# Straight Sinus > Straight sinus for MBBS Anatomy: formation by vein of Galen and inferior sagittal sinus, tentorial course, drainage and Galen malformation notes. - Canonical URL: https://prepelephant.com/topics/mbbs/anatomy/straight-sinus - Exam / course: MBBS · Subject: Anatomy - Publisher: PrepElephant (https://prepelephant.com) — Prepared and reviewed by the PrepElephant Academic Review Team - First published: 2026-10-02 - Last updated: 2026-10-02 - How to cite: "Straight Sinus", PrepElephant, https://prepelephant.com/topics/mbbs/anatomy/straight-sinus ## Direct answer Deep cerebral venous blood leaves the brain through a single short channel in the midline: the straight sinus, formed at the junction of the inferior sagittal sinus and the great cerebral vein of Galen under the splenium of the corpus callosum. It runs backwards and downwards in the line of attachment between the falx cerebri and the tentorium cerebelli, and usually ends by draining into the left transverse sinus at the confluence. Because it collects the entire deep venous return — internal cerebral veins, basal veins and the inferior sagittal sinus — its obstruction or a malformation of its feeding vein is a neurosurgical emergency. ## What you must remember - Formed by the union of the inferior sagittal sinus (in the free lower border of the falx) and the great cerebral vein of Galen, beneath the splenium of the corpus callosum. - Occupies the junction of the falx cerebri with the tentorium cerebelli; traced along this line, it reliably leads the surgeon to the confluence of sinuses. - Receives the internal cerebral veins, the basal veins of Rosenthal and cerebellar veins, so it drains the thalamus, basal ganglia, deep white matter and midbrain. - Usually drains into the left transverse sinus, or directly into the confluence at the internal occipital protuberance. - The vein of Galen is only about 1–2 cm long but carries the whole deep outflow; it lies in the quadrigeminal cistern. - A vein of Galen malformation is the commonest vascular malformation presenting in the neonate, with high-output cardiac failure, a cranial bruit and hydrocephalus from aqueduct compression. - Straight sinus thrombosis is a recognised cause of deep venous infarction with drowsiness and pupillary or gaze abnormalities from midbrain involvement. ## Working through a vein of Galen malformation in a neonate A newborn in distress with bounding pulses, cardiomegaly on chest radiograph and a loud cranial bruit heard over the fontanelle illustrates the anatomy at full volume. An arteriovenous fistula between the choroidal or quadrigeminal arteries and the great cerebral vein shunts blood at low resistance; the vein aneurysmally dilates and the straight sinus must carry a torrent. The heart, forced into a high-output state, fails — hence the neonate presents to the cardiologist first, and the bruit is the clue that the fistula is intracranial. Follow the mass effect along the local relations. The dilated vein sits in the quadrigeminal cistern behind the midbrain; it compresses the cerebral aqueduct, so CSF cannot leave the third ventricle and an obstructive hydrocephalus follows. Venous congestion of the thalami drained by the internal cerebral veins may produce porencephalic change if diagnosis is delayed. Confirmation is by MR angiography and cerebral angiography defining the feeders; treatment per current practice is endovascular embolisation of the fistula, with medical stabilisation of the cardiac failure beforehand. Open surgery on this lesion has largely been abandoned. ## Where students slip The straight sinus is the one examiners use to test whether a candidate truly knows the falx and tentorium as a single tented unit. Asked "which sinus lies at the meeting of the two dural folds", a poorly prepared student guesses the superior sagittal; the correct answer is straight, because the superior sagittal sinus occupies the attached upper border of the falx, the inferior sagittal its free lower border, and only the straight sinus sits where falx meets tentorium. The second classic slip is giving the drainage as "the confluence in all cases" — the left transverse continuation is the usual pattern and the expected answer. Third, remember that the vein of Galen drains into the sinus, never "the sinus arises in the brain"; it is a dural channel receiving a cerebral vein, a distinction of wording that vivas punish. ## Frequently asked questions ### How is the straight sinus formed? By the union of the inferior sagittal sinus with the great cerebral vein of Galen, at the lower border of the splenium of the corpus callosum. ### Where is the straight sinus located? In the midline attachment of the falx cerebri to the tentorium cerebelli, running backwards and downwards to the confluence of sinuses. ### Which structures does the straight sinus drain? The deep cerebral veins — internal cerebral veins and basal veins of Rosenthal — plus the inferior sagittal sinus and cerebellar veins, covering thalamus, basal ganglia and midbrain territory. ### Why does a vein of Galen malformation cause hydrocephalus? The dilated vein lies in the quadrigeminal cistern and compresses the cerebral aqueduct, obstructing CSF outflow from the third ventricle. ### Which transverse sinus usually receives the straight sinus? The left, in most individuals, whereas the superior sagittal sinus usually continues into the right.