Parafalcine and midline arteriovenous malformations: surgical strategy, techniques, and outcomes

Clinical article

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Object

Parafalcine arteriovenous malformations (AVMs) have a midline plane in common, but differ in their location (anterior, middle, or posterior) and depth (superficial or deep). Surgical management varies with AVM location and depth in terms of patient position, head position, craniotomy, and surgical approach. This study examined surgical strategies, patient outcomes, and regional factors influencing results.

Methods

Patients with AVMs located on the medial surface of the cerebral hemisphere were identified retrospectively from a consecutive, single-neurosurgeon series that is registered prospectively as part of the UCSF Brain Arteriovenous Malformation Study Project. During a 12-year period, 443 patients with AVMs were treated surgically. Of these 443 patients, 132 (30%) had parafalcine AVMs, which were distributed in zones as follows: superficial-anterior, 25 (18.9%); superficial-middle, 26 (19.7%); superficial-posterior, 39 (29.5%); deep-anterior, 25 (18.9%); deep-posterior, 17 (12.9%). Five different surgical strategies were used depending on AVM zone.

Results

Complete AVM resection was achieved in 123 (93.2%) of 132 patients. Overall, neurological condition improved in 74 patients (56.1%) and remained unchanged in 41 patients (31.1%). Neurological condition deteriorated in 12 patients (9.1%), and 5 patients (3.8%) died. Patients with AVMs in the superficial-middle zone had the highest rate of neurological deterioration (26.9%).

Conclusions

Parafalcine AVMs lie on a midline surface that, when exposed with a bilateral craniotomy across the superior sagittal sinus and a wide opening of the interhemispheric fissure, makes them superficial. However, unlike convexity AVMs, which are approached perpendicularly, parafalcine AVMs are approached tangentially. Gravity retraction is useful with deeply located AVMs (those in the deep-anterior and deep-posterior zones), because it widens the interhemispheric fissure and accesses deep arterial feeding vessels from the anterior and posterior cerebral arteries. Surgical risks were increased in the superficial-middle zone, which is likely explained by the proximity of sensorimotor cortex. The authors' regional classification of parafalcine AVMs may serve as a guide to surgical planning.

Abbreviations used in this paper: ACA = anterior cerebral artery; AVM = arteriovenous malformation; ICA = internal carotid artery; MCA = middle cerebral artery; PCA = posterior cerebral artery; SSS = superior sagittal sinus; VA = vertebral artery.

Article Information

Address correspondence to: Michael T. Lawton, M.D., Department of Neurological Surgery, 505 Parnassus Avenue, M780, Box 0112, San Francisco, California 94143-0112. email: lawtonm@neurosurg.ucsf.edu.

Please include this information when citing this paper: published online January 21, 2011; DOI: 10.3171/2010.12.JNS101297.

© AANS, except where prohibited by US copyright law.

Headings

Figures

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    AVM location was categorized into 5 zones: superficial-anterior (SA), superficial-middle (SM), superficial-posterior (SP), deep-anterior (DA), and deep-posterior (DP). The cingulate sulcus separated superficial and deep AVMs. The superficial medial hemisphere was divided into thirds. AVMs in the anterior third were anterior to the vertical plane of the coronal suture; AVMs in the posterior third were posterior to the vertical plane of the ascending ramus of the cingulate sulcus; and AVMs in the middle third were between these 2 planes. The deep medial hemisphere was divided into halves by the vertical plane bisecting the corpus callosum. Patient position, head position, and craniotomy are shown for each zone (insets). Dashed lines on the dura represent dural openings. TS = transverse sinus.

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    This left inferomedial frontal, Spetzler-Martin Grade II (S1V1E0) AVM was located in the superficial-anterior zone, as seen on digital subtraction angiography (left ICA injection, lateral [A] and anteroposterior [B] views). The AVM was exposed with a bifrontal craniotomy and the midline aligned vertically (C). The lateral border was exposed with some transcortical dissection into an encephalomalacia cavity from previous hemorrhage (D). Orbitofrontal feeding arteries coursed over olfactory tract (E), and frontopolar feeding arteries were accessed in the interhemispheric fissure (F). The nidus darkened after these feeding arteries were occluded. This patient had a good outcome with no new neurological deficits.

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    This left medial parietal, Spetzler-Martin Grade III+ AVM was located in the back of superficial-middle zone, as seen on digital subtraction angiography (left ICA injection, lateral view [A]; and left VA injection, anterior oblique view [B]). The patient's head was positioned with the midline oriented horizontally, optimizing access to all but the medial side of the AVM (C). However, the medial plane of dissection was accessed with some retraction on the nidus, exposing adhesions to the falx (D). Anterior, posterior, and lateral borders were dissected transcortically, preserving medial draining veins (E). Deep feeding arteries from ACA and PCA were occluded adjacent to the falx, This patient had a good outcome with no new neurological deficits.

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    This patient's occipital-pole, Spetzler-Martin Grade V AVM was treated with volume-staged radiosurgery, with 5 treatments over a 10-year period. She developed left hemianopsia as a result of radiation injury to her right occipital lobe, as seen on MR images (A, axial image). The AVM was not obliterated, as seen on digital subtraction angiograms (right VA injection, lateral view [B], and right ICA injection, lateral view [C]). The AVM was exposed with the patient in the lateral position, right side up, the nose turned down to align the midline vertically (D). A torcular craniotomy exposed 5 sides of this AVM, and dissection along the falx and tentorium accessed feeders from the PCA (E). The deep plane of dissection crossed the occipital horn of lateral ventricle (F). This patient had a good outcome with no new neurological deficits.

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    This corpus callosum and left cingulate gyrus AVM (Spetzler-Martin Grade III) was located in the deep-anterior zone. The patient was positioned supine with the head turned to the left, aligning the midline horizontally and allowing gravity to retract the left hemisphere. The left pericallosal artery coursed over the nidus and its branches supplied the AVM (left). The left pericallosal artery was skeletonized, and the nidus was dissected from the corpus callosum (center). The nidus was removed en bloc, unroofing the lateral ventricles to visualize the septum, septal veins, choroid plexus, and foramina of Monro (right).

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    This right medial occipital, Spetzler-Martin Grade III− AVM was located in the deep-posterior zone, as seen on digital subtraction angiography (right VA injection, anteroposterior [A] and lateral [B] views). The patient was positioned laterally with the right side down, aligning the midline horizontally. A torcular craniotomy exposed the occipital pole, and gravity retracted the right hemisphere as arachnoidal adhesions were released and CSF was drained from corpus callosal and quadrigeminal cisterns (C). Feeding arteries from the PCA were observed to course around the splenium and lead to the nidus (D), which was circumdissected and removed (E). This patient had a good outcome with no new neurological deficits.

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    Patient outcomes, as measured by mRS scores preoperatively and at last follow-up examination.

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    Analysis of surgical results according to AVM zones. AVMs in deep zones had higher rates of hemorrhagic presentation (A). Patients with parafalcine AVMs in the superficial-middle zone had the least improvement in mRS scores, reflecting a high rate of neurological deterioration (B). Patient outcomes after AVM resection in the superficial-middle zone did not correlate with increased percentages of high (Grade IV and V) or intermediate (Grade III) AVMs (C). There were high percentages of patients with AVMs in the superficial-middle zone that had high (Grade IV and V) or intermediate (Grade III) supplementary AVM grades (D). Anatomically, AVMs in the superficial-middle zone had more extensive arterial supply, with the highest percentage of AVMs with supply from 2 arterial territories (58%) and 3 arterial territories (ACA, MCA, and PCA, 23%) (E).

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