Introduction

Posterior fossa arteriovenous malformations (AVMs) account for 7 to 15% of all intracranial AVMs and are mostly represented by cerebellar AVMs, a heterogeneous group that includes 75 to 81.2% of all the posterior fossa AVMs. Even though cerebellar AVMs represent a minority of those lesions, they carry a higher risk of rupture and are associated with considerable higher rates of morbidity and mortality.

Treatment selection must be performed according to the characteristics of each case and the final objective must be the complete obliteration of the AVM with minimal secondary morbidity. Although microsurgical resection remains the gold standard treatment for cerebellar AVMs, endovascular embolization and radiosurgery also play an important role in the multidisciplinary management of those lesions.

Major controversies in decision making addressed in this chapter include:

1. 
   

   Whether or not treatment is indicated.

   
   
2. 
   

   Open versus endovascular versus radiosurgery for ruptured and unruptured cerebellar AVMs.

   
   
3. 
   

   Microsurgical approaches to cerebellar AVMs based on location.

Whether to Treat

The management of AVMs is still one of the most intricate problems in neurosurgery. Although direct surgical treatment remains the ultimate therapy for most cases, there have been a series of advances in neurological imaging, interventional neuroradiology, and radiosurgery that have contributed enormously to the management of these lesions.

Treatment should be based on the anatomical characteristics of the AVM, history of previous hemorrhages, and the expertise of the surgical team. The surgeon should compare the treatment results of his group with the long-term risks of leaving the AVM untreated. Cerebellar AVMs should be treated in specialized neurovascular centers with expertise in the treatment of AVMs, where dedicated microneurosurgeons, endovascular surgeons, and radiosurgeons work together. Whenever such a team is not present, referral to other centers should be considered.

In recent years, important contributions have been made to our understanding of the prognosis and behavior of posterior fossa AVMs. Cerebellar AVMs, unlike supratentorial malformations, present more frequently with subarachnoid hemorrhages. Mortality rates of up to 66.7% have been associated with the rupture of those lesions. In one of the most comprehensive studies about the natural history of AVMs, Hernesniemi et al performed a retrospective analysis of 238 AVM patients with a mean follow-up period of 13.5 years. The authors evaluated risk factors for AVM rupture and the annual incidence of rupture of those lesions. According to this study, an infratentorial location is one of the most important risk factors for rupture. Univariate analysis demonstrates an annual rate of rupture of 11.6% in the first 5 years after admission, with a cumulative rupture rate of 45% in the first 5 years, as compared with an annual rate of 4.3% and a cumulative 5-year rate of 19% for supratentorial AVMs. They concluded that infratentorial location was an independent risk factor for rupture during the whole follow-up period, with a relative risk of rupture of 3.07 (95% confidence interval [CI]: 1.37–6.87) as compared with supratentorial AVMs ( 1 , 2 in algorithm ). Other important risk factors for AVM rupture are previous hemorrhage and anatomic variations of the lesion, such as high feeding artery pressure.

Considering the high risk of bleeding associated with cerebellar AVMs, we recommend treatment to virtually all patients who present with those lesions, in specialized centers, when there are no clinical contraindications ( 1 , 2 in algorithm ). Elderly patients who harbor unruptured AVMs may be followed conservatively if surgical treatment is excessively risky due to comorbidities ( 3 in algorithm ). Patients with a previous history of cerebellar AVM hemorrhage should be specially considered for surgical treatment, since those lesions present significantly higher bleeding rates.

Anatomical Classification

Although the Spetzler–Martin grading system is extremely useful for the evaluation and prediction of outcomes of supratentorial AVMs, the special features of cerebellar AVMs justify the application of a specific system for those lesions. Considering the anatomical characteristics of the cerebellum, we classify cerebellar AVMs according to their location, deepness in the cerebellar parenchyma, size, and involvement of dentate nucleus. With regard to location, we classified AVMs in four categories: tentorial, petrous, suboccipital, or vermian. Once the site of the lesion is defined, AVMs are classified following the criteria specified in ▶ Table 57.1 . Lesions that present dentate nucleus involvement are represented by * in the table. Clinical application of our grading scale is demonstrated in ▶ Figs. 57.1 to 57.4 .

Anatomical Considerations

Anatomical characteristics of the cerebellum, such as size, cerebellar regions, arterial supply, venous drainage, and eloquence differentiate the cerebellar AVMs from their supratentorial counterparts.

Cerebellar Regions

According to location, cerebellar AVMs may be classified in four different groups: tentorial, petrous, suboccipital, and vermian. Moreover, these lesions may be further classified according to their location in the cerebellar parenchyma, as superficial, deep, or mixed. Superficial AVMs are lesions restricted to the cortical surface of cerebellum (▶ Figs. 57.1 , 57.2 ); deep AVMs do not present extension into the cerebellar cortex; and mixed AVMs are defined as lesions with extension from the cortex to the deep cerebellar white matter (▶ Figs. 57.3 , 57.4 ).

Related posts:

54 Spetzler–Martin Grade III Arteriovenous Malformations 56 Brainstem Arteriovenous Malformations 58 Spinal Arteriovenous Malformations 61 Carotid-Cavernous Fistulas 59 Pial Arteriovenous Fistulas 60 Dural Arteriovenous Fistulas

Stay updated, free articles. Join our Telegram channel

Join