**4. Atypical DAVF**

1. Tentorial DAVF It is true that there is no EV on the tent. The name of this type of DAVF may come from the participation of tentorial artery, however the main shunt point is not on the tent but at the clival dura (Fig. 5). The tentorial artery as the feeder usually creates the AV shunt just posterior to its origin, and the shunt flow immediately drains into the subtentorial venous complex. Although there are some classifications of various type of tentorial DAVF25, the most common type of tentorial DAVF at the clivus may be caused by the pathological process of a concerned EV, petrosal bridging vein 26, that connects between the ventral venous system in the posterior fossa and the basilar plexus. The exceptional tentorial DAVFs affecting the posterior tentorial sinus or the confluence are considered to be variants of TS-DAVF with the influence of EV at the petrous and occipital skull.

Fig. 5. Tentorial DAVF. The lateral view of the left carotid angiogram showing the dilated feeder from the tentorial artery (arrow) and AV shunt at the clival portion (asterisk) immediately draining into the prepontine venous network.

2. DAVF at the anterior condylor confluence DAVF at the anterior condylor confluence has been newly defined as the generic clinical entity24, and includes DAVF of the inferior petrosal sinus, DAVF of the marginal sinus, hypoglossal DAVF, DAVF of the anterior condylor vein within the hypoglossal canal, and jugular foramen DAVF27. Anterior condylor confluence (ACC) is extracranially located, and is a major venous crossroad at the posterior base of the skull. Tributaries from the hypoglossal canal, petroclival fissure, and the vertebral venous plexus meet together at the ACC and drain into the jugular bulb

EV at the anterior skull base (Fig. 4A) connecting with the cortical vein will create, secondary to the ethmoidal inflammation, a micro AV shunt at the skull base dura (Fig. 4B). Subsequently the EV will occlude according to the same process as described above (Fig. 4C, D). As a result, all the shunt flow supplied from ethmoidal arteries drains into the cortical veins, which is the common style encountered in the clinical setting. The pathological process at the spine or

1. Tentorial DAVF It is true that there is no EV on the tent. The name of this type of DAVF may come from the participation of tentorial artery, however the main shunt point is not on the tent but at the clival dura (Fig. 5). The tentorial artery as the feeder usually creates the AV shunt just posterior to its origin, and the shunt flow immediately drains into the subtentorial venous complex. Although there are some classifications of various type of tentorial DAVF25, the most common type of tentorial DAVF at the clivus may be caused by the pathological process of a concerned EV, petrosal bridging vein 26, that connects between the ventral venous system in the posterior fossa and the basilar plexus. The exceptional tentorial DAVFs affecting the posterior tentorial sinus or the confluence are considered to be variants of TS-DAVF with the influence of EV at the

Fig. 5. Tentorial DAVF. The lateral view of the left carotid angiogram showing the dilated feeder from the tentorial artery (arrow) and AV shunt at the clival portion (asterisk)

2. DAVF at the anterior condylor confluence DAVF at the anterior condylor confluence has been newly defined as the generic clinical entity24, and includes DAVF of the inferior petrosal sinus, DAVF of the marginal sinus, hypoglossal DAVF, DAVF of the anterior condylor vein within the hypoglossal canal, and jugular foramen DAVF27. Anterior condylor confluence (ACC) is extracranially located, and is a major venous crossroad at the posterior base of the skull. Tributaries from the hypoglossal canal, petroclival fissure, and the vertebral venous plexus meet together at the ACC and drain into the jugular bulb

immediately draining into the prepontine venous network.

craniocervical junction DAVF can be explained by the same mechanism.

**4. Atypical DAVF** 

petrous and occipital skull.

through multiple channels28. As seen in previous nomenclature, one of the important drainage routes is the anterior condylor vein is the EV passing though the hypoglossal canal. However, in most cases, the anterior condylor vein has been already occluded, and other venous systems (including the lateral condylor vein, inferior petroclival vein, and inferior petrosal sinus) may function as a drainage route via ACC. Specific characteristics of this type of DAVF include patients suffering from strong tinnitus just when the DAVF is initially formed. Hypoglossal palsy develops in some cases. DAVF at the ACC tends to be diagnosed in the early stages. Therefore, as the original drainage route, the anterior condylor vein occasionally remains one of the draining veins.


Fig. 6. Mulitple DAVF Multiple DAVF at superior sagittal, tranevers and sigmoid sinus (arrows)
