Traditionally, Salzman’s classification [8] was used for PTAs (Type 1, bilateral absence of the PCoAs; Type 2, bilateral absence of the P1 segment of the PCA [called fetal-origin PCA]; and Type 3, ipsilateral fetal origin of the PCA). Thus, our patient was regarded as having a Type 3 PTA. However, the ipsilateral P1 segment was also present in our patient because the contralateral PCA was also supplied by the fetal origin of the PCA. Weon et al. [13] proposed a modified classification, wherein the PTA is classified into five types; however, our patient could not be precisely classified by this classification. These classifications may be useful for the hemodynamic evaluation of the vertebrobasilar system. However, we believe that these classifications have no meaning with regard to the embryological development of the PTA [5].
Salas et al. [7] classified the PTA into two types according to its relationship to the abducens nerve, lateral and medial types. These two types of PTAs are suggested to have different embryonic development. The lateral type is the usual type, and approximately 90% of PTAs are classified as this type [2, 5, 11]. Medial-type PTAs are rare; however, Deniz et al. [1] recently reported that 3 of 7 PTAs were medial-type. The medial type runs in the pituitary fossa; thus, it is also called intrasellar PTA and is dangerous during transsphenoidal pituitary surgery. A medial-type PTA arises from a slightly more distal portion of the ICA than a lateral-type PTA [10].
In cases of large PTA, similar to our patient, the proximal BA is hypoplastic or aplastic [9]. Huang et al. [2] recently proposed a grading system that classifies the caliber ratio of the proximal BA/PTA into 6 grades. In the present case, the proximal BA/PTA was classified as grade 0 (BA aplasia). In our patient, the ipsilateral PCoA was hyperplastic and supplied bilateral PCAs; thus, the terminal segment of the BA was also aplastic. This unique configuration of the PCoA-PCA system has not been reported in the relevant English-language literature.
Aberrant RSA is the most common aortic arch branching variation that arises from the most distal segment of the aortic arch, and it is usually asymptomatic. Rare symptoms related to aberrant RSAs are dysphagia (arteria lusoria), dyspnea, and retrosternal pain [6]. According to a cadaveric study [4], 5 of 6 aberrant RSAs took a retroesophageal course, and the remaining one took an interesophageotracheal course. Aberrant RSAs are frequently associated with other cardiovascular malformations/variations [3]. In approximately 1/3 patients with an aberrant RSA, bilateral CCAs arise simultaneously from the aortic arch, forming a bicarotid trunk [12]. In patients with an aberrant RSA, because of the branching order, right transradial cerebral angiography cannot be performed. In our patient, an unruptured paraclinoid left ICA aneurysm was successfully treated by coil embolization via a transfemoral approach. Before catheterization of the cerebral arteries, the aortic arch and its branches must be evaluated by MR angiography or CT angiography to prevent catheterization failure via the right transradial approach.