I read with interest the case reported by Patel el al in the January 2003 issue of the AJNR (1). Lasjaunias and Berenstein (2) have noted that they have never seen convincing anatomic or angiographic evidence of a persistent otic artery and suggest that it might not exist. I share the skepticism of Lasjaunias and Berenstein, and I believe that the case reported by Patel et al is an example of a persistent trigeminal artery rather than a persistent otic artery.
Patel et al (1) note that, according to Lie (3), the persistent otic artery arises from the carotid artery within the carotid canal, emerges from the internal acoustic meatus, and joins the basilar artery at a caudal point. The case they report demonstrates none of these three features. The persistent embryonic anastamosis shown in Figure 1A arises distal to the horizontal petrous segment of the internal carotid artery, as the artery turns upward toward the cavernous sinus. The persistent otic artery should pass through the internal acoustic canal, yet Figure 2A demonstrates that the entirety of the persistent embryonic artery is medial to the internal auditory meatus, which is demarcated by the characteristic loop of the anterior inferior cerebellar artery (4). The persistent otic artery supposedly joins the basilar artery at a caudal point, yet Figure 2A demonstrates the artery joining the basilar artery near the junction of the middle and upper thirds. The origin, course, and termination of the persistent embryonic anastamosis described in the report therefore meets none of the criteria of a persistent otic artery but meets all of the criteria for a persistent trigeminal artery.
Finally, the authors state in their discussion that persistent trigeminal, hypoglossal, and proatlantal arteries have been associated with aneurysms distant from the persistent vessels (1). Such an association is dubious. The prevalence of aneurysms associated with persistent trigeminal artery is approximately 3%, which is similar to the prevalence of aneurysms in the general population (5).
Reply
Drs. Bhattacharya et al and Cloft have raised the interesting possibility that the vessel we reported as a primitive otic artery (1) could represent, instead, a low-lying trigeminal artery. The angiographic features of our case match the angiographic appearance of the artery reported previously by Reynolds et al as a primitive otic artery (2). For that reason, we designated it “otic.”
The excellent summary of the theoretical origins, courses, and terminations of primitive otic arteries by Drs. Bhattacharya et al provide an alternate method for characterizing a vessel as “otic.” By their definitions, both our example and that of Reynolds et al could be designated primitive trigeminal arteries.
These differences in interpretation and criteria highlight the difficulty of agreeing on precise definitions for conditions, when the conditions are seen too rarely to know the full range of variation that should be accepted within each defined category.
Establishment of a data base for these variations might well help us to assemble sufficient numbers of actual cases to refine the present ambiguous classifications.
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