Bilateral large saccular aneurysms of the internal carotid artery siphons

This 75 year old female presented with transient aphasia lasting for a few minutes. She had also experienced several episodes of "drop attacks" during the previous months.
Doppler ultrasound of the carotid bifurcations was normal. A CT scan was performed and the diagnosis of a right middle cerebral artery aneurysm without signs of recent subarachnoid hemorrhage was made. For further evaluation and to avoid invasive investigation, complementary MRA was specified.

Bilateral large carotid siphon aneurysms, 0.5T
Fig.1 Transverse T1-weighted spin-echo (above), proton density (middle) and T2-weighted fast spin-echo images. Abnormal inhomogeneous rounded structures (arrows) are seen in conjunction with the internal carotid artery siphons on both sides, suggesting a large saccular aneurysms.
Fig.2 Transverse source images from a non-enhanced single slab 3D TOF MRA acquisition. Confirmation of the presence of both aneurysms.
Fig.3 Transverse source images from a Gadolinium-enhanced single slab 3D TOF MRA acquisition. The flow related enhancement within the aneurysms is significantly improved by the intravenous contrast injection. No evidence for partial intraaneurysmal thrombosis.
Fig.4 Coronal (above) and sagittal (middle) targeted MIP reconstructions from the non-enhanced single slab 3D TOF MRA acquisition data set. Both aneurysms are clearly supracavernous and arise from the internal carotid artery at the level of the posterior communicating arteries. Sagittal targeted MIP reconstructions from the Gadolinium-enhanced single slab 3D TOF MRA acquisition data set for comparison. In this case intravenous Gadolinium injection has a controversial effect. On one hand, some improvement in intravascular signal intensity is achieved and hence the ambiguity about the patency of the right, larger aneurysm is resolved, but at the same time, because of the simultaneous enhancement of the cavernous sinuses, delineation of the internal carotid artery siphons and the aneurysms is less accurate.
Fig.5 Transverse (a and b) and coronal (c and d) targeted MIP reconstructions from the non-enhanced (a and c) and Gadolinium-enhanced (b and d) single slab 3D TOF MRA acquisition data sets. Same observations as on Fig.4.
Fig.6 Coronal averaged modulus (left) and directional phase difference (right) type source images of the left internal carotid artery aneurysm from a Gadolinium-enhanced 3D PC MRA acquisition. The cranio-caudal flow direction encoding clearly demonstrates the regular circular peripheral flow pattern within the aneurysm.
Fig.7 Coronal (a and b) and transverse (c and d) targeted MIP reconstructions from the non-enhanced single volume 3D TOF (b and d) and the Gadolinium enhanced 3D PC (a and c) MRA acquisition data sets for comparison. The TOF technique provides images with better vessel definition in all projections because of the thinner partitions of the sequence, however it is more prone to intravolume saturation problems, resulting in low signal from the larger aneurysm, raising the possibility of partial thrombosis.

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