Treatment of Eloquent Cortex AVMs

Introduction

Arteriovenous malformations (AVMs) become even more challenging to treat when they are located in eloquent cortex. Eloquent cortex is defined as cortex with specific functions, loss of which would result in disabling neurological deficits: the primary motor cortex in the precentral gyrus, the primary sensory cortex in the postcentral gyrus, the supplementary motor area, the primary visual cortex in the medial occipital lobe, the language cortex in the dominant inferior frontal and superior temporal gyri (Broca’s area and Wernicke’s area, respectively), the hypothalamus, the thalamus, the internal capsule, the brainstem, the cerebellar peduncles, and the deep cerebellar nuclei. Involvement of these locations increases the risk of operative morbidity and postoperative neurological deficits, as demonstrated by the Spetzler-Martin grading system. In addition to the nidus size of an AVM and its drainage pattern, eloquence is considered a significant predictor of operative morbidity and must be given the utmost consideration by both the patient and the neurosurgeon.

Disruption of white matter tracts can be equally as devastating as disruption of eloquent cortex. Even though involvement of fiber tracts is not included in any of the AVM grading systems, there are several tracts that need to be taken into consideration when assessing the risks of surgery and selecting the treatment modality and operative approach. The internal capsule encompasses the corticobulbar and corticospinal tracts, which travel from the motor cortex to the brainstem and the spinal cord, respectively. The internal capsule also contains the thalamocortical somatosensory tracts, which travel from the ventroposterior nucleus of the thalamus to the postcentral gyrus. Optic radiations carry visual information from the lateral geniculate nucleus to the primary visual cortex. The uncinate fasciculus connects the frontal lobe with the temporal lobe and plays a major role in language, memory, and emotions. The superior longitudinal fasciculus contains fibers involved in language and motor function. Lastly, damaging structures such as the corpus callosum and the fornix can also be debilitating, causing disconnection syndromes and memory dysfunction, respectively.

A thorough understanding of not only the location of the AVM but also its arterial feeders and venous drainage patterns is imperative. Determining whether the feeding arteries have branches that are en passage, giving supply to eloquent cortex rather than the AVM nidus, is necessary to prevent complications. Similarly, understanding venous drainage patterns and ensuring the preservation of normal draining veins of eloquent structures during the final stages of AVM resection is crucial. Assessment of involved vascular territories remains a critical component of the treatment planning process.

Eloquence in AVM Grading Systems

A number of AVM grading systems are available to guide the neurosurgeon when deciding on the need for treatment and identifying the optimal treatment modality. In addition to the original Spetzler-Martin grading system, the grading systems proposed by Lawton et al. (the Lawton-Young supplementary grading scale), Pasqualin et al., and Shi and Chen also incorporate eloquence in the grading. Other classifications, such as those of Drake, Luessenhop and Gennarelli, and Nataf et al., do not include eloquence in their grading. While each grading system offers a different point of view, there is no doubt at this point that eloquence should be taken into consideration in decision-making for AVM treatment.