Clinical Experience of LINAC-based Stereotactic Radiosurgery for Angiographically Occult Vascular Malformations / 대한방사선종양학회지

PURPOSE: To establish the role of stereotactic radiosurgery (SRS) for the treatment of patients with angiographically occult vascular malformation (AOVM). MATERIALS AND METHODS: Eleven patients (12 lesions) with AOVM were treated with linear accelerator-based SRS between February 1995 and December 1999. A magnetic resonance imaging of each patients showed well-circumscribed vascular lesion with reticulated core of heterogeneous signal intensity and peripheral rim of low signal intensity. SRS were performed with the median peripheral dose of 16 Gy (range 13~25). A single isocenter was used with median collimator size of 14 mm (range 8~20) diameter. RESULTS: With a median follow-up period of 42 months (range 12~56), rebleeding occurred in 3 AOVMs at 5, 6 and 12 months after SRS but no further bleeding did. Two patients experienced radiation-induced necrosis associated with permanent neurologic deficit and one patient showed transient edema of increased T2 signal intensity. CONCLUSION: SRS may be effective for the prevention of rebleeding in AOVM located in surgically inaccessible region of the brain. Careful consideration should be needed in the decision of case selection and dose prescription because the incidence of radiation-induced complications is too high to be accepted.

Clinical Characteristics of Angiographically Occult and Histologically Confirmed Intracranial Vascular Malformations

The medical records of 30 patients with histologically confirmed and angiographically occult intracranial vascular malformations(AOVM), who underwent surgery between May 1988 and May 1993, were reviewed retrospectively to determine whether their radiological and clinical characteristics are helpful in differential diagnosis. Histological diagnoses were cavernous angioma(CA) in 17 cases, arteriovenous malformation(AVM) in nine, venous angioma in one and unclassified vascular malformation in three. The most common initial presenting mode was intracranial hemorrhage(ICH ; 18 cases, 60.0%), followed by seizure(11 cases, 33.3%) and headache(two cases, 6.6%). CA, once it had bled, tended to bleed repeatedly, and this occurred before surgery in seven of nine cases of CA presenting with ICH. On CT scan, calcification was observed only in CA(two cases). On MRI images obtained in 28 patients, a mottled density mass with or without adjacent ICH(ten of 16 CA's) and multiple lesions(three of 16 CA's) were pathognomonic for CA, while single stage ICH(two of eight AVM's) and signal void(three of eight AVM's) were observed only in cases of AVM. Findings of MRI such as multiple stage hemorrhage, low signal intensity rim or edema around the lesion were not helpful in differential diagnosis of the histological type of lesions. After enhancement with gadolinium, one case of AVM and another of venous angioma showed a serpentine pattern of enhancement. In 29 cases, the results of surgery were excellent ; there was no mortality and morbidity in only one case. In conclusion, CA, once it had bled, tended to rebleed and MRI was helpful in the differential diagnosis of AOVM's. MRI findings such as a mottled density mass or multiple lesions were pathognomonic for CA, while single stage hemorrhage or signal void were findings of AVM.

Diagnosis and Treatment of Brain Stem Hemorrhage Caused by Angiographically Occult Vascular Malformation(AOVM)

In cases of symptomatic AOVM of the brainstem, there is a great risk of progressive morbidity caused by repetitive hemorrhage, and the condition can even be fatal. To establish the optimum method of management of this condition, we investigated 15 patients treated between January 1991 and January 1996. Seven lesions were located in the pons, three in the medulla, three in the midbrain, and one each at the pontomedullary and pontomesencephalic junction. Surgery was performed in six cases in which the lesions were close to the dorsal pial surface of the brainstem ; the histological diagnosis was five cases of cavernous angioma and one of arteriovenous malformation. Nine patients with surgically inaccessible lesions, deep seated or located in the midbrain, were treated by gamma knife radiosurgery. All patients who underwent surgery showed neurologic improvement, and among those who underwent radiosurgery, the outcome was favorable. For symptomatic lesions located in the dorsal pial surface of the pons or medulla, surgical resection is the treatment of choice, and prevents further neurological disability and rehemorrhage. For the best possible outcome, intraoperative sonography and electrophysiologic monitoring are mandatory. Gamma knife radiosurgery can be employed in selected cases in which lesions are deep-seated and inaccessible and associated with repeated hemorrhage and progressive neurologic deficit.

Stereotactic Gamma Knife Radiosurgery for the Treatment of Angiographically Occult Vascular Malformations(AOVMs)

In recent years, an increasing number of patient with AOVMs have been recognized using MRI. When an AOVM is located in a region associated with an unacceptable surgical risk, stereotactic radiosurgery offers an alternative treatment. We treated 21 patients with AOVM using gamma knife radiosurgery from June, 1990 to December, 1993 at Asan Medical Center. The indications for radiosurgery were as follows:1) Patients who had episodes of hemorrhage from a lesion that had the characteristic images of AOVM in MRI. 2) Patients who had seizures and the focus of these seizures corresponded to the lesions. 3) Patients were excluded if the lesions were located superficially or were accessible to microsurgery. Nine patients presented with hemorrhages and twelve with seizures. The marginal dose was ranged from 10 to 25 Gy at or above the 50% isodose line. Of eight patients followed 12 months or less after radiosurgery, two patients had improved neurologic deficits and one had decreased the seizure frequency with mediciation. Among seven patients followed 12-24 months, MRI showed a reduction of the lesion in one patient and no change in five patients. One patient had perifocal edema. In two patients with seizures, one patient was seizure free without medication and one patient was controlled with medication. In six patients between 24 and 44 months, two patients had smaller lesions and three patients had perifocal edema. Among four patients who had seizures, one patient was seizure free without medication and three had decreased the seizure frequency with medication. Postoperative complications developed two patients, but one patient showed improvement of neurologic deficits after a short period of steroid medication. Stereotactic radiosurgery offers a treatment to a selective patients with intracranial AOVMs.

Angiographically Occult Vascular Malformations of the Brain: Report of Three Cases

The authors experience 3 cases of angiographically occult vascular malformation(AVOM) of the brain during the last 3 months in 1990. All cases were diagnosis of either operative or pathological finding and were associated with intracerebral hemorrhage. The authors recommend that surgery should be considered even to those angiographically negative intracerebral hemorrhage cases, once clinical features are highly suggestive of AOVM. Surgery can be an effective and define therapy for these entities, which are prone to cause recurrent hemorrhage and persistent neural deficits.