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AJNR - American Journal of Neuroradiology

Published ahead of print on September 26, 2007
doi: 10.3174/ajnr.A0719

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Bilateral Segmental Agenesis of the Vertebrobasilar Junction: Developmental and Angiographic Anatomy

I.M. Burger^a, F. Siclari^a, L. Gregg^b and P. Gailloud^a

^a Division of Interventional Neuroradiology, The Johns Hopkins Medical Institutions, Baltimore, Md
^b School of Art as Applied to Medicine, The Johns Hopkins Medical Institutions, Baltimore, Md

View larger version (70K): [in this window] [in a new window]   Fig 1. A 69-year-old woman with pulsatile tinnitus. A, DSA, left common carotid injection, lateral view, showing a PTA opacifying the BA. Note the common origin of the left PCA and left AchoA from the distal ICA. B, DSA, left common carotid injection, right anterior oblique view, showing the basilar artery fed by the PTA (arrowhead) and the bilateral absence of connection between the basilar and posterior cerebral arteries. The BA ends into the superior cerebellar arteries distally and into prominent AICA proximally. The left AICA also supplies the left PICA territory. The right PICA territory is fed by the left VA (not shown). There is no visible connection between the VAs and the BA. C, DSA, right subclavian injection, showing opacification of the anterior spinal artery (arrowheads) via the right inferior thyroid artery.

View larger version (112K): [in this window] [in a new window]   Fig 2. A 65-year-old man with Wegener granulomatosis. A, DSA, right common carotid injection, lateral view, showing a prominent AchoA supplying the right PCA territory (arrowhead). Note a separate right PcomA feeding the BA (arrow). B, DSA, right common carotid injection, transfascial view, showing the BA fed by the right PcomA. The BA ends into the superior cerebellar arteries (SCAs) distally and into the AICA arteries proximally. Both VAs end as ipsilateral PICAs without connection to the BA (not shown).

View larger version (67K): [in this window] [in a new window]   Fig 3. A 51-year-old man with intermittent dizziness. A, DSA, left VA injection, anteroposterior view, showing disease in the distal VA and proximal BA (arrowhead), including faint opacification of the right AICA (arrow). B, DSA, left common carotid artery injection, lateral view, showing a large PcomA supplying the BA. Note that the PcomA then continues as the left PCA (arrowhead). The hemispheric branch of the right PICA territory is fed through a connection with the BA. C, DSA, left common carotid injection, transfascial view, showing a large left PcomA supplying the BA and continuing its course as the left PCA. Note the opacification of the right AICA (arrow), which confirms the existence of a connection between the left VA and the distal BA.

View larger version (22K): [in this window] [in a new window]   Fig 4. Schematic representation of the vertebrobasilar circulation. Posterior view of the VAs and BA. On the left side, the segments derived from the radicular branch of the proatlantal artery are shown in gray. Ant. Spinal a. indicates anterior spinal artery; Post. Spinal a., posterior spinal artery.

View larger version (30K): [in this window] [in a new window]   Fig 5. Developmental anatomy of the distal BA. A, The anterior circulation supplies the developing posterior circulation (ie, the parallel longitudinal neural arteries [LNA]) via the trigeminal and the posterior communicating arteries (PcomAs). The terminal branches of the carotid axis are the AchoA, which provides the territory of the PcomAs and the anterior cerebral artery (ACA) and its developing branch, the middle cerebral artery (MCA). The VA is not yet connected to the LNA. The PcomA has 2 small branches, the PchoA and the diencephalic artery (Dienceph. A). A indicates artery. B, The VA connects to the proximal end of the LNA/BA. The trigeminal artery involutes, and the PcomA becomes the last of the carotid basilar anastomoses. C, A connection is formed between the AchoA/PCA and the PchoA. D, The connection between the PcomA and the PCA is now well established. The AchoA is not supplying the PCA territory anymore. The latter can be supplied equally by the posterior circulation via the distal segment of the PcomA or by the anterior circulation via the proximal segment of the PcomA. This configuration of equal contribution can persist at the adult stage. Other adult configurations depend on the relative regression of the PcomA, as described in E and F. Note that the diencephalic branch is now called the posterior medial choroidal artery (PMchoA), whereas the original PchoA is now called the posterior lateral choroidal artery (PLchoA).11 Although both arteries are originally derived from the PcomA, they are considered as branches of the PCA at the adult stage. The so-called "P1 segment of the PCA" is in fact the distal portion of the PcomA. E, In this second adult configuration, the distal segment of the PcomA has regressed and the anterior contribution to the PCA becomes dominant. This configuration is often mislabeled as a "fetal origin of the PCA." The true "fetal origin of the PCA," where the transfer of the PCA territory from the AchoA to the PcomA has not occurred, is not illustrated here but would be similar to B. It is illustrated in Fig 2A. F, In this third adult configuration, the proximal segment of the PcomA has regressed and the posterior contribution to the PCA becomes dominant.