The Surgical Treatment of Intracranial Vestigial Aneurysms

The Surgical Treatment of Intracranial Vestigial Aneurysms ALFRED UIHLEIN ROBERT A. HUGHES

THE treatment of the intracranial "berry" or vestigial aneurysms has received much attention in the past decade stimulated by outstanding contributions by neurosurgeons 9 , 11, 13, 14, 22, 24, 26, 27, 33, 38 who have become interested in trying to reduce the mortality and morbidity statistics of the earlier writers. 1 , 10, 12, 28 Cerebral angiography has contributed greatly to this effort as it has provided more accurate localization of the aneurysms and information concerning which ones may be attacked surgically with anticipation of good result. 8 , 16 Analysis of results of the conservative and more radical treatment of these lesions of the cerebral circulation has indicated that more lesions can be operated on with a large measure of success than was realized. Mortality figures are still high in unselected cases, but these are decreasing steadily because of advances in controlled anesthesia, use of the hypothermic state, 7 use of hypotensive drugs, and better interpretation of improved angiograms. Mortality figures run from 42 to 3.6 per cent in series of cases of verified cerebral aneurysms that were attacked surgically. On the other hand, mortality figures of 60 to 80 per cent are reported from conservative management with rest in bed for verified aneurysms. It is generally accepted that conservative treatment is attended by the greater risk as far as life expectancy is concerned10 , 41; however, the controversy still remains whether all patients with intracranial aneurysms of the carotid artery system should be treated by ligation of the internal carotid in the neck3 , 4, 13,16,21 or whether craniotomy is justified in every instance. The middle-of-the-road course seems to have widest acceptance. In other words, aneurysms of the circle of Willis near the junction of major vessels might be considered candidates for carotid ligation if adequate collateral circulation between the right and left carotid systems can be demonstrated, whereas surgical intervention independent of, or in conjunction with, ligation of the internal carotid artery in the neck should~be reserved for aneurysms placed peripheral to the circle of Willis. For aneurysms of the intracranial portion of the internal carotid 1071

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artery, the circle of Willis proper, or on the distal portions of the anterior or middle cerebral arteries, whether ligation of the carotid artery alone is the advisable method of treatment remains an unanswered problem. COMPLICATIONS

Ligation of the common or internal carotid artery in the neck on the side of the aneurysm is not without complications. 5, 20, 26, 35 Delayed hemiplegia as late as one week after ligation is recognized as being a frequent complication. The early development of hemiplegia after ligation frequently can be corrected by the immediate release of the ligature or clamp. Ligation and division of the artery have been recommended to reduce the incidence of postoperative complications in the belief that arterial pulsation sets free emboli distal to the ligature. Results of the Matas test,19 a test whereby the carotid artery is manually compressed and occluded for varying periods by means of a clamp or the fingers, or occlusion of the artery by an artery tape at operation17 to ascertain whether a neurologic deficit will develop have been found to be unreliable. Temporary paralysis of the superior cervical sympathetic ganglion by perfusion of the cervical ganglion and trunk with procaine hydrochloride, crushing of the trunk, or sectioning of the trunk has been advocated to prevent untoward postligation sequelae. 26 No satisfactory method has been found to prevent the development of gross neurologic deficits following the ligation of the internal or common carotid artery. The Poppen or Selverstone artery clamp39 was devised to produce gradual occlusion of the vessel without injury to the intima in the hope that untoward sequelae might be reduced. The theory has worked out reasonably well in practice though there is danger of erosion of the artery when the clamp is left in place permanently. DIAGNOSTIC FEATURES AND EARLY MANAGEMENT

As a general rule, a patient is unaware that he has a cerebral aneurysm until he suddenly experiences a severe headache, followed frequently by nausea, vomiting, with or without gross neurologic deficit, and a stiff neck. When a ruptured aneurysm is suspected, examination of the spinal fluid will usually reveal grossly pink to bloody fluid. However, bloody spinal fluid is not necessarily sufficient evidence for a diagnosis of ruptured aneurysm. The question of a traumatic spinal tap arises. If a traumatic tap is responsible the supernatant liquid of the sample of bloody spinal fluid will clear after the tube of fluid is permitted to stand undisturbed for one to two hours. Occasionally, a patient with a brain tumor will give a similar story and have bloody spinal fluid as the result of hemorrhage into the tumor and leaking of blood into the subarachnoid space. Funduscopic examination may show small petechial retinal hemorrhages on the side of the rupture of the aneurysm. When

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this is found early, it is pathognomonic of a ruptured aneurysm. Palsy of ocular muscles mayor may not develop. Ptosis, due to pressure on the oculomotor nerve, is a common early finding in carotid aneurysms, supraclinoid or infraclinoid in position. Ophthalmoplegia occurs frequently with aneurysms near the posterior communicating artery and at the division of the internal carotid artery into the middle and anterior cerebral arteries. Serious sequelae, such as hemiplegia and fluctuating states of consciousness, frequently indicate leakage of the aneurysm into contiguous brain tissue with or without the presence of a subdural hematoma. Increasing intracranial pressure probably compresses the site of aneurysmal rupture and prevents further hemorrhage in those patients who spontaneously stop bleeding. If bleeding still persists, rupture into the ventricular system may follow. This is usually a fatal complication. During the acute phase of hemorrhage, the patient should be placed at absolute rest in bed with sedation and administration of drugs to lower the blood pressure. The purpose is to afford the patient every opportunity to control the bleeding. In addition, refrigeration of the patient may prove to be a lifesaving measure. Hasty transportation or too active treatment may increase the systemic blood pressure and prevent spontaneous cessation of bleeding. When the patient's condition stabilizes, then steps for definitive treatment should be considered. The Swedish neurosurgeons 23 • 26 have stated that the patient with an acutely ruptured aneurysm should not be subjected to early diagnostic procedures and definitive treatment as few of their patients have withstood early energetic treatment. If the patient can rally from the initial insult and seal over the leaking point, the chances of surviving definitive care are increased the longer the intracranial structures have to assume a state of adjusted tension. It has been repeatedly shown that hemorrhages recur in the second or third weeks after the initial insult. DEFINITIVE MEASURES

Time

The ideal period for definitive measures, therefore, appears to be from one week to ten days after the initial hemorrhage. Angiography can be undertaken then and is attended with fewer complications than earlier, the roentgenograms are of better quality, and the surgical approach is less hazardous because there is less edema of the brain. In certain cases, it might be helpful to ligate the carotid artery in the neck in the acute phase, however, to prevent further bleeding and reduce intra-arterial pressure. 6 • 34. 36. 42 Then when the condition of the patient permits, cerebral angiography can be carried out and the surgeon can decide whether craniotomy is indicated or not.

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Angiography

Cerebral angiography is an accurate diagnostic method. As said before, it demonstrates the site of the aneurysm in a large number of instances; it also demonstrates its size and configuration and the presence of multiple aneurysms, and assists in the determination of whether adequate collateral blood flow remains if one of the major vessels has to be sacrificed. Choice of Procedure

When the aneurysm is localized by angiography, the surgeon must decide on the type of procedure: whether the lesion should be attacked directly by craniotomy or indirectly by ligation of the carotid artery in the neck. The ideal method of management has not been found in every instance. However, the method of treatment which will afford the patient longevity without morbidity may be determined eventually by compilation of data in large series of cases. Aneurysms of the cerebral circulation occur on the carotid and vertebral systems. Few aneurysms on the latter system have been removed surgically and many are inoperable. Occasionally, one can be clipped or removed. 29 • 31 Fortunately few aneurysms occur in the vertebral system; more are found in the carotid system. We shall confine our discussion for the most part, therefore, to the aneurysms of the circle of Willis and its tributaries. The aneurysms of the internal carotid artery can be conveniently grouped into the infra clinoid and supraclinoid types of carotid aneurysms of the circle of Willis. Infraclinoid Aneurysllls

The infraclinoid aneurysms of the carotid artery are usually large and seldom rupture because they are protected by dura. They do, however, compress the parasellar structures and cannot clinically be differentiated from brain tumors in this region. 2 Therefore, angiography is of inestimable value in establishing the diagnosis before craniotomy.I6 These aneurysms can be treated by carotid ligation in the neck alone or as a stage procedure with partial occlusion of the internal or common carotid arteries, with or without paralysis of the cervical sympathetic chain. 26 Then, several days after ligation, the neurosurgeon can decide whether intracranial exploration is justified with a view to trapping the aneurysm by placing a clip or ligature on the intracranial portion of the carotid artery before the division of the internal carotid artery into the anterior and middle cerebral arteries. Ligation of the carotid artery in the neck alone may suffice or be mandatory if bilateral angiography fails to indicate satisfactory cross filling. The patient's life is placed in jeopardy by intracranial trapping when there is no cross filling. It seems, therefore, that the decision must be for ligation of the carotid artery in the neck

r

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to be followed by subsequent craniotomy if the lesion requires craniotomy in the judgment of the surgeon. Supraclinoid AneurysIns

The supraclinoid aneurysms of the carotid artery arise most commonly near the origin of the posterior communicating artery (Fig. 320) or the choroidal artery. These aneurysms are sometimes classified as aneurysms of these respective vessels rather than of the internal carotid artery. It is more appropriate to list them, however, as aneurysms of the internal carotid artery, as they are frequently vestigial and have a neck.

Fig. 320. Intracranial clipping at direct exploration of aneurysm of left internal carotid near posterior communicating artery.

Postmortem studies would indicate that they are carotid aneurysms. Because these aneurysms get their blood supply via the carotid as well as the vertebral arterial systems, intracranial clipping of the aneurysms or their neck seems justified rather than ligation of the carotid artery in the neck to preclude the danger of subsequent rupture. However, no one surgeon has a large enough group of patients with this type of aneurysm to establish a suitable criterion for management. 4 , 14,23 Surgical exposure of these aneurysms is not difficult and seems fraught with less disastrous results than the surgical approach to aneurysms placed more distally. Supportive Measures During Operation

The insertion of a malleable spinal-puncture needle into the lumbar portion of the spinal subarachnoid space permits the anesthetist to withdraw

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varying amounts of cerebrospinal fluid aseptically to increase surgical exposure. Hypotensive drugs, such as hexamethonium bromide or trimethaphan camphorsulfonate (Arfonad), help immeasurably in reducing vascular hypertension and have been of inestimable value to the surgeon in exposing aneurysms. 3 • 32, 40 By use of these drugs at operation the blood pressure can be lowered to the desired level and maintained there until the aneurysmal neck or sac is clipped. The frightening and almost tragic sequelae of the sudden rupture of the aneurysm during surgical exposure can now be mitigated by the judicial use of these hypotensive drugs. However, the intracranial surgical approach to these aneurysms is still accompanied by disheartening results: The advent of refrigeration techniques may further assist the neurosurgeon in the treatment of the patient with an acutely ruptured aneurysm by producing lowered cerebral metabolic requirements which in turn reduce intracranial hypertension and may help reduce cerebral edema. RESULTS OF TREATMENT

Results of the treatment of patients who were seen at the Clinic from 1925 to 1954 and given a presumptive diagnosis of intracranial aneurysm have been analyzed. In presentation of this analysis it should be stated that this material differs in some respects from surveys comprising patients from large cities. From the large-city population more patients gravely ill with ruptured aneurysms are admitted directly to a neurosurgical service. A large percentage of our patients come from distances which prohibit the transfer of the patient gravely ill from a ruptured aneurysm and, therefore, they are not seem at the Clinic until they have survived the initial or repeated hemorrhages. Mter arriving at the Clinic and responding to conservative treatment, they often refuse definitive treatment. Many of our patients then fall into the category of a selected group. In these, the results of treatment should be better than in some other series. 23 , 24 However, some of our patients who were subjected to emergency angiography and emergency neurosurgical procedures failed to rally after operation, as others have found. However, from each such instance, a valuable lesson was learned. Patients are not statistics, and each one must be treated individually. A total of 583 patients has been examined for suspected intracranial arterial vestigial aneurysms exclusive of the arteriovenous malformations at the Clinic in the 20 years. The diagnosis of aneurysm was verified by angiography, at operation, or at postmortem examination in 198 patients, 110 male and 88 female patients (Table 1). The diagnosis of aneurysm could not be verified in 385 patients suspected of having an aneurysm. Those that could be traced by correspondence are either living and well, or if they are deceased, no reliable subsequent examination was carried out to permit an accurate analysis of their condition. For various reasons, 58 patients with verified aneurysms were given

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only supportive medical treatment. Forty-five of them subsequently died of rupture of the aneurysm. This seems proof enough that supportive treatment of verified aneurysms is hazardous. lB. 37 Fifty-one of our patients with verified aneurysms of the circle of Willis (Table 2) were treated by extracranial ligation of the carotid artery. The six deaths in this group were due to subsequent rupture of the aneurysm; 13 patients had disabling neurologic sequelae after the carotid ligation. These results generally support reports of some other authors. Extracranial ligation of the carotid artery seems to prevent Table I SURGICAL TREATMENT OF VERIFIED INTRACRANIAL ANEURYSMS

Extracranial carotid ligation. . . . . . . . . . . . . . . . . Craniotomy with definitive treatment. . Craniotomy without definitive treatment. TOTAL . . . . . . . . . . .

CASES

DEATHS

51 59 30

6 12 14

140

32

Table 2 EXTRACRANIAL LIGATION OF CAROTID ARTERY FOR INTRACRANIAL ANEURYSMS ARTERY

Carotid-cavernous ......................... Carotid .................................. Middle cerebral.. . ....................... Anterior cerebral complex .................. Posterior communicating ...................

CASES

DEATHS

. . . . .

9 30 5 5 2

0 4 2 0 0

TOTAL . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

51

6

subsequent rupture of the aneurysm in many patients.I3 • 21. 22 This procedure alone might be a lifesaving measure, if, in the opinion of the surgeon, the intracranial attack is unwarranted. For example, we wish to cite the case of a 20-year-old man. This patient, who apparently was in excellent health, experienced a severe headache while at work. Shortly, his left leg felt dead and he collapsed to the floor. He was admitted to a hospital and his physician suspected subarachnoid hemorrhage. This diagnosis was confirmed when spinal puncture yielded grossly bloody fluid. After 10 days of absolute rest in bed, the patient was transferred to. the Clinic on November 26,1950. General medical examination revealed blood pressure of 152 to 142 mm. of mercury systolic and more than 70 diastolic in the arms and 110 systolic and odiastolic in the lower extremities. Coarctation of the aorta was suspected, and

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a roentgenogram of the chest revealed notching of a few ribs consistent with coarctation of the aorta. A cerebral aneurysm was also suspected. Bilateral carotid angiograms four days after admission revealed a supraclinoid aneurysm of the right carotid artery near the posterior communicating artery (Fig. 321). Subsequently, on December 7, the right internal carotid artery was doubly ligated in the neck after crushing the superior cervical sympathetic trunk. Transitory left hemiparesis occurred on the second postoperative day, but gradually cleared. Two months after carotid ligation, in February, 1951, one of the general surgeons at the Clinic resected the aorta for coarctation and carried out an end-to-end aortic anastomosis. The patient has had no recurrence of subarachnoid bleeding; the blood pressure is normal. He had a slight neurologic deficit in the left extremities when re-examined at the Clinic 3 years later in January, 1954.

Fig. 321. Angiogram illustrating aneurysm of right internal carotid, supraclinoid in position near right anterior choroidal artery.

The danger of postligation contralateral hemiparesis and hemiplegia or ipsilateral blindness20 is ever present and must be considered, even though some reports in the literature would lead one to believe that these complications are infrequent and their risk less grave than the intracranial attack. In the Clinic's series, 89 patients with verified intracranial aneurysms had craniotomy, 59 with definitive treatment to the aneurysm per se and 30 without any definitive treatment to the aneurysm, at the discretion of the surgeon. Fourteen of these 30 patients died subsequently of rupture of the aneurysm. Two of these patients were suspected of having tumors of the posterior fossa. During surgical exploration of the mass, the aneurysm in each instance ruptured with subsequent fatality (Table 3). Twelve of the 59 patients who received definitive treatment to the aneurysm died during the immediate or early postoperative period

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of either cerebral edema or cerebral infarction (Table 4). The aneurysms of the middle cerebral artery (Fig. 322) near the division of the internal carotid artery carried the highest mortality regardless of the type of treatment of the aneurysm, whether by clipping or wrapping. The 15 patients with aneurysms of the anterior cerebral arterial complex, namely, the anterior cerebral artery, the anterior communicating artery and anterior cerebral artery distal to the anterior communicating artery, fared Table 3 CRANIOTOMY WITHOUT DEFINITIVE TREATMENT TO INTRACRANIAL ANEURYSMS

ARTERY

CASES

Carotid................................... Middle cerebral. . . . . . . . . . . . . . . . . . . . . . . . . . . . Anterior cerebral. . . . . . . . . . . . . . . . . . . . . . . . . . . Basilar-vertebral system. . . . . . . . . . . . . . . . . . . . TOTAL..................................

DEATHS

9 1 6* 14

1 0 5 8

30

14

* Two aneurysms verified at necropsy but not found at operation. Table 4 CRANIOTOMY WITH DEFINITIVE TREATMENT TO INTRACRANIAL ANEURYSMS

ARTERY

CASES

DEATHS

Carotid-cavernous. . . . . . . . . . . . . . . . . . . . . . . . . . Carotid. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Ophthalmic.. .. . . .. . . . . . . . .. . .. . . . . . . . .. . . . Middle cerebral. .. . . . . . . .. . . .. . . . . . . . . . . . . . Anterior cerebral complex. . . . . . . . . . . . . . . . . . .

11 22 2 9 15

0 3 0 4 5

TOTAL..................................

59

12

better after a surgical attack (Fig. 323). Four died in the immediate postoperative period. Two of these four patients were in critical condition at the time of operation. One of these two died one month after the aneurysm was clipped on each side and wrapped with muscle. Of six additional patients with aneurysms of the anterior cerebral arterial complex who underwent craniotomy but had no definitive treatment to the aneurysm at the discretion of the surgeon, five succumbed to subsequent rupture. In two of these six patients, the aneurysm was not found at craniotomy and, therefore, no treatment was carried out. Aneurysms in this location seem to have a poorer prognosis with reference to longevity if not treated either by extracranial carotid ligation when angiography

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Alfred Uihlein, Robert A. Hughes

Fig. 322. Angiogram of aneurysm of right middle cerebral artery.

demonstrates appropriate cross filling or by craniotomy and direct attack on the aneurysm. 25 , 41 Aneurysms of the basilar-vertebral artery system still offer the greatest challenge. Only a few have been successfully attacked when diagnosed. Fourteen aneurysms in this location were verified at the Clinic in the years under consideration and eight of these 14 patients died of aneurysmal rupture SUMMARY AND CONCLUSIONS

During the past year intracranial vestigial aneurysms have been attacked surgically with more gratifying results. This encouragement is due in large measure to improved angiographic technique, better timing of the operative procedures, and the judicious use of hypotensive drugs and controlled anesthesia during the surgical procedure. 30 • 32. 40 The pr€ilent encouraging results suggest that the future management of all patients with intracranial aneurysms should be more gratifying and should contribute valuable information toward better selection of the patient with a view toward more timely intervention to prevent a discouraging result. It is not beyond the realm of possibility in the future management of patients with berry aneurysms who have sustained a .sudden· severe subarachnoid hemorrhage and are in critical condition

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Fig. 323. Intracranial clipping of aneurysm of right anterior cerebral artery.

that these patients may be able to survive such a serious insult if they are treated immediately by a combination of hypotensive drug therapy to reduce their blood pressure and hypothermic measures to lower their metabolic requirements. These two adjuncts to treatment may assist in allaying further bleeding of the aneurysm and may reduce cerebral edema sufficiently to permit earlier and more satisfactory surgical management of these critically ill patients who now comprise a large number of unselected unsuccessfully treated patients with verified cerebral aneurysms. REFERENCES 1. Ask-Upmark, Erik and Ingvar, David: A Follow-up Examination of 138 Cases of Subarachnoid Hemorrhage. Acta med. scandinav. 138: 15-31, 1950. 2. Baker, G. S.: Treatment of Multiple Aneurysms of the Internal Carotid Artery: Report of Case. Proc. Staff Meet., Mayo Clin. 28: 668-672 (Nov. 18) 1953. 3. Bassett, R. C. and Gass, H. H.: Ligation of Internal Carotid Artery for Aneurysmal Lesions of Circle of Willis. J.A.M.A. 147: 842-846 (Oct. 27) 1951. 4. Bassett, R. C., List, C. F. and Lemmen, L. J.: Surgical Treatment of Intracranial Aneurysm. Surg., Gynec. & Obst. 95: 701-708 (Dec.) 1952. 5. Brackett, C. E., Jr.: The Complications of Carotid Artery Ligation in the Neck. J. Neurosurg. 10: 91-106 (Mar.) 1953. 6. Brackett, C. E., Jr. and Mount, L. A.: Some Observations on Intra-carotid Blood Pressure Made During Carotid Ligation for Intracranial Aneurysms. In: Surgical Forum: Proceedings of the Forum Sessions, Thirty-sixth Clinical Congress of the American College of Surgeons, Boston, Massachusetts, October, 1950. Philadelphia, W. B. Saunders Company, 1951, pp. 344-350. 7. Callaghan, J. C., McQueen, D. A., Scott, J. W. and Bigelow, W. G.: Cerebral Effects of Experimental Hypothermia. A.M.A. Arch. Surg. 68: 208-215 (Feb.) 1954. 8. Elvidge, A. R. and Feindel, W. H.: Surgical Treatment of Aneurysm of the Anterior Cerebral and of the Anterior Communicating Arteries Diagnosed by Angiography and Electroenceph&lography. J. Neurosurg. 7: 13-32 (Jan.) 1950. 9. Falconer, M. A.: Surgical Treatment of Bleeding Intracranial Aneurysms. J. Neurol., Neurosurg. & Psychiat. 14: 153-186 (Aug.) 1951.

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10. French, L. A. and Blake, P. S.: Subarachnoid Hemorrhages and Intracranial Aneurysms. Bull. Univ. Minnesota Hosp. & Minnesota M. Found. 21: 279293 (Feb. 24) 1950. 11. Hamby, W. B.: Intracranial Aneurysms. Springfield,l11inois, Charles C Thomas, 1952, pp. 251-360. 12. Hyland, H. H.: Prognosis in Spontaneous Subarachnoid Hemorrhage. Arch. Neurol. & Psychiat. 63: 61-78 (Jan.) 1950. 13. Jefferson, Geoffrey: Discussion. Proc. Roy. Soc. Med. 45: 300-301 (May) 1952. 14. Kirgis, H. D. and Echols, D. H.: Management of Intracranial Arterial Aneurysms. S. Clin. North America 33: 1003-1021 (Aug.) 1953. 15. Krayenbiihl, Hugo: Immediate and Late Results of Carotid Ligature in Intracranial Aneurysms. Schweiz. med. Wchnschr. 76: 908-914, 1946. 16. List, C. F. and Hodges, F. J.: Intracranial Angiography. I. The Diagnosis of Vascular Lesions. J. Neurosurg. 3: 25-45 (Jan.) 1946. 17. Love, J. G.: Restoration of Circulation After Removal of Ligature From Internal Carotid Artery. Proc. Staff Meet., Mayo Clin. 19: 375-376 (July 12) 1944. 18. Magee, C. G.: Spontaneous Subarachnoid Haemorrhage: A Review of 150 Cases. Lancet. 2: 497-500 (Oct. 23) 1943. 19. Matas, R.: Testing the Efficiency of the Collateral Circulation as a Preliminary to the Occlusion of the Great Surgical Arteries. Ann. Surg. 53: 1-43, 1911. 20. Matson, D. D. and Woodhall, B.: Intracranial and Cervical Trap Ligation of Carotid Artery Complicated by Blindness of Homolateral Eye. J. Neurosurg. 5: 567-571 (Nov.) 1948. 21. Murphey, Francis: The Results of Simple Ligation of the Carotid Artery in the Neck for Intracranial Aneurysms of the Internal Carotid Circulation. Read at the meeting of the American Academy of Neurological Surgeons, Rochester, Minnesota, September 28 to 30, 1950. 22. Norlen, G.: The Pathology, Diagnosis and Treatment of Intracranial Saccular Aneurysms. Proc. Roy. Soc. Med. 45: 291-298 (May) 1952. 23. Norlen, G.: Klinik und chirurgische Behandlung der sackfOrmigen Hirnaneurysmen. Deutsche Ztschr. Nervenh. 170: 446-459 (Oct. 21) 1953. 24. Norlen, G. and Olivecrona, H.: The Treatment of Aneurysms of the Circle of Willis. J. Neurosurg. 10: 404-415 (July) 1953. 25. N orlen, Gosta and Barnum, A. S.: Surgical Treatment of Aneurysms of the Anterior Communicating Artery. J. Neurosurg. 10: 634-650 (Nov.) 1953. 26. Poppen, J. L.: Ligation of the Internal Carotid Artery in the Neck: Prevention of Certain Complications. J. Neurosurg. 7: 532-538 (Nov.) 1950. 27. Poppen, J. L.: Specific Treatment of Intracranial Aneurysms: Experiences With 143 Surgically Treated Patients. J. Neurosurg. 8: 75-102 (Jan.) 1951. 28. Richardson, J. C. and Hyland, H. H.: Intracranial Aneurysms: A Clinical and Pathological Study of Subarachnoid and Intracerebral Haemorrhage Caused by Berry Aneurysms. Medicine. 20: 1-83 (Feb.) 1941. 29. Rizzoli, H. V. and Hayes, G. J.: Congenital Berry Aneurysm of the Posterior Fossa: Case Report With Successful Operative Excision. J. Neurosurg. 10: 550-551 (Sept.) 1953. 30. Sadove, M. S., Wyant, G. M., Gittelson, L. A. and Bucy, P. C.: Controlled Hypotension. J. Neurosurg. 10: 272-283 (May) 1953. 31. Schwartz, H. G.: Arterial Aneurysm of Posterior Fossa. J. Neurosurg. 5: 312316 (May) 1948. 32. Scurr, C. F. and Wyman, J. B.: Controlled Hypotension With Arfonad. Lancet. 1: 338-340 (Feb. 13) 1954. 33. Steelman, H. F., Hayes, G. J. and Rizzoli, H. V.: Surgical Treatment of Saccular Intracranial Aneurysms: A Report of 56 Consecutively Treated Patients. J. Neurosurg. 10: 564-576 (Nov.) 1953. 34. Stern, W. E.: Studies of Pressures in the Carotid Artery of Patients Undergoing Cerebral Angiography. J. Neurosurg. 10: 577-582 (Nov.) 1953. 35. Strobos, R. R. J. and Mount, L. A.: Problems Related to Treatment of Intracranial Aneurysms by Carotid Ligation. A.M.A. Arch. Neurol. & Psychiat. 69: 118-128 (Jan.) 1953. 36. Sweet, W. H. and Bennett, H. S.: Changes in Internal Carotid Pressure During

Surgical Treatment of Intracranial Vestigial Aneurysms 37. 38. 39. 40. 41. 42.

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Carotid and Jugular Occlusion and Their Clinical Significance. J. Neurosurg. 5: 178-195 (Mar.) 1948. Walton, J. N.: The Late Prognosis of Subarachnoid Haemorrhage. Brit. M. J. 2: 802-808 (Oct. 11) 1952. Wertheimer, Pierre and Avet, Jacques: Surgical Treatment of Cerebral Arterial Aneurysms. Angiology. 5: 259 (June) 1954. White, J. C. and Selverstone, B.: Personal Communication to the authors. Wiklund, P. E.: Controlled Hypotension at Intracranial Operations. J. Neurosurg. 10: 617-623 (Nov.) 1953. Wolfe, H. R. 1.: Spontaneous Subarachnoid Haemorrhage: A Surgical Challenge. Brit. J. Surg. 40: 319-325 (Jan.) 1953. Woodhall, Barnes, Odom, G. L., Bloor, B. M. and Golden, James: Studies on Cerebral Intravascular Pressure: Further Data Concerning Residual Pressure in Components of the Circle of Willis and in Blind Arterial Segments. J. Neurosurg. 10: 28-34 (Jan.) 1953.