7.1.2

Doppler and Carotid Duplex Sonography

(Fig. 7.11)

Ultra-sonography represents a cost-effective, noninvasive method for the study of intraorbital hemo-

dynamic parameters in patients with CSFs. However, ultra-sonography is not suitable to visualize the complex venous anatomy of the cavernous sinus, or to rule out cortical or leptomeningeal venous drainage (Belden et al. 1995; Flaharty et al. 1991); therefore, its value for treatment planning is limited.

In some studies, Doppler sonography has shown value for diagnosis and follow-up in patients with CSF (Belden et al. 1995; Flaharty et al. 1991; Erickson et al. 1989; Munk et al. 1992). It allows for the assessment of direction and velocity of blood flow, as well as the differentiation of a typical venous flow pattern from an arterialized vein with characteristic bi-phasic flow (Erickson et al. 1989).

De Keizer (1986) performed Doppler flow velocity measurements in 35 patients with direct and indirect fistulas (14 traumatic, 21 spontaneous) and found a specific flow pattern in 100% of direct and in 80% of the indirect communications. He recorded his measurements as hematotachograms (HTGs) and found normalization of flow pattern in patients with direct fistulas after embolization. In a more recent article (de Keizer 2003) he points to the difficulty of separating the arterial flow in the supratrochlear artery from the abnormal arterialized flow velocities and pattern in the ophthalmic veins. When the flow velocity in the ICA was additionally found to be abnormal, a direct fistula could be identified in all cases. Color Doppler methods are helpful in differentiating arterial from venous flow. De Keizer also recommends the use of Doppler measurements for monitoring conservative treatment using manual compression.

Lin et al. (1994) suggested the application of duplex carotid sonography (DCS) for hemodynamic classification of CSFs (see Chap. 4) with special emphasis on the resistance index (RI) and the flow volume, based on 14 cases. The authors suggest the use of sonography for screening and follow-up because DCS cannot accurately identify Type B fistulas and is limited in its differentiation between Types C and D fistulas for which angiography remains indispensable. Chiou et al. (1998) were able to verify the complete obliteration of carotid cavernous fistulas in 13 patients (10 posttraumatic and three spontaneous) with color Doppler ultrasonography. The authors found a spiculated waveform with turbulent flow pattern in most of their direct (Type A) fistulas, while patients with indirect fistulas showed a low-resistive arterial pulsatile pattern. In these six patients with DCSFs, radiosurgery was performed and a cure was documented by sonography, a reasonable approach when repeated angiography can be spared. Nevertheless, for final documentation of anatomical cure, angiography was performed. Arning et al. (2006) studied 17 patients with DAVFs and were able to detect AV shunting lesions in 100% if the ECA was examined. In contrast to brain AVMs

that are detectable only in cases with large shunt volume, most DAVFs can be diagnosed because of their supply by ECA branches that lose their characteristic flow pattern as resistance vessels. Assessment of venous drainage pattern, however, is difficult if not impossible and DSA as an initial diagnostic tool remains necessary. Tsai LK et al. (2005) studied a similar series of patients with DAVFs, one group undergoing endovascular treatment and another undergoing only clinical and sonographic follow-up. The authors found a good correlation between the increase of the RI and the effectiveness of the treatment in DAVF located at major sinuses, but not at the CS. This finding was in agreement with a previous study of the same group (Tsai LK et al. 2004) in which the sensitivity of using the ECA-RI was only 54% for cavernous sinus fistulas while it was 86% for non-cavernous sinus AVFs. This discrepancy is likely explained by the relatively small AV shunting volume in most DCSFs thus having rather little impact on the flow in the ECA. Therefore, it appears advisable to combine DCS with Doppler flow imaging of the superior ophthalmic veins (Chen YW et al. 2000). In patients with solely posterior drainage, it might be impossible to depict an abnormal Doppler flow pattern in the SOV, thus leaving angiography as a last resort for a correct diagnosis.

In summary, modern cross-sectional imaging such as CT and MRI provide a correct diagnosis in many cases or can at least raise the suspicion of a CSF. The combination of transcranial and transorbital Doppler sonography and carotid duplex sonography further increases the sensitivity of non-inva- sive imaging. Sonography provides information on blood flow, while CTA and MRI help to delineate the angiomorphology of the arteriovenous communication.

The venous drainage pattern, representing the main morphological feature of a DCSF, causing mainly the clinical symptoms and being often the potential endovascular approach, can often not be imaged to a satisfactory degree. Low-flow fistulas with small or partially thrombosed SOVs may be completely missed. Therefore, not only patients with unclear symptoms, but all patients with DCSFs should eventually undergo an i.a. (intra-arterial) DSA at least once during the course of the disease, regardless of the planned therapeutic management.