Surgical excision of arteriovenous malformation of the cerebellum and brain stem: a case presentation

Brainstem arteriovenous malformations: anatomical subtypes, assessment of "occlusion in situ" technique, and microsurgical results

OBJECT

The surgical management of brainstem arteriovenous malformations (AVMs) might benefit from the definition of anatomical subtypes and refinements of resection techniques. Many brainstem AVMs sit extrinsically on pia mater rather than intrinsically in the parenchyma, allowing treatment by occluding feeding arteries circumferentially, interrupting draining veins after arteriovenous shunting is eliminated, and leaving the obliterated nidus behind. The authors report here the largest series of brainstem AVMs to define 6 subtypes, assess this "occlusion in situ" technique, and analyze the microsurgical results.

METHODS

Brainstem AVMs were categorized as 1 of 6 types: anterior midbrain, posterior midbrain, anterior pontine, lateral pontine, anterior medullary, and lateral medullary AVMs. Data from a prospectively maintained AVM registry were reviewed to evaluate multidisciplinary treatment results.

RESULTS

During a 15-year period, the authors treated 29 patients with brainstem AVMs located in the midbrain (1 anterior and 6 posterior), pons (6 anterior and 7 lateral), and medulla (1 anterior and 8 lateral). The nidus was pial in 26 cases and parenchymal in 3 cases. Twenty-three patients (79%) presented with hemorrhage. Brainstem AVMs were either resected (18 patients, 62%) or occluded in situ (11 patients, 38%). All lateral pontine AVMs were resected, and the occlusion in situ rate was highest with anterior pontine AVMs (83%). Angiography confirmed complete obliteration in 26 patients (89.6%). The surgical mortality rate was 6.9%, and the rate of permanent neurological deterioration was 13.8%. At follow-up (mean 1.3 years), good outcomes (modified Rankin Scale [mRS] score ≤ 2) were observed in 18 patients (66.7%) and poor outcomes (mRS score of 3-5) were observed in 9 patients (33.3%). The mRS scores in 21 patients (77.8%) were unchanged or improved. The best outcomes were observed with lateral pontine (100%) and lateral medullary (75%) AVMs, and the rate of worsening/death was greatest with posterior midbrain and anterior pontine AVMs (50% each).

CONCLUSIONS

Brainstem AVMs can be differentiated by their location in the brainstem (midbrain, pons, or medulla) and the surface on which they are based (anterior, posterior, or lateral). Anatomical subtypes can help the neurosurgeon determine how to advise patients, with lateral subtypes being a favorable surgical indication along with extrinsic pial location and hemorrhagic presentation. Most AVMs are dissected with the intention to resect them, and occlusion in situ is reserved for those AVMs that do not separate cleanly from the brainstem, that penetrate into the parenchyma, or are more anterior in location, where it is difficult to visualize and preserve perforating arteries (anterior pontine and lateral medullary AVMs). Although surgical morbidity is considerable, surgery results in a better obliteration rate than nonoperative management and is indicated in highly selected patients with high rerupture risks.

[Linear accelerator radiosurgery for brainstem arteriovenous malformations. Long-term results]

OBJECTIVE

Arteriovenous malformations (AVM) in the brainstem carry a high risk of recurrent haemorrhage, mortality and morbidity. Treatment options are limited and mainly based on stereotactic radiosurgery. We studied the results of our series of brainstem AVM treated with linear accelerator (LINAC) and with a long-term follow-up.

METHODS

We retrospectively analysed the clinical and radiological data of 41 consecutive patients with brainstem AVM treated by radiosurgery with a 6MV linear accelerator between 1992 and 2010. Twenty five lesions were located in the mesencephalon, 14 in the pons, one in the medulla oblongata and one was bulbopontine. We analysed the treatment results in relation to survival, rate of radiological obliteration, rebleeding, and treatment toxicity.

RESULTS

The obliteration rate confirmed by angiography/MRA was 59.5% on 38 controlled patients. The mean follow-up period was 61 months (range: 6.7-178) and the margin dose was 14Gy in most treatments. Up to 39% of patients received more than one radiosurgery procedure to achieve closure of the malformation. No statistical correlation was found with the margin dose, presence of pretreatment haemorrhage, nidus diameter or score on the Pollock-Flickinger grading system. The annual haemorrhage rate after radiosurgery was 3.2%. Three patients died from rebleeding and actuarial survival rate was 88% at 5 and 10 years after treatment. Four patients suffered new transient neurological deficits due to toxicity, and only one presented a permanent deficit (2.6%).

CONCLUSIONS

Nidus obliteration in brainstem AVM must be achieved according to three main criteria: maximum obliteration rate forced by the high rate of rebleeding, minimal morbidity given its critical location, and the greatest possible accuracy. Stereotactic radiosurgery with our moderate-dose protocol, which we believe achieved these three premises, may become an elective therapeutic modality for these patients.

Surgical Applications To Arteriovenous Malformations Involving The Brainstem

Objective:

To evaluate possible applications of microsurgical extirpation to arteriovenous malformations (AVMs) involving the brainstem.

Methods:

We retrospectively reviewed clinical records of 25 patients with AVMs involving brainstems who were admitted to our institute from 1984 to 2004. We defined a brainstem AVM as an AVM in which some part was located within the brainstem. The main location of the nidus was classified into ventral midbrain (n = 3), dorsal midbrain (n = 10), pons (n = 5), cerebellopontine angle (n = 6), and medulla oblongata (n = 1). Bleeding risks from the AVMs were calculated, and applied treatment modalities, respectability, and clinical outcomes were analyzed.

Results:

The annual bleeding and rebleeding risks of brainstem AVMs were 15.1 and 14.2%, respectively. Total resection was successfully performed in 0 out of 3, 6 out of 10,2 out of 5,6 out of 6, and 0 out of 1 in each of the groups, respectively. Stereotactic radiosurgery was applied as a main treatment modality in three patients (two ventral midbrain AVMs and one pontine AVM), and after microsurgery in one patient with a medulla oblongata AVM. Microsurgery-related permanent neurological complications were observed in five patients (one postoperative bleeding, one hemiparesis, three hearing deterioration, one abducens nerve palsy). During a follow-up period of 8 years (range, 8 mo-15 yr), one patient with an untreated pontine AVM died owing to hemorrhage and one patient with a subtotally resected dorsal midbrain AVM died owing to an unknown etiology 4 years later.

Conclusion:

Surgical resection can be applied with considerable, but acceptable, morbidity and mortality in some groups of brainstem AVMs with hemorrhagic presentation, particularly dorsal midbrain and cerebellopontine angle types, in which most parts of the nidus located sub- or extrapially.

Stereotactic radiosurgery for brainstem arteriovenous malformations: factors affecting outcome

OBJECT

Management options for arteriovenous malformations (AVMs) of the brainstem are limited. The long-term results of stereotactic radiosurgery for these disease entities are poorly understood. In this report the authors reviewed both neurological and radiological outcomes following stereotactic radiosurgery for brainstem AVMs over 15 years of experience.

METHODS

Fifty patients with brainstem AVMs underwent gamma knife surgery between 1987 and 2002. There were 29 male and 21 female patients with an age range of 7 to 79 years (median 35 years). Anatomical locations of these AVMs included the midbrain (39 lesions), pons (20 lesions), and medulla oblongata (three lesions). The radiation dose applied to the margin of the AVM varied from 12 to 26 Gy (median 20 Gy). Forty-five patients were followed up from 5 to 176 months (mean 72 months). The angiographically confirmed actuarial obliteration rate was 66% at the final follow-up examination. Two patients experienced a hemorrhage before obliteration. The annual hemorrhage rate was 1.7% for the first 3 years after radiosurgery and 0% thereafter. Patients who had received irradiation at two or fewer isocenters had higher obliteration rates (80% compared with 44% for > two isocenters, p = 0.006), and this was related to a more spherical nidus shape. The rate of persistent neurological complications in patients treated using magnetic resonance imaging-based dose planning after 1993 was 7%, compared with 20% in patients treated before 1993. An older patient age, a lesion located in the tectum, and a higher radiosurgery-based score were significantly associated with greater neurological complications.

CONCLUSIONS

Stereotactic radiosurgery provided complete obliteration of AVMs in two thirds of the patients with a low risk of latency-interval hemorrhage. Better three-dimensional imaging studies and conformal dose planning reduced the risk of adverse radiation effects. Younger patients harboring more spherical AVMs that did not involve the tectal plate had the best outcomes.

Arteriovenous malformations of the posterior fossa

AVMs of the posterior fossa are reviewed on the basis of personal experience of 47 cases including 2 venous angiomas, 7 cavernous angiomas, 5 arteriovenous fistulas and 33 true arteriovenous malformations and of the few series reported in the literature. MRI is now an indispensable tool to define the exact localization of any malformation. Combined with angiography, it permits one to choose the most adequate therapeutic strategy and the best surgical approach. Radical cure is to be contemplated in most cases considering the often dramatic consequences of bleeding at the infratentorial level. Deep AVMs and moreover cavernous angiomas, even those located in highly functional structures such as the brain stem, can now be discussed for treatment. Encouraging results have already been obtained using, alone or in association, the recently advanced modalities of treatment: interventional neuroradiology, radiosurgery, and microsurgery.

Total removal of an arteriovenous malformation embedded in the brain stem

The removal of brain stem arteriovenous malformations is one of the most challenging problems in neurosurgery. The authors report a successful total removal of an arteriovenous malformation situated in the middle cerebellar peduncle, which was embedded in the floor of the fourth ventricle. The importance of dissection "flush" with coils of an arteriovenous malformation is stressed.

Surgical management of brain stem vascular malformations

Vascular malformations of the brain stem are a histologically heterogenous collection of lesions which most often present with sudden and progressive neurologic deficit related to haemorrhage. Since 1987 the authors have treated eleven cases of brain stem vascular malformation. Seven of the patients were treated with complete surgical extirpation of the haematoma and malformation because of progressive neurologic deficit. Four additional patients made a full neurologic recovery and are being carefully observed for signs suggestive of the need for surgical treatment. Complete surgical excision of brain stem vascular malformations is mandatory for patients with progressive neurologic deficit related to recurrent haemorrhage.

Vascular malformations of the brain stem

Vascular malformations of the brain stem are unusual lesions that may pose a diagnostic and therapeutic challenge. Seven patients with vascular malformations involving the brain stem were evaluated; six were treated surgically, with complete obliteration of the lesion in five patients. In five patients symptoms developed only after a hemorrhage had occurred, and three of these suffered a rebleed before appropriate treatment was given. Angiography failed to demonstrate lesions in three cases, which did not appear to protect from repeat hemorrhage since two of the three rebled. There were no operative deaths, and no patients were made permanently worse after surgery. Useful recovery occurred commonly after appropriate treatment and appeared to be possible even in patients who had suffered a catastrophic neurological deficit at the time of presentation. These data indicate that surgical removal of the lesion may be warranted in some patients with symptomatic brain-stem vascular malformation.

Arteriovenous malformation in the cerebellopontine angle presenting as trigeminal neuralgia

A case of arteriovenous malformation of the left cerebellopontine angle causing symptoms of ipsilateral trigeminal neuralgia is reported. Pain relief followed microsurgical removal of the malformation. The authors review the literature on the subject.

Management of arteriovenous malformations of the brain stem

In a series of 250 intracranial arteriovenous malformations (AVM's), 12 malformations involved the brain stem. Nine of these lesions were treated surgically, with complete obliteration in eight. There were no operative deaths, and only two patients were made worse by surgery. In the nonsurgically treated group, one patient had embolization therapy and two patients underwent radiation therapy. Results in these three patients have not been satisfactory. These data indicate that brain-stem AVM's can be surgically removed with acceptable morbidity.

Angiographic disappearance and reappearance of an arteriovenous malformation of the cerebellum and brain stem, and its surgical excision. A case report

A case of arteriovenous malformation (AVM) of the cerebellum and brainstem at the cerebellopontine angle is reported. Though a postoperative angiogram after the first operation indicated complete excision of the lesion, the patient returned with subarachnoid haemorrhage, and an angiogram indicated reappearance of the lesion. Total excision was carried out at the second operation.

Angiomas of the cerebellopontine angle

Angiomas situated within the pontocerebellar cistern lie superficially on the ventrolateral aspect of the brain stem. Occasionally, minor extensions penetrate into the adjacent nervous structures. Five patients bearing such lesions were operated upon, using a microsurgical technique. Radical excision was performed in all cases. Within 2 to 12 months the patients had returned to their previous occupations, being fully able to work or attend school. There is increasing evidence for the effectiveness of surgical treatment of angiomas of the ventrolateral aspect of the brain stem and the cerebellopontine angle. The illness usually presents with hemorrhages of varying severity, ranging from mild to devastating. Impairment of consciousness, contralateral hemiparesis and ipsilateral cranial nerve palsies are the most frequent neurological signs after bleeding. The outcome following excision is primarily related to the preoperative condition. No additional deficits or only minor further impairment can be expected from surgical interference. Exploration is advisable whenever the malformation appears to lie on the surface rather than within the brain stem.