Scalp fistula pathoanatomy
When looking at a scalp fistula (or any other fistula) it is important to understand the pathoanatomy of the lesion. For teaching purposes it is helpful to trace these findings:
1. There is a fistula point between the right superficial temporal artery (parietal branch) and the right superficial temporal vein. The vein is filled prematurely indicating this is an AV-fistula. The lateral projection of the right ECA injection shows this best. Notice that this is an extracranial lesion appreciating the involved vessels and the frontal projections.
2. The part of the superficial temporal artery (parietal branch) distal to the fistula point however is not contrasted in the early, but in the late phase of the right ECA injection via several small anastomoses of the frontal STA branch, posterior auricular artery and occipital artery. The distal part of the superficial temporal artery shows retrograde flow and contributes to the AV-fistula point! Appreciating this is key to treatment success.
3. There is contribution to the fistula by the left (contralateral) superficial temporal artery and left occipital artery best seen in the frontal projection of the left ECA.
When treating fistulas like this it is mandatory to occlude the fistula point and its relevant arterial supply. Just occluding the superficial temporal artery branch proximal to the fistula point will not do the job, because there would be persistent retrograde flow in the superficial temporal artery branch distal to the fistula point still supplying the fistula. This symptomatic traumatic scalp fistula was treated with an endovascular approach using a coil and a mixture of histoacryl and lipiodol occluding the superficial temporal artery proximal and distal to the fistula point and additionally the draining vein.
Case imaging courtesy of Prof. R. Chapot (Alfried Krupp Krankenhaus Essen, Germany).