Visualization of Anatomic Variation of the Anterior Septal Vein on Susceptibility-Weighted Imaging

Abstract

Background and purpose: Understanding the anatomy of the anterior septal vein (ASV) is critical for minimally invasive procedures to the third ventricle and for assessing lesion size and venous drainage in the anterior cranial fossa. Accordingly, this study evaluated topographic anatomy and anatomic variation of the ASV using susceptibility-weighted imaging (SWI).

Methods: Sixty volunteers were examined using a 3.0T MR system. The diameter of the ASV and distance between bilateral septal points were measured. ASVs were divided into types 1 (only drains frontal lobe) and 2 (drains both frontal lobe and head of the caudate nucleus). We evaluated the ASV-internal cerebral vein (ICV) junction based on its positional relationship with the appearance of a venous angle or a false venous angle and the foramen of Monro. Fused SW and T1-weighted images were used to observe positional relationships between the course of the ASV and the surrounding brain structures.

Results: The ASV and its small tributaries were clearly visualized in 120 hemispheres (100%). The average diameter of ASVs was 1.05±0.17 mm (range 0.9-1.6 mm). The average distance between bilateral septal points was 2.23±1.03 mm (range 1.3-6.6 mm). The ASV types 1 and 2 were in 77 (64.2%) and 43 (35.8%) hemispheres, respectively. In 83 (69.2%) hemispheres, the ASV-ICV junction was situated at the venous angle and the posterior margin of the foramen of Monro. In 37 (30.8%) hemispheres, the ASV-ICV junction was situated beyond the posterior margin of the foramen of Monro. The average distance between the posteriorly located ASV-ICV junction and the posterior margin of the foramen of Monro was 6.41±3.95 mm (range 2.4-15.9 mm).

Conclusion: Using SWI, the topographic anatomy and anatomic variation of the ASV were clearly demonstrated. Preoperative assessment of anatomic variation of the ASV may be advantageous for minimally invasive neurosurgical procedures.

Fig 1

A, Transverse SW image showing the anterior septal vein and septal points. The distance between bilateral septal points (white arrowhead) is 6.6 mm. B, Transverse T1-weighted image from the same volunteer showing a wider cavum septi pellucidi. (1, anterior septal vein; white arrow, cavum septi pellucidi).

Fig 2. Different types of anterior septal veins.

SW images (A1-F1) and the corresponding T1-weighted images (A2-F2) are fused to show the anterior septal veins and their drainage (A3-F3): A1-C1 and A3-C3 represent type 1, and D1-F1 and D3-F3 represent type 2. (arrow, anterior septal vein; arrowhead, caudate nucleus).

Fig 3. Schematic diagrams showing variations of the ASV-ICV junction.

A, Type IA; B, Type IB; C, Type IIA; D, type IIB. (ASV, anterior septal veins; TSV, thalamostriate vein; FM, foramen of Monro; ICV, internal cerebral vein).

Fig 4. The fused image formed from T1-weighted and SW images.

The positional relationships between the anterior septal vein and the surrounding brain structures are clearly observed. (1, anterior septal vein; 2, anterior horn of lateral ventricle; 3, deep medullary veins; 4, superior frontal gyrus; 5, middle frontal gyrus).

Fig 5. Different types of ASV-ICV junction on SWI.

A, Type IA; B, Type IB (left) and type IIB (right); C, Type IIA; D, Type IIB (left) and type IIA (right). (1, anterior septal vein (ASV); 2, foramen of Monro; 3, thalamostriate vein; 4, internal cerebral vein (ICV)).