Partially thrombosed fusiform aneurysm of the basilar artery

This 65 year old patient had a 10 year history of episodes consistent with vertebrobasilar insufficiency. An "aneurysm of the basilar artery", without further precision or classification, was diagnosed at that time by conventional, catheter based cerebral angiography performed at another hospital.
He was readmitted for worsening of his neurological status. He had progressive and severe headache, associated with internuclear ophthalmoplegia and nystagmus. He also had accentuation of tendon reflexes without motor deficit on the left side.
Brain stem evoked potentials disclosed significant electro-physiological alterations in the anterior portions of the lower brainstem, more markedly on the left side. An MR examination was indicated at this point.

(Fusiform aneurysm of the basilar artery, 0.5T)
Partially thrombosed fusiform aneurysm of the basilar artery.
Fig.1 Sagittal T1-weighted spin-echo images. A large extraaxial lesion is seen in between the clivus and the brain stem, exerting a significant mass effect on the latter. This appearance suggests a partially thrombosed giant aneurysm of the basilar artery with a narrow residual patent channel (arrow).
Fig.2 Transverse proton-density weighted fast spin-echo images. The markedly heterogenous (laminated appearance with low and high signal intensity layers) character of the lesion is consistent with staged intraaneurysmal thrombosis. The patent flowing channel within the aneurysm is impossible to identify, whereas more distally, the terminal segment of the basilar artery is clearly visible as a signal void (arrow).
Fig.3 Transverse T2-weighted fast spin-echo images. Abnormal, increased signal intensity areas in the brain stem parenchyma are seen at the level of the 4th ventricle (probably due to the compression by the aneurysm) and higher in the mesencephalon (possibly due to ischemia). Otherwise, same observations as on Fig. 2.
Fig.4 Transverse source images from a single slab (at that time the MOTSA technique was not available yet) 3D TOF MRA acquisition. Compare the strong intravascular signal from the internal carotid arteries and the absence of flow related enhancement in the basilar artery and the aneurysm.
Fig.5 Coronal (above) and sagittal (below) targeted MIP reconstructions from the single slab 3D TOF MRA acquisition data set. The internal carotid arteries and their primary intracranial branches are well visualized, although some progressive decrease in intravascular signal intensity due to intravolume spin saturation is detectable along the vessel course. The extracranial vertebral arteries are clearly identified but intracranially the vertebro-basilar system is very faintly seen only (arrows). If the PC technique is not available, intravenous Gadolinium injection or the application of the MOTSA technique are the two possible remedies allowing differentiation between signal loss due to slow-flow related progressive intravolume saturation of spins and a possible complete thrombosis of the basilar artery at the level of the aneurysm in this case.
Fig.6 Coronal targeted MIP reconstruction from a 3D PC MRA acquisition data set (Venc 20 cm/s). Demonstration of the patency of the intracranial vertebro-basilary system with this technique, which is less prone to intravolume saturation problems in slow flow conditions.
Fig. 7 The DSA images after selective injection of the left vertebral artery are in good agreement with the PC MRA findings.
Fig.8 Coronal averaged modulus (left) and magnitude of complex differences (right) type source images from the 3D PC MRA acquisition. The "anatomical" averaged modulus images allow excellent appreciation of both the residual patent channel and the intraaneurysmal thrombosis, hence surpassing the limited morphological information (visualization of the patent channel only) provided by the DSA examination.

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