs. Because this cannot be derived from the text, the reader cannot draw useful assumptions for his own practice. Unfortunately, the only two references more recent than 1993 are publications from the author's group. This does not take into account the recent advances in the multimodality treatment of AVMs.
Chapter 8, on stereotactic radiosurgery, reviews the indications for and techniques of radiosurgical AVM treatment. The reader gains an in-depth view of the decision process at a centre with extensive radiosurgical experience. The tables are clear, and the angiograms are illustrative and well chosen. Thereby one realizes that even in best hands and with extensive preplanning the DSA-controlled obliteration rate is in the range from 70 to 80%. One should be aware of the fact, however, that almost two-thirds of the author's patients were rated inoperable. This corroborates the results from the available literature that patients with deep-seated AVM with a volume of less than 10 cm3 who were rejected by neurovascular surgeons may be subject to a reasonable alternative method—radiosurgery—though associated morbidity (11.7%) and mortality (3.8%) cannot be neglected.
Chapter 9 is mainly devoted to computerized (neuro-) vascular modelling. This is an evolving interdisciplinary field and this chapter gives a brief overview on what has been achieved so far and of the author's work on that matter. His model is a single current analogon with the possibility for simulation of vascular resistance and, thereby, the consecutive obliteration of a simple AVM model. The chapter becomes most interesting where the author, a basic neuroscientist, integrates recent knowledge about radiation effects onto the blood–brain barrier and brain metabolism. Though it is not possible with his kind of model to take into account pulsatility, vessel wall elasticity and anatomical individualization, this may be possible with more advanced `higher order models'. The interested reader is referred to those, which may prove to be of value for pretherapeutic risk assessment via computed simulation.
Chapter 10 is authored by Yamada again, and it has subsections on intraoperative electrophysiological monitoring, Magnetic Source Imaging (MSI), colour Doppler ultrasound and endoscopy for AVM surgery. There is no doubt about the proven relevance of intraoperative SSEP-monitoring, whereas more experience is needed with MSI and its possible integration into image-guided surgery. The section on the author's endoscopic technique, which `provides specific precision in ... interruption of shunting arterioles and communicating venules . . .' is interesting, though the reviewer cannot readily appreciate the value of this technical adjunct through his own experience.
Chapter 11 on vasculogenesis and angiogenesis puts the reader on the forefront of vascular research. It is written by the group from Yale University, gives a short and concise overview on the current concepts of the development of cerebral AVMs with initial dysvasculogenesis of the capillary bed, AV-shunting and subsequent recruitment of feeding vessels from adjacent vascular territories. The mechanism of growth factors is explained on the basis of molecular biological studies. Future research will go into this direction, especially since there is evidence that some angiographically eliminated AVMs have a tendency to recur.
The book concludes with an outlook on future AVM therapy given by Professor Yamada, which raises an important issue. The value of fractionated irradiation, which needs to be analysed by the various radiosurgical groups in the future, and which may lead to further improvement of the radiosurgically obtainable obliteration rates.
Despite the excellent chapters on brainstem cavernous malformations, radiosurgery, vascular modelling and vasculogenesis, this book lacks stringent style—in editing as well as in content. Not all concepts have been supported by convincing evidence. The chapters vary considerably in quality and are not balanced enough between each other, since there is obvious repetition. Because this book comprises a large operative series and the pathophysiological view of a single surgeon, it may as well be of interest for specialized vascular neurosurgeons.
Notes
Edited by Shokei Yamada.1999. Pp. 280. Armonk, New York: Futura Publishing Company, Inc.Price $145. ISBN 0-87993-424-7.
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