Right posterior choroidal AVM

This 52 year old female presented with a right thalamic intracerebral hematoma diagnosed on CT.
Subsequent MRI and DSA examinations revealed a deep posterior choroidal arteriovenous malformation. Endovascular embolization was elected as the most appropriate treatment modality for this AVM situated in a surgically difficult location.
MRA was used to follow-up the postembolization evolution of the lesion.

Choroidal arteriovenous malformation, 0.5 T.
Examination 1
Fig.1 Sagittal (above) and coronal (below) T1-weighted spin-echo images. Demonstration of the high signal intensity (subacute) right thalamic hematoma. An abnormal inhomogeneous low intensity area is also seen adjacent to the hematoma, suggesting a vascular malformation.
Fig.2 Transverse proton density (above) and T2-weighted (below) fast spin-echo images. The serpiginous signal void structures (AVM) and the adjacent right thalamic subacute hematoma, exhibiting a high signal intensity center (methemoglobin) surrounded by a thin low signal intensity rim (hemosiderin), are well appreciated.

Examination 2
Fig.3 DSA images after selective injection of the right vertebral artery, showing the small AVM fed by the right postero-lateral choroidal artery (above) and draining towards the vein of Galen (below).
Fig.4 DSA image after superselective catheterization of the right posterior cerebral artery (above) and embolization of the nidus (below).

Examination 3 (5 months post-embolization follow-up)
Fig.5 Sagittal T1-weighted spin-echo images showing the resorption of the hematoma.
Fig.6 Transverse proton density weighted fast spin-echo images. Most of the signal voids within the nidus have disappeared but there is a suggestion of small residual pathological vessels. On these images it is however impossible to identify residual blood vessels from intravascular embolic agent and from hemosiderin deposits, all of which present as low signal intensity or signal void structures.
Fig.7 Transverse T2-weighted fast spin-echo images. Same observations as on Fig.6.
Fig.8 Transverse source images from a non-enhanced single-slab 3D TOF MRA acquisition. On these images small punctate structures exhibiting flow-related enhancement (suggesting residual pathological blood vessels) are detected. Hemosiderin deposits and the embolizing agent are characterized by low signal intensity and are therefore easily identified as such.
Fig.9 Transverse source images from a Gadolinium-enhanced single-slab 3D TOF MRA acquisition. The venous components within the residual AVM are also visualized and hence more accurate delineation of the residual nidus is obtained.
Fig.10 Transverse targeted MIP reconstructions from the single-slab non-enhanced (above) and the Gadolinium-enhanced (below) 3D TOF MRA acquisition (matrix: 512) data sets, for comparison. Interpretation of the non-enhanced 3D TOF MR angiogram, showing a cluster of small punctate vascular structures around the right posterior cerebral artery, is difficult. The Gadolinium-enhanced image, despite the somewhat confusing superimposition of the choroidal plexus, more accurately demonstrates the residual nidus and the draining vein of the AVM.
Fig.11 Transverse averaged modulus (left) and magnitude of complex differences (right) type source images from a non-enhanced 3D PC MRA acquisition (Venc: 45 cm/s). Here again, the differentiation between residual blood vessels from intravascular embolic agent and from hemosiderin deposits, all of which are signal void on the anatomical images, is obtained by the comparative analysis of the two image types. Hence, these images confirm the existence of residual pathological vessels (arrows) in the right thalamic region.
Fig.12 Transverse averaged modulus (left) and magnitude of complex differences (right) type source images from a Gadolinium-enhanced 3D PC MRA acquisition (Venc: 45 cm/s). Comparison of the two image types shows that not all of the enhancing areas on the anatomical images correspond to patent blood vessels on the flow images.
Fig.13 Transverse targeted MIP reconstructions from the non-enhanced (above) and the Gadolinium-enhanced (below) 3D PC MRA acquisition (matrix: 256) data sets, for comparison. Unlike with the 3D TOF technique, here the residual nidus and the draining vein are clearly seen on the non-enhanced image, however, a significant improvement in intravascular signal intensity is achieved after Gadolinium injection, enhancing the conspicuity of the blood vessels (normal and pathological). Confirmation of the presence of a small residual AVM.
Fig.14 Transverse targeted MIP reconstructions from the single-slab non-enhanced (above left) and the Gadolinium-enhanced (above right) 3D TOF, as well as the non-enhanced (below left) and the Gadolinium-enhanced (below right) 3D PC MRA acquisition data sets, for comparison. Except for the equivocal non-enhanced 3D TOF MR angiogram, all other techniques allow the detection of the residual vascular lesion.
N.B. After conventional angiographic confirmation, radiation therapy was elected for the treatment of the residual nidus.

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