Demonstration of Cerebral Venous Variations in the Region of the Third Ventricle on Phase-Sensitive Imaging

Patient Population

Included in this retrospective study were 734 sides in 367 consecutive patients who underwent MR imaging examinations including PSI at our institution between November 2007 and October 2008. PSI images of the brain were obtained for screening of headache or evaluation of hemorrhage, infarction, brain tumor, or degenerative diseases. We excluded 46 sides in 23 patients because the third ventricular area was not included on PSI. Sixteen sides in 8 patients were excluded because of motion artifacts or susceptibility artifacts because of the nasal sinuses or dental prostheses. In addition, 30 sides in 15 patients were excluded because their images could not be evaluated due to susceptibility artifacts caused by an intraventricular or basal ganglion hemorrhage around the third ventricle. A total of 642 sides in 321 consecutive patients (age range, 0–90 years; mean age, 58 years) who underwent PSI on a 3T MR imaging system were enrolled in the study. However, there were no cases of a third ventricular lesion in the present study. The Institutional Review Board approved our study, which did not require informed consent.

MR Imaging Technique

We obtained all brain MR imaging with a 3T MR system (Signa Excite HD; GE Healthcare, Milwaukee, Wisconsin) using an 8-channel high-resolution brain phased array coil (Invivo Corp., Gainesville, Florida).

We acquired PSI with a 3D echo-spoiled gradient-echo sequence with flow compensation using the following imaging parameters: TR, 45 ms; TE, 30 ms; FA, 20°; FOV, 21 cm; matrix, 512 × 192; section thickness, 1.5 mm; acquisition time, 7 min 40 to 50 s. All images were obtained in the axial plane. We postprocessed the phase-sensitive images using a high-pass filter and then converted the images into negative phase masks that were multiplied 4 times into the corresponding magnitude images using research software (PSIRecon; GE Yokogawa Medical Systems, Tokyo, Japan). We used a minimal-intensity projection (PSI) to display the processed data and contiguous 10.5-mm-thick sections with 7-mm overlap in the transverse plane (Advantage workstation version 4.1; GE Healthcare).

Evaluation of the Venous Anatomy in the Region of the Third Ventricle

Two experienced neuroradiologists consensually assessed each side with regard to venous variation on PSI. The reviewers identified the anterior septal vein (ASV) and thalamostriate vein (TSV) as running the following courses. The ASV initially runs posteromedially on the anterior wall of the frontal horn and behind the genu of the corpus callosum. When it reaches the anteromedial corner of the frontal horn, it runs backwards along the septum pellucidum and continues backward along its lower border. It then follows the lateral border of the anterior column of the fornix, generally joining the internal cerebral vein (ICV) at the posterosuperior margin of the foramen of Monro.¹³

The TSV begins in the region of the anterior wall of the atrium or in the inferolateral wall of the body of the lateral ventricle, in the linea terminalis. It passes anteriorly and medially, beneath the stria terminalis, receiving several transverse caudate veins into which the longitudinal caudate veins drain, on its way toward the foramen of Monro. At the level of the foramen of Monro, the TSV runs around the anterior tubercle of the thalamus and receives the vein from the head of the caudate nucleus. It then passes medially, generally joining the ICV at the posterosuperior margin of the foramen of Monro.¹³

The characteristic U-shaped junction of the TSV and ICV adjacent to the posterior margin of the foramen of Monro is referred to as the venous angle (Fig 1). When the junction of the TSV and ICV lies beyond the posterior margin of the foramen of Monro, this variation is referred to as the false venous angle (Fig 1). We classified these into 4 types on the basis of their relationship with the ASV-ICV junction and the presence of a venous angle or a false venous angle, according to the method used in a previous study (Fig 2 ).¹¹

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Fig 1.

Diagram demonstrating the venous angle and false venous angle (lv, lateral ventricles; asv, anterior septal vein; tsv, thalamostriate vein; icv, internal cerebral vein; fm, foramen of Monro; cc, corpus callosum; ln, lentiform nucleus; ch, head of caudate nuclei; th, thalamus).

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Fig 2.

Variations in location of the ASV-ICV junction relative to the foramen of Monro (fm). (Reprinted by permission of Ture U, Yasargil, MG, Al-Mefty O. The transcallosal-transforaminal approach to the third ventricle with regard to the venous variations in this region. J Neurosurg 1997;87:706–15¹¹).

The 4 types were classified as follows:

• Type IA: ASV-ICV junction was located at the venous angle, which lies adjacent to the posterior margin of the foramen of Monro. In the other types, the ASV-ICV junction was located beyond the posterior margin of the foramen of Monro, in 3 different locations.

• Type IB: the ASV joined the mainstem of the ICV posteriorly beyond both the foramen of Monro and the venous angle.

• Type IIA: the ASV joined the false venous angle, which lies beyond the foramen of Monro.

• Type IIB: the ASV joined the mainstem of the ICV far beyond both the foramen of Monro and the false venous angle. We classified any other venous variations as type III.