Giant saccular aneurysm of the basilar artery
This 60 year old female had an MRI examination for left hypacusia, which disclosed a giant saccular aneurysm of the basilar artery. Subsequent conventional, catheter based angiography confirmed the diagnosis but despite the multiple projections obtained, was unable to visualize the neck of the aneurysm with precision.
MRA was performed in order to obtain more information about the size and geometry of the orifice of the aneurysm before therapeutic decision making.
Giant aneurysm of the basilar artery, 1.5 T
Fig.1 The DSA images (lateral views) after selective injection of the left vertebral artery show a giant saccular aneurysm, arising from the proximal segment of the basilar artery.
Fig.2 Clear delineation of the presumed large-based neck is impossible, despite multiple oblique image acquisitions after selective injection of the left (above) and the right (below) vertebral arteries.
Fig.3 Sagittal non-enhanced (above) and Gadolinium-enhanced (below) 2D PC MR angiograms (Venc: 30 cm/s, Tac: 36 sec). These short imaging sequences allow rapid positive diagnosis of giant aneurysms in the event of differential diagnostic problems on conventional images and serve as survey imaging as well. Typical ghost artifacts (arrows) are seen bilaterally at equal distances from the giant aneurysm in the phase-encoding direction, which are however more prominent after Gadolinium injection (see Effects of spin motion on the MR signal: motion artifacts).
Fig.4 Transverse source images from a non-enhanced multislab 3D TOF MRA acquisition. The aneurysm has a wide neck (arrows) at its origin from the basilar artery as evidenced by analysis of the relationship between the aneurysm and the parent artery on the adjacent individual partitions.
Fig.5 Targeted MIP reconstruction from the non-enhanced multislab 3D TOF MRA acquisition data set. The inflow channel (arrows) of the aneurysm in continuity with the right vertebral artery is clearly identified due to the maximal flow-related enhancement in the entry area and progressive saturation in the other parts of the aneurysmal sac. Poor visualization of the distal basilar artery is also explained by progressive saturation of the spins within the aneurysm.
Fig.6 Transverse source images from a Gadolinium-enhanced multislab 3D TOF MRA acquisition. Same observations as in Fig.3, except that intraaneurysmal flow-related enhancement is more marked and homogeneous because of the Gadolinium injection, reducing the signal loss related to the intravolume spin saturation.
Fig.7 Targeted MIP reconstruction from the Gadolinium-enhanced multislab 3D TOF MRA acquisition data set. Same observations as in Fig.5 and Fig.6.
Fig.8 Transverse targeted MIP reconstructions from the non-enhanced (above) and Gadolinium-enhanced (below) multislab 3D TOF MRA acquisition data sets, for comparison of the effect of Gadolinium injection on intraaneurysmal signal intensity (flow-related enhancement).
Fig.9 Transverse averaged modulus (left) and corresponding magnitude of complex differences (right) type source images of the lower part of the giant basilar artery aneurysm from a Gadolinium-enhanced 3D PC MRA sequence. The mass effect from the aneurysm on the brain stem is well demonstrated on the averaged modulus ("anatomical") images. The magnitude of complex differences images show the neck area (red arrows on the uppermost image), evidenced by the direct communication between the parent artery and the aneurysm lumen, and the essentially circular peripheral (yellow arrows) intraaneurysmal flow pattern with slow central flow.
Fig.10 Transverse averaged modulus (left) and corresponding magnitude of complex differences (right) type source images of the upper part of the giant basilar artery aneurysm from a Gadolinium-enhanced 3D PC MRA sequence. Here again, the magnitude of complex differences images show the neck area (red arrows on the uppermost image) evidenced by the direct communication between the parent artery and the aneurysm lumen and the essentially circular peripheral (yellow arrows) intraaneurysmal flow pattern with slow central flow.
Video 1.
Cine demonstration of the intraaneurysmal flow with averaged modulus type images (transverse thick-slice 3D Phase Contrast MRA acquisition with retrospective cardiac gating).
Video 2
Cine demonstration of the intraaneurysmal flow with magnitude of complex differences type images (transverse thick-slice 3D Phase Contrast MRA acquisition with retrospective cardiac gating).
Fig.11 Coronal, sagittal and transverse targeted MIP reconstructions from the Gadolinium-enhanced 3D PC MRA acquisition data set. On the coronal and sagittal images the inflow pathway (arrows), in continuity with the left vertebral artery, is clearly seen, in agreement with the findings on the TOF images. The signal drop out in the basilar artery, immediately distal to the aneurysm, is presumably due to the mixed deleterious effects of turbulence (phase dispersion) and intravolume spin saturation (inflow effects also contribute to signal in the Phase Contrast technique) on intravascular signal, as well as an additional error in the MIP reconstruction algorithm (overlapped vessels may be displayed connected, because one single highest intensity pixel is selected for both structures under some projections) (see Image presentation and postprocessing).
Fig.12 Sagittal averaged modulus (left) and corresponding magnitude of complex differences (right) type source images from a Gadolinium-enhanced 3D PC acquisition. Analysis of the adjacent individual magnitude of complex differences partitions allows better identification of the inflow (red arrows) and outflow (blue arrows) pathways of the aneurysm.
Fig.13 The DSA image (lateral view) from the early arterial phase of a left vertebral artery angiogram shows a similar inflow pattern as demonstrated in Fig.11.
Video 3.
Cine demonstration of the inflow channel and the intraaneurysmal flow with magnitude of complex differences type images (sagittal thick-slice Gadolinium enhanced 3D Phase Contrast MRA acquisition with retrospective cardiac gating).
Fig.14 Sagittal directional phase difference type source images (Gadolinium-enhanced thick 3D PC acquisition with retrospective cardiac gating). The circular intraaneurysmal flow pattern is well appreciated on both images with cranio-caudal (above) and with antero-posterior (below) encoding (compare with the known physiological flow directions of the venous structures of the midline).
Video 5.
14 Cine demonstration of the intraaneurysmal flow with directional phase differences type images (sagittal thick-slice Gadolinium-enhanced 3D Phase Contrast MRA acquisition with retrospective cardiac gating, cranio-caudal encoding).
Video 4.
Cine demonstration of the intraaneurysmal flow with directional phase differences type images (sagittal thick-slice Gadolinium enhanced 3D Phase Contrast MRA acquisition with retrospective cardiac gating, antero-posterior encoding).
Fig.15 The relatively regular, fast peripheral circular and the slow, almost stagnating central intraaneurysmal flow pattern with little mixing between the two (felt to be similar to the above case) is well demonstrated in this giant internal carotid artery aneurysm from another patient (DSA images, lateral view) after selective injection of the left internal carotid artery.
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