0148-396X/88/2301-0101$02.00/0 NEUROSURGERY Copyright © 1988 by the Congress of Neurological Surgeons Vol. 23, No. 1, 1988 Printed in U.S.A. Marked Growth of an Angiographically Occult Arteriovenous Malformation: Case Report Takato Morioka, M.D., Shunji Nishio, M.D., Takashi Hikita, M.D., Lau Hui Chung, M.D., and Tohru Soejima, M.D. Department of Neurosurgery (TM, SN, TH) and Stroke Unit (LHC), Kyushu Rosai Hospital, Kitakyushu, and Department of Neurosurgery (TS), University of Occupational and Environmental Health, Kitakyushu, Fukuoka, Japan The authors report a case of an angiographically occult arteriovenous malformation (AVM) that showed a marked increase in size over a period of 7 years. The importance of accurate diagnosis, follow-up computed tomography and repeated angiography, if needed, is stressed in cases where enlargement of an occult AVM is suspected. (Neurosurgery 23:101-103, 1988) Key words: Angiographically occult arteriovenous malformation, Computed tomography INTRODUCTION Cerebral arteriovenous malformation (AVM) is not a true neoplasm, but a congenital maldevelopment of blood vessels during an early embryonic stage. Therefore, theoretically there cannot be true growth of an AVM. Since the first description by Olivecrona and Riives (13), however, many cases with enlargement of this lesion have been reported (4, 7, 9-12, 14, 17-19, 21, 22). We report the case of a large AVM that is considered to have grown from an angiographically occult AVM over a period of 7 years. CASE REPORT A 15-year-old boy was found lying unconscious in a bath- room on November 16, 1975, On admission to our hospital, he was semicomatose with a right hemiparesis and signs of meningeal irritation. Lumbar puncture revealed hemorrhagic cerebrospinal fluid. Conservative treatment was instituted, and he recovered gradually. On the 20th day after the onset of symptoms, left carotid and vertebral angiography failed to show any vascular abnormalities (Fig. 1). Neither spasm of vessels nor mass effect was demonstrated angiographically. On the 37th day after onset, the patient returned home with a mild right hemiparesis, which was improving. In 1980, the patient developed generalized seizures followed by postictal right hemiparesis. He was readmitted to our hospital without physical and neurological deficits on March 29, 1983, at 23 years of age. Computed tomography (CT) showed a ringed, high density area with marked contrast enhancement in the left posterior frontal lobe and a linear low density area in the frontal lobe, which was considered to be the previous hematoma cavity (Fig. 2). Left carotid an- giography revealed a large AVM in the left posterior frontal lobe. It was fed by branches of the left anterior and middle cerebral arteries and drained into the superior sagittal sinus Fic. 1. Left carotid angiogram on the first admission (subtraction of venous phase). No abnormal vessels are visualized, 101 102 MORIOKA et al. through cortical veins (Fig. 3). Comparing it with the previous angiogram, it was obvious that marked dilatation of the left anterior cerebral artery had occurred due to high arterial blood flow to the AVM. On April 28, 1983, a left frontoparietal craniotomy was performed. The AVM was located in the premotor area facing the midline. After cauterization and clipping of feeding arter- ies (that is, the frontopolar artery, the callosomarginal artery, and a branch of the middle cerebral artery), the nidus was totally removed. During the procedure, the previous hema- toma cavity was not encountered. Postoperatively a right hemiparesis occurred; however, it gradually improved. The patient was discharged with mild impairment of skilled movements of his right hand. DISCUSSION The initial angiogram, performed when the patient devel- oped subarachnoid hemorrhage, failed to demonstrate any Fic. 2. CT on the second admission reveals a ringed high density area with marked enhancement and a linear low density area in the left posterior frontal lobe. Neurosurgery, Vol. 23, No. 1 vascular abnormalities. Seven years later, however, the angio- gram showed a large AVM in the frontal lobe. An AVM that is verified operatively and/or pathologically but is not detected angiographically is usually called an angiographically occult AVM. Several authors have tried to explain why angiography failed to demonstrate a vascular malformation. Some AVMs may have undergone partial or complete thrombosis, either spontaneously or secondary to hemorrhage (1-3, 6, 8, 15, 16). Several authors have suggested that the vascular malforma- tions may either be compressed by adjacent hematoma or destroyed at the time of hemorrhage (3, 8, 23). One of the most common explanations is that some malformations are not visualized because of their small size (1, 3, 13, 20, 23), but many cases in which the AVM has grown since a previous observation have been reported. Waltimo reviewed 21 such cases and pointed out that smaller AVMs have a tendency to increase in size (21). In 1977, Krayenbihl reported almost identical observations (9). It may be possible, therefore, that initially cryptic or angiographically occult small AVMs also grow in size. In our case, the anterior cerebral artery, which was a main feeder of the nidus on the second angiogram, was larger on the second than on the first angiogram. We think that this large AVM had grown from a small cryptic AVM, as in the case reported by Watanabe et al. (22). There are several possible mechanisms of growth or enlarge- ment of AVMs on sequential angiograms: (a) progressive vascular dilatation or pseudoaneurysmal formation occurring as a result of repeated occult hemorrhages that destroy the extravascular neural tissues (9, 14, 21); (6) continuous hemo- dynamic stress causing progressive enlargement of the thin- walled, undifferentiated vessels forming the fistulous shunts of the AVM (7); (c) the presence of more room for growth, for example, in the sylvian fissure (7, 21); (d) autonomic growth (9, 19): and (e) the presence of a “reserve” nidus, which was not opacified initially and becomes visible angio- graphically after a change in hemodynamics (17). In our case, * “ Fic. 3. Left carotid angiogram on the second admission. There is a large AVM in the posterior frontal lobe with markedly dilated feeding arteries. July 1988 repeated convulsive seizures might have indicated minor hem- orrhages followed by AVM enlargement. In addition, the previous hematoma cavity might have served as an area for growth of the AVM. Becker et al. (1) and Wilson and Martin (23) emphasized that intracerebral hematoma in young patients and in unusual locations should be explored surgically, even if angiography does not disclose a vascular lesion such as an AVM or angioma. We emphasize the importance of neuroradiological examination with CT, which usually visualizes an angiograph- ically occult AVM as a hyperdense lesion with little or no contrast enhancement (2, 3, 5, 6, 8, 11, 15, 23). Unfortunately, our patient was initially hospitalized during our pre-CT era. He developed repeated epileptic seizures, however, which might be related to the increase in size of an initially small cryptic AVM. As in our case, follow-up CT and repeated angiography may be necessary, especially in young patients who have episodes of intracranial hemorrhage of unknown cause. ACKNOWLEDGMENT Greatful acknowledgement is made to Dr. K. Fujii, De- partment of Neurosurgery, Kyushu University, for his valua- ble suggestion and helpful comments. Received for publication, November 5, 1987; accepted, December 18, 1987. Reprint requests: Takato Morioka, M.D., Department of Neuro- surgery, Neurological Institute, Faculty of Medicine, Kyushu Univer- sity, 3-1-1, Maidashi, Higashi-ku, Fukuoka 812, Japan. REFERENCES 1. Becker DH, Townsend JJ, Kramer RA, Newton TH: Occult cerebrovascular malformations: A series of 18 histologically ver- ified cases with negative angiography. Brain 102:249-287, 1979. 2. Chin D, Harper C: Angiographically occult cerebral vascular malformations with abnormal computed tomography. Surg Neu- rol 20:138-142, 1983. 3. Cohen HCM, Tucker WS, Humphreys RP, Perrin RJ: Angio- graphically cryptic histologically verified cerebrovascular malfor- mations. Neurosurgery 10:704-714, 1982. 4. Delitala A, Delfini R, Vagnozzi R, Esposito S: Increase in size of cerebral angiomas: Case report. 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Mendelow AD, Erfurth A, Grossart K, Macpherson P: Do cere- bral arteriovenous malformations increase in size? J Neurol Neurosurg Psychiatry 50:980-987, 1987. 12. Mori K, Murata T, Hashimoto N. Handa H: Clinical analysis of arteriovenous malformations in children. Childs Brain 6:13-25, 1980. MARKED GROWTH OF AN AVM 103 13. Olivecrona H, Riives J: Arteriovenous ancurysms of the brain: Their diagnosis and treatment. Arch Neurol Psychiatry 59:567- 602, 1948. 14. Paterson JH, McKissock W: A clinical survey of intracranial angiomas with special reference to their mode of progression and surgical treatment: A report of 110 cases. Brain 79:233-266, 1956. 15. Patil AA: Angiographically occult arteriovenous malformation of the brain: A case report. Acta Neurochir (Wien) 58:99-104, 1981. 16. Prakash B, Beohar PC, Misra RC: Low flow (cryptic) arteriove- nous malformation and spontaneous haematoma. Acta Neuro- chir (Wien) 69:61-67, 1983. 17. 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Baltimore, Williams and Wilkins, 1984, pp 184-208. COMMENTS Morioka et al., in their report of a single case, document extremely well the development of an AVM in an area where none was previously demonstrated, although there had been a hemorrhage. This certainly indicates that these abnormali- ties, previously thought to be congenital, can be acquired, and it underscores the fact that they can grow. In this case, considerable growth was witnessed. In my personal experi- ence, I have not had a case where an AVM was proven to be absent at one point in time and subsequently present. The growth in AVMs that we have witnessed, which occurs rarely, has generally been subtle. In this particular case, the AVM, for all intents and purposes, was nonvisualized and then appeared as a large lesion. Bennett M. Stein New York, New York Dr. Morioka et al. have demonstrated another dramatic example of the enlargement of an AVM. Although numerous such cases have been identified, the growth of this lesion over a 7-year period is striking. I have thought over the past 10 years that our whole concept of arteriovenous malformations may be inappropriate. The exceedingly small rate of incidental arteriovenous malformations in large pediatric angiographic series suggests that these lesions may grow during childhood and young adulthood and are not all present at birth. The more patients with multiple arteriograms separated over years, the more it becomes apparent that arteriovenous malforma- tions are often dynamic lesions. Certainly, this additional case highlights the dramatic changes in AVMs that may occur over time. Robert F. Spetzler Phoenix, Arizona