**7. References**

[1] Hamada Y, Goto K, Inoue T, et al. Histopathological aspects of dural arteriovenous fistulas in the transverse-sigmoid sinus region in nine patients. *Neurosurgery.*  1997; 40:452–458

follows; the occlusive change of drainage site might occur at the channel between venous lacunae and SSS after the formation of AV shunt, therefore SSS as the normal cortical drainage route is independent from DAVF and can be preserved. It may suggest that the shunt point is located not the sinus wall of SSS but venous lacunae, exit of EV. In the early stage of CS-DAVF without ocular symptoms there are various drainage routes into the pterygoid plexus as well as the superior ophthalmic vein and inferior petrosal sinus. Similarly, the anterior condylor vein is patent in the initial stage of ACC-DAVF. In such young DAVF, EV of the foramen ovale or foramen lacerum and hypoglossal EV still remain as the original drainage pathway. This fact suggests the possibility that the EV plays an

One often encounters a multiplicity about the location or TS-SS-DAVF. This fact is also explainable using the present hypothesis. At the confluence, the lateral side and the sigmoid junction, the initially affected EVs: may be torcular, petrosquamosal and mastoid EVs,

Unfortunately, our hypothesis has not yet been proven in a pathological specimen of clinical cases as well as from the animal experiments. Further, it is difficult to explain the etiology of DAVF in locations without emissary veins or those without arterial supply coming from emissary arteries with the exception of osteodural AV shunts. Although our theory was not based on the anatomical, physiopathological or clinical observational convincing background, if the very early stage of DAVF is incidentally found, inflammatory investigation into the inflammation and meticulous observation of the flow change will be

According to previous theories concerning the mechanism of DAVF, it is very important to consider the occlusive pathway and hypertension of the affected sinus. However, previous theories did not indicate an initiation of this pathological situation which can explain both sinus and non-sinus type DAVF and the promoting factors to develop the extension of DAVF. We propose a new theory: the inflammatory vascular network at the penetration site of emissary veins may induce local shunt formation. Subsequent occlusion of the affected EV completes the usual figure of DAVF, and, the sinus (venous) occlusive pathway and arterial recruitment are important steps in the maturation of the DAVF. Previous mechanistic hypotheses focusing on sinus hypertension and sinus thromboses cannot explain the pathogenesis of non-sinus type of DAVF. Although the etiology of DAVF may be concerned by the thrombo-occlusive change of sinus, and our theory is only a speculation without the base of experimental study, it may enable to understanding the common etiology of the two (sinus & non-sinus) types of DAVF, and is not contradictory to the previous sinus-oriented

Abbreviations: DAVF: dural arteriovenous fistula, EV: emissary vein, CS: cavernous sinus, SSS: superior sagittal sinus, TS: transvers sinus, SS: sigmoid sinus, ACC: anterior condylor

[1] Hamada Y, Goto K, Inoue T, et al. Histopathological aspects of dural arteriovenous

fistulas in the transverse-sigmoid sinus region in nine patients. *Neurosurgery.* 

helpful to predict the development of DAVF and also to support this theory.

theory. Pathological proof of the initial stage of DAVF will be mandatory.

confluence, CCJ: craniocervical junction

1997; 40:452–458

important role in the initial stages of newly developed DAVF.

respectively.

**6. Conclusion** 

**7. References** 


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