The intracranial venous sinuses drain the venous blood from the brain. They are composed by 2 distinct groups connected by the superior petrosal sinus:
• The anterior-lower group, centered on the cavernous sinus which is not the subject of this review
• The upper-posterior group
Most of the sinuses of the upper-posterior group are sinuses located in infoldings of the dura-mater.
The anatomic section and all the anatomic drawings are extracted from the web site of neuro-anatomy (http://www.chups.jussieu.fr/ext/neuranat/). They are published with the kind permission of the authors (H. Fournie and D. Hasboun).
Image 1: Coronal anatomic section. Note the openings out of the dura mater and the corresponding sinuses. (SSS = sagittal superior sinus, SS = straight sinus, TS = transverse sinus).
Sinuses of dura-mater in the upper-posterior group are imbedded in dura mater folds. The dura mater folds include the falx cerebri and the tentorium. There are three sinuses in the falx cerebri:
• The superior sagittal sinus (SSS): running along the superior border of the falx cerebri;
• The inferior sagittal sinus (ISS): running along the inferior border of the falx cerebri;
• The straight sinus (SS): running along the base of the falx cerebri.
The sinuses in relation with the peripheral border of the tentorium cerebelli are:
• Transverse sinuses (TS);
• Superior petrosal sinus (SPS).
A sigmoid sinus (SigS) is an independent structure related neither to the falx cerebri nor to the tentorium cerebelli and we will discuss it latter.
Images 2, 3: Image 2 - Anatomic drawing showing the falx cerebri (FC) and tentorium (TC) position. Image 3 - Anatomic drawing illustrating the relationship between venous sinuses and folds of the dura mater.
Images 4, 5: Image 4 - Schematic representation of the “spacial position” of the venous sinuses of the upper-posterior group. Image 5: Endocranial view showing the cavernous sinus (CS), the straight sinus (SS), the transverse sinuses (TS). Note that the transverse sinuses prolong as a sigmoid sinuses (SigS) after the junction with the superior petrosal sinus (SPS).
The straight sinus
The straight sinus is a median single sinus that runs along the base of the falx cerebri, where it is in contact with the superior face of tentorium cerebelli. The straight sinus runs in an oblique direction, going downward and backward. It is constituted by the junction of the sagittal inferior sinus and the vein of Galen. The straight sinus ends in the back-end part of the sagittal superior sinus. In this area, this sinus fuse in the confluence of the sinuses also called “Torcular Herophilus". During an ultrasound examination, the straight sinus is easily recognized in the three planes.
Image 6: Coronal section: the straight sinus appears at the junction between the falx cerebri and the tentorium cerebelli.
Images 7, 8: Oblique axial sections (downward and backward).
Image 9: Sagittal section. Note the sagittal inferior sinus (SIS) and the vein of Gallen (VG) that fuse to constitute the straight sinus (SS). In the posterior end, the straight sinus is joined by the sagittal superior sinus (SSS) constituting the confluence of the sinuses or Torcular (T).
Image 10: Color Doppler. The Doppler spectrum of the straight sinus is not pulsatile (upper part of the image). Doppler spectrum from the axial section (lower part of the image).
The superior sagittal sinus
The superior sagittal sinus follows the superior edge of the falx cerebri. It begins very anteriorly at the frontal level and ends posteriorly at the occipital level joining with the straight sinus to constitute the torcular. It is also a median single structure (just like the straight sinus and the inferior sagittal sinus). The sagittal superior sinus has two different functions. First, it drains the superior cerebral veins. It also participates in the resorption of the cerebral-spinal fluid thanks to the Pacchioni’s granulations. It is easily recognized during the ultrasound scan done through the inter-parietal suture.
Images 11, 12: Image 11 - Sagittal section showing the sagittal superior sinus. Note the peri-callosal artery and its branches). Image 12 - Coronal view obtained by vaginal scan. The sagittal superior sinus is clearly visible along with the falx cerebri.
Image 13: In the color Doppler, the spectrum appears to be pulsatile. The spectrum could become flat in cases of high intracranial pressure as in hydrocephaly or craniostenosis.
The inferior Sagittal sinus
The sagittal inferior sinus follows the inferior open edge of the falx cerebri. It is also a single median sinus. It drains the blood from the inferior part of the falx, the corpus callosum. It terminates by joining the straight sinus as the vein of Galen. Its ultrasound detection is not easy, probably because of its small size and richness of the vasculateure of the pericallosal area.
Image 14: Sagittal section. Note the extreme end of the sagittal inferior sinus before the junction with the straight sinus.
The transverse sinuses
The transverse sinuses are paired sinuses that arise from the torcular and run, right as left, in the inferior or peripheric edge of the tentorium cerebelli. They extend into the sigmoid sinuses. The limits between the transverse sinuses and the sigmoid sinuses is represented by the connection of the superior petrosal sinus. The superior petrosal sinus is located in the insertion of the tentorium and drains a part of the cavernous sinus blood. Because of their curvature, only short segments can be visualized at a time.
Images 15, 16: Image 15 - Axial section showing the beginning of the transverse sinus from the torcular. Image 16 - Axial section: medium part of the transverse sinus.