IMAGING FINDINGS
Cross-sectional imaging such as MRI and CT can be useful as initial diagnostic procedures, especially when employing intravenous contrast and angiographic techniques. Indirect signs that may clue the underlying pathology are [11,12]:
- Cavernous sinus asymmetry,
- Early enhancement of the sinus (Fig. 7),
- Dilated or thrombosed ophthalmic veins,
- Extraocular muscle thickening,
- Proptosis (Fig. 8),
- Periocular soft tissues oedema,
- Skull fractures (Fig. 9),
- Flow void indicating high flow within the sinus (T2-weighted and SWI sequences of MRI) (Fig. 10),
- Intracranial haemorrhage (complication).
However, there are limitations to MRI and CT in the study of dCCF, as they may not show the very defect in the wall of the ICA or delay diagnosis if the fistula is draining posteriorly and thus not producing any orbital manifestations [10,13].
Ultrasound may play a secondary role by showing tortuosity, arterialized blood flow or reversal of blood flow, or thrombosis in the superior ophthalmic vein [11–13].
Four-vessel digital subtraction cerebral arteriography (DSA) is mandatory if the clinical suspicion is high and remains the gold standard. DSA is useful because it can delineate the defect in the wall of the artery (Fig. 11), discern whether the fistula is high or low flow, evaluate the haemodynamic changes, detect abnormal venous reflux and the presence of steal (Fig. 12, Fig. 13, Fig. 14). Collateral circulation must be evaluated by executing contralateral carotid and vertebral injections [1,4].
Two manoeuvres can help to further analyse the anatomy of high-flow fistulas by reducing the unopacified blood flow and slowing down the influx (1,4,14):
- The Mehringer-Hieshima manoeuvre: compression of the ipsilateral carotid common artery during ipsilateral ICA low rate contrast injection.
- The Huber manoeuvre: compression of the ipsilateral carotid common artery during dominant vertebral artery contrast injection. The fistula opacifies if there is a patent posterior communicating artery.
Finally, the DSA can serve as a guide for endovascular treatment.
ENDOVASCULAR TREATMENT OPTIONS
The endovascular treatment is the therapeutic modality of choice for most cases. The aim of the interventional radiologist is to treat the abnormal anatomy by resolving the defect in the ICA which is responsible for the dCCF. This is preferably done with one of the following techniques that allow for the preservation of the ICA:
- Transarterial ipsilateral cavernous sinus embolization with a detachable balloon.
- Transarterial or transvenous ipsilateral cavernous sinus embolization with coils or other materials (Fig. 15, Fig. 16).
- Covered stent repair of the ICA.
The carotid sacrifice may be resorted to if the above options are ineffective, but the patency of the circle of Willis and viable collaterals should be assessed first via the balloon test occlusion [1,15].