Introduction

Deep arteriovenous malformations (AVMs) in the thalamus and brainstem are rare and challenging lesions. The management of these AVMs is demanding because the skull base limits the surgical exposure of the brainstem. Therapy includes observation with noninterventional follow-up, as well as surgical resection, endovascular embolization, stereotactic radiosurgery (SRS), or some combination of these options. The risks of any intervention must be balanced against the risk of spontaneous rupture and hemorrhage when selecting the treatment for a patient. ^{1 , 2} The current treatment of AVMs is multimodal and often includes SRS and endovascular embolization, but in appropriately selected patients, microsurgical resection is associated with superior cure rates and little surgical morbidity and mortality. ^{3 , 4 , 5} The Spetzler-Martin and Lawton-Young supplementary grading systems predict surgical complications and guide treatment selection for patients. ^{6 , 7} The grading systems allocate points for various features of AVMs, including AVM size, eloquent location, venous drainage, patient age, nidal diffuseness, and hemorrhagic presentation. Patients with Spetzler-Martin grade IV and V AVMs or with supplemented scores greater than 6 have unacceptably high surgical morbidity and mortality.

Deep AVMs in the thalamus and brainstem are invariably high-grade lesions because they are located in inviolable brain close to cranial nerves (CNs), CN nuclei, and brainstem pyramidal tracts. All have deep venous drainage. Although patients with deep AVMs and brainstem AVMs are more likely, compared with patients with supratentorial AVMs, to present with hemorrhage and to have worse outcomes because of the relationship of these AVMs to eloquent structures, careful treatment selection can help to avoid complications and poor outcomes from surgery. ^{8 , 9 , 10}

When it is safe to obliterate deep surgically inaccessible feeding arteries, preoperative endovascular embolization is routinely performed to reduce blood flow to the AVM, to minimize blood loss during surgery, and to reduce operating time. Despite advances in endovascular techniques, including microcatheter systems and liquid embolic agents, embolization of AVMs still presents considerable risk. ^{11 , 12 , 13} For deep AVMs arising from thalamoperforators or brainstem perforators, the escape of the embolic agent from the vasculature may cause a stroke. Although access and embolization are technically feasible and safe in some cases, endovascular cures are rare. ¹⁴ Furthermore, there is no evidence that partial obliteration reduces the risk of rebleeding.

SRS is often selected as an alternative to microsurgical resection for deep AVMs to avoid the morbidity and possible mortality associated with resection of deep or high-grade AVMs. However, obliteration rates are lower than those for surgery, and there is a risk of hemorrhage during the latency period and from complications secondary to adverse radiation effects. ¹⁵ Rates of developing these complications are higher for AVMs in the brainstem and thalamus than for AVMs located in other areas of the brain. ¹⁶ The best results are observed with small AVMs.

Compelling indications for intervention include hemorrhage, preexisting deficits, failure of SRS, and young age. Favorable outcomes are possible with surgery, particularly for small and superficially located AVMs along established surgical corridors. Solomon and Stein ¹⁷ reported outcomes for 12 patients with brainstem AVMs, 9 of whom underwent surgery. There were no deaths, only two patients had a worse outcome after surgery, and AVM obliteration was achieved in eight of the nine surgically treated patients. In a similar surgical series of 32 patients, Batjer and Samson ¹⁸ reported an operative mortality of 7% (n = 2) and significant morbidity in 13% (n = 4) of the 30 patients who underwent surgery. In another large surgical series of brainstem AVMs, Han et al ¹⁹ achieved complete obliteration in 90% (26 of 29 patients), with surgical mortality and morbidity of 7% (n = 2) and 14% (n = 4), respectively. The best outcomes were in patients with lateral pontine and medullary AVMs, whereas the worst outcomes were in patients with anterior pontine and midbrain lesions ( Table 28.1 ).

Defining anatomical subtypes of AVMs, including deep lesions in the thalamus and brainstem, allows for further refinement of established approaches and surgical techniques and for identification of the subtypes amenable to a surgical cure, with acceptable mortality and morbidity. Thalamic AVMs are categorized along with sylvian, insular, and basal ganglial AVMs as deep AVMs, whereas brainstem AVMs are divided into 6 separate subtypes according to their location and the surface on which they are based in the brainstem. ²⁰

Thalamic Arteriovenous Malformations

Anatomy

The thalamus is encircled by the lateral ventricles and divided by the third ventricle. Thalamic AVMs are supplied by anterior thalamoperforators from the posterior communicating artery, by posterior thalamoperforators from the P1 segment of the posterior cerebral artery (PCA), and by the lateral and medial posterior choroidal arteries. Venous drainage is always deep. More superiorly located thalamic AVMs drain to the internal cerebral vein ( Fig. 28.1 ), while those on the medial wall drain to the basal vein of Rosenthal ( Fig. 28.2 ).

Related posts:

25 Brainstem and Thalamic Intraparenchymal Hemorrhage 29 Endovascular Management of Brainstem and Thalamic Arteriovenous Malformations 30 Surgery for Thalamic and Brainstem Cavernous Malformations 23 Brainstem Ischemia, Stroke, and Endovascular Revascularization of the Posterior Circulation 27 Endovascular Management of Aneurysms of the Posterior Circulation 31 Revascularization of the Brainstem

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