MR cerebral venography
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MR cerebral venography (MRV) is an MRI examination of the head with either contrast-enhanced or non-contrast sequences to assess patency of the dural venous sinuses and cerebral veins.
NB: This article is intended to outline some general principles of protocol design. The specifics will vary depending on MRI hardware and software, radiologists' and referrers' preferences, institutional protocols, patient factors and time constraints.
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Suspected cerebral venous thrombosis is the primary indication. Preoperative assessment of anatomy, particularly for posterior fossa surgery where the sigmoid sinuses may be compressed (e.g. retrosigmoid craniotomies) may also warrant an MRV. CT venography is a reliable and very rapid alternative exam, however it utilizes ionizing radiation and iodinated contrast media.
The purpose of this exam is to visualize the cerebral veins and venous sinuses allowing their anatomy and patency to be assessed either using non-contrast or contrast-enhanced depiction of venous blood flow.
Multiple MRI techniques can be used to visualize the cerebral veins 1.
Non-contrast-enhanced flow related MRI
Time-of-flight (TOF) MRV
The main advantages are sensitivity to slow flow, and no need for contrast media, as well as relatively rapid acquisition time. However it is prone to artifacts due to e.g. in-plane flow mimicking thrombus, while tissues with short T1 relaxation can obscure smaller thrombi.
The technique offers excellent contrast compared to background signal, and can determine the direction of flow. However it is vulnerable to motion-derived artifacts and turbulent flow within vessels. It is also significantly longer to acquire than e.g. TOF.
Native contrast thrombus MRI
These methods depict the thrombus due to the presence of paramagnetic blood products: deoxyhemoglobin, methemoglobin, or hemosiderin. In the first 5 days after clotting the thrombus is typically isointense on T1 and hypointense on T2-weighted images due to its high deoxyhemoglobin content. After 15 days the thrombus can become iso to hyperintense on T2 and isointense on T1-weighted sequences. On gradient-recalled echo (GRE) and susceptibility weighted (SW) sequences the thrombus causes signal loss, which can accentuate clots not well depicted by other sequences.
The main benefits are relatively short acquisition time and absent artifacts caused by e.g in-plane flow or background signal. Time-resolved (4D) techniques allow a dynamic evaulation of both flow and vessel patency. Contrast-enhanced dynamic MRV is more sensitive and specific in the diagnosis of intracranial venous sinus thrombosis than non-contrast techniques such as time of flight 2,3. However, it necessitates the use of gadolinium-based contrast media, and enhancing clots can be challenging to detect with this technique.
MRV takes generally longer to obtain than a CTV, and accessibility is generally also more limited. However, the accompanying standard sequences are more sensitive to cerebral morphological changes, such as edema, and focal lesions than CT 1. Furthermore, the lack of ionizing radiation and need for iodinated contrast media are important factors to consider e.g. in pediatric patients and in those with a history of iodinated contrast media adverse reactions.
- 1. van Dam L, van Walderveen M, Kroft L et al. Current Imaging Modalities for Diagnosing Cerebral Vein Thrombosis – A Critical Review. Thromb Res. 2020;189:132-9. doi:10.1016/j.thromres.2020.03.011 - Pubmed
- 2. S. Meckel, C. Reisinger, J. Bremerich, D. Damm, M. Wolbers, S. Engelter, K. Scheffler, S.G. Wetzel. Cerebral Venous Thrombosis: Diagnostic Accuracy of Combined, Dynamic and Static, Contrast-Enhanced 4D MR Venography. (2010) American Journal of Neuroradiology. 31 (3): 527. doi:10.3174/ajnr.A1869 - Pubmed
- 3. Paoletti M, Germani G, De Icco R, Asteggiano C, Zamboni P, Bastianello S. Intra- and Extracranial MR Venography: Technical Notes, Clinical Application, and Imaging Development. (2016) Behavioural neurology. 2016: 2694504. doi:10.1155/2016/2694504 - Pubmed