Encephalic venous drainage is ensured by a large venous network resulting from the connection of two types of vessels, one made up of classic veins with walls formed of three layers end other, made of dural sinuses whose walls are made up of two layers.
The absence of venous valves, one of the characteristics of this venous system, implies the existence of other mechanisms in the regulation of is drainag. The search for these mechanisms other than this valve system has been the subject of several studies
[1]
-
[8]
. Those interested in the morphological description of the walls of these vessels and of their veno-sinus junctions and vice versa, the among human beeings, have provided architectural data and details on the components, necessary for the understanding, among other things, this regulation
[5]
[6]
[9]
.
On an architectural level, these junctions, which result from the contact of two walls with different constitutions, as reported at the beginning, are considered as areas of weakness according to certain authors
[10]
and incriminated in the occurrence of cerebral hematomas especial among infants
[10]
. The walls of the junction zone, it has been reported the existence of particular elements such as nerve cells and especially the presence of muscle cells in the endothelial layer which some author have attributed to a metaplastic process, due to the high age of its study subjects
[9]
.
The Confirmation of these findings by other studies using a different has justified the carrying out of study which focuses on the morphology of the walls of the sigmoido-jugular junctional zone among younger subjects.
The general objective of this study is to describe the microscopic parietal structuration of this junction in third-trimester fetuses.
2. Material and Method
This is a descriptive study, carried out over a period of 7 months (January-July 2023). It was carried out at the anatomy and organogenesis laboratory of the Faculty of Health Sciences of the Marien N’GOUABI University, at the Pathological anatomy and cytology laboratory of the Brazzaville University Hospital Center (BUHC) and at the Pathology center of Pointe Noire after approval from the Health Sciences Research Ethics Committee (CERSA).
Fifteen (15) pairs of anatomical parts of the sigmoido-jugular junction were taken from fetus, all of sexes taken into account, aged between 34 and 38 weeks of gestation, without visible phenotype malformation and recruited after informed consent of the parents.
These parts were included in paraffin, then cut with a microtome (3 µm) in order to carry out the classic stains for a morphological approach, using standard stains [Hematoxylin-eosin (HE), Hematoxylin-eosin-saffran (HES)] and special stains [Masson’s Trichrome (MT) and Orcein solution]; and also in order to have a functional approach using anti-smooth muscle actin antibodies.
The slides were read by a pathologist. The sigmoido-jugular junction was therefore divided into three portions which are cranio-caudally: the sigmoïd, the junctional and jugular portions.
2.1. Morphological Approach
The results of microscopic observations on histochemical preparations showed similar characteristics and some differences:
From the innermost to the outermost, the observed layers are:
First Layer (Endothelium) (yellow arrow,
Figure 1
): Clearer in the junctional and jugular portions, where the cells are more flattened.
Figure 1. Histological section of the sigmoid sinus wall of a fetus of 36 weeks gestational (CF: Collagen fiber; L: lumen; yellow arrow: internal tunic; black arrow: marks the transition zone). Source: Pathological anatomy and cytology laboratory BUHC.
1) Sigmoidal Portion: Composed exclusively of collagen fibers (CF) arranged longitudinally relative to the lumen (L) (
Figure 2
and
Figure 3
).
2) Junctional Portion: Fibers primarily longitudinal, with some semi-circular arrangement also present
3) Jugular portion: initially exhibits a collagen-elastic component with a predominance of elastic fibers, followed by a portion with characteristics identical to extracranial veins, including smooth muscle fibers (
Figure 4
and
Figure 5
).
Figure 2. Histological section of the sigmoid sinus wall of a fetus of 36 weeks gestational (CF: Collagen fiber; L: lumen; yellow arrow: internal tunic). Source: Pathology Center of Pointe Noire.
Figure 3. Histological section of the sigmoid sinus wall of a fetus of 36 weeks gestational. (CF: Collagen fiber). Source: Pathology Center of Pointe Noire.
Figure 4. Histological section of the wall of the internal jugular vein in a fetus of 34 weeks gestational (L: lumen; yellow arrow: internal tunic; black arrow: Adventice). Source: Pathological anatomy and cytology laboratory BUHC.
Figure 5. Histological section of the wall of the internal jugular vein in a fetus of 34 weeks gestational. Source: Pathological anatomy and cytology laboratory BUHC.
Exclusively found in the jugular portion.
2.2. Functional Approach
Immunostaining revealed significant results in the sigmoid and junctional portions:
1) Sigmoidal portion: Immunostaining for smooth muscle actin was found to be positive, showing weak and discontinuous cytoplasmic staining of a few flattened or elongated cells that are likely smooth muscle cells at the level of the inner tunic (
Figure 6
).
Figure 6. Histological section of the sigmoidal portion in a fetus of 36 weeks gestational (L: lumen; yellow arrow: indicates the marking of smooth muscle cells at the level of the internal tunic; blue arrow: indicates the marking of muscle cells at the level of the small circulation). Source: Pathology Center of Pointe Noire.
2) Junctional Portion: the staining was intense and continuous (
Figure 7
). Additionally, intense staining was noted in the wall of the sinus related to small circulation (blue arrow).
Figure 7. Histological section of the junctional portion in a fetus of 36 weeks gestational (GA). L: lumen; yellow arrow: indicates the marking of smooth muscle cells at the level of the internal tunic; blue arrow: indicates the marking of muscle cells at the level of the small circulation. Source: Pathology Center of Pointe Noire.
3. Comments
It is reported in the literature that the wall of the dural sinuses consists of two tunics: an outer tunic made of collagen fibers and an inner tunic identical to the endothelium of veins. This architecture confers special properties to the sinuses, such as inextensibility, irretractability, and indeformability. We have confirmed these findings in our study.
We observed that the tunica interna became clearer at the sigmoidl portion, while the tunica externa was composed entirely of collagen fibers arranged predominantly longitudinally. In addition to collagen fibers, Piffer
[9]
noted the presence of fine elastic fibers. Bucciante, as cited by Piffer, reported circularly arranged muscular elements in the tunica interna of the sigmoid sinus in elderly individuals, attributing their presence to a degenerative phenomenon. In our study, we also found smooth muscle cells in small proportions and discontinuously in the sigmoidal portion, while they were present intensely and continuously in the junctional portion. The age of our subjects contradicts the degenerative theory proposed by Bucciante. Our findings align with those of Dagain et al. in their studies
[5]
[6]
concerning venosinus abutments (inferior cortical veins in the transverse sinus and great brain vein-right sinus).
The jugular part has an endothelium at the internal layer, identical to that of classic veins. Its middle collagen-elastic layer at its origin is reinforced with smooth muscular fibers over time. The collagen fibers are less abundant and arranged longitudinally in relation to the vascular lumen. The outer layer which appears at this level constitutes the adventitia. Our results are consistent with those reported by Piffer.
In our study, as well as in those examining junctions of inferior cortical veins in the transverse sinus and great brain vein-right sinus
[5]
[6]
, the presence of smooth muscle cells within the endothelium of all portions of these junctional zones highlights a unique characteristic of intracranial vessels that facilitate venous return from the brain. Additionally, this presence suggests that these muscle cells may contract, potentially serving a sphincter role in regulating cerebral venous drainage. These cells could be activated either by nerve endings or by vasomotor substances released into circulation
[5]
.
The sigmoido-jugular junction does not appear to be a zone of weakness (hemorrhagic risk), despite the semicircular arrangement of dural collagen fibers at the junctional portion. Indeed, it is believed that collagen fibers present in both the wall of the sigmoid sinus and the internal jugular vein play a protective role during forced head movements. Conversely, the spiral architectural arrangement of these collagen fibers in cortical veins prior to the junction may explain instances of cortical vein ruptures observed in infants and adults.
4. Conclusions
Microscopic study has detailed the histostructure of the sigmoido-jugular junction, revealing that the tunica interna of the sigmoid sinus and jugular vein contains smooth muscle cells that are more pronounced at the junction.
These cells likely function as a sphincter, regulating venous drainage from the brain by interacting with nerve endings and releasing vasomotor substances.
However, the absence of nerve cell markers limits our findings, suggesting that future research, particularly on fetal subjects, is needed. Experimental animal models could further clarify the role of muscle and nerve cells in venous drainage regulation.
Ethical Considerations
This article was taken from the medical thesis entitled “Histological aspects of the sigmoido-jugular junction in the foetus”, defended publicly in December 2023 at the Faculty of Health Sciences, Marien Ngouabi University, Brazzaville, Congo.
At its ordinary session on 03 November 2023, and in accordance with its internal regulations, the Health Sciences Research Ethics Committee (CERSSA) issued a favourable opinion on this study under number 068-40/MESRSIT/DGRST/CERSSA/-23.
Funding
This work was funded by the Congolese Society of Neurosurgery.
Acknowledgements
We sincerely thank:
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