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Christopher S. Ogilvy, Roberto C. Heros, Robert G. Ojemann and Paul F. New

T he existence of vascular malformations of the brain which are not visualized on angiography has been recognized for many years. These “occult” or “cryptic” lesions have usually been diagnosed pathologically after surgical removal 2, 3, 6, 11, 18, 29, 35, 38–40 or at autopsy. 17, 24, 25, 28 Computerized tomography (CT) has helped in the diagnosis of angiographically occult arteriovenous malformations (AVM's). Although CT scans can suggest the diagnosis of AVM's occult to angiography, the differential diagnosis of these lesions includes intra-axial neoplasm

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John R. Robinson, Issam A. Awad and John R. Little

negative types. J Neurol Neurosurg Psychiatry 52 : 167 – 175 , 1989 Abe M, Kjellberg RN, Adams RD: Clinical presentations of vascular malformations of the brain stem: comparison of angiographically positive and negative types. J Neurol Neurosurg Psychiatry 52: 167–175, 1989 2. Bell BA , Kendall BE , Symon L : Angiographically occult arteriovenous malformations of the brain. J Neurol Neurosurg Psychiatry 41 : 1057 – 1064 , 1978 Bell BA, Kendall BE, Symon L: Angiographically occult arteriovenous

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Dudley H. Davis and Patrick J. Kelly

occult vascular malformations of the brain. AJNR 5: 985–993, 1986 14. Ogilvy CS , Heros RC : Angiographically occult intracranial vascular malformations. J Neurosurg 69 : 960 – 961 , 1988 (Letter) Ogilvy CS, Heros RC: Angiographically occult intracranial vascular malformations. J Neurosurg 69: 960–961, 1988 (Letter) 15. Ogilvy CS , Heros RC , Ojemann RG , et al : Angiographically occult arteriovenous malformations. J Neurosurg 69 : 350 – 355 , 1988 Ogilvy CS, Heros RC

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O. Del Curling Jr., David L. Kelly Jr., Allen D. Elster and Timothy E. Craven

✓ The advent of magnetic resonance (MR) imaging has permitted the recognition of many angiographically occult vascular malformations before the development of complications and subsequent surgical removal. This study reviews all patients at one institution who had radiographically identifiable vascular malformations believed to represent cavernous angiomas in order to obtain information on the natural history of this particular lesion. All 8131 craniospinal MR images performed at our medical center from January 1, 1986, to November 30, 1989, were reviewed, and 32 patients were identified with 76 lesions meeting the MR imaging criteria for cavernous angioma. Medical histories, physical examination records, and other data from these patients were then reviewed to determine the frequency of complications. Their mean age at latest follow-up examination (or at surgical removal of the lesion) was 37.6 years (range 16 to 72 years). Sixteen patients (50%) had a history of seizures, seven (22%) had focal neurological deficits, and three (9%) had clinically significant hemorrhage attributable to the cavernous angioma; six patients (19%) were asymptomatic. The estimated risk of hemorrhage for this population is 0.25%/person-year of exposure; the estimated risk of seizure development is 1.51%/person-year. Eight patients underwent surgical procedures, resulting in improved seizure control and/or lessened neurological deficit. Although these lesions are often excised with relative ease and minimal morbidity, the potential risks and benefits of surgery must be weighed carefully before removal of these relatively benign malformations.

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Neurosurgical Forum: Letters to the Editor To The Editor Roberto C. Heros , M.D. Massachusetts General Hospital Boston, Massachusetts 293 293 In our recent article (Ogilvy CS, Heros RC, Ojemann RG, et al: Angiographically occult arteriovenous malformations. J Neurosurg 69: 350–355, September, 1988), we failed to cite an important chapter on venous and cavernous malformations that has influenced our thinking considerably. 1 For this we would like to apologize. Reference 1. Martin NA

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Daniela Lombardi, Bernd W. Scheithauer, David Piepgras, Fredric B. Meyer and Glenn S. Forbes

✓ The term “angioglioma” denotes a highly vascular glioma, most of which are low-grade lesions associated with a favorable prognosis. The authors encountered an example of this pathology, a cystic oligodendroglioma associated with prominent vasculature which both clinically and histologically mimicked an occult arteriovenous malformation (AVM). This case and reports of the association of AVM and glioma prompted a histological review of 1034 surgically resected AVM's, both angiographically occult and visible, among which no oligodendroglial or astrocytic forms of “angioglioma” were found. Eight cases were observed, however, wherein oligodendroglial cells were increased in number within or about the malformation. Two basic histological patterns of oligodendroglial cell excess were seen; one appeared to be malformative in nature with abnormal disposition of oligodendroglial cells being an integral part of the AVM, whereas in the other an apparent increase in cellularity seemed the result of chronic ischemia with condensation of white matter. It appeared that the areas of increased oligodendrocyte content seen in association with AVM are non-neoplastic lesions that exhibit two rather distinct histological patterns of differing origin.

In an effort to determine the frequency of “angioglioma,” the authors examined Tissue Registry data for several glioma groups in which highly vascular examples are prone to occur. Tumors selected for study included 104 cerebellar-type (pilocytic) astrocytomas, 82 oligodendrogliomas, and 51 supratentorial pilocytic astrocytomas. Histological hypervascularity mimicking a vascular malformation (that is, an “angioglioma”) was encountered in 5%, 4%, and 12% of the cases, respectively. Based upon clinical, radiological, and pathological reviews of these cases, as well as a careful review of the literature, it was concluded that 1) “angiogliomas” are neither rare nor represent a distinct clinicopathological entity; 2) in histological but not necessarily angiographic surgical terms, they represent simply highly vascular gliomas, usually of low grade; and 3) the clinicopathological and angiographic features as well as the prognosis of such lesions do not differ from those of similar gliomas without angioma-like vasculature. Finally, “angiogliomas” must not be confused with gliomas of high-grade malignancy which, due to neovascularity, may be highly vascular at angiography and at surgery.

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medulla due to an angiographically occult arteriovenous malformation (AVM), which was removed successfully. 2 The authors of the second paper stated that biopsy of suspicious portions of the hematoma wall was routinely performed and produced evidence of a “cryptic” AVM in two more cases. I do not think that biopsy is sufficient to prevent recurrent hemorrhage. Again, removal of all abnormal vascular tissues would be needed, although total removal is difficult in some cases as mentioned by the authors of the first paper. To verify an underlying cause of a given

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, Stein BM (eds): Intracranial Arteriovenous Malformations. Baltimore : Williams & Wilkins , 1984 , pp 234 – 245 Martin NA, Wilson CB, Stein BM: Venous and cavernous malformations, in Wilson CB, Stein BM (eds): Intracranial Arteriovenous Malformations. Baltimore: Williams & Wilkins, 1984, pp 234–245 3. Ogilvy CS , Heros RC , Qjemann RG , et al : Angiographically occult arteriovenous malformations. J Neurosurg 69 : 350 – 355 , 1988 Ogilvy CS, Heros RC, Qjemann RG, et al: Angiographically

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Howard Tung, Steven L. Giannotta, Parakrama T. Chandrasoma and Chi-Shing Zee

arteriovenous malformations of the brain. J Neurol Neurosurg Psychiatry 41 : 1057 – 1064 , 1978 Bell BA, Kendell BE, Symon L: Angiographically occult arteriovenous malformations of the brain. J Neurol Neurosurg Psychiatry 41: 1057–1064, 1978 3. Bitoh S , Hasegawa H , Fujiwara M , et al : Angiographically occult vascular malformations causing intracranial hemorrhage. Surg Neurol 17 : 35 – 42 , 1982 Bitoh S, Hasegawa H, Fujiwara M, et al: Angiographically occult vascular malformations causing intracranial

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Neurosurgical Forum: Letters to the Editor To The Editor Robert F. Spetzler , M.D. Barrow Neurological Institute Phoenix, Arizona 500 501 A nice article by Ogilvy, et al. , discusses the differences in the presentation of cavernous angiomas, venous angiomas, and occult arteriovenous malformations (AVM's) (Ogilvy CS, Heros RC, Ojemann RG: Angiographically occult arteriovenous malformations. J Neurosurg 69: 350–355, September, 1988). The broad area of angiographically occult AVM's continues to be confusing. 3