Basal vein in the posterior incisural space: An anatomical comparison based on autopsy,digital subtraction angiography and computed tomographic venography

Abstract

BACKGROUND:

During surgical procedures, the basal vein in the posterior incisural space is susceptible to obstruction. In such circumstances, venous infarction can occur along with venous damage.

OBJECTIVE:

The aim of this study was to correlate the microanatomy of the basal vein in the posterior incisural space with the digital subtraction angiography (DSA) and computed tomographic venography (CTV).

METHODS:

Twenty cadavers and 42 patients were examined in this study. The head of each cadaver was injected with blue-colored gelatin via the internal jugular veins. Venograms for each patient were obtained from the venous phases of DSA or CTV.

RESULTS:

Compared to the cadavers, in the patients, DSA and CTV revealed 90% and 95% of the basal vein, respectively. According to difference of entrance, three types of basal veins were identified. No statistical difference of typing was found among the cadavers, DSA images and CTV images. On three sides of the cadavers and one side of the CTV images, the basal vein entered the straight sinus through the meningeal vein in the tentorium cerebelli.

CONCLUSIONS:

Preoperative DSA and CTV are useful in the design of individualized surgical approaches and the preservation of the basal vein in the posterior incisural space.

Keywords

Basal vein posterior incisural space microanatomy digital subtraction angiography computed tomographic venography

1 Introduction

The deep cerebral venous system comprises the internal cerebral vein, the Galen’s vein, the basal vein, and their respective tributaries. The basal vein is formed by the union of veins that drain the walls of the anterior incisural space below the anterior perforated substance. It proceeds posteriorly between the midbrain and the temporal lobe to drain the walls of the middle incisural space, and it terminates within the posterior incisural space, usually into the Galen’s vein. It may also drain into the straight sinus or the internal cerebral veins. In correspondence with the parts of the vein that course within the anterior, middle, and posterior incisural regions, the basal vein is divided into anterior, middle, and posterior segments [1].

The posterior incisural space lies posterior to the midbrain, and the main part corresponds to the pineal region [2]. The posterior segment of the basal vein exits the ambient cistern to reach the posterior incisural space, and it joins the internal cerebral vein to form the Galen’s vein. Lesions in the posterior incisural space include pineal tumours, gliomas of the cerebellum, aneurysms and malformation of the Galen’s vein, inter alia [3, 4]. Given the narrowness of the posterior incisural space, the posterior segment of the basal vein is susceptible to becoming obstructed during surgical procedures. Venous infarction or venous edema of the pons, midbrain and diencephalons may occur during surgery, along with venous damage [5].

Preoperative evaluation of the basal vein is very important in the design of various approaches and it can mitigate basal vein injury [6]. In recent years, intense efforts have been made to evaluate the anatomy of the basal vein, concluding its diameter, its course and the nature of its tributaries [1 , 8].Basal vein variations have been evaluated through the use of neuroimaging techniques [6 , 9–20]. In recent years, Han et al. have indicated that the sensitivity of neuroimaging techniques in assessing the cerebral superficial vein is relative high, using data from the cadavers as reference [21 –23]. However, few studies have compared the basal vein in the posterior incisural space between cadavers and the neuroimaging. Therefore, the aim of this study was to correlate the microanatomy of the basal vein in the posterior incisural space with digital subtraction angiography (DSA) and computed tomographic venography (CTV); in so doing, this study provides a basis for preserving the basal vein in the posterior incisural space during the surgical approach.

2 Materials and methods

2.1 Study subjects

The study protocols were approved by the Ethics Committee of Anhui Medical University (Hefei, China, 2012238). A total of 20 adult cadavers (14 males, 6 females; age range, 20–69 years; mean age, 40 years) and 42 patients (27 males, 15 females; age range, 18–76 years; mean age, 49 years) were examined in this study.

The cadavers assigned to this project were those used for research and educational purposes by the Department of Anatomy of our institution, and informed written consent was obtained from the relatives of the deceased. All patients included in this study provided informed written consent, and between Jun 2014 and Jun 2015, they were examined at the Department of Radiology, the First Affiliated Hospital of Anhui Medical University.

2.2 Autopsy analysis

The cadavers were fixed with a 10% formalin solution via the right femoral artery perfusion within 36 hours after death. After the head was placed in a warm water bath (36°C) for 2 h, the internal jugular veins were perfused with 8% blue-colored gelatine. One day later, the cranium was removed, and the dura mater of the temporal and occipital lobe was separated from the skull carefully. Since the dura mater was opened 8 mm above the transverse sinus, the posterior incisural space was exposed following the removal of two cerebral hemispheres. The basal vein in the posterior incisural space was observed in the surgery microscope (4×magnification). The number, diameter, and distribution of the entrance of the basal vein were measured and recorded. The diameter was measured at the site 5 mm before the entrance. No intracranial pathology was noted in any specimen. A total of 40 sets of data were collected from 40 sides of 20 cadavers.

2.3 Digital subtraction angiography analysis

The indications for DSA were suspicion of an intracranial lesion (eight patients), evaluation of an aneurysm (four patients), and evaluation of lacunar cerebral infarction (ten patients). The DSA (Siemens, Axiom Artis Erlangen, Germany; matrix 512×512 matrix, 40-cm image intensifier) was performed by means of femoral artery catheterization. Venous phase from selected carotid or vertebral arterial injections were obtained. The number, diameter, and distribution of the entrance of the basal vein were measured and recorded as described in our autopsy analysis. A total of 40 sets of data were collected from 40 sides of 22 patients.

2.4 Computed tomographic venography analysis

The indications for CTV were suspicion of an intracranial lesion (seven patients), evaluation of an aneurysm (five patients), and evaluation of lacunar cerebral infarction (eight patients). Spiral CT images were obtained using a high-speed advantage scanner (64-slice GE-LightSpeed VCT; General Electric, Milwaukee, WI, USA). Nonionic contrast medium (Omnipaque, 100 ml of 350 mgI/ml solution; Amersham Health, Princeton, NJ, USA) was injected into a cubical vein at a rate of 3 4 ml/second. Scanning was started after a delay of 40 seconds. The main scanning parameters were 0.625-mm section thickness, 1-mm/s table speed, a 512×512 matrix, 120 kV, and 335 mA. The axial source images were transferred to an Advantage Windows 3D workstation (version 4.2, General Electric Medical Systems) for 3D reconstruction. The 3D CTV images were obtained through a volume rendering method, with a minimum density threshold of approximately 60–80 HU and a maximum density threshold of 300-400 HU. The number, diameter, and distribution of the entrance of the basal vein were measured and recorded as described in the autopsy analysis. A total of 40 sets of data were collected from 20 sides of 20 patients.

2.5 Statistical analysis

Measurements of the basal vein in the anatomic specimens obtained from the cadavers were made independently by two anatomy specialists and a neurosurgery specialist. Each image of the cerebral vein in patients was double-reviewed and interpreted independently by two neuroradiologists and a neurosurgeon. The data were used to generate the mean values based on three views. All the statistical analyses were performed with SPSS software for Windows, and are presented as the mean ± standard deviation (SD). Statistical comparisons of the diameter of the basal vein among the cadavers, DSA images and CTV images were tested by ANOVA (single factor) analysis. Statistical comparisons of the location of the basal vein were made by the chi square test. No difference was found between the right and left sides in either the cadavers or the medical images (paired t-test, P > 0.05). The P value < 0.05 was considered to indicate a significant difference.

3 Results

3.1 Number and diameter of the basal vein

For the cadavers, there were 0.98 ± 0.16 basal veins per side in the posterior incisural space and the diameter was 1.77 ± 0.47 mm (Table 1). Using that of the cadavers as a reference, we found that DSA and CTV revealed 90% (0.88 basal veins per side) and 95% (0.93 basal veins per side) of the basal veins in the posterior incisural space, respectively (Table 1). The diameter of the basal veins measured by DSA and CTV were 2.43 ± 0.27 mm, and 2.42 ± 0.60 mm respectively; these values are both 37% larger than that measured in the cadavers (Table 1).

3.2 Distribution of the entrance of the basal vein

Based on scatterplots of the entrance of the basal vein in the posterior incisural space, the distribution of the entrance of the basal vein was found to be clustered along the medial segment of the Galen’s vein, the initial segment of the Galen’s vein and the end of the internal cerebral vein (Fig. 1).

According to differences of entrance, three types of basal veins were identified (Table 2). Type I: The basal veins entered the medial segment of the Galen’s vein (Fig. 2); this type was found in 36% of cadavers, 31% of DSA images, and 34% of CTV images. Type II: The basal veins entered the initial segment of the Galen’s vein (Fig. 3); this type was found in 28% of cadavers, 26% of DSA images, and 26% of CTV images. Type III: The basal veins entered the end of the internal cerebral vein (Fig. 4); this type was found in 36% of cadavers, 43% of DSA images, and 40% of CTV images. There was no statistical difference in the numbers of different types of basal veins among the cadavers, DSA images, and CTV images (χ² = 0.360, P = 0.986).

When the basal vein entered the medial segment of the Galen’s vein, the gap between the basal veins and the ipsilateral internal cerebral veins was relatively large (Fig. 2). When the basal vein entered the end of the internal cerebral vein, on the other hand, the gap between the basal veins and the ipsilateral Galen’s vein was relatively large (Fig. 4). When the basal vein entered the initial part of the Galen’s vein, the gaps between the basal veins and each of the ipsilateral internal cerebral veins and the Galen’s vein were relatively small (Fig. 3).

3.3 Variation in the basal veins

The basal vein was not found in the posterior incisural space in one side of the cadaver, five sides of the DSA images, and four sides of CTV images. On three sides of the cadaver and one side of the CTV images, the posterior segment of the basal vein entered the meningeal vein in the tentorium cerebelli, and finally entered the straight sinus through this meningeal vein (Fig. 5). The gap between the basal veins and each of the ipsilateral internal cerebral veins and the Galen’s vein was relatively large.

4 Discussion

4.1 Design of a surgical approach in the posterior incisural space

There are many approaches to dissecting the lesions in the posterior incisural space, including the occipital transtentorial approach, the posterior interhemispheric transcallosal approach, and the infratentoral supracerbellar approach [24 –30]. During the procedures related to these approaches, the deep cerebral venous system is the main structure to influence the operative field [31, 32]. In the posterior incisural space, there were two important gaps near the basal vein which are the main operative spaces that allow various approaches: the gap between the basal veins and the ipsilateral internal cerebral veins and the gap between the basal veins and the ipsilateral Galen’s vein [2]. Therefore, the posterior segment of the basal vein is the most frequently encountered vein encountered during surgical intervention. Although some authors think that no obvious complications arise from cutting off the basal vein, the sacrifice of the deep cerebral veins may lead to venous edema and venous infarction of the deep cerebral structure [5, 33].

When the basal vein entered the medial segment of the Galen’s vein, the gap between the basal veins and the ipsilateral internal cerebral veins was found to be relatively large. An operation procedure through this gap is beneficial to resection of during the tumour operation and protection of the vein. When the basal vein entered the internal cerebral vein, the gap between the basal veins and the ipsilateral Galen’s vein was found to be relatively large, the operation procedure that takes place through this gap should change. When the basal vein entered the initial segment of the Galen’s vein, the gaps between the basal veins and each of ipsilateral internal cerebral veins and the Galen’s vein were found to be relatively small. Thus, the operation should change through other side of the operating space.

4.2 Role of neuroimaging in preoperative clinical decision-making

In the past, DSA was considered to be the most sensitive examination of cerebral vessels. With rapid developments in medical imaging technology, computed tomography angiography and magnetic resonance angiography have become the first choices in examining cerebrovascular diseases. Kilic et al. found that the sensitivity of DSA to the cerebral venous system is only about 40% [34]. However, in the current study, we used the microsurgical anatomical results as the reference standard, DSA and CTV observed 90% and 95% of the basal vein, respectively, in the posterior incisural space. The diameter in the neuroimaging was 37% larger than that of the cadavers. It may be that the diameter of the basal veins in the cadavers maybe contracted after fixation with 10% formalin.

The results of the current study show that more than 89% of the basal veins can be observed in the neuroimaging. In addition, both the DSA and CTV can reflect the distribution of the basal vein entering the sinus, which is in turn important to the design of the operation. One interesting finding was that the sensitivity of CTV was slightly higher than that of DSA. Compared to DSA, CTV is more convenient and less traumatic; as such, CTV is a better choice for examination of the basal vein.

4.3 Variation in the basal veins

During an operation in the posterior incisural space, obstruction of the Galen’s vein alone can be compensated by anastomoses via the basal vein [7]. However, the results of our study indicated that the basal vein was not found in the posterior incisural space in one side of the cadaver, five sides of the DSA images, and four sides of the CTV images. In these patients, obstruction of the Galen’s vein can cause great damage, as there is not enough compensation.

On three sides of the cadaver and one side of the CTV images, the basal vein entered the meningeal vein in the tentorium cerebelli, and finally entered the straight sinus through this meningeal vein. In these patients, both the gap between the basal veins and the ipsilateral internal cerebral veins and the gap between the basal veins and the ipsilateral Galen’s vein was relatively large. The operation is easy to implement when there is sufficient operative space. However, if the tentorium cerebelli were cut near the straight sinus, the meningeal vein would be damaged and there would be massivehemorrhaging.

5 Conclusion

In summary, this study compared the basal vein in the posterior incisural space, between that seen in microanatomy and that seen in imaging; the results indicated that the preoperative image-based examinations are helpful in the design of individualized surgical approaches in the posterior incisural space. The results provide important information with respect to precluding the basal vein damage and reducing postoperative complications.

Competing interests

The authors declare that they have no competing interests.

Footnotes

Acknowledgments

The project was funded by the National Natural Science Foundation of China (Reference No: 81200895).

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