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ANATOMY FOR DIAGNOSTIC IMAGING
pulsation of the middle cerebral vessels can be seen in the insula. The anterior cerebral artery can be seen in the interhemispheric fissure on coronal scanning and, on parasagittal scanning, the pericallosal and callosomarginal arteries may be identifiable. Radionuclide cerebral angiography During the arterial phase in the AP position a five-pointed star pattern is formed by the two carotid arteries, the two middle cerebral arteries and the two anterior cerebral arteries, which are superimposed upon each other. VENOUS DRAINAGE OF THE BRAIN The veins draining the central nervous system do not follow the same courses as the arteries that supply it. Generally, venous blood drains to the nearest venous sinus, except in the case of that draining from the deepest structures, which drain to deep veins. These, in turn, drain to the venous sinuses. The intracerebral veins do not have valves. Venous sinuses (Fig. 2. 26) These are large low-pressure veins within the folds of dura - between fibrous dura and endosteum, except for the inferior sagittal and the straight sinuses which are between two layers of fibrous dura. They receive blood from the brain and the skull (diploic veins) and communicate with veins of the scalp and face (emissary veins). The superior sagittal sinus starts anteriorly and runs posteriorly in the midline to the internal occipital protuberance. Veins enter the sinus obliquely against the flow of blood. Three or four venous lakes project laterally from the sinus between the dura and the endosteum. Into these the arachnoid (pacchionian) granulations and villi project to return CSF to the blood. Posteriorly the sinus turns to one side - usually the right - to become the transverse sinus.
The inferior sagittal sinus runs in the lower free edge of the falx cerebri. Posteriorly it joins with the great cerebral vein to become the straight sinus. The straight sinus runs in the tentorium, where the falx is attached to it to the internal occipital protuberance - the confluence of the sinuses (torcula herophili). Here it turns to one side - usually the left - to become the transverse sinus. The transverse and sigmoid sinuses - the transverse sinuses run right and left from the confluence of the sinuses to the mastoid bone, where they turn inferiorly and become the sigmoid sinus (the transverse and sigmoid sinuses are sometimes referred to together as the lateral sinus), which continues at the jugular foramen as the internal jugular vein. A focal dilatation of the vein within the foramen is called the jugular bulb. The cavernous sinus (see Fig. 2. 11) - this sinus is on either side of the pituitary gland and the body of the sphenoid bone connected across the midline by intercavernous sinuses. It lies between layers of dura mater. The internal carotid artery passes through this sinus with the sixth cranial nerve lateral and inferior to it. The third and fourth cranial nerves and the ophthalmic and maxillary divisions of the fifth pass along the lateral wall of the cavernous sinus. After emerging from the sinus the carotid artery folds back on itself so that it comes to lie on the roof of the sinus. Above the sinus lies the optic tract. The cavernous sinus receives the ophthalmic vein, the sphenoid sinus and the superficial middle cerebral vein, and drains via the petrosal sinuses to the sigmoid sinus and the beginning of the internal jugular vein. The superior petrosal sinus runs from the cavernous to the sigmoid sinus in the attached margin of the tentorium on the superior border of the petrous part of the temporal bone. The inferior petrosal sinus runs from the cavernous sinus to the internal jugular vein at the base of the petrous temporal bone. The sphenoparietal sinus runs along the free edge of the lesser wing of the sphenoid bone to the cavernous sinus. It may drain the anterior temporal diploic vein, a large vein in the wall of the middle cranial fossa, or the latter may drain separately to the cavernous sinus. Superficial cerebral veins (see Fig. 2. 26) These veins are very variable. They drain to the nearest dural sinus - thus the superolateral surface of the hemisphere drains to the superior sagittal sinus and the posteroinferior aspect drains to the transverse sinus. These named veins are variably seen: • The superior anastomostic vein (of Trolard), which runs from the posterior end of the lateral sulcus posterosuperiorly to the superior sagittal sinus in the parietal region;
