Anterior Fossa, Superior Sagittal Sinus, and Convexity Dural Arteriovenous Malformations

Patient Selection

34.1.1 Indications

Patients typically present with symptoms due to hemorrhage, ischemia, or hydrocephalus. They may also present with headache or a bruit, although bruits are less common than with transverse and sigmoid sinus dural arteriovenous fistulas (DAVFs). The overall risk of hemorrhage from a DAVF is 2% per year, but hemorrhage is rare unless there is leptomeningeal venous drainage, in which case the risk rises to 8% per year. Some studies suggest that DAVFs with leptomeningeal venous drainage have a risk of hemorrhage of 2% per year unless they have a history of hemorrhage, in which case the risk of hemorrhage increases to 7% per year. ¹^, ² The hemorrhage may be intraparenchymal, subarachnoid, subdural, and/or intraventricular and may be distant from the site of the dural nidus. Symptoms of hemorrhage include headache, seizures, focal deficit, or decreased level of consciousness.

Neurological symptoms not related to hemorrhage can result from venous congestion. Congestive ischemia may cause a focal deficit or seizures. Hydrocephalus may result from venous sinus hypertension or progressive arachnoid villous fibrosis due to repeated subarachnoid hemorrhage. Chronic neurological deficits may improve with treatment of an underlying DAVF.

The principal indications for treatment of a DAVF include prior hemorrhage, neurological deficit, or high risk of hemorrhage based on angiographic features. Expeditious treatment is recommended for any DAVF that has hemorrhaged and generally for those with leptomeningeal venous drainage. ² Patients without these indications may be observed, with intervention considered if symptoms such as headache or bruit are unbearable.

34.1.2 Imaging and Anatomical Considerations

The most useful imaging modality is catheter angiography, which should include selective injections of the internal, external, and vertebral arteries ( ▶ Fig. 34.1, ▶ Fig. 34.2, ▶ Fig. 34.3). Useful information can be gathered from computed tomography (CT) and magnetic resonance imaging (MRI) regarding anatomical location as well, but catheter angiography remains the gold standard. CT remains the most practical and sensitive method for detecting hemorrhages and may also show hydrocephalus or prominent venous channels in the calvarium. MRI is most useful for detecting ischemia, edema, or hemosiderin deposition from old hemorrhage. CT and MR angiography and venography may show an occluded sinus as well as anatomical details such as dilated cortical veins ( ▶ Fig. 34.4). Image guidance may be helpful to localize convexity and sagittal sinus lesions.

Fig. 34.1 Normal blood supply to the anterior fossa dura. The four sites of anastomosis between the ophthalmic artery and meningeal branches of the external carotid artery are shown. (1) Middle meningeal artery to the recurrent meningeal artery. (2) Middle meningeal artery to the meningeal branch of the posterior ethmoidal artery. (3) Middle meningeal artery to the anterior falcine branch of the anterior ethmoidal artery. (4) Middle meningeal artery to the meningeal branch of anterior ethmoidal artery.

(Reproduced with permission from Patel AB, King WA, Martin NA. Operative management of anterior fossa, superior sagittal sinus and convexity dural arteriovenous malformations. Neurosurgical Operative Atlas. 1st ed. 1999;8:70.)

Fig. 34.2 Diagnostic angiogram demonstrating a superior sagittal sinus fistula. (a) The fistula was supplied exclusively by the anterior ethmoidal artery in the early arterial phase (arrow), (b) there was venous varix noted during the late venous phase, (c) both feeding and early venous drainage are seen clearly in the late arterial phase preoperatively), (d) complete absence of flow is noted in the later arterial phase postoperatively.

Fig. 34.3 Diagnostic angiogram demonstrating a superior sagittal sinus fistula. (a) Anteroposterior view demonstrating dual supply by both the middle meningeal artery and the superficial temporal artery, (b) lateral view demonstrating dual supply by both the middle meningeal artery and the superficial temporal artery.

Fig. 34.4 Computed tomography angiogram demonstrating the anatomic location of a superior sagittal sinus fistula. (a) Axial view demonstrating the arterial ethmoidal feeding vessel, (b) sagittal view demonstrating the arterial feeder as well as associated venous varix deep to the feeder.

A useful way to classify DAVFs is the Borden system. ³ Borden type I DAVFs do not have venous sinus obstruction, and venous drainage is anterograde through a patent venous sinus and meningeal veins with no retrograde leptomeningeal drainage. Type II DAVFs have anterograde venous sinus and meningeal flow with retrograde leptomeningeal venous drainage. Type III DAVFs drain only via retrograde leptomeningeal venous flow. Classically, only types II and III are considered at risk for hemorrhage. DAVFs of the anterior fossa are more likely than those of the sigmoid or transverse sinus to be types II and III, accounting for their increased risk of hemorrhage.

Arterial supply is typically from the anterior ethmoidal artery and is bilateral in about half of the cases. Additional feeders may arise from the posterior ethmoidal artery, anterior falx artery, and branches from the external carotid system. Venous drainage usually occurs via cortical veins that drain to the superior sagittal and/or cavernous sinuses.

Superior sagittal sinus DAVFs typically involve the middle and posterior thirds of the sinus. They may be subclassified into those that drain directly into the superior sagittal sinus and are at a very low risk of hemorrhage and those that drain via a cortical vein and are at high risk of hemorrhage. Arterial supply is typically from the middle meningeal artery and may be bilateral with additional supply from the superficial temporal and occipital arteries ( ▶ Fig. 34.3).

34.1.3 Treatment Options

These include observation, compression therapy, endovascular therapy, open surgery, and stereotactic radiosurgery. ⁴^, ⁵^, ⁶ Almost all DAVFs without leptomeningeal drainage can be managed conservatively; however, most anterior fossa or superior sagittal sinus DAVFs exhibit leptomeningeal drainage. With low-risk DAVFs, manual compression of the principal arterial supply may lead to resolution of the fistula in approximately 30% of the cases. Compression therapy for anterior fossa DAVFs is not recommended due to concerns of ischemic stroke, hypotension, and bradycardia. With superior sagittal sinus DAVFs fed only by branches of the superficial temporal artery, compression therapy may be attempted.

Endovascular treatment of DAVFs requires placement of embolic material at the site of the fistula and preferentially extending into the draining vein. ⁵ Coils have been replaced by liquid embolics as the mainstay of endovascular treatment. This can be accomplished via a transarterial or transvenous route from the internal carotid artery, external carotid artery, or internal jugular vein. In extreme circumstances, if there is an arterialized segment of superior sagittal sinus, a burr hole can be drilled over the sinus, which is approached with an angiographic catheter for coil-occlusion of the sinus. However, it is important not to disrupt normal venous drainage, so this approach should not be used when there is anterograde flow through the sinus. When surgery is considered too great a risk and embolization is unlikely to cure the fistula alone, partial embolization may be appropriate for palliation of symptoms or as an adjunct to radiosurgery.

Radiosurgery has been used to treat DAVFs, with complete obliteration documented in up to two thirds of patients in initial studies. ⁶ Patients with small, localized fistulas are the best candidates, and this strategy has also been used for patients who are poor candidates for open microsurgical or endovascular treatment. Adjunctive embolization after radiosurgery may be used for palliation of symptoms and possibly to decrease the risk of hemorrhage.

DAVFs often have anatomic considerations that make them more amenable to an open or an endonasal approach. The floor of the anterior cranial fossa and the superior sagittal sinus, where arterial access is impaired by vessel size and distance or where sacrifice of delicate venous drainage is undesirable. If preoperative angiography demonstrates feeding vessels with significant contribution to eloquent structures, these are often better managed selectively with surgery or a combined approach. Further, pediatric patients presenting with DAVFs are more likely to require a surgical or multimodality approach. Endovascular therapy alone carries greater risk in children when compared to adults due to difficult with selective microcatherization, femoral access, and limits in contrast quantity as well as ionizing radiation tolerance.

34.2 Preoperative Preparation

Precautions for possible air embolism, including a central venous catheter, precordial Doppler, and endtidal CO₂ monitoring are used. Perioperative coverage with antiseizure medicines is recommended, as is standard antibiotic prophylaxis. Furosemide and mannitol are administered to achieve appropriate brain relaxation. A radiolucent head holder should be placed to facilitate the use of intraoperative angiography. Ability to intraoperatively manipulate the positioning of the head, in particular the height of the head with respect to the heart, is highly desirable. This can assist in both regulation of venous bleeding and enhancement of the operative corridor. With any sizeable DAVF there is a risk of torrential hemorrhage for which provisions should be made including availability of blood and good venous access.

34.3 Operative Procedure

34.3.1 Anterior Fossa Dural Arteriovenous Fistulas

The patient is positioned supine with the head elevated to maximize venous drainage and extended to minimize retraction of the frontal lobes. A lumbar drain may be placed to facilitate exposure. A unilateral subfrontal approach on the side of the DAVF is preferred to avoid bilateral olfactory nerve injury ( ▶ Fig. 34.5). If contralateral leptomeningeal draining veins are present, these may be treated via a transfalcine approach. Rarely, extensive involvement of the falx or dura along the floor of the anterior fossa will require a bifrontal approach. In rare cases, a transfrontal sinus approach may allow for better surgical precision, such as in cases where the fistula is closely adherent to midline and anterior or in situations where there is substantial concern for significant dural adhesion to the inner table. The frontal sinus adjacent to the bone may be drilled with less risk to the dura and minimally exposes brain parenchyma while allowing visualization of select DAVFs without retraction. This approach may require deepithelialization of the frontal sinus depending on the extent of exposure and potentially could increase risks of infection. A robust sinus must also be present.

Fig. 34.5 Anterior fossa dural arteriovenous fistula in the region of the cribriform plate and the anterior falx. The lesion has an enlarged anterior ethmoidal artery with a fistulous connection to the leptomeningeal veins. This connection is dilated into a varix, which is usually the site of hemorrhage. The operative goal is to obliterate this fistulous connection.

(Reproduced with permission from Patel, King, Martin. Operative management of anterior fossa, superior sagittal sinus and convexity dural arteriovenous malformations. Neurosurgical Operative Atlas. 1st ed. 1999;8:71.)

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